refs: retry acquiring reference locks for 100ms

[thirdparty/git.git] / refs.c

/*
 * The backend-independent part of the reference module.
 */

#include "cache.h"
#include "config.h"
#include "hashmap.h"
#include "lockfile.h"
#include "iterator.h"
#include "refs.h"
#include "refs/refs-internal.h"
#include "object.h"
#include "tag.h"
#include "submodule.h"
#include "worktree.h"

/*
 * List of all available backends
 */
static struct ref_storage_be *refs_backends = &refs_be_files;

static struct ref_storage_be *find_ref_storage_backend(const char *name)
{
        struct ref_storage_be *be;
        for (be = refs_backends; be; be = be->next)
                if (!strcmp(be->name, name))
                        return be;
        return NULL;
}

int ref_storage_backend_exists(const char *name)
{
        return find_ref_storage_backend(name) != NULL;
}

/*
 * How to handle various characters in refnames:
 * 0: An acceptable character for refs
 * 1: End-of-component
 * 2: ., look for a preceding . to reject .. in refs
 * 3: {, look for a preceding @ to reject @{ in refs
 * 4: A bad character: ASCII control characters, and
 *    ":", "?", "[", "\", "^", "~", SP, or TAB
 * 5: *, reject unless REFNAME_REFSPEC_PATTERN is set
 */
static unsigned char refname_disposition[256] = {
        1, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4,
        4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4,
        4, 0, 0, 0, 0, 0, 0, 0, 0, 0, 5, 0, 0, 0, 2, 1,
        0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 4, 0, 0, 0, 0, 4,
        0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
        0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 4, 4, 0, 4, 0,
        0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
        0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 3, 0, 0, 4, 4
};

/*
 * Try to read one refname component from the front of refname.
 * Return the length of the component found, or -1 if the component is
 * not legal.  It is legal if it is something reasonable to have under
 * ".git/refs/"; We do not like it if:
 *
 * - any path component of it begins with ".", or
 * - it has double dots "..", or
 * - it has ASCII control characters, or
 * - it has ":", "?", "[", "\", "^", "~", SP, or TAB anywhere, or
 * - it has "*" anywhere unless REFNAME_REFSPEC_PATTERN is set, or
 * - it ends with a "/", or
 * - it ends with ".lock", or
 * - it contains a "@{" portion
 */
static int check_refname_component(const char *refname, int *flags)
{
        const char *cp;
        char last = '\0';

        for (cp = refname; ; cp++) {
                int ch = *cp & 255;
                unsigned char disp = refname_disposition[ch];
                switch (disp) {
                case 1:
                        goto out;
                case 2:
                        if (last == '.')
                                return -1; /* Refname contains "..". */
                        break;
                case 3:
                        if (last == '@')
                                return -1; /* Refname contains "@{". */
                        break;
                case 4:
                        return -1;
                case 5:
                        if (!(*flags & REFNAME_REFSPEC_PATTERN))
                                return -1; /* refspec can't be a pattern */

                        /*
                         * Unset the pattern flag so that we only accept
                         * a single asterisk for one side of refspec.
                         */
                        *flags &= ~ REFNAME_REFSPEC_PATTERN;
                        break;
                }
                last = ch;
        }
out:
        if (cp == refname)
                return 0; /* Component has zero length. */
        if (refname[0] == '.')
                return -1; /* Component starts with '.'. */
        if (cp - refname >= LOCK_SUFFIX_LEN &&
            !memcmp(cp - LOCK_SUFFIX_LEN, LOCK_SUFFIX, LOCK_SUFFIX_LEN))
                return -1; /* Refname ends with ".lock". */
        return cp - refname;
}

int check_refname_format(const char *refname, int flags)
{
        int component_len, component_count = 0;

        if (!strcmp(refname, "@"))
                /* Refname is a single character '@'. */
                return -1;

        while (1) {
                /* We are at the start of a path component. */
                component_len = check_refname_component(refname, &flags);
                if (component_len <= 0)
                        return -1;

                component_count++;
                if (refname[component_len] == '\0')
                        break;
                /* Skip to next component. */
                refname += component_len + 1;
        }

        if (refname[component_len - 1] == '.')
                return -1; /* Refname ends with '.'. */
        if (!(flags & REFNAME_ALLOW_ONELEVEL) && component_count < 2)
                return -1; /* Refname has only one component. */
        return 0;
}

int refname_is_safe(const char *refname)
{
        const char *rest;

        if (skip_prefix(refname, "refs/", &rest)) {
                char *buf;
                int result;
                size_t restlen = strlen(rest);

                /* rest must not be empty, or start or end with "/" */
                if (!restlen || *rest == '/' || rest[restlen - 1] == '/')
                        return 0;

                /*
                 * Does the refname try to escape refs/?
                 * For example: refs/foo/../bar is safe but refs/foo/../../bar
                 * is not.
                 */
                buf = xmallocz(restlen);
                result = !normalize_path_copy(buf, rest) && !strcmp(buf, rest);
                free(buf);
                return result;
        }

        do {
                if (!isupper(*refname) && *refname != '_')
                        return 0;
                refname++;
        } while (*refname);
        return 1;
}

char *refs_resolve_refdup(struct ref_store *refs,
                          const char *refname, int resolve_flags,
                          unsigned char *sha1, int *flags)
{
        const char *result;

        result = refs_resolve_ref_unsafe(refs, refname, resolve_flags,
                                         sha1, flags);
        return xstrdup_or_null(result);
}

char *resolve_refdup(const char *refname, int resolve_flags,
                     unsigned char *sha1, int *flags)
{
        return refs_resolve_refdup(get_main_ref_store(),
                                   refname, resolve_flags,
                                   sha1, flags);
}

/* The argument to filter_refs */
struct ref_filter {
        const char *pattern;
        each_ref_fn *fn;
        void *cb_data;
};

int refs_read_ref_full(struct ref_store *refs, const char *refname,
                       int resolve_flags, unsigned char *sha1, int *flags)
{
        if (refs_resolve_ref_unsafe(refs, refname, resolve_flags, sha1, flags))
                return 0;
        return -1;
}

int read_ref_full(const char *refname, int resolve_flags, unsigned char *sha1, int *flags)
{
        return refs_read_ref_full(get_main_ref_store(), refname,
                                  resolve_flags, sha1, flags);
}

int read_ref(const char *refname, unsigned char *sha1)
{
        return read_ref_full(refname, RESOLVE_REF_READING, sha1, NULL);
}

int ref_exists(const char *refname)
{
        unsigned char sha1[20];
        return !!resolve_ref_unsafe(refname, RESOLVE_REF_READING, sha1, NULL);
}

static int filter_refs(const char *refname, const struct object_id *oid,
                           int flags, void *data)
{
        struct ref_filter *filter = (struct ref_filter *)data;

        if (wildmatch(filter->pattern, refname, 0))
                return 0;
        return filter->fn(refname, oid, flags, filter->cb_data);
}

enum peel_status peel_object(const unsigned char *name, unsigned char *sha1)
{
        struct object *o = lookup_unknown_object(name);

        if (o->type == OBJ_NONE) {
                int type = sha1_object_info(name, NULL);
                if (type < 0 || !object_as_type(o, type, 0))
                        return PEEL_INVALID;
        }

        if (o->type != OBJ_TAG)
                return PEEL_NON_TAG;

        o = deref_tag_noverify(o);
        if (!o)
                return PEEL_INVALID;

        hashcpy(sha1, o->oid.hash);
        return PEEL_PEELED;
}

struct warn_if_dangling_data {
        FILE *fp;
        const char *refname;
        const struct string_list *refnames;
        const char *msg_fmt;
};

static int warn_if_dangling_symref(const char *refname, const struct object_id *oid,
                                   int flags, void *cb_data)
{
        struct warn_if_dangling_data *d = cb_data;
        const char *resolves_to;
        struct object_id junk;

        if (!(flags & REF_ISSYMREF))
                return 0;

        resolves_to = resolve_ref_unsafe(refname, 0, junk.hash, NULL);
        if (!resolves_to
            || (d->refname
                ? strcmp(resolves_to, d->refname)
                : !string_list_has_string(d->refnames, resolves_to))) {
                return 0;
        }

        fprintf(d->fp, d->msg_fmt, refname);
        fputc('\n', d->fp);
        return 0;
}

void warn_dangling_symref(FILE *fp, const char *msg_fmt, const char *refname)
{
        struct warn_if_dangling_data data;

        data.fp = fp;
        data.refname = refname;
        data.refnames = NULL;
        data.msg_fmt = msg_fmt;
        for_each_rawref(warn_if_dangling_symref, &data);
}

void warn_dangling_symrefs(FILE *fp, const char *msg_fmt, const struct string_list *refnames)
{
        struct warn_if_dangling_data data;

        data.fp = fp;
        data.refname = NULL;
        data.refnames = refnames;
        data.msg_fmt = msg_fmt;
        for_each_rawref(warn_if_dangling_symref, &data);
}

int refs_for_each_tag_ref(struct ref_store *refs, each_ref_fn fn, void *cb_data)
{
        return refs_for_each_ref_in(refs, "refs/tags/", fn, cb_data);
}

int for_each_tag_ref(each_ref_fn fn, void *cb_data)
{
        return refs_for_each_tag_ref(get_main_ref_store(), fn, cb_data);
}

int for_each_tag_ref_submodule(const char *submodule, each_ref_fn fn, void *cb_data)
{
        return refs_for_each_tag_ref(get_submodule_ref_store(submodule),
                                     fn, cb_data);
}

int refs_for_each_branch_ref(struct ref_store *refs, each_ref_fn fn, void *cb_data)
{
        return refs_for_each_ref_in(refs, "refs/heads/", fn, cb_data);
}

int for_each_branch_ref(each_ref_fn fn, void *cb_data)
{
        return refs_for_each_branch_ref(get_main_ref_store(), fn, cb_data);
}

int for_each_branch_ref_submodule(const char *submodule, each_ref_fn fn, void *cb_data)
{
        return refs_for_each_branch_ref(get_submodule_ref_store(submodule),
                                        fn, cb_data);
}

int refs_for_each_remote_ref(struct ref_store *refs, each_ref_fn fn, void *cb_data)
{
        return refs_for_each_ref_in(refs, "refs/remotes/", fn, cb_data);
}

int for_each_remote_ref(each_ref_fn fn, void *cb_data)
{
        return refs_for_each_remote_ref(get_main_ref_store(), fn, cb_data);
}

int for_each_remote_ref_submodule(const char *submodule, each_ref_fn fn, void *cb_data)
{
        return refs_for_each_remote_ref(get_submodule_ref_store(submodule),
                                        fn, cb_data);
}

int head_ref_namespaced(each_ref_fn fn, void *cb_data)
{
        struct strbuf buf = STRBUF_INIT;
        int ret = 0;
        struct object_id oid;
        int flag;

        strbuf_addf(&buf, "%sHEAD", get_git_namespace());
        if (!read_ref_full(buf.buf, RESOLVE_REF_READING, oid.hash, &flag))
                ret = fn(buf.buf, &oid, flag, cb_data);
        strbuf_release(&buf);

        return ret;
}

int for_each_glob_ref_in(each_ref_fn fn, const char *pattern,
        const char *prefix, void *cb_data)
{
        struct strbuf real_pattern = STRBUF_INIT;
        struct ref_filter filter;
        int ret;

        if (!prefix && !starts_with(pattern, "refs/"))
                strbuf_addstr(&real_pattern, "refs/");
        else if (prefix)
                strbuf_addstr(&real_pattern, prefix);
        strbuf_addstr(&real_pattern, pattern);

        if (!has_glob_specials(pattern)) {
                /* Append implied '/' '*' if not present. */
                strbuf_complete(&real_pattern, '/');
                /* No need to check for '*', there is none. */
                strbuf_addch(&real_pattern, '*');
        }

        filter.pattern = real_pattern.buf;
        filter.fn = fn;
        filter.cb_data = cb_data;
        ret = for_each_ref(filter_refs, &filter);

        strbuf_release(&real_pattern);
        return ret;
}

int for_each_glob_ref(each_ref_fn fn, const char *pattern, void *cb_data)
{
        return for_each_glob_ref_in(fn, pattern, NULL, cb_data);
}

const char *prettify_refname(const char *name)
{
        if (skip_prefix(name, "refs/heads/", &name) ||
            skip_prefix(name, "refs/tags/", &name) ||
            skip_prefix(name, "refs/remotes/", &name))
                ; /* nothing */
        return name;
}

static const char *ref_rev_parse_rules[] = {
        "%.*s",
        "refs/%.*s",
        "refs/tags/%.*s",
        "refs/heads/%.*s",
        "refs/remotes/%.*s",
        "refs/remotes/%.*s/HEAD",
        NULL
};

int refname_match(const char *abbrev_name, const char *full_name)
{
        const char **p;
        const int abbrev_name_len = strlen(abbrev_name);

        for (p = ref_rev_parse_rules; *p; p++) {
                if (!strcmp(full_name, mkpath(*p, abbrev_name_len, abbrev_name))) {
                        return 1;
                }
        }

        return 0;
}

/*
 * *string and *len will only be substituted, and *string returned (for
 * later free()ing) if the string passed in is a magic short-hand form
 * to name a branch.
 */
static char *substitute_branch_name(const char **string, int *len)
{
        struct strbuf buf = STRBUF_INIT;
        int ret = interpret_branch_name(*string, *len, &buf, 0);

        if (ret == *len) {
                size_t size;
                *string = strbuf_detach(&buf, &size);
                *len = size;
                return (char *)*string;
        }

        return NULL;
}

int dwim_ref(const char *str, int len, unsigned char *sha1, char **ref)
{
        char *last_branch = substitute_branch_name(&str, &len);
        int   refs_found  = expand_ref(str, len, sha1, ref);
        free(last_branch);
        return refs_found;
}

int expand_ref(const char *str, int len, unsigned char *sha1, char **ref)
{
        const char **p, *r;
        int refs_found = 0;
        struct strbuf fullref = STRBUF_INIT;

        *ref = NULL;
        for (p = ref_rev_parse_rules; *p; p++) {
                unsigned char sha1_from_ref[20];
                unsigned char *this_result;
                int flag;

                this_result = refs_found ? sha1_from_ref : sha1;
                strbuf_reset(&fullref);
                strbuf_addf(&fullref, *p, len, str);
                r = resolve_ref_unsafe(fullref.buf, RESOLVE_REF_READING,
                                       this_result, &flag);
                if (r) {
                        if (!refs_found++)
                                *ref = xstrdup(r);
                        if (!warn_ambiguous_refs)
                                break;
                } else if ((flag & REF_ISSYMREF) && strcmp(fullref.buf, "HEAD")) {
                        warning("ignoring dangling symref %s.", fullref.buf);
                } else if ((flag & REF_ISBROKEN) && strchr(fullref.buf, '/')) {
                        warning("ignoring broken ref %s.", fullref.buf);
                }
        }
        strbuf_release(&fullref);
        return refs_found;
}

int dwim_log(const char *str, int len, unsigned char *sha1, char **log)
{
        char *last_branch = substitute_branch_name(&str, &len);
        const char **p;
        int logs_found = 0;
        struct strbuf path = STRBUF_INIT;

        *log = NULL;
        for (p = ref_rev_parse_rules; *p; p++) {
                unsigned char hash[20];
                const char *ref, *it;

                strbuf_reset(&path);
                strbuf_addf(&path, *p, len, str);
                ref = resolve_ref_unsafe(path.buf, RESOLVE_REF_READING,
                                         hash, NULL);
                if (!ref)
                        continue;
                if (reflog_exists(path.buf))
                        it = path.buf;
                else if (strcmp(ref, path.buf) && reflog_exists(ref))
                        it = ref;
                else
                        continue;
                if (!logs_found++) {
                        *log = xstrdup(it);
                        hashcpy(sha1, hash);
                }
                if (!warn_ambiguous_refs)
                        break;
        }
        strbuf_release(&path);
        free(last_branch);
        return logs_found;
}

static int is_per_worktree_ref(const char *refname)
{
        return !strcmp(refname, "HEAD") ||
                starts_with(refname, "refs/bisect/");
}

static int is_pseudoref_syntax(const char *refname)
{
        const char *c;

        for (c = refname; *c; c++) {
                if (!isupper(*c) && *c != '-' && *c != '_')
                        return 0;
        }

        return 1;
}

enum ref_type ref_type(const char *refname)
{
        if (is_per_worktree_ref(refname))
                return REF_TYPE_PER_WORKTREE;
        if (is_pseudoref_syntax(refname))
                return REF_TYPE_PSEUDOREF;
       return REF_TYPE_NORMAL;
}

long get_files_ref_lock_timeout_ms(void)
{
        static int configured = 0;

        /* The default timeout is 100 ms: */
        static int timeout_ms = 100;

        if (!configured) {
                git_config_get_int("core.filesreflocktimeout", &timeout_ms);
                configured = 1;
        }

        return timeout_ms;
}

static int write_pseudoref(const char *pseudoref, const unsigned char *sha1,
                           const unsigned char *old_sha1, struct strbuf *err)
{
        const char *filename;
        int fd;
        static struct lock_file lock;
        struct strbuf buf = STRBUF_INIT;
        int ret = -1;

        strbuf_addf(&buf, "%s\n", sha1_to_hex(sha1));

        filename = git_path("%s", pseudoref);
        fd = hold_lock_file_for_update_timeout(&lock, filename,
                                               LOCK_DIE_ON_ERROR,
                                               get_files_ref_lock_timeout_ms());
        if (fd < 0) {
                strbuf_addf(err, "could not open '%s' for writing: %s",
                            filename, strerror(errno));
                return -1;
        }

        if (old_sha1) {
                unsigned char actual_old_sha1[20];

                if (read_ref(pseudoref, actual_old_sha1))
                        die("could not read ref '%s'", pseudoref);
                if (hashcmp(actual_old_sha1, old_sha1)) {
                        strbuf_addf(err, "unexpected sha1 when writing '%s'", pseudoref);
                        rollback_lock_file(&lock);
                        goto done;
                }
        }

        if (write_in_full(fd, buf.buf, buf.len) != buf.len) {
                strbuf_addf(err, "could not write to '%s'", filename);
                rollback_lock_file(&lock);
                goto done;
        }

        commit_lock_file(&lock);
        ret = 0;
done:
        strbuf_release(&buf);
        return ret;
}

static int delete_pseudoref(const char *pseudoref, const unsigned char *old_sha1)
{
        static struct lock_file lock;
        const char *filename;

        filename = git_path("%s", pseudoref);

        if (old_sha1 && !is_null_sha1(old_sha1)) {
                int fd;
                unsigned char actual_old_sha1[20];

                fd = hold_lock_file_for_update_timeout(
                                &lock, filename, LOCK_DIE_ON_ERROR,
                                get_files_ref_lock_timeout_ms());
                if (fd < 0)
                        die_errno(_("Could not open '%s' for writing"), filename);
                if (read_ref(pseudoref, actual_old_sha1))
                        die("could not read ref '%s'", pseudoref);
                if (hashcmp(actual_old_sha1, old_sha1)) {
                        warning("Unexpected sha1 when deleting %s", pseudoref);
                        rollback_lock_file(&lock);
                        return -1;
                }

                unlink(filename);
                rollback_lock_file(&lock);
        } else {
                unlink(filename);
        }

        return 0;
}

int refs_delete_ref(struct ref_store *refs, const char *msg,
                    const char *refname,
                    const unsigned char *old_sha1,
                    unsigned int flags)
{
        struct ref_transaction *transaction;
        struct strbuf err = STRBUF_INIT;

        if (ref_type(refname) == REF_TYPE_PSEUDOREF) {
                assert(refs == get_main_ref_store());
                return delete_pseudoref(refname, old_sha1);
        }

        transaction = ref_store_transaction_begin(refs, &err);
        if (!transaction ||
            ref_transaction_delete(transaction, refname, old_sha1,
                                   flags, msg, &err) ||
            ref_transaction_commit(transaction, &err)) {
                error("%s", err.buf);
                ref_transaction_free(transaction);
                strbuf_release(&err);
                return 1;
        }
        ref_transaction_free(transaction);
        strbuf_release(&err);
        return 0;
}

int delete_ref(const char *msg, const char *refname,
               const unsigned char *old_sha1, unsigned int flags)
{
        return refs_delete_ref(get_main_ref_store(), msg, refname,
                               old_sha1, flags);
}

int copy_reflog_msg(char *buf, const char *msg)
{
        char *cp = buf;
        char c;
        int wasspace = 1;

        *cp++ = '\t';
        while ((c = *msg++)) {
                if (wasspace && isspace(c))
                        continue;
                wasspace = isspace(c);
                if (wasspace)
                        c = ' ';
                *cp++ = c;
        }
        while (buf < cp && isspace(cp[-1]))
                cp--;
        *cp++ = '\n';
        return cp - buf;
}

int should_autocreate_reflog(const char *refname)
{
        switch (log_all_ref_updates) {
        case LOG_REFS_ALWAYS:
                return 1;
        case LOG_REFS_NORMAL:
                return starts_with(refname, "refs/heads/") ||
                        starts_with(refname, "refs/remotes/") ||
                        starts_with(refname, "refs/notes/") ||
                        !strcmp(refname, "HEAD");
        default:
                return 0;
        }
}

int is_branch(const char *refname)
{
        return !strcmp(refname, "HEAD") || starts_with(refname, "refs/heads/");
}

struct read_ref_at_cb {
        const char *refname;
        timestamp_t at_time;
        int cnt;
        int reccnt;
        unsigned char *sha1;
        int found_it;

        unsigned char osha1[20];
        unsigned char nsha1[20];
        int tz;
        timestamp_t date;
        char **msg;
        timestamp_t *cutoff_time;
        int *cutoff_tz;
        int *cutoff_cnt;
};

static int read_ref_at_ent(struct object_id *ooid, struct object_id *noid,
                const char *email, timestamp_t timestamp, int tz,
                const char *message, void *cb_data)
{
        struct read_ref_at_cb *cb = cb_data;

        cb->reccnt++;
        cb->tz = tz;
        cb->date = timestamp;

        if (timestamp <= cb->at_time || cb->cnt == 0) {
                if (cb->msg)
                        *cb->msg = xstrdup(message);
                if (cb->cutoff_time)
                        *cb->cutoff_time = timestamp;
                if (cb->cutoff_tz)
                        *cb->cutoff_tz = tz;
                if (cb->cutoff_cnt)
                        *cb->cutoff_cnt = cb->reccnt - 1;
                /*
                 * we have not yet updated cb->[n|o]sha1 so they still
                 * hold the values for the previous record.
                 */
                if (!is_null_sha1(cb->osha1)) {
                        hashcpy(cb->sha1, noid->hash);
                        if (hashcmp(cb->osha1, noid->hash))
                                warning("Log for ref %s has gap after %s.",
                                        cb->refname, show_date(cb->date, cb->tz, DATE_MODE(RFC2822)));
                }
                else if (cb->date == cb->at_time)
                        hashcpy(cb->sha1, noid->hash);
                else if (hashcmp(noid->hash, cb->sha1))
                        warning("Log for ref %s unexpectedly ended on %s.",
                                cb->refname, show_date(cb->date, cb->tz,
                                                       DATE_MODE(RFC2822)));
                hashcpy(cb->osha1, ooid->hash);
                hashcpy(cb->nsha1, noid->hash);
                cb->found_it = 1;
                return 1;
        }
        hashcpy(cb->osha1, ooid->hash);
        hashcpy(cb->nsha1, noid->hash);
        if (cb->cnt > 0)
                cb->cnt--;
        return 0;
}

static int read_ref_at_ent_oldest(struct object_id *ooid, struct object_id *noid,
                                  const char *email, timestamp_t timestamp,
                                  int tz, const char *message, void *cb_data)
{
        struct read_ref_at_cb *cb = cb_data;

        if (cb->msg)
                *cb->msg = xstrdup(message);
        if (cb->cutoff_time)
                *cb->cutoff_time = timestamp;
        if (cb->cutoff_tz)
                *cb->cutoff_tz = tz;
        if (cb->cutoff_cnt)
                *cb->cutoff_cnt = cb->reccnt;
        hashcpy(cb->sha1, ooid->hash);
        if (is_null_sha1(cb->sha1))
                hashcpy(cb->sha1, noid->hash);
        /* We just want the first entry */
        return 1;
}

int read_ref_at(const char *refname, unsigned int flags, timestamp_t at_time, int cnt,
                unsigned char *sha1, char **msg,
                timestamp_t *cutoff_time, int *cutoff_tz, int *cutoff_cnt)
{
        struct read_ref_at_cb cb;

        memset(&cb, 0, sizeof(cb));
        cb.refname = refname;
        cb.at_time = at_time;
        cb.cnt = cnt;
        cb.msg = msg;
        cb.cutoff_time = cutoff_time;
        cb.cutoff_tz = cutoff_tz;
        cb.cutoff_cnt = cutoff_cnt;
        cb.sha1 = sha1;

        for_each_reflog_ent_reverse(refname, read_ref_at_ent, &cb);

        if (!cb.reccnt) {
                if (flags & GET_SHA1_QUIETLY)
                        exit(128);
                else
                        die("Log for %s is empty.", refname);
        }
        if (cb.found_it)
                return 0;

        for_each_reflog_ent(refname, read_ref_at_ent_oldest, &cb);

        return 1;
}

struct ref_transaction *ref_store_transaction_begin(struct ref_store *refs,
                                                    struct strbuf *err)
{
        struct ref_transaction *tr;
        assert(err);

        tr = xcalloc(1, sizeof(struct ref_transaction));
        tr->ref_store = refs;
        return tr;
}

struct ref_transaction *ref_transaction_begin(struct strbuf *err)
{
        return ref_store_transaction_begin(get_main_ref_store(), err);
}

void ref_transaction_free(struct ref_transaction *transaction)
{
        size_t i;

        if (!transaction)
                return;

        switch (transaction->state) {
        case REF_TRANSACTION_OPEN:
        case REF_TRANSACTION_CLOSED:
                /* OK */
                break;
        case REF_TRANSACTION_PREPARED:
                die("BUG: free called on a prepared reference transaction");
                break;
        default:
                die("BUG: unexpected reference transaction state");
                break;
        }

        for (i = 0; i < transaction->nr; i++) {
                free(transaction->updates[i]->msg);
                free(transaction->updates[i]);
        }
        free(transaction->updates);
        free(transaction);
}

struct ref_update *ref_transaction_add_update(
                struct ref_transaction *transaction,
                const char *refname, unsigned int flags,
                const unsigned char *new_sha1,
                const unsigned char *old_sha1,
                const char *msg)
{
        struct ref_update *update;

        if (transaction->state != REF_TRANSACTION_OPEN)
                die("BUG: update called for transaction that is not open");

        if ((flags & REF_ISPRUNING) && !(flags & REF_NODEREF))
                die("BUG: REF_ISPRUNING set without REF_NODEREF");

        FLEX_ALLOC_STR(update, refname, refname);
        ALLOC_GROW(transaction->updates, transaction->nr + 1, transaction->alloc);
        transaction->updates[transaction->nr++] = update;

        update->flags = flags;

        if (flags & REF_HAVE_NEW)
                hashcpy(update->new_oid.hash, new_sha1);
        if (flags & REF_HAVE_OLD)
                hashcpy(update->old_oid.hash, old_sha1);
        update->msg = xstrdup_or_null(msg);
        return update;
}

int ref_transaction_update(struct ref_transaction *transaction,
                           const char *refname,
                           const unsigned char *new_sha1,
                           const unsigned char *old_sha1,
                           unsigned int flags, const char *msg,
                           struct strbuf *err)
{
        assert(err);

        if ((new_sha1 && !is_null_sha1(new_sha1)) ?
            check_refname_format(refname, REFNAME_ALLOW_ONELEVEL) :
            !refname_is_safe(refname)) {
                strbuf_addf(err, "refusing to update ref with bad name '%s'",
                            refname);
                return -1;
        }

        flags |= (new_sha1 ? REF_HAVE_NEW : 0) | (old_sha1 ? REF_HAVE_OLD : 0);

        ref_transaction_add_update(transaction, refname, flags,
                                   new_sha1, old_sha1, msg);
        return 0;
}

int ref_transaction_create(struct ref_transaction *transaction,
                           const char *refname,
                           const unsigned char *new_sha1,
                           unsigned int flags, const char *msg,
                           struct strbuf *err)
{
        if (!new_sha1 || is_null_sha1(new_sha1))
                die("BUG: create called without valid new_sha1");
        return ref_transaction_update(transaction, refname, new_sha1,
                                      null_sha1, flags, msg, err);
}

int ref_transaction_delete(struct ref_transaction *transaction,
                           const char *refname,
                           const unsigned char *old_sha1,
                           unsigned int flags, const char *msg,
                           struct strbuf *err)
{
        if (old_sha1 && is_null_sha1(old_sha1))
                die("BUG: delete called with old_sha1 set to zeros");
        return ref_transaction_update(transaction, refname,
                                      null_sha1, old_sha1,
                                      flags, msg, err);
}

int ref_transaction_verify(struct ref_transaction *transaction,
                           const char *refname,
                           const unsigned char *old_sha1,
                           unsigned int flags,
                           struct strbuf *err)
{
        if (!old_sha1)
                die("BUG: verify called with old_sha1 set to NULL");
        return ref_transaction_update(transaction, refname,
                                      NULL, old_sha1,
                                      flags, NULL, err);
}

int update_ref_oid(const char *msg, const char *refname,
               const struct object_id *new_oid, const struct object_id *old_oid,
               unsigned int flags, enum action_on_err onerr)
{
        return update_ref(msg, refname, new_oid ? new_oid->hash : NULL,
                old_oid ? old_oid->hash : NULL, flags, onerr);
}

int refs_update_ref(struct ref_store *refs, const char *msg,
                    const char *refname, const unsigned char *new_sha1,
                    const unsigned char *old_sha1, unsigned int flags,
                    enum action_on_err onerr)
{
        struct ref_transaction *t = NULL;
        struct strbuf err = STRBUF_INIT;
        int ret = 0;

        if (ref_type(refname) == REF_TYPE_PSEUDOREF) {
                assert(refs == get_main_ref_store());
                ret = write_pseudoref(refname, new_sha1, old_sha1, &err);
        } else {
                t = ref_store_transaction_begin(refs, &err);
                if (!t ||
                    ref_transaction_update(t, refname, new_sha1, old_sha1,
                                           flags, msg, &err) ||
                    ref_transaction_commit(t, &err)) {
                        ret = 1;
                        ref_transaction_free(t);
                }
        }
        if (ret) {
                const char *str = "update_ref failed for ref '%s': %s";

                switch (onerr) {
                case UPDATE_REFS_MSG_ON_ERR:
                        error(str, refname, err.buf);
                        break;
                case UPDATE_REFS_DIE_ON_ERR:
                        die(str, refname, err.buf);
                        break;
                case UPDATE_REFS_QUIET_ON_ERR:
                        break;
                }
                strbuf_release(&err);
                return 1;
        }
        strbuf_release(&err);
        if (t)
                ref_transaction_free(t);
        return 0;
}

int update_ref(const char *msg, const char *refname,
               const unsigned char *new_sha1,
               const unsigned char *old_sha1,
               unsigned int flags, enum action_on_err onerr)
{
        return refs_update_ref(get_main_ref_store(), msg, refname, new_sha1,
                               old_sha1, flags, onerr);
}

char *shorten_unambiguous_ref(const char *refname, int strict)
{
        int i;
        static char **scanf_fmts;
        static int nr_rules;
        char *short_name;
        struct strbuf resolved_buf = STRBUF_INIT;

        if (!nr_rules) {
                /*
                 * Pre-generate scanf formats from ref_rev_parse_rules[].
                 * Generate a format suitable for scanf from a
                 * ref_rev_parse_rules rule by interpolating "%s" at the
                 * location of the "%.*s".
                 */
                size_t total_len = 0;
                size_t offset = 0;

                /* the rule list is NULL terminated, count them first */
                for (nr_rules = 0; ref_rev_parse_rules[nr_rules]; nr_rules++)
                        /* -2 for strlen("%.*s") - strlen("%s"); +1 for NUL */
                        total_len += strlen(ref_rev_parse_rules[nr_rules]) - 2 + 1;

                scanf_fmts = xmalloc(st_add(st_mult(sizeof(char *), nr_rules), total_len));

                offset = 0;
                for (i = 0; i < nr_rules; i++) {
                        assert(offset < total_len);
                        scanf_fmts[i] = (char *)&scanf_fmts[nr_rules] + offset;
                        offset += snprintf(scanf_fmts[i], total_len - offset,
                                           ref_rev_parse_rules[i], 2, "%s") + 1;
                }
        }

        /* bail out if there are no rules */
        if (!nr_rules)
                return xstrdup(refname);

        /* buffer for scanf result, at most refname must fit */
        short_name = xstrdup(refname);

        /* skip first rule, it will always match */
        for (i = nr_rules - 1; i > 0 ; --i) {
                int j;
                int rules_to_fail = i;
                int short_name_len;

                if (1 != sscanf(refname, scanf_fmts[i], short_name))
                        continue;

                short_name_len = strlen(short_name);

                /*
                 * in strict mode, all (except the matched one) rules
                 * must fail to resolve to a valid non-ambiguous ref
                 */
                if (strict)
                        rules_to_fail = nr_rules;

                /*
                 * check if the short name resolves to a valid ref,
                 * but use only rules prior to the matched one
                 */
                for (j = 0; j < rules_to_fail; j++) {
                        const char *rule = ref_rev_parse_rules[j];

                        /* skip matched rule */
                        if (i == j)
                                continue;

                        /*
                         * the short name is ambiguous, if it resolves
                         * (with this previous rule) to a valid ref
                         * read_ref() returns 0 on success
                         */
                        strbuf_reset(&resolved_buf);
                        strbuf_addf(&resolved_buf, rule,
                                    short_name_len, short_name);
                        if (ref_exists(resolved_buf.buf))
                                break;
                }

                /*
                 * short name is non-ambiguous if all previous rules
                 * haven't resolved to a valid ref
                 */
                if (j == rules_to_fail) {
                        strbuf_release(&resolved_buf);
                        return short_name;
                }
        }

        strbuf_release(&resolved_buf);
        free(short_name);
        return xstrdup(refname);
}

static struct string_list *hide_refs;

int parse_hide_refs_config(const char *var, const char *value, const char *section)
{
        const char *key;
        if (!strcmp("transfer.hiderefs", var) ||
            (!parse_config_key(var, section, NULL, NULL, &key) &&
             !strcmp(key, "hiderefs"))) {
                char *ref;
                int len;

                if (!value)
                        return config_error_nonbool(var);
                ref = xstrdup(value);
                len = strlen(ref);
                while (len && ref[len - 1] == '/')
                        ref[--len] = '\0';
                if (!hide_refs) {
                        hide_refs = xcalloc(1, sizeof(*hide_refs));
                        hide_refs->strdup_strings = 1;
                }
                string_list_append(hide_refs, ref);
        }
        return 0;
}

int ref_is_hidden(const char *refname, const char *refname_full)
{
        int i;

        if (!hide_refs)
                return 0;
        for (i = hide_refs->nr - 1; i >= 0; i--) {
                const char *match = hide_refs->items[i].string;
                const char *subject;
                int neg = 0;
                int len;

                if (*match == '!') {
                        neg = 1;
                        match++;
                }

                if (*match == '^') {
                        subject = refname_full;
                        match++;
                } else {
                        subject = refname;
                }

                /* refname can be NULL when namespaces are used. */
                if (!subject || !starts_with(subject, match))
                        continue;
                len = strlen(match);
                if (!subject[len] || subject[len] == '/')
                        return !neg;
        }
        return 0;
}

const char *find_descendant_ref(const char *dirname,
                                const struct string_list *extras,
                                const struct string_list *skip)
{
        int pos;

        if (!extras)
                return NULL;

        /*
         * Look at the place where dirname would be inserted into
         * extras. If there is an entry at that position that starts
         * with dirname (remember, dirname includes the trailing
         * slash) and is not in skip, then we have a conflict.
         */
        for (pos = string_list_find_insert_index(extras, dirname, 0);
             pos < extras->nr; pos++) {
                const char *extra_refname = extras->items[pos].string;

                if (!starts_with(extra_refname, dirname))
                        break;

                if (!skip || !string_list_has_string(skip, extra_refname))
                        return extra_refname;
        }
        return NULL;
}

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, &err);
        if (!ok)
                error("%s", err.buf);

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

int head_ref_submodule(const char *submodule, each_ref_fn fn, void *cb_data)
{
        struct object_id oid;
        int flag;

        if (submodule) {
                if (resolve_gitlink_ref(submodule, "HEAD", oid.hash) == 0)
                        return fn("HEAD", &oid, 0, cb_data);

                return 0;
        }

        if (!read_ref_full("HEAD", RESOLVE_REF_READING, oid.hash, &flag))
                return fn("HEAD", &oid, flag, cb_data);

        return 0;
}

int head_ref(each_ref_fn fn, void *cb_data)
{
        return head_ref_submodule(NULL, fn, cb_data);
}

struct ref_iterator *refs_ref_iterator_begin(
                struct ref_store *refs,
                const char *prefix, int trim, int flags)
{
        struct ref_iterator *iter;

        if (ref_paranoia < 0)
                ref_paranoia = git_env_bool("GIT_REF_PARANOIA", 0);
        if (ref_paranoia)
                flags |= DO_FOR_EACH_INCLUDE_BROKEN;

        iter = refs->be->iterator_begin(refs, prefix, flags);

        /*
         * `iterator_begin()` already takes care of prefix, but we
         * might need to do some trimming:
         */
        if (trim)
                iter = prefix_ref_iterator_begin(iter, "", trim);

        return iter;
}

/*
 * Call fn for each reference in the specified submodule for which the
 * refname begins with prefix. If trim is non-zero, then trim that
 * many characters off the beginning of each refname before passing
 * the refname to fn. flags can be DO_FOR_EACH_INCLUDE_BROKEN to
 * include broken references in the iteration. If fn ever returns a
 * non-zero value, stop the iteration and return that value;
 * otherwise, return 0.
 */
static int do_for_each_ref(struct ref_store *refs, const char *prefix,
                           each_ref_fn fn, int trim, int flags, void *cb_data)
{
        struct ref_iterator *iter;

        if (!refs)
                return 0;

        iter = refs_ref_iterator_begin(refs, prefix, trim, flags);

        return do_for_each_ref_iterator(iter, fn, cb_data);
}

int refs_for_each_ref(struct ref_store *refs, each_ref_fn fn, void *cb_data)
{
        return do_for_each_ref(refs, "", fn, 0, 0, cb_data);
}

int for_each_ref(each_ref_fn fn, void *cb_data)
{
        return refs_for_each_ref(get_main_ref_store(), fn, cb_data);
}

int for_each_ref_submodule(const char *submodule, each_ref_fn fn, void *cb_data)
{
        return refs_for_each_ref(get_submodule_ref_store(submodule), fn, cb_data);
}

int refs_for_each_ref_in(struct ref_store *refs, const char *prefix,
                         each_ref_fn fn, void *cb_data)
{
        return do_for_each_ref(refs, prefix, fn, strlen(prefix), 0, cb_data);
}

int for_each_ref_in(const char *prefix, each_ref_fn fn, void *cb_data)
{
        return refs_for_each_ref_in(get_main_ref_store(), prefix, fn, cb_data);
}

int for_each_fullref_in(const char *prefix, each_ref_fn fn, void *cb_data, unsigned int broken)
{
        unsigned int flag = 0;

        if (broken)
                flag = DO_FOR_EACH_INCLUDE_BROKEN;
        return do_for_each_ref(get_main_ref_store(),
                               prefix, fn, 0, flag, cb_data);
}

int for_each_ref_in_submodule(const char *submodule, const char *prefix,
                              each_ref_fn fn, void *cb_data)
{
        return refs_for_each_ref_in(get_submodule_ref_store(submodule),
                                    prefix, fn, cb_data);
}

int for_each_fullref_in_submodule(const char *submodule, const char *prefix,
                                  each_ref_fn fn, void *cb_data,
                                  unsigned int broken)
{
        unsigned int flag = 0;

        if (broken)
                flag = DO_FOR_EACH_INCLUDE_BROKEN;
        return do_for_each_ref(get_submodule_ref_store(submodule),
                               prefix, fn, 0, flag, cb_data);
}

int for_each_replace_ref(each_ref_fn fn, void *cb_data)
{
        return do_for_each_ref(get_main_ref_store(),
                               git_replace_ref_base, fn,
                               strlen(git_replace_ref_base),
                               0, cb_data);
}

int for_each_namespaced_ref(each_ref_fn fn, void *cb_data)
{
        struct strbuf buf = STRBUF_INIT;
        int ret;
        strbuf_addf(&buf, "%srefs/", get_git_namespace());
        ret = do_for_each_ref(get_main_ref_store(),
                              buf.buf, fn, 0, 0, cb_data);
        strbuf_release(&buf);
        return ret;
}

int refs_for_each_rawref(struct ref_store *refs, each_ref_fn fn, void *cb_data)
{
        return do_for_each_ref(refs, "", fn, 0,
                               DO_FOR_EACH_INCLUDE_BROKEN, cb_data);
}

int for_each_rawref(each_ref_fn fn, void *cb_data)
{
        return refs_for_each_rawref(get_main_ref_store(), fn, cb_data);
}

int refs_read_raw_ref(struct ref_store *ref_store,
                      const char *refname, unsigned char *sha1,
                      struct strbuf *referent, unsigned int *type)
{
        return ref_store->be->read_raw_ref(ref_store, refname, sha1, referent, type);
}

/* This function needs to return a meaningful errno on failure */
const char *refs_resolve_ref_unsafe(struct ref_store *refs,
                                    const char *refname,
                                    int resolve_flags,
                                    unsigned char *sha1, int *flags)
{
        static struct strbuf sb_refname = STRBUF_INIT;
        int unused_flags;
        int symref_count;

        if (!flags)
                flags = &unused_flags;

        *flags = 0;

        if (check_refname_format(refname, REFNAME_ALLOW_ONELEVEL)) {
                if (!(resolve_flags & RESOLVE_REF_ALLOW_BAD_NAME) ||
                    !refname_is_safe(refname)) {
                        errno = EINVAL;
                        return NULL;
                }

                /*
                 * dwim_ref() uses REF_ISBROKEN to distinguish between
                 * missing refs and refs that were present but invalid,
                 * to complain about the latter to stderr.
                 *
                 * We don't know whether the ref exists, so don't set
                 * REF_ISBROKEN yet.
                 */
                *flags |= REF_BAD_NAME;
        }

        for (symref_count = 0; symref_count < SYMREF_MAXDEPTH; symref_count++) {
                unsigned int read_flags = 0;

                if (refs_read_raw_ref(refs, refname,
                                      sha1, &sb_refname, &read_flags)) {
                        *flags |= read_flags;
                        if (errno != ENOENT || (resolve_flags & RESOLVE_REF_READING))
                                return NULL;
                        hashclr(sha1);
                        if (*flags & REF_BAD_NAME)
                                *flags |= REF_ISBROKEN;
                        return refname;
                }

                *flags |= read_flags;

                if (!(read_flags & REF_ISSYMREF)) {
                        if (*flags & REF_BAD_NAME) {
                                hashclr(sha1);
                                *flags |= REF_ISBROKEN;
                        }
                        return refname;
                }

                refname = sb_refname.buf;
                if (resolve_flags & RESOLVE_REF_NO_RECURSE) {
                        hashclr(sha1);
                        return refname;
                }
                if (check_refname_format(refname, REFNAME_ALLOW_ONELEVEL)) {
                        if (!(resolve_flags & RESOLVE_REF_ALLOW_BAD_NAME) ||
                            !refname_is_safe(refname)) {
                                errno = EINVAL;
                                return NULL;
                        }

                        *flags |= REF_ISBROKEN | REF_BAD_NAME;
                }
        }

        errno = ELOOP;
        return NULL;
}

/* backend functions */
int refs_init_db(struct strbuf *err)
{
        struct ref_store *refs = get_main_ref_store();

        return refs->be->init_db(refs, err);
}

const char *resolve_ref_unsafe(const char *refname, int resolve_flags,
                               unsigned char *sha1, int *flags)
{
        return refs_resolve_ref_unsafe(get_main_ref_store(), refname,
                                       resolve_flags, sha1, flags);
}

int resolve_gitlink_ref(const char *submodule, const char *refname,
                        unsigned char *sha1)
{
        size_t len = strlen(submodule);
        struct ref_store *refs;
        int flags;

        while (len && submodule[len - 1] == '/')
                len--;

        if (!len)
                return -1;

        if (submodule[len]) {
                /* We need to strip off one or more trailing slashes */
                char *stripped = xmemdupz(submodule, len);

                refs = get_submodule_ref_store(stripped);
                free(stripped);
        } else {
                refs = get_submodule_ref_store(submodule);
        }

        if (!refs)
                return -1;

        if (!refs_resolve_ref_unsafe(refs, refname, 0, sha1, &flags) ||
            is_null_sha1(sha1))
                return -1;
        return 0;
}

struct ref_store_hash_entry
{
        struct hashmap_entry ent; /* must be the first member! */

        struct ref_store *refs;

        /* NUL-terminated identifier of the ref store: */
        char name[FLEX_ARRAY];
};

static int ref_store_hash_cmp(const void *unused_cmp_data,
                              const void *entry, const void *entry_or_key,
                              const void *keydata)
{
        const struct ref_store_hash_entry *e1 = entry, *e2 = entry_or_key;
        const char *name = keydata ? keydata : e2->name;

        return strcmp(e1->name, name);
}

static struct ref_store_hash_entry *alloc_ref_store_hash_entry(
                const char *name, struct ref_store *refs)
{
        struct ref_store_hash_entry *entry;

        FLEX_ALLOC_STR(entry, name, name);
        hashmap_entry_init(entry, strhash(name));
        entry->refs = refs;
        return entry;
}

/* A pointer to the ref_store for the main repository: */
static struct ref_store *main_ref_store;

/* A hashmap of ref_stores, stored by submodule name: */
static struct hashmap submodule_ref_stores;

/* A hashmap of ref_stores, stored by worktree id: */
static struct hashmap worktree_ref_stores;

/*
 * Look up a ref store by name. If that ref_store hasn't been
 * registered yet, return NULL.
 */
static struct ref_store *lookup_ref_store_map(struct hashmap *map,
                                              const char *name)
{
        struct ref_store_hash_entry *entry;

        if (!map->tablesize)
                /* It's initialized on demand in register_ref_store(). */
                return NULL;

        entry = hashmap_get_from_hash(map, strhash(name), name);
        return entry ? entry->refs : NULL;
}

/*
 * Create, record, and return a ref_store instance for the specified
 * gitdir.
 */
static struct ref_store *ref_store_init(const char *gitdir,
                                        unsigned int flags)
{
        const char *be_name = "files";
        struct ref_storage_be *be = find_ref_storage_backend(be_name);
        struct ref_store *refs;

        if (!be)
                die("BUG: reference backend %s is unknown", be_name);

        refs = be->init(gitdir, flags);
        return refs;
}

struct ref_store *get_main_ref_store(void)
{
        if (main_ref_store)
                return main_ref_store;

        main_ref_store = ref_store_init(get_git_dir(), REF_STORE_ALL_CAPS);
        return main_ref_store;
}

/*
 * Associate a ref store with a name. It is a fatal error to call this
 * function twice for the same name.
 */
static void register_ref_store_map(struct hashmap *map,
                                   const char *type,
                                   struct ref_store *refs,
                                   const char *name)
{
        if (!map->tablesize)
                hashmap_init(map, ref_store_hash_cmp, NULL, 0);

        if (hashmap_put(map, alloc_ref_store_hash_entry(name, refs)))
                die("BUG: %s ref_store '%s' initialized twice", type, name);
}

struct ref_store *get_submodule_ref_store(const char *submodule)
{
        struct strbuf submodule_sb = STRBUF_INIT;
        struct ref_store *refs;
        int ret;

        if (!submodule || !*submodule) {
                /*
                 * FIXME: This case is ideally not allowed. But that
                 * can't happen until we clean up all the callers.
                 */
                return get_main_ref_store();
        }

        refs = lookup_ref_store_map(&submodule_ref_stores, submodule);
        if (refs)
                return refs;

        strbuf_addstr(&submodule_sb, submodule);
        ret = is_nonbare_repository_dir(&submodule_sb);
        strbuf_release(&submodule_sb);
        if (!ret)
                return NULL;

        ret = submodule_to_gitdir(&submodule_sb, submodule);
        if (ret) {
                strbuf_release(&submodule_sb);
                return NULL;
        }

        /* assume that add_submodule_odb() has been called */
        refs = ref_store_init(submodule_sb.buf,
                              REF_STORE_READ | REF_STORE_ODB);
        register_ref_store_map(&submodule_ref_stores, "submodule",
                               refs, submodule);

        strbuf_release(&submodule_sb);
        return refs;
}

struct ref_store *get_worktree_ref_store(const struct worktree *wt)
{
        struct ref_store *refs;
        const char *id;

        if (wt->is_current)
                return get_main_ref_store();

        id = wt->id ? wt->id : "/";
        refs = lookup_ref_store_map(&worktree_ref_stores, id);
        if (refs)
                return refs;

        if (wt->id)
                refs = ref_store_init(git_common_path("worktrees/%s", wt->id),
                                      REF_STORE_ALL_CAPS);
        else
                refs = ref_store_init(get_git_common_dir(),
                                      REF_STORE_ALL_CAPS);

        if (refs)
                register_ref_store_map(&worktree_ref_stores, "worktree",
                                       refs, id);
        return refs;
}

void base_ref_store_init(struct ref_store *refs,
                         const struct ref_storage_be *be)
{
        refs->be = be;
}

/* backend functions */
int refs_pack_refs(struct ref_store *refs, unsigned int flags)
{
        return refs->be->pack_refs(refs, flags);
}

int refs_peel_ref(struct ref_store *refs, const char *refname,
                  unsigned char *sha1)
{
        return refs->be->peel_ref(refs, refname, sha1);
}

int peel_ref(const char *refname, unsigned char *sha1)
{
        return refs_peel_ref(get_main_ref_store(), refname, sha1);
}

int refs_create_symref(struct ref_store *refs,
                       const char *ref_target,
                       const char *refs_heads_master,
                       const char *logmsg)
{
        return refs->be->create_symref(refs, ref_target,
                                       refs_heads_master,
                                       logmsg);
}

int create_symref(const char *ref_target, const char *refs_heads_master,
                  const char *logmsg)
{
        return refs_create_symref(get_main_ref_store(), ref_target,
                                  refs_heads_master, logmsg);
}

int ref_update_reject_duplicates(struct string_list *refnames,
                                 struct strbuf *err)
{
        size_t i, n = refnames->nr;

        assert(err);

        for (i = 1; i < n; i++) {
                int cmp = strcmp(refnames->items[i - 1].string,
                                 refnames->items[i].string);

                if (!cmp) {
                        strbuf_addf(err,
                                    "multiple updates for ref '%s' not allowed.",
                                    refnames->items[i].string);
                        return 1;
                } else if (cmp > 0) {
                        die("BUG: ref_update_reject_duplicates() received unsorted list");
                }
        }
        return 0;
}

int ref_transaction_prepare(struct ref_transaction *transaction,
                            struct strbuf *err)
{
        struct ref_store *refs = transaction->ref_store;

        switch (transaction->state) {
        case REF_TRANSACTION_OPEN:
                /* Good. */
                break;
        case REF_TRANSACTION_PREPARED:
                die("BUG: prepare called twice on reference transaction");
                break;
        case REF_TRANSACTION_CLOSED:
                die("BUG: prepare called on a closed reference transaction");
                break;
        default:
                die("BUG: unexpected reference transaction state");
                break;
        }

        if (getenv(GIT_QUARANTINE_ENVIRONMENT)) {
                strbuf_addstr(err,
                              _("ref updates forbidden inside quarantine environment"));
                return -1;
        }

        return refs->be->transaction_prepare(refs, transaction, err);
}

int ref_transaction_abort(struct ref_transaction *transaction,
                          struct strbuf *err)
{
        struct ref_store *refs = transaction->ref_store;
        int ret = 0;

        switch (transaction->state) {
        case REF_TRANSACTION_OPEN:
                /* No need to abort explicitly. */
                break;
        case REF_TRANSACTION_PREPARED:
                ret = refs->be->transaction_abort(refs, transaction, err);
                break;
        case REF_TRANSACTION_CLOSED:
                die("BUG: abort called on a closed reference transaction");
                break;
        default:
                die("BUG: unexpected reference transaction state");
                break;
        }

        ref_transaction_free(transaction);
        return ret;
}

int ref_transaction_commit(struct ref_transaction *transaction,
                           struct strbuf *err)
{
        struct ref_store *refs = transaction->ref_store;
        int ret;

        switch (transaction->state) {
        case REF_TRANSACTION_OPEN:
                /* Need to prepare first. */
                ret = ref_transaction_prepare(transaction, err);
                if (ret)
                        return ret;
                break;
        case REF_TRANSACTION_PREPARED:
                /* Fall through to finish. */
                break;
        case REF_TRANSACTION_CLOSED:
                die("BUG: commit called on a closed reference transaction");
                break;
        default:
                die("BUG: unexpected reference transaction state");
                break;
        }

        return refs->be->transaction_finish(refs, transaction, err);
}

int refs_verify_refname_available(struct ref_store *refs,
                                  const char *refname,
                                  const struct string_list *extras,
                                  const struct string_list *skip,
                                  struct strbuf *err)
{
        const char *slash;
        const char *extra_refname;
        struct strbuf dirname = STRBUF_INIT;
        struct strbuf referent = STRBUF_INIT;
        struct object_id oid;
        unsigned int type;
        struct ref_iterator *iter;
        int ok;
        int ret = -1;

        /*
         * For the sake of comments in this function, suppose that
         * refname is "refs/foo/bar".
         */

        assert(err);

        strbuf_grow(&dirname, strlen(refname) + 1);
        for (slash = strchr(refname, '/'); slash; slash = strchr(slash + 1, '/')) {
                /* Expand dirname to the new prefix, not including the trailing slash: */
                strbuf_add(&dirname, refname + dirname.len, slash - refname - dirname.len);

                /*
                 * We are still at a leading dir of the refname (e.g.,
                 * "refs/foo"; if there is a reference with that name,
                 * it is a conflict, *unless* it is in skip.
                 */
                if (skip && string_list_has_string(skip, dirname.buf))
                        continue;

                if (!refs_read_raw_ref(refs, dirname.buf, oid.hash, &referent, &type)) {
                        strbuf_addf(err, "'%s' exists; cannot create '%s'",
                                    dirname.buf, refname);
                        goto cleanup;
                }

                if (extras && string_list_has_string(extras, dirname.buf)) {
                        strbuf_addf(err, "cannot process '%s' and '%s' at the same time",
                                    refname, dirname.buf);
                        goto cleanup;
                }
        }

        /*
         * We are at the leaf of our refname (e.g., "refs/foo/bar").
         * There is no point in searching for a reference with that
         * name, because a refname isn't considered to conflict with
         * itself. But we still need to check for references whose
         * names are in the "refs/foo/bar/" namespace, because they
         * *do* conflict.
         */
        strbuf_addstr(&dirname, refname + dirname.len);
        strbuf_addch(&dirname, '/');

        iter = refs_ref_iterator_begin(refs, dirname.buf, 0,
                                       DO_FOR_EACH_INCLUDE_BROKEN);
        while ((ok = ref_iterator_advance(iter)) == ITER_OK) {
                if (skip &&
                    string_list_has_string(skip, iter->refname))
                        continue;

                strbuf_addf(err, "'%s' exists; cannot create '%s'",
                            iter->refname, refname);
                ref_iterator_abort(iter);
                goto cleanup;
        }

        if (ok != ITER_DONE)
                die("BUG: error while iterating over references");

        extra_refname = find_descendant_ref(dirname.buf, extras, skip);
        if (extra_refname)
                strbuf_addf(err, "cannot process '%s' and '%s' at the same time",
                            refname, extra_refname);
        else
                ret = 0;

cleanup:
        strbuf_release(&referent);
        strbuf_release(&dirname);
        return ret;
}

int refs_for_each_reflog(struct ref_store *refs, each_ref_fn fn, void *cb_data)
{
        struct ref_iterator *iter;

        iter = refs->be->reflog_iterator_begin(refs);

        return do_for_each_ref_iterator(iter, fn, cb_data);
}

int for_each_reflog(each_ref_fn fn, void *cb_data)
{
        return refs_for_each_reflog(get_main_ref_store(), fn, cb_data);
}

int refs_for_each_reflog_ent_reverse(struct ref_store *refs,
                                     const char *refname,
                                     each_reflog_ent_fn fn,
                                     void *cb_data)
{
        return refs->be->for_each_reflog_ent_reverse(refs, refname,
                                                     fn, cb_data);
}

int for_each_reflog_ent_reverse(const char *refname, each_reflog_ent_fn fn,
                                void *cb_data)
{
        return refs_for_each_reflog_ent_reverse(get_main_ref_store(),
                                                refname, fn, cb_data);
}

int refs_for_each_reflog_ent(struct ref_store *refs, const char *refname,
                             each_reflog_ent_fn fn, void *cb_data)
{
        return refs->be->for_each_reflog_ent(refs, refname, fn, cb_data);
}

int for_each_reflog_ent(const char *refname, each_reflog_ent_fn fn,
                        void *cb_data)
{
        return refs_for_each_reflog_ent(get_main_ref_store(), refname,
                                        fn, cb_data);
}

int refs_reflog_exists(struct ref_store *refs, const char *refname)
{
        return refs->be->reflog_exists(refs, refname);
}

int reflog_exists(const char *refname)
{
        return refs_reflog_exists(get_main_ref_store(), refname);
}

int refs_create_reflog(struct ref_store *refs, const char *refname,
                       int force_create, struct strbuf *err)
{
        return refs->be->create_reflog(refs, refname, force_create, err);
}

int safe_create_reflog(const char *refname, int force_create,
                       struct strbuf *err)
{
        return refs_create_reflog(get_main_ref_store(), refname,
                                  force_create, err);
}

int refs_delete_reflog(struct ref_store *refs, const char *refname)
{
        return refs->be->delete_reflog(refs, refname);
}

int delete_reflog(const char *refname)
{
        return refs_delete_reflog(get_main_ref_store(), refname);
}

int refs_reflog_expire(struct ref_store *refs,
                       const char *refname, const unsigned char *sha1,
                       unsigned int 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)
{
        return refs->be->reflog_expire(refs, refname, sha1, flags,
                                       prepare_fn, should_prune_fn,
                                       cleanup_fn, policy_cb_data);
}

int reflog_expire(const char *refname, const unsigned char *sha1,
                  unsigned int 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)
{
        return refs_reflog_expire(get_main_ref_store(),
                                  refname, sha1, flags,
                                  prepare_fn, should_prune_fn,
                                  cleanup_fn, policy_cb_data);
}

int initial_ref_transaction_commit(struct ref_transaction *transaction,
                                   struct strbuf *err)
{
        struct ref_store *refs = transaction->ref_store;

        return refs->be->initial_transaction_commit(refs, transaction, err);
}

int refs_delete_refs(struct ref_store *refs, const char *msg,
                     struct string_list *refnames, unsigned int flags)
{
        return refs->be->delete_refs(refs, msg, refnames, flags);
}

int delete_refs(const char *msg, struct string_list *refnames,
                unsigned int flags)
{
        return refs_delete_refs(get_main_ref_store(), msg, refnames, flags);
}

int refs_rename_ref(struct ref_store *refs, const char *oldref,
                    const char *newref, const char *logmsg)
{
        return refs->be->rename_ref(refs, oldref, newref, logmsg);
}

int rename_ref(const char *oldref, const char *newref, const char *logmsg)
{
        return refs_rename_ref(get_main_ref_store(), oldref, newref, logmsg);
}