[thirdparty/git.git] / refs / files-backend.c

#define USE_THE_REPOSITORY_VARIABLE
#define DISABLE_SIGN_COMPARE_WARNINGS

#include "../git-compat-util.h"
#include "../abspath.h"
#include "../config.h"
#include "../copy.h"
#include "../environment.h"
#include "../gettext.h"
#include "../hash.h"
#include "../hex.h"
#include "../fsck.h"
#include "../refs.h"
#include "../repo-settings.h"
#include "refs-internal.h"
#include "ref-cache.h"
#include "packed-backend.h"
#include "../ident.h"
#include "../iterator.h"
#include "../dir-iterator.h"
#include "../lockfile.h"
#include "../object.h"
#include "../path.h"
#include "../dir.h"
#include "../chdir-notify.h"
#include "../setup.h"
#include "../worktree.h"
#include "../wrapper.h"
#include "../write-or-die.h"
#include "../revision.h"
#include <wildmatch.h>

/*
 * This backend uses the following flags in `ref_update::flags` for
 * internal bookkeeping purposes. Their numerical values must not
 * conflict with REF_NO_DEREF, REF_FORCE_CREATE_REFLOG, REF_HAVE_NEW,
 * or REF_HAVE_OLD, which are also stored in `ref_update::flags`.
 */

/*
 * Used as a flag in ref_update::flags when a loose ref is being
 * pruned. This flag must only be used when REF_NO_DEREF is set.
 */
#define REF_IS_PRUNING (1 << 4)

/*
 * Flag passed to lock_ref_sha1_basic() telling it to tolerate broken
 * refs (i.e., because the reference is about to be deleted anyway).
 */
#define REF_DELETING (1 << 5)

/*
 * Used as a flag in ref_update::flags when the lockfile needs to be
 * committed.
 */
#define REF_NEEDS_COMMIT (1 << 6)

/*
 * Used as a flag in ref_update::flags when the ref_update was via an
 * update to HEAD.
 */
#define REF_UPDATE_VIA_HEAD (1 << 8)

/*
 * Used as a flag in ref_update::flags when a reference has been
 * deleted and the ref's parent directories may need cleanup.
 */
#define REF_DELETED_RMDIR (1 << 9)

/*
 * Used to indicate that the reflog-only update has been created via
 * `split_head_update()`.
 */
#define REF_LOG_VIA_SPLIT (1 << 14)

struct ref_lock {
        char *ref_name;
        struct lock_file lk;
        struct object_id old_oid;
        unsigned int count; /* track users of the lock (ref update + reflog updates) */
};

struct files_ref_store {
        struct ref_store base;
        unsigned int store_flags;

        char *gitcommondir;
        enum log_refs_config log_all_ref_updates;
        int prefer_symlink_refs;

        struct ref_cache *loose;

        struct ref_store *packed_ref_store;
};

static void clear_loose_ref_cache(struct files_ref_store *refs)
{
        if (refs->loose) {
                free_ref_cache(refs->loose);
                refs->loose = NULL;
        }
}

/*
 * Create a new submodule ref cache and add it to the internal
 * set of caches.
 */
static struct ref_store *files_ref_store_init(struct repository *repo,
                                              const char *gitdir,
                                              unsigned int flags)
{
        struct files_ref_store *refs = xcalloc(1, sizeof(*refs));
        struct ref_store *ref_store = (struct ref_store *)refs;
        struct strbuf sb = STRBUF_INIT;

        base_ref_store_init(ref_store, repo, gitdir, &refs_be_files);
        refs->store_flags = flags;
        get_common_dir_noenv(&sb, gitdir);
        refs->gitcommondir = strbuf_detach(&sb, NULL);
        refs->packed_ref_store =
                packed_ref_store_init(repo, refs->gitcommondir, flags);
        refs->log_all_ref_updates = repo_settings_get_log_all_ref_updates(repo);
        repo_config_get_bool(repo, "core.prefersymlinkrefs", &refs->prefer_symlink_refs);

        chdir_notify_reparent("files-backend $GIT_DIR", &refs->base.gitdir);
        chdir_notify_reparent("files-backend $GIT_COMMONDIR",
                              &refs->gitcommondir);

        return ref_store;
}

/*
 * Die if refs is not the main ref store. caller is used in any
 * necessary error messages.
 */
static void files_assert_main_repository(struct files_ref_store *refs,
                                         const char *caller)
{
        if (refs->store_flags & REF_STORE_MAIN)
                return;

        BUG("operation %s only allowed for main ref store", caller);
}

/*
 * Downcast ref_store to files_ref_store. Die if ref_store is not a
 * files_ref_store. required_flags is compared with ref_store's
 * store_flags to ensure the ref_store has all required capabilities.
 * "caller" is used in any necessary error messages.
 */
static struct files_ref_store *files_downcast(struct ref_store *ref_store,
                                              unsigned int required_flags,
                                              const char *caller)
{
        struct files_ref_store *refs;

        if (ref_store->be != &refs_be_files)
                BUG("ref_store is type \"%s\" not \"files\" in %s",
                    ref_store->be->name, caller);

        refs = (struct files_ref_store *)ref_store;

        if ((refs->store_flags & required_flags) != required_flags)
                BUG("operation %s requires abilities 0x%x, but only have 0x%x",
                    caller, required_flags, refs->store_flags);

        return refs;
}

static void files_ref_store_release(struct ref_store *ref_store)
{
        struct files_ref_store *refs = files_downcast(ref_store, 0, "release");
        free_ref_cache(refs->loose);
        free(refs->gitcommondir);
        ref_store_release(refs->packed_ref_store);
        free(refs->packed_ref_store);
}

static void files_reflog_path(struct files_ref_store *refs,
                              struct strbuf *sb,
                              const char *refname)
{
        const char *bare_refname;
        const char *wtname;
        int wtname_len;
        enum ref_worktree_type wt_type = parse_worktree_ref(
                refname, &wtname, &wtname_len, &bare_refname);

        switch (wt_type) {
        case REF_WORKTREE_CURRENT:
                strbuf_addf(sb, "%s/logs/%s", refs->base.gitdir, refname);
                break;
        case REF_WORKTREE_SHARED:
        case REF_WORKTREE_MAIN:
                strbuf_addf(sb, "%s/logs/%s", refs->gitcommondir, bare_refname);
                break;
        case REF_WORKTREE_OTHER:
                strbuf_addf(sb, "%s/worktrees/%.*s/logs/%s", refs->gitcommondir,
                            wtname_len, wtname, bare_refname);
                break;
        default:
                BUG("unknown ref type %d of ref %s", wt_type, refname);
        }
}

static void files_ref_path(struct files_ref_store *refs,
                           struct strbuf *sb,
                           const char *refname)
{
        const char *bare_refname;
        const char *wtname;
        int wtname_len;
        enum ref_worktree_type wt_type = parse_worktree_ref(
                refname, &wtname, &wtname_len, &bare_refname);
        switch (wt_type) {
        case REF_WORKTREE_CURRENT:
                strbuf_addf(sb, "%s/%s", refs->base.gitdir, refname);
                break;
        case REF_WORKTREE_OTHER:
                strbuf_addf(sb, "%s/worktrees/%.*s/%s", refs->gitcommondir,
                            wtname_len, wtname, bare_refname);
                break;
        case REF_WORKTREE_SHARED:
        case REF_WORKTREE_MAIN:
                strbuf_addf(sb, "%s/%s", refs->gitcommondir, bare_refname);
                break;
        default:
                BUG("unknown ref type %d of ref %s", wt_type, refname);
        }
}

/*
 * Manually add refs/bisect, refs/rewritten and refs/worktree, which, being
 * per-worktree, might not appear in the directory listing for
 * refs/ in the main repo.
 */
static void add_per_worktree_entries_to_dir(struct ref_dir *dir, const char *dirname)
{
        const char *prefixes[] = { "refs/bisect/", "refs/worktree/", "refs/rewritten/" };
        int ip;

        if (strcmp(dirname, "refs/"))
                return;

        for (ip = 0; ip < ARRAY_SIZE(prefixes); ip++) {
                const char *prefix = prefixes[ip];
                int prefix_len = strlen(prefix);
                struct ref_entry *child_entry;
                int pos;

                pos = search_ref_dir(dir, prefix, prefix_len);
                if (pos >= 0)
                        continue;
                child_entry = create_dir_entry(dir->cache, prefix, prefix_len);
                add_entry_to_dir(dir, child_entry);
        }
}

static void loose_fill_ref_dir_regular_file(struct files_ref_store *refs,
                                            const char *refname,
                                            struct ref_dir *dir)
{
        struct object_id oid;
        int flag;
        const char *referent = refs_resolve_ref_unsafe(&refs->base,
                                                       refname,
                                                       RESOLVE_REF_READING,
                                                       &oid, &flag);

        if (!referent) {
                oidclr(&oid, refs->base.repo->hash_algo);
                flag |= REF_ISBROKEN;
        } else if (is_null_oid(&oid)) {
                /*
                 * It is so astronomically unlikely
                 * that null_oid is the OID of an
                 * actual object that we consider its
                 * appearance in a loose reference
                 * file to be repo corruption
                 * (probably due to a software bug).
                 */
                flag |= REF_ISBROKEN;
        }

        if (check_refname_format(refname, REFNAME_ALLOW_ONELEVEL)) {
                if (!refname_is_safe(refname))
                        die("loose refname is dangerous: %s", refname);
                oidclr(&oid, refs->base.repo->hash_algo);
                flag |= REF_BAD_NAME | REF_ISBROKEN;
        }

        if (!(flag & REF_ISSYMREF))
                referent = NULL;

        add_entry_to_dir(dir, create_ref_entry(refname, referent, &oid, flag));
}

/*
 * Read the loose references from the namespace dirname into dir
 * (without recursing).  dirname must end with '/'.  dir must be the
 * directory entry corresponding to dirname.
 */
static void loose_fill_ref_dir(struct ref_store *ref_store,
                               struct ref_dir *dir, const char *dirname)
{
        struct files_ref_store *refs =
                files_downcast(ref_store, REF_STORE_READ, "fill_ref_dir");
        DIR *d;
        struct dirent *de;
        int dirnamelen = strlen(dirname);
        struct strbuf refname;
        struct strbuf path = STRBUF_INIT;

        files_ref_path(refs, &path, dirname);

        d = opendir(path.buf);
        if (!d) {
                strbuf_release(&path);
                return;
        }

        strbuf_init(&refname, dirnamelen + 257);
        strbuf_add(&refname, dirname, dirnamelen);

        while ((de = readdir(d)) != NULL) {
                unsigned char dtype;

                if (de->d_name[0] == '.')
                        continue;
                if (ends_with(de->d_name, ".lock"))
                        continue;
                strbuf_addstr(&refname, de->d_name);

                dtype = get_dtype(de, &path, 1);
                if (dtype == DT_DIR) {
                        strbuf_addch(&refname, '/');
                        add_entry_to_dir(dir,
                                         create_dir_entry(dir->cache, refname.buf,
                                                          refname.len));
                } else if (dtype == DT_REG) {
                        loose_fill_ref_dir_regular_file(refs, refname.buf, dir);
                }
                strbuf_setlen(&refname, dirnamelen);
        }
        strbuf_release(&refname);
        strbuf_release(&path);
        closedir(d);

        add_per_worktree_entries_to_dir(dir, dirname);
}

static int for_each_root_ref(struct files_ref_store *refs,
                             int (*cb)(const char *refname, void *cb_data),
                             void *cb_data)
{
        struct strbuf path = STRBUF_INIT, refname = STRBUF_INIT;
        const char *dirname = refs->loose->root->name;
        struct dirent *de;
        size_t dirnamelen;
        int ret;
        DIR *d;

        files_ref_path(refs, &path, dirname);

        d = opendir(path.buf);
        if (!d) {
                strbuf_release(&path);
                return -1;
        }

        strbuf_addstr(&refname, dirname);
        dirnamelen = refname.len;

        while ((de = readdir(d)) != NULL) {
                unsigned char dtype;

                if (de->d_name[0] == '.')
                        continue;
                if (ends_with(de->d_name, ".lock"))
                        continue;
                strbuf_addstr(&refname, de->d_name);

                dtype = get_dtype(de, &path, 1);
                if (dtype == DT_REG && is_root_ref(de->d_name)) {
                        ret = cb(refname.buf, cb_data);
                        if (ret)
                                goto done;
                }

                strbuf_setlen(&refname, dirnamelen);
        }

        ret = 0;

done:
        strbuf_release(&refname);
        strbuf_release(&path);
        closedir(d);
        return ret;
}

struct fill_root_ref_data {
        struct files_ref_store *refs;
        struct ref_dir *dir;
};

static int fill_root_ref(const char *refname, void *cb_data)
{
        struct fill_root_ref_data *data = cb_data;
        loose_fill_ref_dir_regular_file(data->refs, refname, data->dir);
        return 0;
}

/*
 * Add root refs to the ref dir by parsing the directory for any files which
 * follow the root ref syntax.
 */
static void add_root_refs(struct files_ref_store *refs,
                          struct ref_dir *dir)
{
        struct fill_root_ref_data data = {
                .refs = refs,
                .dir = dir,
        };

        for_each_root_ref(refs, fill_root_ref, &data);
}

static struct ref_cache *get_loose_ref_cache(struct files_ref_store *refs,
                                             unsigned int flags)
{
        if (!refs->loose) {
                struct ref_dir *dir;

                /*
                 * Mark the top-level directory complete because we
                 * are about to read the only subdirectory that can
                 * hold references:
                 */
                refs->loose = create_ref_cache(&refs->base, loose_fill_ref_dir);

                /* We're going to fill the top level ourselves: */
                refs->loose->root->flag &= ~REF_INCOMPLETE;

                dir = get_ref_dir(refs->loose->root);

                if (flags & DO_FOR_EACH_INCLUDE_ROOT_REFS)
                        add_root_refs(refs, dir);

                /*
                 * Add an incomplete entry for "refs/" (to be filled
                 * lazily):
                 */
                add_entry_to_dir(dir, create_dir_entry(refs->loose, "refs/", 5));
        }
        return refs->loose;
}

static int read_ref_internal(struct ref_store *ref_store, const char *refname,
                             struct object_id *oid, struct strbuf *referent,
                             unsigned int *type, int *failure_errno, int skip_packed_refs)
{
        struct files_ref_store *refs =
                files_downcast(ref_store, REF_STORE_READ, "read_raw_ref");
        struct strbuf sb_contents = STRBUF_INIT;
        struct strbuf sb_path = STRBUF_INIT;
        const char *path;
        const char *buf;
        struct stat st;
        int fd;
        int ret = -1;
        int remaining_retries = 3;
        int myerr = 0;

        *type = 0;
        strbuf_reset(&sb_path);

        files_ref_path(refs, &sb_path, refname);

        path = sb_path.buf;

stat_ref:
        /*
         * We might have to loop back here to avoid a race
         * condition: first we lstat() the file, then we try
         * to read it as a link or as a file.  But if somebody
         * changes the type of the file (file <-> directory
         * <-> symlink) between the lstat() and reading, then
         * we don't want to report that as an error but rather
         * try again starting with the lstat().
         *
         * We'll keep a count of the retries, though, just to avoid
         * any confusing situation sending us into an infinite loop.
         */

        if (remaining_retries-- <= 0)
                goto out;

        if (lstat(path, &st) < 0) {
                int ignore_errno;
                myerr = errno;
                if (myerr != ENOENT || skip_packed_refs)
                        goto out;
                if (refs_read_raw_ref(refs->packed_ref_store, refname, oid,
                                      referent, type, &ignore_errno)) {
                        myerr = ENOENT;
                        goto out;
                }
                ret = 0;
                goto out;
        }

        /* Follow "normalized" - ie "refs/.." symlinks by hand */
        if (S_ISLNK(st.st_mode)) {
                strbuf_reset(&sb_contents);
                if (strbuf_readlink(&sb_contents, path, st.st_size) < 0) {
                        myerr = errno;
                        if (myerr == ENOENT || myerr == EINVAL)
                                /* inconsistent with lstat; retry */
                                goto stat_ref;
                        else
                                goto out;
                }
                if (starts_with(sb_contents.buf, "refs/") &&
                    !check_refname_format(sb_contents.buf, 0)) {
                        strbuf_swap(&sb_contents, referent);
                        *type |= REF_ISSYMREF;
                        ret = 0;
                        goto out;
                }
                /*
                 * It doesn't look like a refname; fall through to just
                 * treating it like a non-symlink, and reading whatever it
                 * points to.
                 */
        }

        /* Is it a directory? */
        if (S_ISDIR(st.st_mode)) {
                int ignore_errno;
                /*
                 * Even though there is a directory where the loose
                 * ref is supposed to be, there could still be a
                 * packed ref:
                 */
                if (skip_packed_refs ||
                    refs_read_raw_ref(refs->packed_ref_store, refname, oid,
                                      referent, type, &ignore_errno)) {
                        myerr = EISDIR;
                        goto out;
                }
                ret = 0;
                goto out;
        }

        /*
         * Anything else, just open it and try to use it as
         * a ref
         */
        fd = open(path, O_RDONLY);
        if (fd < 0) {
                myerr = errno;
                if (myerr == ENOENT && !S_ISLNK(st.st_mode))
                        /* inconsistent with lstat; retry */
                        goto stat_ref;
                else
                        goto out;
        }
        strbuf_reset(&sb_contents);
        if (strbuf_read(&sb_contents, fd, 256) < 0) {
                myerr = errno;
                close(fd);
                goto out;
        }
        close(fd);
        strbuf_rtrim(&sb_contents);
        buf = sb_contents.buf;

        ret = parse_loose_ref_contents(ref_store->repo->hash_algo, buf,
                                       oid, referent, type, NULL, &myerr);

out:
        if (ret && !myerr)
                BUG("returning non-zero %d, should have set myerr!", ret);
        *failure_errno = myerr;

        strbuf_release(&sb_path);
        strbuf_release(&sb_contents);
        errno = 0;
        return ret;
}

static int files_read_raw_ref(struct ref_store *ref_store, const char *refname,
                              struct object_id *oid, struct strbuf *referent,
                              unsigned int *type, int *failure_errno)
{
        return read_ref_internal(ref_store, refname, oid, referent, type, failure_errno, 0);
}

static int files_read_symbolic_ref(struct ref_store *ref_store, const char *refname,
                                   struct strbuf *referent)
{
        struct object_id oid;
        int failure_errno, ret;
        unsigned int type;

        ret = read_ref_internal(ref_store, refname, &oid, referent, &type, &failure_errno, 1);
        if (!ret && !(type & REF_ISSYMREF))
                return NOT_A_SYMREF;
        return ret;
}

int parse_loose_ref_contents(const struct git_hash_algo *algop,
                             const char *buf, struct object_id *oid,
                             struct strbuf *referent, unsigned int *type,
                             const char **trailing, int *failure_errno)
{
        const char *p;
        if (skip_prefix(buf, "ref:", &buf)) {
                while (isspace(*buf))
                        buf++;

                strbuf_reset(referent);
                strbuf_addstr(referent, buf);
                *type |= REF_ISSYMREF;
                return 0;
        }

        /*
         * FETCH_HEAD has additional data after the sha.
         */
        if (parse_oid_hex_algop(buf, oid, &p, algop) ||
            (*p != '\0' && !isspace(*p))) {
                *type |= REF_ISBROKEN;
                *failure_errno = EINVAL;
                return -1;
        }

        if (trailing)
                *trailing = p;

        return 0;
}

static void unlock_ref(struct ref_lock *lock)
{
        lock->count--;
        if (!lock->count) {
                rollback_lock_file(&lock->lk);
                free(lock->ref_name);
                free(lock);
        }
}

/*
 * Check if the transaction has another update with a case-insensitive refname
 * match.
 *
 * If the update is part of the transaction, we only check up to that index.
 * Further updates are expected to call this function to match previous indices.
 */
static bool transaction_has_case_conflicting_update(struct ref_transaction *transaction,
                                                    struct ref_update *update)
{
        for (size_t i = 0; i < transaction->nr; i++) {
                if (transaction->updates[i] == update)
                        break;

                if (!strcasecmp(transaction->updates[i]->refname, update->refname))
                        return true;
        }
        return false;
}

/*
 * Lock refname, without following symrefs, and set *lock_p to point
 * at a newly-allocated lock object. Fill in lock->old_oid, referent,
 * and type similarly to read_raw_ref().
 *
 * The caller must verify that refname is a "safe" reference name (in
 * the sense of refname_is_safe()) before calling this function.
 *
 * If the reference doesn't already exist, verify that refname doesn't
 * have a D/F conflict with any existing references. extras and skip
 * are passed to refs_verify_refname_available() for this check.
 *
 * If mustexist is not set and the reference is not found or is
 * broken, lock the reference anyway but clear old_oid.
 *
 * Return 0 on success. On failure, write an error message to err and
 * return REF_TRANSACTION_ERROR_NAME_CONFLICT or REF_TRANSACTION_ERROR_GENERIC.
 *
 * Implementation note: This function is basically
 *
 *     lock reference
 *     read_raw_ref()
 *
 * but it includes a lot more code to
 * - Deal with possible races with other processes
 * - Avoid calling refs_verify_refname_available() when it can be
 *   avoided, namely if we were successfully able to read the ref
 * - Generate informative error messages in the case of failure
 */
static enum ref_transaction_error lock_raw_ref(struct files_ref_store *refs,
                                               struct ref_transaction *transaction,
                                               size_t update_idx,
                                               int mustexist,
                                               struct string_list *refnames_to_check,
                                               struct ref_lock **lock_p,
                                               struct strbuf *referent,
                                               struct strbuf *err)
{
        enum ref_transaction_error ret = REF_TRANSACTION_ERROR_GENERIC;
        struct ref_update *update = transaction->updates[update_idx];
        const struct string_list *extras = &transaction->refnames;
        const char *refname = update->refname;
        unsigned int *type = &update->type;
        struct ref_lock *lock;
        struct strbuf ref_file = STRBUF_INIT;
        int attempts_remaining = 3;
        int failure_errno;

        assert(err);
        files_assert_main_repository(refs, "lock_raw_ref");

        *type = 0;

        /* First lock the file so it can't change out from under us. */

        *lock_p = CALLOC_ARRAY(lock, 1);

        lock->ref_name = xstrdup(refname);
        lock->count = 1;
        files_ref_path(refs, &ref_file, refname);

retry:
        switch (safe_create_leading_directories(the_repository, ref_file.buf)) {
        case SCLD_OK:
                break; /* success */
        case SCLD_EXISTS:
                /*
                 * Suppose refname is "refs/foo/bar". We just failed
                 * to create the containing directory, "refs/foo",
                 * because there was a non-directory in the way. This
                 * indicates a D/F conflict, probably because of
                 * another reference such as "refs/foo". There is no
                 * reason to expect this error to be transitory.
                 */
                if (refs_verify_refname_available(&refs->base, refname,
                                                  extras, NULL, 0, err)) {
                        if (mustexist) {
                                /*
                                 * To the user the relevant error is
                                 * that the "mustexist" reference is
                                 * missing:
                                 */
                                strbuf_reset(err);
                                strbuf_addf(err, "unable to resolve reference '%s'",
                                            refname);
                                ret = REF_TRANSACTION_ERROR_NONEXISTENT_REF;
                        } else {
                                /*
                                 * The error message set by
                                 * refs_verify_refname_available() is
                                 * OK.
                                 */
                                ret = REF_TRANSACTION_ERROR_NAME_CONFLICT;
                        }
                } else {
                        /*
                         * The file that is in the way isn't a loose
                         * reference. Report it as a low-level
                         * failure.
                         */
                        strbuf_addf(err, "unable to create lock file %s.lock; "
                                    "non-directory in the way",
                                    ref_file.buf);
                }
                goto error_return;
        case SCLD_VANISHED:
                /* Maybe another process was tidying up. Try again. */
                if (--attempts_remaining > 0)
                        goto retry;
                /* fall through */
        default:
                strbuf_addf(err, "unable to create directory for %s",
                            ref_file.buf);
                goto error_return;
        }

        if (hold_lock_file_for_update_timeout(
                            &lock->lk, ref_file.buf, LOCK_NO_DEREF,
                            get_files_ref_lock_timeout_ms()) < 0) {
                int myerr = errno;
                errno = 0;
                if (myerr == ENOENT && --attempts_remaining > 0) {
                        /*
                         * Maybe somebody just deleted one of the
                         * directories leading to ref_file.  Try
                         * again:
                         */
                        goto retry;
                } else {
                        unable_to_lock_message(ref_file.buf, myerr, err);
                        if (myerr == EEXIST) {
                                if (ignore_case &&
                                    transaction_has_case_conflicting_update(transaction, update)) {
                                        /*
                                         * In case-insensitive filesystems, ensure that conflicts within a
                                         * given transaction are handled. Pre-existing refs on a
                                         * case-insensitive system will be overridden without any issue.
                                         */
                                        ret = REF_TRANSACTION_ERROR_CASE_CONFLICT;
                                } else {
                                        /*
                                         * Pre-existing case-conflicting reference locks should also be
                                         * specially categorized to avoid failing all batched updates.
                                         */
                                        ret = REF_TRANSACTION_ERROR_CREATE_EXISTS;
                                }
                        }

                        goto error_return;
                }
        }

        /*
         * Now we hold the lock and can read the reference without
         * fear that its value will change.
         */

        if (files_read_raw_ref(&refs->base, refname, &lock->old_oid, referent,
                               type, &failure_errno)) {
                struct string_list_item *item;

                if (failure_errno == ENOENT) {
                        if (mustexist) {
                                /* Garden variety missing reference. */
                                strbuf_addf(err, "unable to resolve reference '%s'",
                                            refname);
                                ret = REF_TRANSACTION_ERROR_NONEXISTENT_REF;
                                goto error_return;
                        } else {
                                /*
                                 * Reference is missing, but that's OK. We
                                 * know that there is not a conflict with
                                 * another loose reference because
                                 * (supposing that we are trying to lock
                                 * reference "refs/foo/bar"):
                                 *
                                 * - We were successfully able to create
                                 *   the lockfile refs/foo/bar.lock, so we
                                 *   know there cannot be a loose reference
                                 *   named "refs/foo".
                                 *
                                 * - We got ENOENT and not EISDIR, so we
                                 *   know that there cannot be a loose
                                 *   reference named "refs/foo/bar/baz".
                                 */
                        }
                } else if (failure_errno == EISDIR) {
                        /*
                         * There is a directory in the way. It might have
                         * contained references that have been deleted. If
                         * we don't require that the reference already
                         * exists, try to remove the directory so that it
                         * doesn't cause trouble when we want to rename the
                         * lockfile into place later.
                         */
                        if (mustexist) {
                                /* Garden variety missing reference. */
                                strbuf_addf(err, "unable to resolve reference '%s'",
                                            refname);
                                ret = REF_TRANSACTION_ERROR_NONEXISTENT_REF;
                                goto error_return;
                        } else if (remove_dir_recursively(&ref_file,
                                                          REMOVE_DIR_EMPTY_ONLY)) {
                                ret = REF_TRANSACTION_ERROR_NAME_CONFLICT;
                                if (refs_verify_refname_available(
                                                    &refs->base, refname,
                                                    extras, NULL, 0, err)) {
                                        /*
                                         * The error message set by
                                         * verify_refname_available() is OK.
                                         */
                                        goto error_return;
                                } else {
                                        /*
                                         * Directory conflicts can occur if there
                                         * is an existing lock file in the directory
                                         * or if the filesystem is case-insensitive
                                         * and the directory contains a valid reference
                                         * but conflicts with the update.
                                         */
                                        strbuf_addf(err, "there is a non-empty directory '%s' "
                                                    "blocking reference '%s'",
                                                    ref_file.buf, refname);
                                        goto error_return;
                                }
                        }
                } else if (failure_errno == EINVAL && (*type & REF_ISBROKEN)) {
                        strbuf_addf(err, "unable to resolve reference '%s': "
                                    "reference broken", refname);
                        goto error_return;
                } else {
                        strbuf_addf(err, "unable to resolve reference '%s': %s",
                                    refname, strerror(failure_errno));
                        goto error_return;
                }

                /*
                 * If the ref did not exist and we are creating it, we have to
                 * make sure there is no existing packed ref that conflicts
                 * with refname. This check is deferred so that we can batch it.
                 *
                 * For case-insensitive filesystems, we should also check for F/D
                 * conflicts between 'foo' and 'Foo/bar'. So let's lowercase
                 * the refname.
                 */
                if (ignore_case) {
                        struct strbuf lower = STRBUF_INIT;

                        strbuf_addstr(&lower, refname);
                        strbuf_tolower(&lower);

                        item = string_list_append_nodup(refnames_to_check,
                                                        strbuf_detach(&lower, NULL));
                } else {
                        item = string_list_append(refnames_to_check, refname);
                }

                item->util = xmalloc(sizeof(update_idx));
                memcpy(item->util, &update_idx, sizeof(update_idx));
        }

        ret = 0;
        goto out;

error_return:
        unlock_ref(lock);
        *lock_p = NULL;

out:
        strbuf_release(&ref_file);
        return ret;
}

struct files_ref_iterator {
        struct ref_iterator base;

        struct ref_iterator *iter0;
        struct repository *repo;
        unsigned int flags;
};

static int files_ref_iterator_advance(struct ref_iterator *ref_iterator)
{
        struct files_ref_iterator *iter =
                (struct files_ref_iterator *)ref_iterator;
        int ok;

        while ((ok = ref_iterator_advance(iter->iter0)) == ITER_OK) {
                if (iter->flags & DO_FOR_EACH_PER_WORKTREE_ONLY &&
                    parse_worktree_ref(iter->iter0->refname, NULL, NULL,
                                       NULL) != REF_WORKTREE_CURRENT)
                        continue;

                if ((iter->flags & DO_FOR_EACH_OMIT_DANGLING_SYMREFS) &&
                    (iter->iter0->flags & REF_ISSYMREF) &&
                    (iter->iter0->flags & REF_ISBROKEN))
                        continue;

                if (!(iter->flags & DO_FOR_EACH_INCLUDE_BROKEN) &&
                    !ref_resolves_to_object(iter->iter0->refname,
                                            iter->repo,
                                            iter->iter0->oid,
                                            iter->iter0->flags))
                        continue;

                iter->base.refname = iter->iter0->refname;
                iter->base.oid = iter->iter0->oid;
                iter->base.flags = iter->iter0->flags;
                iter->base.referent = iter->iter0->referent;

                return ITER_OK;
        }

        return ok;
}

static int files_ref_iterator_seek(struct ref_iterator *ref_iterator,
                                   const char *refname, unsigned int flags)
{
        struct files_ref_iterator *iter =
                (struct files_ref_iterator *)ref_iterator;
        return ref_iterator_seek(iter->iter0, refname, flags);
}

static int files_ref_iterator_peel(struct ref_iterator *ref_iterator,
                                   struct object_id *peeled)
{
        struct files_ref_iterator *iter =
                (struct files_ref_iterator *)ref_iterator;

        return ref_iterator_peel(iter->iter0, peeled);
}

static void files_ref_iterator_release(struct ref_iterator *ref_iterator)
{
        struct files_ref_iterator *iter =
                (struct files_ref_iterator *)ref_iterator;
        ref_iterator_free(iter->iter0);
}

static struct ref_iterator_vtable files_ref_iterator_vtable = {
        .advance = files_ref_iterator_advance,
        .seek = files_ref_iterator_seek,
        .peel = files_ref_iterator_peel,
        .release = files_ref_iterator_release,
};

static struct ref_iterator *files_ref_iterator_begin(
                struct ref_store *ref_store,
                const char *prefix, const char **exclude_patterns,
                unsigned int flags)
{
        struct files_ref_store *refs;
        struct ref_iterator *loose_iter, *packed_iter, *overlay_iter;
        struct files_ref_iterator *iter;
        struct ref_iterator *ref_iterator;
        unsigned int required_flags = REF_STORE_READ;

        if (!(flags & DO_FOR_EACH_INCLUDE_BROKEN))
                required_flags |= REF_STORE_ODB;

        refs = files_downcast(ref_store, required_flags, "ref_iterator_begin");

        /*
         * We must make sure that all loose refs are read before
         * accessing the packed-refs file; this avoids a race
         * condition if loose refs are migrated to the packed-refs
         * file by a simultaneous process, but our in-memory view is
         * from before the migration. We ensure this as follows:
         * First, we call start the loose refs iteration with its
         * `prime_ref` argument set to true. This causes the loose
         * references in the subtree to be pre-read into the cache.
         * (If they've already been read, that's OK; we only need to
         * guarantee that they're read before the packed refs, not
         * *how much* before.) After that, we call
         * packed_ref_iterator_begin(), which internally checks
         * whether the packed-ref cache is up to date with what is on
         * disk, and re-reads it if not.
         */

        loose_iter = cache_ref_iterator_begin(get_loose_ref_cache(refs, flags),
                                              prefix, ref_store->repo, 1);

        /*
         * The packed-refs file might contain broken references, for
         * example an old version of a reference that points at an
         * object that has since been garbage-collected. This is OK as
         * long as there is a corresponding loose reference that
         * overrides it, and we don't want to emit an error message in
         * this case. So ask the packed_ref_store for all of its
         * references, and (if needed) do our own check for broken
         * ones in files_ref_iterator_advance(), after we have merged
         * the packed and loose references.
         */
        packed_iter = refs_ref_iterator_begin(
                        refs->packed_ref_store, prefix, exclude_patterns, 0,
                        DO_FOR_EACH_INCLUDE_BROKEN);

        overlay_iter = overlay_ref_iterator_begin(loose_iter, packed_iter);

        CALLOC_ARRAY(iter, 1);
        ref_iterator = &iter->base;
        base_ref_iterator_init(ref_iterator, &files_ref_iterator_vtable);
        iter->iter0 = overlay_iter;
        iter->repo = ref_store->repo;
        iter->flags = flags;

        return ref_iterator;
}

/*
 * Callback function for raceproof_create_file(). This function is
 * expected to do something that makes dirname(path) permanent despite
 * the fact that other processes might be cleaning up empty
 * directories at the same time. Usually it will create a file named
 * path, but alternatively it could create another file in that
 * directory, or even chdir() into that directory. The function should
 * return 0 if the action was completed successfully. On error, it
 * should return a nonzero result and set errno.
 * raceproof_create_file() treats two errno values specially:
 *
 * - ENOENT -- dirname(path) does not exist. In this case,
 *             raceproof_create_file() tries creating dirname(path)
 *             (and any parent directories, if necessary) and calls
 *             the function again.
 *
 * - EISDIR -- the file already exists and is a directory. In this
 *             case, raceproof_create_file() removes the directory if
 *             it is empty (and recursively any empty directories that
 *             it contains) and calls the function again.
 *
 * Any other errno causes raceproof_create_file() to fail with the
 * callback's return value and errno.
 *
 * Obviously, this function should be OK with being called again if it
 * fails with ENOENT or EISDIR. In other scenarios it will not be
 * called again.
 */
typedef int create_file_fn(const char *path, void *cb);

/*
 * Create a file in dirname(path) by calling fn, creating leading
 * directories if necessary. Retry a few times in case we are racing
 * with another process that is trying to clean up the directory that
 * contains path. See the documentation for create_file_fn for more
 * details.
 *
 * Return the value and set the errno that resulted from the most
 * recent call of fn. fn is always called at least once, and will be
 * called more than once if it returns ENOENT or EISDIR.
 */
static int raceproof_create_file(const char *path, create_file_fn fn, void *cb)
{
        /*
         * The number of times we will try to remove empty directories
         * in the way of path. This is only 1 because if another
         * process is racily creating directories that conflict with
         * us, we don't want to fight against them.
         */
        int remove_directories_remaining = 1;

        /*
         * The number of times that we will try to create the
         * directories containing path. We are willing to attempt this
         * more than once, because another process could be trying to
         * clean up empty directories at the same time as we are
         * trying to create them.
         */
        int create_directories_remaining = 3;

        /* A scratch copy of path, filled lazily if we need it: */
        struct strbuf path_copy = STRBUF_INIT;

        int ret, save_errno;

        /* Sanity check: */
        assert(*path);

retry_fn:
        ret = fn(path, cb);
        save_errno = errno;
        if (!ret)
                goto out;

        if (errno == EISDIR && remove_directories_remaining-- > 0) {
                /*
                 * A directory is in the way. Maybe it is empty; try
                 * to remove it:
                 */
                if (!path_copy.len)
                        strbuf_addstr(&path_copy, path);

                if (!remove_dir_recursively(&path_copy, REMOVE_DIR_EMPTY_ONLY))
                        goto retry_fn;
        } else if (errno == ENOENT && create_directories_remaining-- > 0) {
                /*
                 * Maybe the containing directory didn't exist, or
                 * maybe it was just deleted by a process that is
                 * racing with us to clean up empty directories. Try
                 * to create it:
                 */
                enum scld_error scld_result;

                if (!path_copy.len)
                        strbuf_addstr(&path_copy, path);

                do {
                        scld_result = safe_create_leading_directories(the_repository, path_copy.buf);
                        if (scld_result == SCLD_OK)
                                goto retry_fn;
                } while (scld_result == SCLD_VANISHED && create_directories_remaining-- > 0);
        }

out:
        strbuf_release(&path_copy);
        errno = save_errno;
        return ret;
}

static int remove_empty_directories(struct strbuf *path)
{
        /*
         * we want to create a file but there is a directory there;
         * if that is an empty directory (or a directory that contains
         * only empty directories), remove them.
         */
        return remove_dir_recursively(path, REMOVE_DIR_EMPTY_ONLY);
}

static int create_reflock(const char *path, void *cb)
{
        struct lock_file *lk = cb;

        return hold_lock_file_for_update_timeout(
                        lk, path, LOCK_NO_DEREF,
                        get_files_ref_lock_timeout_ms()) < 0 ? -1 : 0;
}

/*
 * Locks a ref returning the lock on success and NULL on failure.
 */
static struct ref_lock *lock_ref_oid_basic(struct files_ref_store *refs,
                                           const char *refname,
                                           struct strbuf *err)
{
        struct strbuf ref_file = STRBUF_INIT;
        struct ref_lock *lock;

        files_assert_main_repository(refs, "lock_ref_oid_basic");
        assert(err);

        CALLOC_ARRAY(lock, 1);

        files_ref_path(refs, &ref_file, refname);

        /*
         * If the ref did not exist and we are creating it, make sure
         * there is no existing packed ref whose name begins with our
         * refname, nor a packed ref whose name is a proper prefix of
         * our refname.
         */
        if (is_null_oid(&lock->old_oid) &&
            refs_verify_refname_available(refs->packed_ref_store, refname,
                                          NULL, NULL, 0, err))
                goto error_return;

        lock->ref_name = xstrdup(refname);
        lock->count = 1;

        if (raceproof_create_file(ref_file.buf, create_reflock, &lock->lk)) {
                unable_to_lock_message(ref_file.buf, errno, err);
                goto error_return;
        }

        if (!refs_resolve_ref_unsafe(&refs->base, lock->ref_name, 0,
                                     &lock->old_oid, NULL))
                oidclr(&lock->old_oid, refs->base.repo->hash_algo);
        goto out;

 error_return:
        unlock_ref(lock);
        lock = NULL;

 out:
        strbuf_release(&ref_file);
        return lock;
}

struct ref_to_prune {
        struct ref_to_prune *next;
        struct object_id oid;
        char name[FLEX_ARRAY];
};

enum {
        REMOVE_EMPTY_PARENTS_REF = 0x01,
        REMOVE_EMPTY_PARENTS_REFLOG = 0x02
};

/*
 * Remove empty parent directories associated with the specified
 * reference and/or its reflog, but spare [logs/]refs/ and immediate
 * subdirs. flags is a combination of REMOVE_EMPTY_PARENTS_REF and/or
 * REMOVE_EMPTY_PARENTS_REFLOG.
 */
static void try_remove_empty_parents(struct files_ref_store *refs,
                                     const char *refname,
                                     unsigned int flags)
{
        struct strbuf buf = STRBUF_INIT;
        struct strbuf sb = STRBUF_INIT;
        char *p, *q;
        int i;

        strbuf_addstr(&buf, refname);
        p = buf.buf;
        for (i = 0; i < 2; i++) { /* refs/{heads,tags,...}/ */
                while (*p && *p != '/')
                        p++;
                /* tolerate duplicate slashes; see check_refname_format() */
                while (*p == '/')
                        p++;
        }
        q = buf.buf + buf.len;
        while (flags & (REMOVE_EMPTY_PARENTS_REF | REMOVE_EMPTY_PARENTS_REFLOG)) {
                while (q > p && *q != '/')
                        q--;
                while (q > p && *(q-1) == '/')
                        q--;
                if (q == p)
                        break;
                strbuf_setlen(&buf, q - buf.buf);

                strbuf_reset(&sb);
                files_ref_path(refs, &sb, buf.buf);
                if ((flags & REMOVE_EMPTY_PARENTS_REF) && rmdir(sb.buf))
                        flags &= ~REMOVE_EMPTY_PARENTS_REF;

                strbuf_reset(&sb);
                files_reflog_path(refs, &sb, buf.buf);
                if ((flags & REMOVE_EMPTY_PARENTS_REFLOG) && rmdir(sb.buf))
                        flags &= ~REMOVE_EMPTY_PARENTS_REFLOG;
        }
        strbuf_release(&buf);
        strbuf_release(&sb);
}

/* make sure nobody touched the ref, and unlink */
static void prune_ref(struct files_ref_store *refs, struct ref_to_prune *r)
{
        struct ref_transaction *transaction;
        struct strbuf err = STRBUF_INIT;
        int ret = -1;

        if (check_refname_format(r->name, 0))
                return;

        transaction = ref_store_transaction_begin(&refs->base, 0, &err);
        if (!transaction)
                goto cleanup;
        ref_transaction_add_update(
                        transaction, r->name,
                        REF_NO_DEREF | REF_HAVE_NEW | REF_HAVE_OLD | REF_IS_PRUNING,
                        null_oid(the_hash_algo), &r->oid, NULL, NULL, NULL, NULL);
        if (ref_transaction_commit(transaction, &err))
                goto cleanup;

        ret = 0;

cleanup:
        if (ret)
                error("%s", err.buf);
        strbuf_release(&err);
        ref_transaction_free(transaction);
        return;
}

/*
 * Prune the loose versions of the references in the linked list
 * `*refs_to_prune`, freeing the entries in the list as we go.
 */
static void prune_refs(struct files_ref_store *refs, struct ref_to_prune **refs_to_prune)
{
        while (*refs_to_prune) {
                struct ref_to_prune *r = *refs_to_prune;
                *refs_to_prune = r->next;
                prune_ref(refs, r);
                free(r);
        }
}

/*
 * Return true if the specified reference should be packed.
 */
static int should_pack_ref(struct files_ref_store *refs,
                           const char *refname,
                           const struct object_id *oid, unsigned int ref_flags,
                           struct pack_refs_opts *opts)
{
        struct string_list_item *item;

        /* Do not pack per-worktree refs: */
        if (parse_worktree_ref(refname, NULL, NULL, NULL) !=
            REF_WORKTREE_SHARED)
                return 0;

        /* Do not pack symbolic refs: */
        if (ref_flags & REF_ISSYMREF)
                return 0;

        /* Do not pack broken refs: */
        if (!ref_resolves_to_object(refname, refs->base.repo, oid, ref_flags))
                return 0;

        if (ref_excluded(opts->exclusions, refname))
                return 0;

        for_each_string_list_item(item, opts->includes)
                if (!wildmatch(item->string, refname, 0))
                        return 1;

        return 0;
}

static int should_pack_refs(struct files_ref_store *refs,
                            struct pack_refs_opts *opts)
{
        struct ref_iterator *iter;
        size_t packed_size;
        size_t refcount = 0;
        size_t limit;
        int ret;

        if (!(opts->flags & PACK_REFS_AUTO))
                return 1;

        ret = packed_refs_size(refs->packed_ref_store, &packed_size);
        if (ret < 0)
                die("cannot determine packed-refs size");

        /*
         * Packing loose references into the packed-refs file scales with the
         * number of references we're about to write. We thus decide whether we
         * repack refs by weighing the current size of the packed-refs file
         * against the number of loose references. This is done such that we do
         * not repack too often on repositories with a huge number of
         * references, where we can expect a lot of churn in the number of
         * references.
         *
         * As a heuristic, we repack if the number of loose references in the
         * repository exceeds `log2(nr_packed_refs) * 5`, where we estimate
         * `nr_packed_refs = packed_size / 100`, which scales as following:
         *
         * - 1kB ~ 10 packed refs: 16 refs
         * - 10kB ~ 100 packed refs: 33 refs
         * - 100kB ~ 1k packed refs: 49 refs
         * - 1MB ~ 10k packed refs: 66 refs
         * - 10MB ~ 100k packed refs: 82 refs
         * - 100MB ~ 1m packed refs: 99 refs
         *
         * We thus allow roughly 16 additional loose refs per factor of ten of
         * packed refs. This heuristic may be tweaked in the future, but should
         * serve as a sufficiently good first iteration.
         */
        limit = log2u(packed_size / 100) * 5;
        if (limit < 16)
                limit = 16;

        iter = cache_ref_iterator_begin(get_loose_ref_cache(refs, 0), NULL,
                                        refs->base.repo, 0);
        while ((ret = ref_iterator_advance(iter)) == ITER_OK) {
                if (should_pack_ref(refs, iter->refname, iter->oid,
                                    iter->flags, opts))
                        refcount++;
                if (refcount >= limit) {
                        ref_iterator_free(iter);
                        return 1;
                }
        }

        if (ret != ITER_DONE)
                die("error while iterating over references");

        ref_iterator_free(iter);
        return 0;
}

static int files_pack_refs(struct ref_store *ref_store,
                           struct pack_refs_opts *opts)
{
        struct files_ref_store *refs =
                files_downcast(ref_store, REF_STORE_WRITE | REF_STORE_ODB,
                               "pack_refs");
        struct ref_iterator *iter;
        int ok;
        struct ref_to_prune *refs_to_prune = NULL;
        struct strbuf err = STRBUF_INIT;
        struct ref_transaction *transaction;

        if (!should_pack_refs(refs, opts))
                return 0;

        transaction = ref_store_transaction_begin(refs->packed_ref_store,
                                                  0, &err);
        if (!transaction)
                return -1;

        packed_refs_lock(refs->packed_ref_store, LOCK_DIE_ON_ERROR, &err);

        iter = cache_ref_iterator_begin(get_loose_ref_cache(refs, 0), NULL,
                                        refs->base.repo, 0);
        while ((ok = ref_iterator_advance(iter)) == ITER_OK) {
                /*
                 * If the loose reference can be packed, add an entry
                 * in the packed ref cache. If the reference should be
                 * pruned, also add it to refs_to_prune.
                 */
                if (!should_pack_ref(refs, iter->refname, iter->oid, iter->flags, opts))
                        continue;

                /*
                 * Add a reference creation for this reference to the
                 * packed-refs transaction:
                 */
                if (ref_transaction_update(transaction, iter->refname,
                                           iter->oid, NULL, NULL, NULL,
                                           REF_NO_DEREF, NULL, &err))
                        die("failure preparing to create packed reference %s: %s",
                            iter->refname, err.buf);

                /* Schedule the loose reference for pruning if requested. */
                if ((opts->flags & PACK_REFS_PRUNE)) {
                        struct ref_to_prune *n;
                        FLEX_ALLOC_STR(n, name, iter->refname);
                        oidcpy(&n->oid, iter->oid);
                        n->next = refs_to_prune;
                        refs_to_prune = n;
                }
        }
        if (ok != ITER_DONE)
                die("error while iterating over references");

        if (ref_transaction_commit(transaction, &err))
                die("unable to write new packed-refs: %s", err.buf);

        ref_transaction_free(transaction);

        packed_refs_unlock(refs->packed_ref_store);

        prune_refs(refs, &refs_to_prune);
        ref_iterator_free(iter);
        strbuf_release(&err);
        return 0;
}

static int files_optimize(struct ref_store *ref_store, struct pack_refs_opts *opts)
{
        /*
         * For the "files" backend, "optimizing" is the same as "packing".
         * So, we just call the existing worker function for packing.
         */
        return files_pack_refs(ref_store, opts);
}

/*
 * People using contrib's git-new-workdir have .git/logs/refs ->
 * /some/other/path/.git/logs/refs, and that may live on another device.
 *
 * IOW, to avoid cross device rename errors, the temporary renamed log must
 * live into logs/refs.
 */
#define TMP_RENAMED_LOG  "refs/.tmp-renamed-log"

struct rename_cb {
        const char *tmp_renamed_log;
        int true_errno;
};

static int rename_tmp_log_callback(const char *path, void *cb_data)
{
        struct rename_cb *cb = cb_data;

        if (rename(cb->tmp_renamed_log, path)) {
                /*
                 * rename(a, b) when b is an existing directory ought
                 * to result in ISDIR, but Solaris 5.8 gives ENOTDIR.
                 * Sheesh. Record the true errno for error reporting,
                 * but report EISDIR to raceproof_create_file() so
                 * that it knows to retry.
                 */
                cb->true_errno = errno;
                if (errno == ENOTDIR)
                        errno = EISDIR;
                return -1;
        } else {
                return 0;
        }
}

static int rename_tmp_log(struct files_ref_store *refs, const char *newrefname)
{
        struct strbuf path = STRBUF_INIT;
        struct strbuf tmp = STRBUF_INIT;
        struct rename_cb cb;
        int ret;

        files_reflog_path(refs, &path, newrefname);
        files_reflog_path(refs, &tmp, TMP_RENAMED_LOG);
        cb.tmp_renamed_log = tmp.buf;
        ret = raceproof_create_file(path.buf, rename_tmp_log_callback, &cb);
        if (ret) {
                if (errno == EISDIR)
                        error("directory not empty: %s", path.buf);
                else
                        error("unable to move logfile %s to %s: %s",
                              tmp.buf, path.buf,
                              strerror(cb.true_errno));
        }

        strbuf_release(&path);
        strbuf_release(&tmp);
        return ret;
}

static enum ref_transaction_error write_ref_to_lockfile(struct files_ref_store *refs,
                                                        struct ref_lock *lock,
                                                        const struct object_id *oid,
                                                        int skip_oid_verification,
                                                        struct strbuf *err);
static int commit_ref_update(struct files_ref_store *refs,
                             struct ref_lock *lock,
                             const struct object_id *oid, const char *logmsg,
                             int flags,
                             struct strbuf *err);

/*
 * Emit a better error message than lockfile.c's
 * unable_to_lock_message() would in case there is a D/F conflict with
 * another existing reference. If there would be a conflict, emit an error
 * message and return false; otherwise, return true.
 *
 * Note that this function is not safe against all races with other
 * processes, and that's not its job. We'll emit a more verbose error on D/f
 * conflicts if we get past it into lock_ref_oid_basic().
 */
static int refs_rename_ref_available(struct ref_store *refs,
                              const char *old_refname,
                              const char *new_refname)
{
        struct string_list skip = STRING_LIST_INIT_NODUP;
        struct strbuf err = STRBUF_INIT;
        int ok;

        string_list_insert(&skip, old_refname);
        ok = !refs_verify_refname_available(refs, new_refname,
                                            NULL, &skip, 0, &err);
        if (!ok)
                error("%s", err.buf);

        string_list_clear(&skip, 0);
        strbuf_release(&err);
        return ok;
}

static int files_copy_or_rename_ref(struct ref_store *ref_store,
                            const char *oldrefname, const char *newrefname,
                            const char *logmsg, int copy)
{
        struct files_ref_store *refs =
                files_downcast(ref_store, REF_STORE_WRITE, "rename_ref");
        struct object_id orig_oid;
        int flag = 0, logmoved = 0;
        struct ref_lock *lock;
        struct stat loginfo;
        struct strbuf sb_oldref = STRBUF_INIT;
        struct strbuf sb_newref = STRBUF_INIT;
        struct strbuf tmp_renamed_log = STRBUF_INIT;
        int log, ret;
        struct strbuf err = STRBUF_INIT;

        files_reflog_path(refs, &sb_oldref, oldrefname);
        files_reflog_path(refs, &sb_newref, newrefname);
        files_reflog_path(refs, &tmp_renamed_log, TMP_RENAMED_LOG);

        log = !lstat(sb_oldref.buf, &loginfo);
        if (log && S_ISLNK(loginfo.st_mode)) {
                ret = error("reflog for %s is a symlink", oldrefname);
                goto out;
        }

        if (!refs_resolve_ref_unsafe(&refs->base, oldrefname,
                                     RESOLVE_REF_READING | RESOLVE_REF_NO_RECURSE,
                                     &orig_oid, &flag)) {
                ret = error("refname %s not found", oldrefname);
                goto out;
        }

        if (flag & REF_ISSYMREF) {
                if (copy)
                        ret = error("refname %s is a symbolic ref, copying it is not supported",
                                    oldrefname);
                else
                        ret = error("refname %s is a symbolic ref, renaming it is not supported",
                                    oldrefname);
                goto out;
        }
        if (!refs_rename_ref_available(&refs->base, oldrefname, newrefname)) {
                ret = 1;
                goto out;
        }

        if (!copy && log && rename(sb_oldref.buf, tmp_renamed_log.buf)) {
                ret = error("unable to move logfile logs/%s to logs/"TMP_RENAMED_LOG": %s",
                            oldrefname, strerror(errno));
                goto out;
        }

        if (copy && log && copy_file(tmp_renamed_log.buf, sb_oldref.buf, 0644)) {
                ret = error("unable to copy logfile logs/%s to logs/"TMP_RENAMED_LOG": %s",
                            oldrefname, strerror(errno));
                goto out;
        }

        if (!copy && refs_delete_ref(&refs->base, logmsg, oldrefname,
                            &orig_oid, REF_NO_DEREF)) {
                error("unable to delete old %s", oldrefname);
                goto rollback;
        }

        /*
         * Since we are doing a shallow lookup, oid is not the
         * correct value to pass to delete_ref as old_oid. But that
         * doesn't matter, because an old_oid check wouldn't add to
         * the safety anyway; we want to delete the reference whatever
         * its current value.
         */
        if (!copy && refs_resolve_ref_unsafe(&refs->base, newrefname,
                                             RESOLVE_REF_READING | RESOLVE_REF_NO_RECURSE,
                                             NULL, NULL) &&
            refs_delete_ref(&refs->base, NULL, newrefname,
                            NULL, REF_NO_DEREF)) {
                if (errno == EISDIR) {
                        struct strbuf path = STRBUF_INIT;
                        int result;

                        files_ref_path(refs, &path, newrefname);
                        result = remove_empty_directories(&path);
                        strbuf_release(&path);

                        if (result) {
                                error("Directory not empty: %s", newrefname);
                                goto rollback;
                        }
                } else {
                        error("unable to delete existing %s", newrefname);
                        goto rollback;
                }
        }

        if (log && rename_tmp_log(refs, newrefname))
                goto rollback;

        logmoved = log;

        lock = lock_ref_oid_basic(refs, newrefname, &err);
        if (!lock) {
                if (copy)
                        error("unable to copy '%s' to '%s': %s", oldrefname, newrefname, err.buf);
                else
                        error("unable to rename '%s' to '%s': %s", oldrefname, newrefname, err.buf);
                strbuf_release(&err);
                goto rollback;
        }
        oidcpy(&lock->old_oid, &orig_oid);

        if (write_ref_to_lockfile(refs, lock, &orig_oid, 0, &err) ||
            commit_ref_update(refs, lock, &orig_oid, logmsg, 0, &err)) {
                error("unable to write current sha1 into %s: %s", newrefname, err.buf);
                strbuf_release(&err);
                goto rollback;
        }

        ret = 0;
        goto out;

 rollback:
        lock = lock_ref_oid_basic(refs, oldrefname, &err);
        if (!lock) {
                error("unable to lock %s for rollback: %s", oldrefname, err.buf);
                strbuf_release(&err);
                goto rollbacklog;
        }

        if (write_ref_to_lockfile(refs, lock, &orig_oid, 0, &err) ||
            commit_ref_update(refs, lock, &orig_oid, NULL, REF_SKIP_CREATE_REFLOG, &err)) {
                error("unable to write current sha1 into %s: %s", oldrefname, err.buf);
                strbuf_release(&err);
        }

 rollbacklog:
        if (logmoved && rename(sb_newref.buf, sb_oldref.buf))
                error("unable to restore logfile %s from %s: %s",
                        oldrefname, newrefname, strerror(errno));
        if (!logmoved && log &&
            rename(tmp_renamed_log.buf, sb_oldref.buf))
                error("unable to restore logfile %s from logs/"TMP_RENAMED_LOG": %s",
                        oldrefname, strerror(errno));
        ret = 1;
 out:
        strbuf_release(&sb_newref);
        strbuf_release(&sb_oldref);
        strbuf_release(&tmp_renamed_log);

        return ret;
}

static int files_rename_ref(struct ref_store *ref_store,
                            const char *oldrefname, const char *newrefname,
                            const char *logmsg)
{
        return files_copy_or_rename_ref(ref_store, oldrefname,
                                 newrefname, logmsg, 0);
}

static int files_copy_ref(struct ref_store *ref_store,
                            const char *oldrefname, const char *newrefname,
                            const char *logmsg)
{
        return files_copy_or_rename_ref(ref_store, oldrefname,
                                 newrefname, logmsg, 1);
}

static int close_ref_gently(struct ref_lock *lock)
{
        if (close_lock_file_gently(&lock->lk))
                return -1;
        return 0;
}

static int commit_ref(struct ref_lock *lock)
{
        char *path = get_locked_file_path(&lock->lk);
        struct stat st;

        if (!lstat(path, &st) && S_ISDIR(st.st_mode)) {
                /*
                 * There is a directory at the path we want to rename
                 * the lockfile to. Hopefully it is empty; try to
                 * delete it.
                 */
                size_t len = strlen(path);
                struct strbuf sb_path = STRBUF_INIT;

                strbuf_attach(&sb_path, path, len, len);

                /*
                 * If this fails, commit_lock_file() will also fail
                 * and will report the problem.
                 */
                remove_empty_directories(&sb_path);
                strbuf_release(&sb_path);
        } else {
                free(path);
        }

        if (commit_lock_file(&lock->lk))
                return -1;
        return 0;
}

static int open_or_create_logfile(const char *path, void *cb)
{
        int *fd = cb;

        *fd = open(path, O_APPEND | O_WRONLY | O_CREAT, 0666);
        return (*fd < 0) ? -1 : 0;
}

/*
 * Create a reflog for a ref. If force_create = 0, only create the
 * reflog for certain refs (those for which should_autocreate_reflog
 * returns non-zero). Otherwise, create it regardless of the reference
 * name. If the logfile already existed or was created, return 0 and
 * set *logfd to the file descriptor opened for appending to the file.
 * If no logfile exists and we decided not to create one, return 0 and
 * set *logfd to -1. On failure, fill in *err, set *logfd to -1, and
 * return -1.
 */
static int log_ref_setup(struct files_ref_store *refs,
                         const char *refname, int force_create,
                         int *logfd, struct strbuf *err)
{
        enum log_refs_config log_refs_cfg = refs->log_all_ref_updates;
        struct strbuf logfile_sb = STRBUF_INIT;
        char *logfile;

        if (log_refs_cfg == LOG_REFS_UNSET)
                log_refs_cfg = is_bare_repository() ? LOG_REFS_NONE : LOG_REFS_NORMAL;

        files_reflog_path(refs, &logfile_sb, refname);
        logfile = strbuf_detach(&logfile_sb, NULL);

        if (force_create || should_autocreate_reflog(log_refs_cfg, refname)) {
                if (raceproof_create_file(logfile, open_or_create_logfile, logfd)) {
                        if (errno == ENOENT)
                                strbuf_addf(err, "unable to create directory for '%s': "
                                            "%s", logfile, strerror(errno));
                        else if (errno == EISDIR)
                                strbuf_addf(err, "there are still logs under '%s'",
                                            logfile);
                        else
                                strbuf_addf(err, "unable to append to '%s': %s",
                                            logfile, strerror(errno));

                        goto error;
                }
        } else {
                *logfd = open(logfile, O_APPEND | O_WRONLY);
                if (*logfd < 0) {
                        if (errno == ENOENT || errno == EISDIR) {
                                /*
                                 * The logfile doesn't already exist,
                                 * but that is not an error; it only
                                 * means that we won't write log
                                 * entries to it.
                                 */
                                ;
                        } else {
                                strbuf_addf(err, "unable to append to '%s': %s",
                                            logfile, strerror(errno));
                                goto error;
                        }
                }
        }

        if (*logfd >= 0)
                adjust_shared_perm(the_repository, logfile);

        free(logfile);
        return 0;

error:
        free(logfile);
        return -1;
}

static int files_create_reflog(struct ref_store *ref_store, const char *refname,
                               struct strbuf *err)
{
        struct files_ref_store *refs =
                files_downcast(ref_store, REF_STORE_WRITE, "create_reflog");
        int fd;

        if (log_ref_setup(refs, refname, 1, &fd, err))
                return -1;

        if (fd >= 0)
                close(fd);

        return 0;
}

static int log_ref_write_fd(int fd, const struct object_id *old_oid,
                            const struct object_id *new_oid,
                            const char *committer, const char *msg)
{
        struct strbuf sb = STRBUF_INIT;
        int ret = 0;

        if (!committer)
                committer = git_committer_info(0);

        strbuf_addf(&sb, "%s %s %s", oid_to_hex(old_oid), oid_to_hex(new_oid), committer);
        if (msg && *msg) {
                strbuf_addch(&sb, '\t');
                strbuf_addstr(&sb, msg);
        }
        strbuf_addch(&sb, '\n');
        if (write_in_full(fd, sb.buf, sb.len) < 0)
                ret = -1;
        strbuf_release(&sb);
        return ret;
}

static int files_log_ref_write(struct files_ref_store *refs,
                               const char *refname,
                               const struct object_id *old_oid,
                               const struct object_id *new_oid,
                               const char *committer_info, const char *msg,
                               int flags, struct strbuf *err)
{
        int logfd, result;

        if (flags & REF_SKIP_CREATE_REFLOG)
                return 0;

        result = log_ref_setup(refs, refname,
                               flags & REF_FORCE_CREATE_REFLOG,
                               &logfd, err);

        if (result)
                return result;

        if (logfd < 0)
                return 0;
        result = log_ref_write_fd(logfd, old_oid, new_oid, committer_info, msg);
        if (result) {
                struct strbuf sb = STRBUF_INIT;
                int save_errno = errno;

                files_reflog_path(refs, &sb, refname);
                strbuf_addf(err, "unable to append to '%s': %s",
                            sb.buf, strerror(save_errno));
                strbuf_release(&sb);
                close(logfd);
                return -1;
        }
        if (close(logfd)) {
                struct strbuf sb = STRBUF_INIT;
                int save_errno = errno;

                files_reflog_path(refs, &sb, refname);
                strbuf_addf(err, "unable to append to '%s': %s",
                            sb.buf, strerror(save_errno));
                strbuf_release(&sb);
                return -1;
        }
        return 0;
}

/*
 * Write oid into the open lockfile, then close the lockfile. On
 * errors, rollback the lockfile, fill in *err and return -1.
 */
static enum ref_transaction_error write_ref_to_lockfile(struct files_ref_store *refs,
                                                        struct ref_lock *lock,
                                                        const struct object_id *oid,
                                                        int skip_oid_verification,
                                                        struct strbuf *err)
{
        static char term = '\n';
        struct object *o;
        int fd;

        if (!skip_oid_verification) {
                o = parse_object(refs->base.repo, oid);
                if (!o) {
                        strbuf_addf(
                                err,
                                "trying to write ref '%s' with nonexistent object %s",
                                lock->ref_name, oid_to_hex(oid));
                        unlock_ref(lock);
                        return REF_TRANSACTION_ERROR_INVALID_NEW_VALUE;
                }
                if (o->type != OBJ_COMMIT && is_branch(lock->ref_name)) {
                        strbuf_addf(
                                err,
                                "trying to write non-commit object %s to branch '%s'",
                                oid_to_hex(oid), lock->ref_name);
                        unlock_ref(lock);
                        return REF_TRANSACTION_ERROR_INVALID_NEW_VALUE;
                }
        }
        fd = get_lock_file_fd(&lock->lk);
        if (write_in_full(fd, oid_to_hex(oid), refs->base.repo->hash_algo->hexsz) < 0 ||
            write_in_full(fd, &term, 1) < 0 ||
            fsync_component(FSYNC_COMPONENT_REFERENCE, get_lock_file_fd(&lock->lk)) < 0 ||
            close_ref_gently(lock) < 0) {
                strbuf_addf(err,
                            "couldn't write '%s'", get_lock_file_path(&lock->lk));
                unlock_ref(lock);
                return REF_TRANSACTION_ERROR_GENERIC;
        }
        return 0;
}

/*
 * Commit a change to a loose reference that has already been written
 * to the loose reference lockfile. Also update the reflogs if
 * necessary, using the specified lockmsg (which can be NULL).
 */
static int commit_ref_update(struct files_ref_store *refs,
                             struct ref_lock *lock,
                             const struct object_id *oid, const char *logmsg,
                             int flags,
                             struct strbuf *err)
{
        files_assert_main_repository(refs, "commit_ref_update");

        clear_loose_ref_cache(refs);
        if (files_log_ref_write(refs, lock->ref_name, &lock->old_oid, oid, NULL,
                                logmsg, flags, err)) {
                char *old_msg = strbuf_detach(err, NULL);
                strbuf_addf(err, "cannot update the ref '%s': %s",
                            lock->ref_name, old_msg);
                free(old_msg);
                unlock_ref(lock);
                return -1;
        }

        if (strcmp(lock->ref_name, "HEAD") != 0) {
                /*
                 * Special hack: If a branch is updated directly and HEAD
                 * points to it (may happen on the remote side of a push
                 * for example) then logically the HEAD reflog should be
                 * updated too.
                 * A generic solution implies reverse symref information,
                 * but finding all symrefs pointing to the given branch
                 * would be rather costly for this rare event (the direct
                 * update of a branch) to be worth it.  So let's cheat and
                 * check with HEAD only which should cover 99% of all usage
                 * scenarios (even 100% of the default ones).
                 */
                int head_flag;
                const char *head_ref;

                head_ref = refs_resolve_ref_unsafe(&refs->base, "HEAD",
                                                   RESOLVE_REF_READING,
                                                   NULL, &head_flag);
                if (head_ref && (head_flag & REF_ISSYMREF) &&
                    !strcmp(head_ref, lock->ref_name)) {
                        struct strbuf log_err = STRBUF_INIT;
                        if (files_log_ref_write(refs, "HEAD", &lock->old_oid,
                                                oid, NULL, logmsg, flags,
                                                &log_err)) {
                                error("%s", log_err.buf);
                                strbuf_release(&log_err);
                        }
                }
        }

        if (commit_ref(lock)) {
                strbuf_addf(err, "couldn't set '%s'", lock->ref_name);
                unlock_ref(lock);
                return -1;
        }

        unlock_ref(lock);
        return 0;
}

#if defined(NO_SYMLINK_HEAD) || defined(WITH_BREAKING_CHANGES)
#define create_ref_symlink(a, b) (-1)
#else
static int create_ref_symlink(struct ref_lock *lock, const char *target)
{
        static int warn_once = 1;
        char *ref_path;
        int ret = -1;

        ref_path = get_locked_file_path(&lock->lk);
        unlink(ref_path);
        ret = symlink(target, ref_path);
        free(ref_path);

        if (ret)
                fprintf(stderr, "no symlink - falling back to symbolic ref\n");

        if (warn_once)
                warning(_("'core.preferSymlinkRefs=true' is nominated for removal.\n"
                          "hint: The use of symbolic links for symbolic refs is deprecated\n"
                          "hint: and will be removed in Git 3.0. The configuration that\n"
                          "hint: tells Git to use them is thus going away. You can unset\n"
                          "hint: it with:\n"
                          "hint:\n"
                          "hint:\tgit config unset core.preferSymlinkRefs\n"
                          "hint:\n"
                          "hint: Git will then use the textual symref format instead."));
        warn_once = 0;

        return ret;
}
#endif

static int create_symref_lock(struct ref_lock *lock, const char *target,
                              struct strbuf *err)
{
        if (!fdopen_lock_file(&lock->lk, "w")) {
                strbuf_addf(err, "unable to fdopen %s: %s",
                             get_lock_file_path(&lock->lk), strerror(errno));
                return -1;
        }

        if (fprintf(get_lock_file_fp(&lock->lk), "ref: %s\n", target) < 0) {
                strbuf_addf(err, "unable to write to %s: %s",
                             get_lock_file_path(&lock->lk), strerror(errno));
                return -1;
        }

        return 0;
}

static int files_reflog_exists(struct ref_store *ref_store,
                               const char *refname)
{
        struct files_ref_store *refs =
                files_downcast(ref_store, REF_STORE_READ, "reflog_exists");
        struct strbuf sb = STRBUF_INIT;
        struct stat st;
        int ret;

        files_reflog_path(refs, &sb, refname);
        ret = !lstat(sb.buf, &st) && S_ISREG(st.st_mode);
        strbuf_release(&sb);
        return ret;
}

static int files_delete_reflog(struct ref_store *ref_store,
                               const char *refname)
{
        struct files_ref_store *refs =
                files_downcast(ref_store, REF_STORE_WRITE, "delete_reflog");
        struct strbuf sb = STRBUF_INIT;
        int ret;

        files_reflog_path(refs, &sb, refname);
        ret = remove_path(sb.buf);
        strbuf_release(&sb);
        return ret;
}

static int show_one_reflog_ent(struct files_ref_store *refs,
                               const char *refname,
                               struct strbuf *sb,
                               each_reflog_ent_fn fn, void *cb_data)
{
        struct object_id ooid, noid;
        char *email_end, *message;
        timestamp_t timestamp;
        int tz;
        const char *p = sb->buf;

        /* old SP new SP name <email> SP time TAB msg LF */
        if (!sb->len || sb->buf[sb->len - 1] != '\n' ||
            parse_oid_hex_algop(p, &ooid, &p, refs->base.repo->hash_algo) || *p++ != ' ' ||
            parse_oid_hex_algop(p, &noid, &p, refs->base.repo->hash_algo) || *p++ != ' ' ||
            !(email_end = strchr(p, '>')) ||
            email_end[1] != ' ' ||
            !(timestamp = parse_timestamp(email_end + 2, &message, 10)) ||
            !message || message[0] != ' ' ||
            (message[1] != '+' && message[1] != '-') ||
            !isdigit(message[2]) || !isdigit(message[3]) ||
            !isdigit(message[4]) || !isdigit(message[5]))
                return 0; /* corrupt? */
        email_end[1] = '\0';
        tz = strtol(message + 1, NULL, 10);
        if (message[6] != '\t')
                message += 6;
        else
                message += 7;
        return fn(refname, &ooid, &noid, p, timestamp, tz, message, cb_data);
}

static char *find_beginning_of_line(char *bob, char *scan)
{
        while (bob < scan && *(--scan) != '\n')
                ; /* keep scanning backwards */
        /*
         * Return either beginning of the buffer, or LF at the end of
         * the previous line.
         */
        return scan;
}

static int files_for_each_reflog_ent_reverse(struct ref_store *ref_store,
                                             const char *refname,
                                             each_reflog_ent_fn fn,
                                             void *cb_data)
{
        struct files_ref_store *refs =
                files_downcast(ref_store, REF_STORE_READ,
                               "for_each_reflog_ent_reverse");
        struct strbuf sb = STRBUF_INIT;
        FILE *logfp;
        long pos;
        int ret = 0, at_tail = 1;

        files_reflog_path(refs, &sb, refname);
        logfp = fopen(sb.buf, "r");
        strbuf_release(&sb);
        if (!logfp)
                return -1;

        /* Jump to the end */
        if (fseek(logfp, 0, SEEK_END) < 0)
                ret = error("cannot seek back reflog for %s: %s",
                            refname, strerror(errno));
        pos = ftell(logfp);
        while (!ret && 0 < pos) {
                int cnt;
                size_t nread;
                char buf[BUFSIZ];
                char *endp, *scanp;

                /* Fill next block from the end */
                cnt = (sizeof(buf) < pos) ? sizeof(buf) : pos;
                if (fseek(logfp, pos - cnt, SEEK_SET)) {
                        ret = error("cannot seek back reflog for %s: %s",
                                    refname, strerror(errno));
                        break;
                }
                nread = fread(buf, cnt, 1, logfp);
                if (nread != 1) {
                        ret = error("cannot read %d bytes from reflog for %s: %s",
                                    cnt, refname, strerror(errno));
                        break;
                }
                pos -= cnt;

                scanp = endp = buf + cnt;
                if (at_tail && scanp[-1] == '\n')
                        /* Looking at the final LF at the end of the file */
                        scanp--;
                at_tail = 0;

                while (buf < scanp) {
                        /*
                         * terminating LF of the previous line, or the beginning
                         * of the buffer.
                         */
                        char *bp;

                        bp = find_beginning_of_line(buf, scanp);

                        if (*bp == '\n') {
                                /*
                                 * The newline is the end of the previous line,
                                 * so we know we have complete line starting
                                 * at (bp + 1). Prefix it onto any prior data
                                 * we collected for the line and process it.
                                 */
                                strbuf_splice(&sb, 0, 0, bp + 1, endp - (bp + 1));
                                scanp = bp;
                                endp = bp + 1;
                                ret = show_one_reflog_ent(refs, refname, &sb, fn, cb_data);
                                strbuf_reset(&sb);
                                if (ret)
                                        break;
                        } else if (!pos) {
                                /*
                                 * We are at the start of the buffer, and the
                                 * start of the file; there is no previous
                                 * line, and we have everything for this one.
                                 * Process it, and we can end the loop.
                                 */
                                strbuf_splice(&sb, 0, 0, buf, endp - buf);
                                ret = show_one_reflog_ent(refs, refname, &sb, fn, cb_data);
                                strbuf_reset(&sb);
                                break;
                        }

                        if (bp == buf) {
                                /*
                                 * We are at the start of the buffer, and there
                                 * is more file to read backwards. Which means
                                 * we are in the middle of a line. Note that we
                                 * may get here even if *bp was a newline; that
                                 * just means we are at the exact end of the
                                 * previous line, rather than some spot in the
                                 * middle.
                                 *
                                 * Save away what we have to be combined with
                                 * the data from the next read.
                                 */
                                strbuf_splice(&sb, 0, 0, buf, endp - buf);
                                break;
                        }
                }

        }
        if (!ret && sb.len)
                BUG("reverse reflog parser had leftover data");

        fclose(logfp);
        strbuf_release(&sb);
        return ret;
}

static int files_for_each_reflog_ent(struct ref_store *ref_store,
                                     const char *refname,
                                     each_reflog_ent_fn fn, void *cb_data)
{
        struct files_ref_store *refs =
                files_downcast(ref_store, REF_STORE_READ,
                               "for_each_reflog_ent");
        FILE *logfp;
        struct strbuf sb = STRBUF_INIT;
        int ret = 0;

        files_reflog_path(refs, &sb, refname);
        logfp = fopen(sb.buf, "r");
        strbuf_release(&sb);
        if (!logfp)
                return -1;

        while (!ret && !strbuf_getwholeline(&sb, logfp, '\n'))
                ret = show_one_reflog_ent(refs, refname, &sb, fn, cb_data);
        fclose(logfp);
        strbuf_release(&sb);
        return ret;
}

struct files_reflog_iterator {
        struct ref_iterator base;
        struct ref_store *ref_store;
        struct dir_iterator *dir_iterator;
};

static int files_reflog_iterator_advance(struct ref_iterator *ref_iterator)
{
        struct files_reflog_iterator *iter =
                (struct files_reflog_iterator *)ref_iterator;
        struct dir_iterator *diter = iter->dir_iterator;
        int ok;

        while ((ok = dir_iterator_advance(diter)) == ITER_OK) {
                if (!S_ISREG(diter->st.st_mode))
                        continue;
                if (check_refname_format(diter->basename,
                                         REFNAME_ALLOW_ONELEVEL))
                        continue;

                iter->base.refname = diter->relative_path;
                return ITER_OK;
        }

        return ok;
}

static int files_reflog_iterator_seek(struct ref_iterator *ref_iterator UNUSED,
                                      const char *refname UNUSED,
                                      unsigned int flags UNUSED)
{
        BUG("ref_iterator_seek() called for reflog_iterator");
}

static int files_reflog_iterator_peel(struct ref_iterator *ref_iterator UNUSED,
                                      struct object_id *peeled UNUSED)
{
        BUG("ref_iterator_peel() called for reflog_iterator");
}

static void files_reflog_iterator_release(struct ref_iterator *ref_iterator)
{
        struct files_reflog_iterator *iter =
                (struct files_reflog_iterator *)ref_iterator;
        dir_iterator_free(iter->dir_iterator);
}

static struct ref_iterator_vtable files_reflog_iterator_vtable = {
        .advance = files_reflog_iterator_advance,
        .seek = files_reflog_iterator_seek,
        .peel = files_reflog_iterator_peel,
        .release = files_reflog_iterator_release,
};

static struct ref_iterator *reflog_iterator_begin(struct ref_store *ref_store,
                                                  const char *gitdir)
{
        struct dir_iterator *diter;
        struct files_reflog_iterator *iter;
        struct ref_iterator *ref_iterator;
        struct strbuf sb = STRBUF_INIT;

        strbuf_addf(&sb, "%s/logs", gitdir);

        diter = dir_iterator_begin(sb.buf, DIR_ITERATOR_SORTED);
        if (!diter) {
                strbuf_release(&sb);
                return empty_ref_iterator_begin();
        }

        CALLOC_ARRAY(iter, 1);
        ref_iterator = &iter->base;

        base_ref_iterator_init(ref_iterator, &files_reflog_iterator_vtable);
        iter->dir_iterator = diter;
        iter->ref_store = ref_store;
        strbuf_release(&sb);

        return ref_iterator;
}

static struct ref_iterator *files_reflog_iterator_begin(struct ref_store *ref_store)
{
        struct files_ref_store *refs =
                files_downcast(ref_store, REF_STORE_READ,
                               "reflog_iterator_begin");

        if (!strcmp(refs->base.gitdir, refs->gitcommondir)) {
                return reflog_iterator_begin(ref_store, refs->gitcommondir);
        } else {
                return merge_ref_iterator_begin(
                        reflog_iterator_begin(ref_store, refs->base.gitdir),
                        reflog_iterator_begin(ref_store, refs->gitcommondir),
                        ref_iterator_select, refs);
        }
}

/*
 * If update is a direct update of head_ref (the reference pointed to
 * by HEAD), then add an extra REF_LOG_ONLY update for HEAD.
 */
static enum ref_transaction_error split_head_update(struct ref_update *update,
                                                    struct ref_transaction *transaction,
                                                    const char *head_ref,
                                                    struct strbuf *err)
{
        struct ref_update *new_update;

        if ((update->flags & REF_LOG_ONLY) ||
            (update->flags & REF_SKIP_CREATE_REFLOG) ||
            (update->flags & REF_IS_PRUNING) ||
            (update->flags & REF_UPDATE_VIA_HEAD))
                return 0;

        if (strcmp(update->refname, head_ref))
                return 0;

        /*
         * First make sure that HEAD is not already in the
         * transaction. This check is O(lg N) in the transaction
         * size, but it happens at most once per transaction.
         */
        if (string_list_has_string(&transaction->refnames, "HEAD")) {
                /* An entry already existed */
                strbuf_addf(err,
                            "multiple updates for 'HEAD' (including one "
                            "via its referent '%s') are not allowed",
                            update->refname);
                return REF_TRANSACTION_ERROR_NAME_CONFLICT;
        }

        new_update = ref_transaction_add_update(
                        transaction, "HEAD",
                        update->flags | REF_LOG_ONLY | REF_NO_DEREF | REF_LOG_VIA_SPLIT,
                        &update->new_oid, &update->old_oid,
                        NULL, NULL, update->committer_info, update->msg);
        new_update->parent_update = update;

        /*
         * Add "HEAD". This insertion is O(N) in the transaction
         * size, but it happens at most once per transaction.
         * Add new_update->refname instead of a literal "HEAD".
         */
        if (strcmp(new_update->refname, "HEAD"))
                BUG("%s unexpectedly not 'HEAD'", new_update->refname);

        return 0;
}

/*
 * update is for a symref that points at referent and doesn't have
 * REF_NO_DEREF set. Split it into two updates:
 * - The original update, but with REF_LOG_ONLY and REF_NO_DEREF set
 * - A new, separate update for the referent reference
 * Note that the new update will itself be subject to splitting when
 * the iteration gets to it.
 */
static enum ref_transaction_error split_symref_update(struct ref_update *update,
                                                      const char *referent,
                                                      struct ref_transaction *transaction,
                                                      struct strbuf *err)
{
        struct ref_update *new_update;
        unsigned int new_flags;

        /*
         * First make sure that referent is not already in the
         * transaction. This check is O(lg N) in the transaction
         * size, but it happens at most once per symref in a
         * transaction.
         */
        if (string_list_has_string(&transaction->refnames, referent)) {
                /* An entry already exists */
                strbuf_addf(err,
                            "multiple updates for '%s' (including one "
                            "via symref '%s') are not allowed",
                            referent, update->refname);
                return REF_TRANSACTION_ERROR_NAME_CONFLICT;
        }

        new_flags = update->flags;
        if (!strcmp(update->refname, "HEAD")) {
                /*
                 * Record that the new update came via HEAD, so that
                 * when we process it, split_head_update() doesn't try
                 * to add another reflog update for HEAD. Note that
                 * this bit will be propagated if the new_update
                 * itself needs to be split.
                 */
                new_flags |= REF_UPDATE_VIA_HEAD;
        }

        new_update = ref_transaction_add_update(
                        transaction, referent, new_flags,
                        update->new_target ? NULL : &update->new_oid,
                        update->old_target ? NULL : &update->old_oid,
                        update->new_target, update->old_target, NULL,
                        update->msg);

        new_update->parent_update = update;

        /*
         * Change the symbolic ref update to log only. Also, it
         * doesn't need to check its old OID value, as that will be
         * done when new_update is processed.
         */
        update->flags |= REF_LOG_ONLY | REF_NO_DEREF;

        return 0;
}

/*
 * Check whether the REF_HAVE_OLD and old_oid values stored in update
 * are consistent with oid, which is the reference's current value. If
 * everything is OK, return 0; otherwise, write an error message to
 * err and return -1.
 */
static enum ref_transaction_error check_old_oid(struct ref_update *update,
                                                struct object_id *oid,
                                                struct strbuf *referent,
                                                struct strbuf *err)
{
        if (update->flags & REF_LOG_ONLY ||
            !(update->flags & REF_HAVE_OLD))
                return 0;

        if (oideq(oid, &update->old_oid)) {
                /*
                 * Normally matching the expected old oid is enough. Either we
                 * found the ref at the expected state, or we are creating and
                 * expect the null oid (and likewise found nothing).
                 *
                 * But there is one exception for the null oid: if we found a
                 * symref pointing to nothing we'll also get the null oid. In
                 * regular recursive mode, that's good (we'll write to what the
                 * symref points to, which doesn't exist). But in no-deref
                 * mode, it means we'll clobber the symref, even though the
                 * caller asked for this to be a creation event. So flag
                 * that case to preserve the dangling symref.
                 */
                if ((update->flags & REF_NO_DEREF) && referent->len &&
                    is_null_oid(oid)) {
                        strbuf_addf(err, "cannot lock ref '%s': "
                                    "dangling symref already exists",
                                    ref_update_original_update_refname(update));
                        return REF_TRANSACTION_ERROR_CREATE_EXISTS;
                }
                return 0;
        }

        if (is_null_oid(&update->old_oid)) {
                strbuf_addf(err, "cannot lock ref '%s': "
                            "reference already exists",
                            ref_update_original_update_refname(update));
                return REF_TRANSACTION_ERROR_CREATE_EXISTS;
        } else if (is_null_oid(oid)) {
                strbuf_addf(err, "cannot lock ref '%s': "
                            "reference is missing but expected %s",
                            ref_update_original_update_refname(update),
                            oid_to_hex(&update->old_oid));
                return REF_TRANSACTION_ERROR_NONEXISTENT_REF;
        }

        strbuf_addf(err, "cannot lock ref '%s': is at %s but expected %s",
                    ref_update_original_update_refname(update), oid_to_hex(oid),
                    oid_to_hex(&update->old_oid));

        return REF_TRANSACTION_ERROR_INCORRECT_OLD_VALUE;
}

struct files_transaction_backend_data {
        struct ref_transaction *packed_transaction;
        int packed_refs_locked;
        struct strmap ref_locks;
};

/*
 * Prepare for carrying out update:
 * - Lock the reference referred to by update.
 * - Read the reference under lock.
 * - Check that its old OID value (if specified) is correct, and in
 *   any case record it in update->lock->old_oid for later use when
 *   writing the reflog.
 * - If it is a symref update without REF_NO_DEREF, split it up into a
 *   REF_LOG_ONLY update of the symref and add a separate update for
 *   the referent to transaction.
 * - If it is an update of head_ref, add a corresponding REF_LOG_ONLY
 *   update of HEAD.
 */
static enum ref_transaction_error lock_ref_for_update(struct files_ref_store *refs,
                                                      struct ref_update *update,
                                                      size_t update_idx,
                                                      struct ref_transaction *transaction,
                                                      const char *head_ref,
                                                      struct string_list *refnames_to_check,
                                                      struct strbuf *err)
{
        struct strbuf referent = STRBUF_INIT;
        int mustexist = ref_update_expects_existing_old_ref(update);
        struct files_transaction_backend_data *backend_data;
        enum ref_transaction_error ret = 0;
        struct ref_lock *lock;

        files_assert_main_repository(refs, "lock_ref_for_update");

        backend_data = transaction->backend_data;

        if ((update->flags & REF_HAVE_NEW) && ref_update_has_null_new_value(update))
                update->flags |= REF_DELETING;

        if (head_ref) {
                ret = split_head_update(update, transaction, head_ref, err);
                if (ret)
                        goto out;
        }

        lock = strmap_get(&backend_data->ref_locks, update->refname);
        if (lock) {
                lock->count++;
        } else {
                ret = lock_raw_ref(refs, transaction, update_idx, mustexist,
                                   refnames_to_check, &lock, &referent, err);
                if (ret) {
                        char *reason;

                        reason = strbuf_detach(err, NULL);
                        strbuf_addf(err, "cannot lock ref '%s': %s",
                                    ref_update_original_update_refname(update), reason);
                        free(reason);
                        goto out;
                }

                strmap_put(&backend_data->ref_locks, update->refname, lock);
        }

        update->backend_data = lock;

        if (update->flags & REF_LOG_VIA_SPLIT) {
                struct ref_lock *parent_lock;

                if (!update->parent_update)
                        BUG("split update without a parent");

                parent_lock = update->parent_update->backend_data;

                /*
                 * Check that "HEAD" didn't racily change since we have looked
                 * it up. If it did we must refuse to write the reflog entry.
                 *
                 * Note that this does not catch all races: if "HEAD" was
                 * racily changed to point to one of the refs part of the
                 * transaction then we would miss writing the split reflog
                 * entry for "HEAD".
                 */
                if (!(update->type & REF_ISSYMREF) ||
                    strcmp(update->parent_update->refname, referent.buf)) {
                        strbuf_addstr(err, "HEAD has been racily updated");
                        ret = REF_TRANSACTION_ERROR_GENERIC;
                        goto out;
                }

                if (update->flags & REF_HAVE_OLD) {
                        oidcpy(&lock->old_oid, &update->old_oid);
                } else {
                        oidcpy(&lock->old_oid, &parent_lock->old_oid);
                }
        } else if (update->type & REF_ISSYMREF) {
                if (update->flags & REF_NO_DEREF) {
                        /*
                         * We won't be reading the referent as part of
                         * the transaction, so we have to read it here
                         * to record and possibly check old_oid:
                         */
                        if (!refs_resolve_ref_unsafe(&refs->base,
                                                     referent.buf, 0,
                                                     &lock->old_oid, NULL)) {
                                if (update->flags & REF_HAVE_OLD) {
                                        strbuf_addf(err, "cannot lock ref '%s': "
                                                    "error reading reference",
                                                    ref_update_original_update_refname(update));
                                        ret = REF_TRANSACTION_ERROR_GENERIC;
                                        goto out;
                                }
                        }

                        if (update->old_target)
                                ret = ref_update_check_old_target(referent.buf, update, err);
                        else
                                ret = check_old_oid(update, &lock->old_oid,
                                                    &referent, err);
                        if (ret)
                                goto out;
                } else {
                        /*
                         * Create a new update for the reference this
                         * symref is pointing at. Also, we will record
                         * and verify old_oid for this update as part
                         * of processing the split-off update, so we
                         * don't have to do it here.
                         */
                        ret = split_symref_update(update, referent.buf,
                                                  transaction, err);
                        if (ret)
                                goto out;
                }
        } else {
                struct ref_update *parent_update;

                /*
                 * Even if the ref is a regular ref, if `old_target` is set, we
                 * fail with an error.
                 */
                if (update->old_target) {
                        strbuf_addf(err, _("cannot lock ref '%s': "
                                           "expected symref with target '%s': "
                                           "but is a regular ref"),
                                    ref_update_original_update_refname(update),
                                    update->old_target);
                        ret = REF_TRANSACTION_ERROR_EXPECTED_SYMREF;
                        goto out;
                } else {
                        ret = check_old_oid(update, &lock->old_oid,
                                            &referent, err);
                        if  (ret) {
                                goto out;
                        }
                }

                /*
                 * If this update is happening indirectly because of a
                 * symref update, record the old OID in the parent
                 * update:
                 */
                for (parent_update = update->parent_update;
                     parent_update;
                     parent_update = parent_update->parent_update) {
                        struct ref_lock *parent_lock = parent_update->backend_data;
                        oidcpy(&parent_lock->old_oid, &lock->old_oid);
                }
        }

        if (update->new_target && !(update->flags & REF_LOG_ONLY)) {
                if (create_symref_lock(lock, update->new_target, err)) {
                        ret = REF_TRANSACTION_ERROR_GENERIC;
                        goto out;
                }

                if (close_ref_gently(lock)) {
                        strbuf_addf(err, "couldn't close '%s.lock'",
                                    update->refname);
                        ret = REF_TRANSACTION_ERROR_GENERIC;
                        goto out;
                }

                /*
                 * Once we have created the symref lock, the commit
                 * phase of the transaction only needs to commit the lock.
                 */
                update->flags |= REF_NEEDS_COMMIT;
        } else if ((update->flags & REF_HAVE_NEW) &&
                   !(update->flags & REF_DELETING) &&
                   !(update->flags & REF_LOG_ONLY)) {
                if (!(update->type & REF_ISSYMREF) &&
                    oideq(&lock->old_oid, &update->new_oid)) {
                        /*
                         * The reference already has the desired
                         * value, so we don't need to write it.
                         */
                } else {
                        ret = write_ref_to_lockfile(
                                refs, lock, &update->new_oid,
                                update->flags & REF_SKIP_OID_VERIFICATION,
                                err);
                        if (ret) {
                                char *write_err = strbuf_detach(err, NULL);

                                /*
                                 * The lock was freed upon failure of
                                 * write_ref_to_lockfile():
                                 */
                                update->backend_data = NULL;
                                strbuf_addf(err,
                                            "cannot update ref '%s': %s",
                                            update->refname, write_err);
                                free(write_err);
                                goto out;
                        } else {
                                update->flags |= REF_NEEDS_COMMIT;
                        }
                }
        }
        if (!(update->flags & REF_NEEDS_COMMIT)) {
                /*
                 * We didn't call write_ref_to_lockfile(), so
                 * the lockfile is still open. Close it to
                 * free up the file descriptor:
                 */
                if (close_ref_gently(lock)) {
                        strbuf_addf(err, "couldn't close '%s.lock'",
                                    update->refname);
                        ret = REF_TRANSACTION_ERROR_GENERIC;
                        goto out;
                }
        }

out:
        strbuf_release(&referent);
        return ret;
}

/*
 * Unlock any references in `transaction` that are still locked, and
 * mark the transaction closed.
 */
static void files_transaction_cleanup(struct files_ref_store *refs,
                                      struct ref_transaction *transaction)
{
        size_t i;
        struct files_transaction_backend_data *backend_data =
                transaction->backend_data;
        struct strbuf err = STRBUF_INIT;

        for (i = 0; i < transaction->nr; i++) {
                struct ref_update *update = transaction->updates[i];
                struct ref_lock *lock = update->backend_data;

                if (lock) {
                        unlock_ref(lock);
                        try_remove_empty_parents(refs, update->refname,
                                                 REMOVE_EMPTY_PARENTS_REF);
                        update->backend_data = NULL;
                }
        }

        if (backend_data) {
                if (backend_data->packed_transaction &&
                    ref_transaction_abort(backend_data->packed_transaction, &err)) {
                        error("error aborting transaction: %s", err.buf);
                        strbuf_release(&err);
                }

                if (backend_data->packed_refs_locked)
                        packed_refs_unlock(refs->packed_ref_store);

                strmap_clear(&backend_data->ref_locks, 0);

                free(backend_data);
        }

        transaction->state = REF_TRANSACTION_CLOSED;
}

static int files_transaction_prepare(struct ref_store *ref_store,
                                     struct ref_transaction *transaction,
                                     struct strbuf *err)
{
        struct files_ref_store *refs =
                files_downcast(ref_store, REF_STORE_WRITE,
                               "ref_transaction_prepare");
        size_t i;
        int ret = 0;
        struct string_list refnames_to_check = STRING_LIST_INIT_DUP;
        char *head_ref = NULL;
        int head_type;
        struct files_transaction_backend_data *backend_data;
        struct ref_transaction *packed_transaction = NULL;

        assert(err);

        if (transaction->flags & REF_TRANSACTION_FLAG_INITIAL)
                goto cleanup;
        if (!transaction->nr)
                goto cleanup;

        CALLOC_ARRAY(backend_data, 1);
        strmap_init(&backend_data->ref_locks);
        transaction->backend_data = backend_data;

        /*
         * Fail if any of the updates use REF_IS_PRUNING without REF_NO_DEREF.
         */
        for (i = 0; i < transaction->nr; i++) {
                struct ref_update *update = transaction->updates[i];

                if ((update->flags & REF_IS_PRUNING) &&
                    !(update->flags & REF_NO_DEREF))
                        BUG("REF_IS_PRUNING set without REF_NO_DEREF");
        }

        /*
         * Special hack: If a branch is updated directly and HEAD
         * points to it (may happen on the remote side of a push
         * for example) then logically the HEAD reflog should be
         * updated too.
         *
         * A generic solution would require reverse symref lookups,
         * but finding all symrefs pointing to a given branch would be
         * rather costly for this rare event (the direct update of a
         * branch) to be worth it. So let's cheat and check with HEAD
         * only, which should cover 99% of all usage scenarios (even
         * 100% of the default ones).
         *
         * So if HEAD is a symbolic reference, then record the name of
         * the reference that it points to. If we see an update of
         * head_ref within the transaction, then split_head_update()
         * arranges for the reflog of HEAD to be updated, too.
         */
        head_ref = refs_resolve_refdup(ref_store, "HEAD",
                                       RESOLVE_REF_NO_RECURSE,
                                       NULL, &head_type);

        if (head_ref && !(head_type & REF_ISSYMREF)) {
                FREE_AND_NULL(head_ref);
        }

        /*
         * Acquire all locks, verify old values if provided, check
         * that new values are valid, and write new values to the
         * lockfiles, ready to be activated. Only keep one lockfile
         * open at a time to avoid running out of file descriptors.
         * Note that lock_ref_for_update() might append more updates
         * to the transaction.
         */
        for (i = 0; i < transaction->nr; i++) {
                struct ref_update *update = transaction->updates[i];

                ret = lock_ref_for_update(refs, update, i, transaction,
                                          head_ref, &refnames_to_check,
                                          err);
                if (ret) {
                        if (ref_transaction_maybe_set_rejected(transaction, i, ret)) {
                                strbuf_reset(err);
                                ret = 0;

                                continue;
                        }
                        goto cleanup;
                }

                if (update->flags & REF_DELETING &&
                    !(update->flags & REF_LOG_ONLY) &&
                    !(update->flags & REF_IS_PRUNING)) {
                        /*
                         * This reference has to be deleted from
                         * packed-refs if it exists there.
                         */
                        if (!packed_transaction) {
                                packed_transaction = ref_store_transaction_begin(
                                                refs->packed_ref_store,
                                                transaction->flags, err);
                                if (!packed_transaction) {
                                        ret = REF_TRANSACTION_ERROR_GENERIC;
                                        goto cleanup;
                                }

                                backend_data->packed_transaction =
                                        packed_transaction;
                        }

                        ref_transaction_add_update(
                                        packed_transaction, update->refname,
                                        REF_HAVE_NEW | REF_NO_DEREF,
                                        &update->new_oid, NULL,
                                        NULL, NULL, NULL, NULL);
                }
        }

        /*
         * Verify that none of the loose reference that we're about to write
         * conflict with any existing packed references. Ideally, we'd do this
         * check after the packed-refs are locked so that the file cannot
         * change underneath our feet. But introducing such a lock now would
         * probably do more harm than good as users rely on there not being a
         * global lock with the "files" backend.
         *
         * Another alternative would be to do the check after the (optional)
         * lock, but that would extend the time we spend in the globally-locked
         * state.
         *
         * So instead, we accept the race for now.
         */
        if (refs_verify_refnames_available(refs->packed_ref_store, &refnames_to_check,
                                           &transaction->refnames, NULL, transaction,
                                           0, err)) {
                ret = REF_TRANSACTION_ERROR_NAME_CONFLICT;
                goto cleanup;
        }

        if (packed_transaction) {
                if (packed_refs_lock(refs->packed_ref_store, 0, err)) {
                        ret = REF_TRANSACTION_ERROR_GENERIC;
                        goto cleanup;
                }
                backend_data->packed_refs_locked = 1;

                if (is_packed_transaction_needed(refs->packed_ref_store,
                                                 packed_transaction)) {
                        ret = ref_transaction_prepare(packed_transaction, err);
                        /*
                         * A failure during the prepare step will abort
                         * itself, but not free. Do that now, and disconnect
                         * from the files_transaction so it does not try to
                         * abort us when we hit the cleanup code below.
                         */
                        if (ret) {
                                ref_transaction_free(packed_transaction);
                                backend_data->packed_transaction = NULL;
                        }
                } else {
                        /*
                         * We can skip rewriting the `packed-refs`
                         * file. But we do need to leave it locked, so
                         * that somebody else doesn't pack a reference
                         * that we are trying to delete.
                         *
                         * We need to disconnect our transaction from
                         * backend_data, since the abort (whether successful or
                         * not) will free it.
                         */
                        backend_data->packed_transaction = NULL;
                        if (ref_transaction_abort(packed_transaction, err)) {
                                ret = REF_TRANSACTION_ERROR_GENERIC;
                                goto cleanup;
                        }
                }
        }

cleanup:
        free(head_ref);
        string_list_clear(&refnames_to_check, 1);

        if (ret)
                files_transaction_cleanup(refs, transaction);
        else
                transaction->state = REF_TRANSACTION_PREPARED;

        return ret;
}

static int parse_and_write_reflog(struct files_ref_store *refs,
                                  struct ref_update *update,
                                  struct ref_lock *lock,
                                  struct strbuf *err)
{
        struct object_id *old_oid = &lock->old_oid;

        if (update->flags & REF_LOG_USE_PROVIDED_OIDS) {
                if (!(update->flags & REF_HAVE_OLD) ||
                    !(update->flags & REF_HAVE_NEW) ||
                    !(update->flags & REF_LOG_ONLY)) {
                        strbuf_addf(err, _("trying to write reflog for '%s' "
                                           "with incomplete values"), update->refname);
                        return REF_TRANSACTION_ERROR_GENERIC;
                }

                old_oid = &update->old_oid;
        }

        if (update->new_target) {
                /*
                 * We want to get the resolved OID for the target, to ensure
                 * that the correct value is added to the reflog.
                 */
                if (!refs_resolve_ref_unsafe(&refs->base, update->new_target,
                                             RESOLVE_REF_READING,
                                             &update->new_oid, NULL)) {
                        /*
                         * TODO: currently we skip creating reflogs for dangling
                         * symref updates. It would be nice to capture this as
                         * zero oid updates however.
                         */
                        return 0;
                }
        }

        if (files_log_ref_write(refs, lock->ref_name, old_oid,
                                &update->new_oid, update->committer_info,
                                update->msg, update->flags, err)) {
                char *old_msg = strbuf_detach(err, NULL);

                strbuf_addf(err, "cannot update the ref '%s': %s",
                            lock->ref_name, old_msg);
                free(old_msg);
                unlock_ref(lock);
                update->backend_data = NULL;
                return -1;
        }

        return 0;
}

static int ref_present(const char *refname, const char *referent UNUSED,
                       const struct object_id *oid UNUSED,
                       int flags UNUSED,
                       void *cb_data)
{
        struct string_list *affected_refnames = cb_data;

        return string_list_has_string(affected_refnames, refname);
}

static int files_transaction_finish_initial(struct files_ref_store *refs,
                                            struct ref_transaction *transaction,
                                            struct strbuf *err)
{
        size_t i;
        int ret = 0;
        struct string_list affected_refnames = STRING_LIST_INIT_NODUP;
        struct string_list refnames_to_check = STRING_LIST_INIT_NODUP;
        struct ref_transaction *packed_transaction = NULL;
        struct ref_transaction *loose_transaction = NULL;

        assert(err);

        if (transaction->state != REF_TRANSACTION_PREPARED)
                BUG("commit called for transaction that is not prepared");

        /*
         * It's really undefined to call this function in an active
         * repository or when there are existing references: we are
         * only locking and changing packed-refs, so (1) any
         * simultaneous processes might try to change a reference at
         * the same time we do, and (2) any existing loose versions of
         * the references that we are setting would have precedence
         * over our values. But some remote helpers create the remote
         * "HEAD" and "master" branches before calling this function,
         * so here we really only check that none of the references
         * that we are creating already exists.
         */
        if (refs_for_each_rawref(&refs->base, ref_present,
                                 &transaction->refnames))
                BUG("initial ref transaction called with existing refs");

        packed_transaction = ref_store_transaction_begin(refs->packed_ref_store,
                                                         transaction->flags, err);
        if (!packed_transaction) {
                ret = REF_TRANSACTION_ERROR_GENERIC;
                goto cleanup;
        }

        for (i = 0; i < transaction->nr; i++) {
                struct ref_update *update = transaction->updates[i];

                if (!(update->flags & REF_LOG_ONLY) &&
                    (update->flags & REF_HAVE_OLD) &&
                    !is_null_oid(&update->old_oid))
                        BUG("initial ref transaction with old_sha1 set");

                string_list_append(&refnames_to_check, update->refname);

                /*
                 * packed-refs don't support symbolic refs, root refs and reflogs,
                 * so we have to queue these references via the loose transaction.
                 */
                if (update->new_target ||
                    is_root_ref(update->refname) ||
                    (update->flags & REF_LOG_ONLY)) {
                        if (!loose_transaction) {
                                loose_transaction = ref_store_transaction_begin(&refs->base, 0, err);
                                if (!loose_transaction) {
                                        ret = REF_TRANSACTION_ERROR_GENERIC;
                                        goto cleanup;
                                }
                        }

                        if (update->flags & REF_LOG_ONLY)
                                ref_transaction_add_update(loose_transaction, update->refname,
                                                           update->flags, &update->new_oid,
                                                           &update->old_oid, NULL, NULL,
                                                           update->committer_info, update->msg);
                        else
                                ref_transaction_add_update(loose_transaction, update->refname,
                                                           update->flags & ~REF_HAVE_OLD,
                                                           update->new_target ? NULL : &update->new_oid, NULL,
                                                           update->new_target, NULL, update->committer_info,
                                                           NULL);
                } else {
                        ref_transaction_add_update(packed_transaction, update->refname,
                                                   update->flags & ~REF_HAVE_OLD,
                                                   &update->new_oid, &update->old_oid,
                                                   NULL, NULL, update->committer_info, NULL);
                }
        }

        if (packed_refs_lock(refs->packed_ref_store, 0, err)) {
                ret = REF_TRANSACTION_ERROR_GENERIC;
                goto cleanup;
        }

        if (refs_verify_refnames_available(&refs->base, &refnames_to_check,
                                           &affected_refnames, NULL, transaction,
                                           1, err)) {
                packed_refs_unlock(refs->packed_ref_store);
                ret = REF_TRANSACTION_ERROR_NAME_CONFLICT;
                goto cleanup;
        }

        if (ref_transaction_commit(packed_transaction, err)) {
                ret = REF_TRANSACTION_ERROR_GENERIC;
                goto cleanup;
        }
        packed_refs_unlock(refs->packed_ref_store);

        if (loose_transaction) {
                if (ref_transaction_prepare(loose_transaction, err) ||
                    ref_transaction_commit(loose_transaction, err)) {
                        ret = REF_TRANSACTION_ERROR_GENERIC;
                        goto cleanup;
                }
        }

cleanup:
        if (loose_transaction)
                ref_transaction_free(loose_transaction);
        if (packed_transaction)
                ref_transaction_free(packed_transaction);
        transaction->state = REF_TRANSACTION_CLOSED;
        string_list_clear(&affected_refnames, 0);
        string_list_clear(&refnames_to_check, 0);
        return ret;
}

static int files_transaction_finish(struct ref_store *ref_store,
                                    struct ref_transaction *transaction,
                                    struct strbuf *err)
{
        struct files_ref_store *refs =
                files_downcast(ref_store, 0, "ref_transaction_finish");
        size_t i;
        int ret = 0;
        struct strbuf sb = STRBUF_INIT;
        struct files_transaction_backend_data *backend_data;
        struct ref_transaction *packed_transaction;


        assert(err);

        if (transaction->flags & REF_TRANSACTION_FLAG_INITIAL)
                return files_transaction_finish_initial(refs, transaction, err);
        if (!transaction->nr) {
                transaction->state = REF_TRANSACTION_CLOSED;
                return 0;
        }

        backend_data = transaction->backend_data;
        packed_transaction = backend_data->packed_transaction;

        /* Perform updates first so live commits remain referenced */
        for (i = 0; i < transaction->nr; i++) {
                struct ref_update *update = transaction->updates[i];
                struct ref_lock *lock = update->backend_data;

                if (update->rejection_err)
                        continue;

                if (update->flags & REF_NEEDS_COMMIT ||
                    update->flags & REF_LOG_ONLY) {
                        if (parse_and_write_reflog(refs, update, lock, err)) {
                                ret = REF_TRANSACTION_ERROR_GENERIC;
                                goto cleanup;
                        }
                }

                /*
                 * We try creating a symlink, if that succeeds we continue to the
                 * next update. If not, we try and create a regular symref.
                 */
                if (update->new_target && refs->prefer_symlink_refs)
                        /*
                         * By using the `NOT_CONSTANT()` trick, we can avoid
                         * errors by `clang`'s `-Wunreachable` logic that would
                         * report that the `continue` statement is not reachable
                         * when `NO_SYMLINK_HEAD` is `#define`d.
                         */
                        if (NOT_CONSTANT(!create_ref_symlink(lock, update->new_target)))
                                continue;

                if (update->flags & REF_NEEDS_COMMIT) {
                        clear_loose_ref_cache(refs);
                        if (commit_ref(lock)) {
                                strbuf_addf(err, "couldn't set '%s'", lock->ref_name);
                                unlock_ref(lock);
                                update->backend_data = NULL;
                                ret = REF_TRANSACTION_ERROR_GENERIC;
                                goto cleanup;
                        }
                }
        }

        /*
         * Now that updates are safely completed, we can perform
         * deletes. First delete the reflogs of any references that
         * will be deleted, since (in the unexpected event of an
         * error) leaving a reference without a reflog is less bad
         * than leaving a reflog without a reference (the latter is a
         * mildly invalid repository state):
         */
        for (i = 0; i < transaction->nr; i++) {
                struct ref_update *update = transaction->updates[i];

                if (update->rejection_err)
                        continue;

                if (update->flags & REF_DELETING &&
                    !(update->flags & REF_LOG_ONLY) &&
                    !(update->flags & REF_IS_PRUNING)) {
                        strbuf_reset(&sb);
                        files_reflog_path(refs, &sb, update->refname);
                        if (!unlink_or_warn(sb.buf))
                                try_remove_empty_parents(refs, update->refname,
                                                         REMOVE_EMPTY_PARENTS_REFLOG);
                }
        }

        /*
         * Perform deletes now that updates are safely completed.
         *
         * First delete any packed versions of the references, while
         * retaining the packed-refs lock:
         */
        if (packed_transaction) {
                ret = ref_transaction_commit(packed_transaction, err);
                ref_transaction_free(packed_transaction);
                packed_transaction = NULL;
                backend_data->packed_transaction = NULL;
                if (ret)
                        goto cleanup;
        }

        /* Now delete the loose versions of the references: */
        for (i = 0; i < transaction->nr; i++) {
                struct ref_update *update = transaction->updates[i];
                struct ref_lock *lock = update->backend_data;

                if (update->rejection_err)
                        continue;

                if (update->flags & REF_DELETING &&
                    !(update->flags & REF_LOG_ONLY)) {
                        update->flags |= REF_DELETED_RMDIR;
                        if (!(update->type & REF_ISPACKED) ||
                            update->type & REF_ISSYMREF) {
                                /* It is a loose reference. */
                                strbuf_reset(&sb);
                                files_ref_path(refs, &sb, lock->ref_name);
                                if (unlink_or_msg(sb.buf, err)) {
                                        ret = REF_TRANSACTION_ERROR_GENERIC;
                                        goto cleanup;
                                }
                        }
                }
        }

        clear_loose_ref_cache(refs);

cleanup:
        files_transaction_cleanup(refs, transaction);

        for (i = 0; i < transaction->nr; i++) {
                struct ref_update *update = transaction->updates[i];

                if (update->flags & REF_DELETED_RMDIR) {
                        /*
                         * The reference was deleted. Delete any
                         * empty parent directories. (Note that this
                         * can only work because we have already
                         * removed the lockfile.)
                         */
                        try_remove_empty_parents(refs, update->refname,
                                                 REMOVE_EMPTY_PARENTS_REF);
                }
        }

        strbuf_release(&sb);
        return ret;
}

static int files_transaction_abort(struct ref_store *ref_store,
                                   struct ref_transaction *transaction,
                                   struct strbuf *err UNUSED)
{
        struct files_ref_store *refs =
                files_downcast(ref_store, 0, "ref_transaction_abort");

        files_transaction_cleanup(refs, transaction);
        return 0;
}

struct expire_reflog_cb {
        reflog_expiry_should_prune_fn *should_prune_fn;
        void *policy_cb;
        FILE *newlog;
        struct object_id last_kept_oid;
        unsigned int rewrite:1,
                     dry_run:1;
};

static int expire_reflog_ent(const char *refname UNUSED,
                             struct object_id *ooid, struct object_id *noid,
                             const char *email, timestamp_t timestamp, int tz,
                             const char *message, void *cb_data)
{
        struct expire_reflog_cb *cb = cb_data;
        reflog_expiry_should_prune_fn *fn = cb->should_prune_fn;

        if (cb->rewrite)
                ooid = &cb->last_kept_oid;

        if (fn(ooid, noid, email, timestamp, tz, message, cb->policy_cb))
                return 0;

        if (cb->dry_run)
                return 0; /* --dry-run */

        fprintf(cb->newlog, "%s %s %s %"PRItime" %+05d\t%s", oid_to_hex(ooid),
                oid_to_hex(noid), email, timestamp, tz, message);
        oidcpy(&cb->last_kept_oid, noid);

        return 0;
}

static int files_reflog_expire(struct ref_store *ref_store,
                               const char *refname,
                               unsigned int expire_flags,
                               reflog_expiry_prepare_fn prepare_fn,
                               reflog_expiry_should_prune_fn should_prune_fn,
                               reflog_expiry_cleanup_fn cleanup_fn,
                               void *policy_cb_data)
{
        struct files_ref_store *refs =
                files_downcast(ref_store, REF_STORE_WRITE, "reflog_expire");
        struct lock_file reflog_lock = LOCK_INIT;
        struct expire_reflog_cb cb;
        struct ref_lock *lock;
        struct strbuf log_file_sb = STRBUF_INIT;
        char *log_file;
        int status = 0;
        struct strbuf err = STRBUF_INIT;
        const struct object_id *oid;

        memset(&cb, 0, sizeof(cb));
        cb.rewrite = !!(expire_flags & EXPIRE_REFLOGS_REWRITE);
        cb.dry_run = !!(expire_flags & EXPIRE_REFLOGS_DRY_RUN);
        cb.policy_cb = policy_cb_data;
        cb.should_prune_fn = should_prune_fn;

        /*
         * The reflog file is locked by holding the lock on the
         * reference itself, plus we might need to update the
         * reference if --updateref was specified:
         */
        lock = lock_ref_oid_basic(refs, refname, &err);
        if (!lock) {
                error("cannot lock ref '%s': %s", refname, err.buf);
                strbuf_release(&err);
                return -1;
        }
        oid = &lock->old_oid;

        /*
         * When refs are deleted, their reflog is deleted before the
         * ref itself is deleted. This is because there is no separate
         * lock for reflog; instead we take a lock on the ref with
         * lock_ref_oid_basic().
         *
         * If a race happens and the reflog doesn't exist after we've
         * acquired the lock that's OK. We've got nothing more to do;
         * We were asked to delete the reflog, but someone else
         * deleted it! The caller doesn't care that we deleted it,
         * just that it is deleted. So we can return successfully.
         */
        if (!refs_reflog_exists(ref_store, refname)) {
                unlock_ref(lock);
                return 0;
        }

        files_reflog_path(refs, &log_file_sb, refname);
        log_file = strbuf_detach(&log_file_sb, NULL);
        if (!cb.dry_run) {
                /*
                 * Even though holding $GIT_DIR/logs/$reflog.lock has
                 * no locking implications, we use the lock_file
                 * machinery here anyway because it does a lot of the
                 * work we need, including cleaning up if the program
                 * exits unexpectedly.
                 */
                if (hold_lock_file_for_update(&reflog_lock, log_file, 0) < 0) {
                        struct strbuf err = STRBUF_INIT;
                        unable_to_lock_message(log_file, errno, &err);
                        error("%s", err.buf);
                        strbuf_release(&err);
                        goto failure;
                }
                cb.newlog = fdopen_lock_file(&reflog_lock, "w");
                if (!cb.newlog) {
                        error("cannot fdopen %s (%s)",
                              get_lock_file_path(&reflog_lock), strerror(errno));
                        goto failure;
                }
        }

        (*prepare_fn)(refname, oid, cb.policy_cb);
        refs_for_each_reflog_ent(ref_store, refname, expire_reflog_ent, &cb);
        (*cleanup_fn)(cb.policy_cb);

        if (!cb.dry_run) {
                /*
                 * It doesn't make sense to adjust a reference pointed
                 * to by a symbolic ref based on expiring entries in
                 * the symbolic reference's reflog. Nor can we update
                 * a reference if there are no remaining reflog
                 * entries.
                 */
                int update = 0;

                if ((expire_flags & EXPIRE_REFLOGS_UPDATE_REF) &&
                    !is_null_oid(&cb.last_kept_oid)) {
                        int type;
                        const char *ref;

                        ref = refs_resolve_ref_unsafe(&refs->base, refname,
                                                      RESOLVE_REF_NO_RECURSE,
                                                      NULL, &type);
                        update = !!(ref && !(type & REF_ISSYMREF));
                }

                if (close_lock_file_gently(&reflog_lock)) {
                        status |= error("couldn't write %s: %s", log_file,
                                        strerror(errno));
                        rollback_lock_file(&reflog_lock);
                } else if (update &&
                           (write_in_full(get_lock_file_fd(&lock->lk),
                                oid_to_hex(&cb.last_kept_oid), refs->base.repo->hash_algo->hexsz) < 0 ||
                            write_str_in_full(get_lock_file_fd(&lock->lk), "\n") < 0 ||
                            close_ref_gently(lock) < 0)) {
                        status |= error("couldn't write %s",
                                        get_lock_file_path(&lock->lk));
                        rollback_lock_file(&reflog_lock);
                } else if (commit_lock_file(&reflog_lock)) {
                        status |= error("unable to write reflog '%s' (%s)",
                                        log_file, strerror(errno));
                } else if (update && commit_ref(lock)) {
                        status |= error("couldn't set %s", lock->ref_name);
                }
        }
        free(log_file);
        unlock_ref(lock);
        return status;

 failure:
        rollback_lock_file(&reflog_lock);
        free(log_file);
        unlock_ref(lock);
        return -1;
}

static int files_ref_store_create_on_disk(struct ref_store *ref_store,
                                          int flags,
                                          struct strbuf *err UNUSED)
{
        struct files_ref_store *refs =
                files_downcast(ref_store, REF_STORE_WRITE, "create");
        struct strbuf sb = STRBUF_INIT;

        /*
         * We need to create a "refs" dir in any case so that older versions of
         * Git can tell that this is a repository. This serves two main purposes:
         *
         * - Clients will know to stop walking the parent-directory chain when
         *   detecting the Git repository. Otherwise they may end up detecting
         *   a Git repository in a parent directory instead.
         *
         * - Instead of failing to detect a repository with unknown reference
         *   format altogether, old clients will print an error saying that
         *   they do not understand the reference format extension.
         */
        strbuf_addf(&sb, "%s/refs", ref_store->gitdir);
        safe_create_dir(the_repository, sb.buf, 1);
        adjust_shared_perm(the_repository, sb.buf);

        /*
         * There is no need to create directories for common refs when creating
         * a worktree ref store.
         */
        if (!(flags & REF_STORE_CREATE_ON_DISK_IS_WORKTREE)) {
                /*
                 * Create .git/refs/{heads,tags}
                 */
                strbuf_reset(&sb);
                files_ref_path(refs, &sb, "refs/heads");
                safe_create_dir(the_repository, sb.buf, 1);

                strbuf_reset(&sb);
                files_ref_path(refs, &sb, "refs/tags");
                safe_create_dir(the_repository, sb.buf, 1);
        }

        strbuf_release(&sb);
        return 0;
}

struct remove_one_root_ref_data {
        const char *gitdir;
        struct strbuf *err;
};

static int remove_one_root_ref(const char *refname,
                               void *cb_data)
{
        struct remove_one_root_ref_data *data = cb_data;
        struct strbuf buf = STRBUF_INIT;
        int ret = 0;

        strbuf_addf(&buf, "%s/%s", data->gitdir, refname);

        ret = unlink(buf.buf);
        if (ret < 0)
                strbuf_addf(data->err, "could not delete %s: %s\n",
                            refname, strerror(errno));

        strbuf_release(&buf);
        return ret;
}

static int files_ref_store_remove_on_disk(struct ref_store *ref_store,
                                          struct strbuf *err)
{
        struct files_ref_store *refs =
                files_downcast(ref_store, REF_STORE_WRITE, "remove");
        struct remove_one_root_ref_data data = {
                .gitdir = refs->base.gitdir,
                .err = err,
        };
        struct strbuf sb = STRBUF_INIT;
        int ret = 0;

        strbuf_addf(&sb, "%s/refs", refs->base.gitdir);
        if (remove_dir_recursively(&sb, 0) < 0) {
                strbuf_addf(err, "could not delete refs: %s",
                            strerror(errno));
                ret = -1;
        }
        strbuf_reset(&sb);

        strbuf_addf(&sb, "%s/logs", refs->base.gitdir);
        if (remove_dir_recursively(&sb, 0) < 0) {
                strbuf_addf(err, "could not delete logs: %s",
                            strerror(errno));
                ret = -1;
        }
        strbuf_reset(&sb);

        if (for_each_root_ref(refs, remove_one_root_ref, &data) < 0)
                ret = -1;

        if (ref_store_remove_on_disk(refs->packed_ref_store, err) < 0)
                ret = -1;

        strbuf_release(&sb);
        return ret;
}

/*
 * For refs and reflogs, they share a unified interface when scanning
 * the whole directory. This function is used as the callback for each
 * regular file or symlink in the directory.
 */
typedef int (*files_fsck_refs_fn)(struct ref_store *ref_store,
                                  struct fsck_options *o,
                                  const char *refname,
                                  struct dir_iterator *iter);

static int files_fsck_symref_target(struct fsck_options *o,
                                    struct fsck_ref_report *report,
                                    struct strbuf *referent,
                                    unsigned int symbolic_link)
{
        int is_referent_root;
        char orig_last_byte;
        size_t orig_len;
        int ret = 0;

        orig_len = referent->len;
        orig_last_byte = referent->buf[orig_len - 1];
        if (!symbolic_link)
                strbuf_rtrim(referent);

        is_referent_root = is_root_ref(referent->buf);
        if (!is_referent_root &&
            !starts_with(referent->buf, "refs/") &&
            !starts_with(referent->buf, "worktrees/")) {
                ret = fsck_report_ref(o, report,
                                      FSCK_MSG_SYMREF_TARGET_IS_NOT_A_REF,
                                      "points to non-ref target '%s'", referent->buf);

        }

        if (!is_referent_root && check_refname_format(referent->buf, 0)) {
                ret = fsck_report_ref(o, report,
                                      FSCK_MSG_BAD_REFERENT_NAME,
                                      "points to invalid refname '%s'", referent->buf);
                goto out;
        }

        if (symbolic_link)
                goto out;

        if (referent->len == orig_len ||
            (referent->len < orig_len && orig_last_byte != '\n')) {
                ret = fsck_report_ref(o, report,
                                      FSCK_MSG_REF_MISSING_NEWLINE,
                                      "misses LF at the end");
        }

        if (referent->len != orig_len && referent->len != orig_len - 1) {
                ret = fsck_report_ref(o, report,
                                      FSCK_MSG_TRAILING_REF_CONTENT,
                                      "has trailing whitespaces or newlines");
        }

out:
        return ret;
}

static int files_fsck_refs_content(struct ref_store *ref_store,
                                   struct fsck_options *o,
                                   const char *target_name,
                                   struct dir_iterator *iter)
{
        struct strbuf ref_content = STRBUF_INIT;
        struct strbuf abs_gitdir = STRBUF_INIT;
        struct strbuf referent = STRBUF_INIT;
        struct fsck_ref_report report = { 0 };
        const char *trailing = NULL;
        unsigned int type = 0;
        int failure_errno = 0;
        struct object_id oid;
        int ret = 0;

        report.path = target_name;

        if (S_ISLNK(iter->st.st_mode)) {
                const char *relative_referent_path = NULL;

                ret = fsck_report_ref(o, &report,
                                      FSCK_MSG_SYMLINK_REF,
                                      "use deprecated symbolic link for symref");

                strbuf_add_absolute_path(&abs_gitdir, ref_store->repo->gitdir);
                strbuf_normalize_path(&abs_gitdir);
                if (!is_dir_sep(abs_gitdir.buf[abs_gitdir.len - 1]))
                        strbuf_addch(&abs_gitdir, '/');

                strbuf_add_real_path(&ref_content, iter->path.buf);
                skip_prefix(ref_content.buf, abs_gitdir.buf,
                            &relative_referent_path);

                if (relative_referent_path)
                        strbuf_addstr(&referent, relative_referent_path);
                else
                        strbuf_addbuf(&referent, &ref_content);

                ret |= files_fsck_symref_target(o, &report, &referent, 1);
                goto cleanup;
        }

        if (strbuf_read_file(&ref_content, iter->path.buf, 0) < 0) {
                /*
                 * Ref file could be removed by another concurrent process. We should
                 * ignore this error and continue to the next ref.
                 */
                if (errno == ENOENT)
                        goto cleanup;

                ret = error_errno(_("cannot read ref file '%s'"), iter->path.buf);
                goto cleanup;
        }

        if (parse_loose_ref_contents(ref_store->repo->hash_algo,
                                     ref_content.buf, &oid, &referent,
                                     &type, &trailing, &failure_errno)) {
                strbuf_rtrim(&ref_content);
                ret = fsck_report_ref(o, &report,
                                      FSCK_MSG_BAD_REF_CONTENT,
                                      "%s", ref_content.buf);
                goto cleanup;
        }

        if (!(type & REF_ISSYMREF)) {
                if (!*trailing) {
                        ret = fsck_report_ref(o, &report,
                                              FSCK_MSG_REF_MISSING_NEWLINE,
                                              "misses LF at the end");
                        goto cleanup;
                }
                if (*trailing != '\n' || *(trailing + 1)) {
                        ret = fsck_report_ref(o, &report,
                                              FSCK_MSG_TRAILING_REF_CONTENT,
                                              "has trailing garbage: '%s'", trailing);
                        goto cleanup;
                }
        } else {
                ret = files_fsck_symref_target(o, &report, &referent, 0);
                goto cleanup;
        }

cleanup:
        strbuf_release(&ref_content);
        strbuf_release(&referent);
        strbuf_release(&abs_gitdir);
        return ret;
}

static int files_fsck_refs_name(struct ref_store *ref_store UNUSED,
                                struct fsck_options *o,
                                const char *refname,
                                struct dir_iterator *iter)
{
        struct strbuf sb = STRBUF_INIT;
        int ret = 0;

        /*
         * Ignore the files ending with ".lock" as they may be lock files
         * However, do not allow bare ".lock" files.
         */
        if (iter->basename[0] != '.' && ends_with(iter->basename, ".lock"))
                goto cleanup;

        /*
         * This works right now because we never check the root refs.
         */
        if (check_refname_format(refname, 0)) {
                struct fsck_ref_report report = { 0 };

                report.path = refname;
                ret = fsck_report_ref(o, &report,
                                      FSCK_MSG_BAD_REF_NAME,
                                      "invalid refname format");
        }

cleanup:
        strbuf_release(&sb);
        return ret;
}

static int files_fsck_refs_dir(struct ref_store *ref_store,
                               struct fsck_options *o,
                               const char *refs_check_dir,
                               struct worktree *wt,
                               files_fsck_refs_fn *fsck_refs_fn)
{
        struct strbuf refname = STRBUF_INIT;
        struct strbuf sb = STRBUF_INIT;
        struct dir_iterator *iter;
        int iter_status;
        int ret = 0;

        strbuf_addf(&sb, "%s/%s", ref_store->gitdir, refs_check_dir);

        iter = dir_iterator_begin(sb.buf, 0);
        if (!iter) {
                if (errno == ENOENT && !is_main_worktree(wt))
                        goto out;

                ret = error_errno(_("cannot open directory %s"), sb.buf);
                goto out;
        }

        while ((iter_status = dir_iterator_advance(iter)) == ITER_OK) {
                if (S_ISDIR(iter->st.st_mode)) {
                        continue;
                } else if (S_ISREG(iter->st.st_mode) ||
                           S_ISLNK(iter->st.st_mode)) {
                        strbuf_reset(&refname);

                        if (!is_main_worktree(wt))
                                strbuf_addf(&refname, "worktrees/%s/", wt->id);
                        strbuf_addf(&refname, "%s/%s", refs_check_dir,
                                    iter->relative_path);

                        if (o->verbose)
                                fprintf_ln(stderr, "Checking %s", refname.buf);

                        for (size_t i = 0; fsck_refs_fn[i]; i++) {
                                if (fsck_refs_fn[i](ref_store, o, refname.buf, iter))
                                        ret = -1;
                        }
                } else {
                        struct fsck_ref_report report = { .path = iter->basename };
                        if (fsck_report_ref(o, &report,
                                            FSCK_MSG_BAD_REF_FILETYPE,
                                            "unexpected file type"))
                                ret = -1;
                }
        }

        if (iter_status != ITER_DONE)
                ret = error(_("failed to iterate over '%s'"), sb.buf);

out:
        dir_iterator_free(iter);
        strbuf_release(&sb);
        strbuf_release(&refname);
        return ret;
}

static int files_fsck_refs(struct ref_store *ref_store,
                           struct fsck_options *o,
                           struct worktree *wt)
{
        files_fsck_refs_fn fsck_refs_fn[]= {
                files_fsck_refs_name,
                files_fsck_refs_content,
                NULL,
        };

        return files_fsck_refs_dir(ref_store, o, "refs", wt, fsck_refs_fn);
}

static int files_fsck(struct ref_store *ref_store,
                      struct fsck_options *o,
                      struct worktree *wt)
{
        struct files_ref_store *refs =
                files_downcast(ref_store, REF_STORE_READ, "fsck");

        return files_fsck_refs(ref_store, o, wt) |
               refs->packed_ref_store->be->fsck(refs->packed_ref_store, o, wt);
}

struct ref_storage_be refs_be_files = {
        .name = "files",
        .init = files_ref_store_init,
        .release = files_ref_store_release,
        .create_on_disk = files_ref_store_create_on_disk,
        .remove_on_disk = files_ref_store_remove_on_disk,

        .transaction_prepare = files_transaction_prepare,
        .transaction_finish = files_transaction_finish,
        .transaction_abort = files_transaction_abort,

        .pack_refs = files_pack_refs,
        .optimize = files_optimize,
        .rename_ref = files_rename_ref,
        .copy_ref = files_copy_ref,

        .iterator_begin = files_ref_iterator_begin,
        .read_raw_ref = files_read_raw_ref,
        .read_symbolic_ref = files_read_symbolic_ref,

        .reflog_iterator_begin = files_reflog_iterator_begin,
        .for_each_reflog_ent = files_for_each_reflog_ent,
        .for_each_reflog_ent_reverse = files_for_each_reflog_ent_reverse,
        .reflog_exists = files_reflog_exists,
        .create_reflog = files_create_reflog,
        .delete_reflog = files_delete_reflog,
        .reflog_expire = files_reflog_expire,

        .fsck = files_fsck,
};