Merge branch 'js/rebase-i-with-colliding-hash'

[thirdparty/git.git] / builtin / pack-objects.c

#include "builtin.h"
#include "cache.h"
#include "repository.h"
#include "config.h"
#include "attr.h"
#include "object.h"
#include "blob.h"
#include "commit.h"
#include "tag.h"
#include "tree.h"
#include "delta.h"
#include "pack.h"
#include "pack-revindex.h"
#include "csum-file.h"
#include "tree-walk.h"
#include "diff.h"
#include "revision.h"
#include "list-objects.h"
#include "list-objects-filter.h"
#include "list-objects-filter-options.h"
#include "pack-objects.h"
#include "progress.h"
#include "refs.h"
#include "streaming.h"
#include "thread-utils.h"
#include "pack-bitmap.h"
#include "delta-islands.h"
#include "reachable.h"
#include "sha1-array.h"
#include "argv-array.h"
#include "list.h"
#include "packfile.h"
#include "object-store.h"
#include "dir.h"
#include "midx.h"
#include "trace2.h"

#define IN_PACK(obj) oe_in_pack(&to_pack, obj)
#define SIZE(obj) oe_size(&to_pack, obj)
#define SET_SIZE(obj,size) oe_set_size(&to_pack, obj, size)
#define DELTA_SIZE(obj) oe_delta_size(&to_pack, obj)
#define DELTA(obj) oe_delta(&to_pack, obj)
#define DELTA_CHILD(obj) oe_delta_child(&to_pack, obj)
#define DELTA_SIBLING(obj) oe_delta_sibling(&to_pack, obj)
#define SET_DELTA(obj, val) oe_set_delta(&to_pack, obj, val)
#define SET_DELTA_EXT(obj, oid) oe_set_delta_ext(&to_pack, obj, oid)
#define SET_DELTA_SIZE(obj, val) oe_set_delta_size(&to_pack, obj, val)
#define SET_DELTA_CHILD(obj, val) oe_set_delta_child(&to_pack, obj, val)
#define SET_DELTA_SIBLING(obj, val) oe_set_delta_sibling(&to_pack, obj, val)

static const char *pack_usage[] = {
        N_("git pack-objects --stdout [<options>...] [< <ref-list> | < <object-list>]"),
        N_("git pack-objects [<options>...] <base-name> [< <ref-list> | < <object-list>]"),
        NULL
};

/*
 * Objects we are going to pack are collected in the `to_pack` structure.
 * It contains an array (dynamically expanded) of the object data, and a map
 * that can resolve SHA1s to their position in the array.
 */
static struct packing_data to_pack;

static struct pack_idx_entry **written_list;
static uint32_t nr_result, nr_written, nr_seen;
static struct bitmap_index *bitmap_git;
static uint32_t write_layer;

static int non_empty;
static int reuse_delta = 1, reuse_object = 1;
static int keep_unreachable, unpack_unreachable, include_tag;
static timestamp_t unpack_unreachable_expiration;
static int pack_loose_unreachable;
static int local;
static int have_non_local_packs;
static int incremental;
static int ignore_packed_keep_on_disk;
static int ignore_packed_keep_in_core;
static int allow_ofs_delta;
static struct pack_idx_option pack_idx_opts;
static const char *base_name;
static int progress = 1;
static int window = 10;
static unsigned long pack_size_limit;
static int depth = 50;
static int delta_search_threads;
static int pack_to_stdout;
static int sparse;
static int thin;
static int num_preferred_base;
static struct progress *progress_state;

static struct packed_git *reuse_packfile;
static uint32_t reuse_packfile_objects;
static struct bitmap *reuse_packfile_bitmap;

static int use_bitmap_index_default = 1;
static int use_bitmap_index = -1;
static int allow_pack_reuse = 1;
static enum {
        WRITE_BITMAP_FALSE = 0,
        WRITE_BITMAP_QUIET,
        WRITE_BITMAP_TRUE,
} write_bitmap_index;
static uint16_t write_bitmap_options = BITMAP_OPT_HASH_CACHE;

static int exclude_promisor_objects;

static int use_delta_islands;

static unsigned long delta_cache_size = 0;
static unsigned long max_delta_cache_size = DEFAULT_DELTA_CACHE_SIZE;
static unsigned long cache_max_small_delta_size = 1000;

static unsigned long window_memory_limit = 0;

static struct list_objects_filter_options filter_options;

enum missing_action {
        MA_ERROR = 0,      /* fail if any missing objects are encountered */
        MA_ALLOW_ANY,      /* silently allow ALL missing objects */
        MA_ALLOW_PROMISOR, /* silently allow all missing PROMISOR objects */
};
static enum missing_action arg_missing_action;
static show_object_fn fn_show_object;

/*
 * stats
 */
static uint32_t written, written_delta;
static uint32_t reused, reused_delta;

/*
 * Indexed commits
 */
static struct commit **indexed_commits;
static unsigned int indexed_commits_nr;
static unsigned int indexed_commits_alloc;

static void index_commit_for_bitmap(struct commit *commit)
{
        if (indexed_commits_nr >= indexed_commits_alloc) {
                indexed_commits_alloc = (indexed_commits_alloc + 32) * 2;
                REALLOC_ARRAY(indexed_commits, indexed_commits_alloc);
        }

        indexed_commits[indexed_commits_nr++] = commit;
}

static void *get_delta(struct object_entry *entry)
{
        unsigned long size, base_size, delta_size;
        void *buf, *base_buf, *delta_buf;
        enum object_type type;

        buf = read_object_file(&entry->idx.oid, &type, &size);
        if (!buf)
                die(_("unable to read %s"), oid_to_hex(&entry->idx.oid));
        base_buf = read_object_file(&DELTA(entry)->idx.oid, &type,
                                    &base_size);
        if (!base_buf)
                die("unable to read %s",
                    oid_to_hex(&DELTA(entry)->idx.oid));
        delta_buf = diff_delta(base_buf, base_size,
                               buf, size, &delta_size, 0);
        /*
         * We successfully computed this delta once but dropped it for
         * memory reasons. Something is very wrong if this time we
         * recompute and create a different delta.
         */
        if (!delta_buf || delta_size != DELTA_SIZE(entry))
                BUG("delta size changed");
        free(buf);
        free(base_buf);
        return delta_buf;
}

static unsigned long do_compress(void **pptr, unsigned long size)
{
        git_zstream stream;
        void *in, *out;
        unsigned long maxsize;

        git_deflate_init(&stream, pack_compression_level);
        maxsize = git_deflate_bound(&stream, size);

        in = *pptr;
        out = xmalloc(maxsize);
        *pptr = out;

        stream.next_in = in;
        stream.avail_in = size;
        stream.next_out = out;
        stream.avail_out = maxsize;
        while (git_deflate(&stream, Z_FINISH) == Z_OK)
                ; /* nothing */
        git_deflate_end(&stream);

        free(in);
        return stream.total_out;
}

static unsigned long write_large_blob_data(struct git_istream *st, struct hashfile *f,
                                           const struct object_id *oid)
{
        git_zstream stream;
        unsigned char ibuf[1024 * 16];
        unsigned char obuf[1024 * 16];
        unsigned long olen = 0;

        git_deflate_init(&stream, pack_compression_level);

        for (;;) {
                ssize_t readlen;
                int zret = Z_OK;
                readlen = read_istream(st, ibuf, sizeof(ibuf));
                if (readlen == -1)
                        die(_("unable to read %s"), oid_to_hex(oid));

                stream.next_in = ibuf;
                stream.avail_in = readlen;
                while ((stream.avail_in || readlen == 0) &&
                       (zret == Z_OK || zret == Z_BUF_ERROR)) {
                        stream.next_out = obuf;
                        stream.avail_out = sizeof(obuf);
                        zret = git_deflate(&stream, readlen ? 0 : Z_FINISH);
                        hashwrite(f, obuf, stream.next_out - obuf);
                        olen += stream.next_out - obuf;
                }
                if (stream.avail_in)
                        die(_("deflate error (%d)"), zret);
                if (readlen == 0) {
                        if (zret != Z_STREAM_END)
                                die(_("deflate error (%d)"), zret);
                        break;
                }
        }
        git_deflate_end(&stream);
        return olen;
}

/*
 * we are going to reuse the existing object data as is.  make
 * sure it is not corrupt.
 */
static int check_pack_inflate(struct packed_git *p,
                struct pack_window **w_curs,
                off_t offset,
                off_t len,
                unsigned long expect)
{
        git_zstream stream;
        unsigned char fakebuf[4096], *in;
        int st;

        memset(&stream, 0, sizeof(stream));
        git_inflate_init(&stream);
        do {
                in = use_pack(p, w_curs, offset, &stream.avail_in);
                stream.next_in = in;
                stream.next_out = fakebuf;
                stream.avail_out = sizeof(fakebuf);
                st = git_inflate(&stream, Z_FINISH);
                offset += stream.next_in - in;
        } while (st == Z_OK || st == Z_BUF_ERROR);
        git_inflate_end(&stream);
        return (st == Z_STREAM_END &&
                stream.total_out == expect &&
                stream.total_in == len) ? 0 : -1;
}

static void copy_pack_data(struct hashfile *f,
                struct packed_git *p,
                struct pack_window **w_curs,
                off_t offset,
                off_t len)
{
        unsigned char *in;
        unsigned long avail;

        while (len) {
                in = use_pack(p, w_curs, offset, &avail);
                if (avail > len)
                        avail = (unsigned long)len;
                hashwrite(f, in, avail);
                offset += avail;
                len -= avail;
        }
}

/* Return 0 if we will bust the pack-size limit */
static unsigned long write_no_reuse_object(struct hashfile *f, struct object_entry *entry,
                                           unsigned long limit, int usable_delta)
{
        unsigned long size, datalen;
        unsigned char header[MAX_PACK_OBJECT_HEADER],
                      dheader[MAX_PACK_OBJECT_HEADER];
        unsigned hdrlen;
        enum object_type type;
        void *buf;
        struct git_istream *st = NULL;
        const unsigned hashsz = the_hash_algo->rawsz;

        if (!usable_delta) {
                if (oe_type(entry) == OBJ_BLOB &&
                    oe_size_greater_than(&to_pack, entry, big_file_threshold) &&
                    (st = open_istream(&entry->idx.oid, &type, &size, NULL)) != NULL)
                        buf = NULL;
                else {
                        buf = read_object_file(&entry->idx.oid, &type, &size);
                        if (!buf)
                                die(_("unable to read %s"),
                                    oid_to_hex(&entry->idx.oid));
                }
                /*
                 * make sure no cached delta data remains from a
                 * previous attempt before a pack split occurred.
                 */
                FREE_AND_NULL(entry->delta_data);
                entry->z_delta_size = 0;
        } else if (entry->delta_data) {
                size = DELTA_SIZE(entry);
                buf = entry->delta_data;
                entry->delta_data = NULL;
                type = (allow_ofs_delta && DELTA(entry)->idx.offset) ?
                        OBJ_OFS_DELTA : OBJ_REF_DELTA;
        } else {
                buf = get_delta(entry);
                size = DELTA_SIZE(entry);
                type = (allow_ofs_delta && DELTA(entry)->idx.offset) ?
                        OBJ_OFS_DELTA : OBJ_REF_DELTA;
        }

        if (st) /* large blob case, just assume we don't compress well */
                datalen = size;
        else if (entry->z_delta_size)
                datalen = entry->z_delta_size;
        else
                datalen = do_compress(&buf, size);

        /*
         * The object header is a byte of 'type' followed by zero or
         * more bytes of length.
         */
        hdrlen = encode_in_pack_object_header(header, sizeof(header),
                                              type, size);

        if (type == OBJ_OFS_DELTA) {
                /*
                 * Deltas with relative base contain an additional
                 * encoding of the relative offset for the delta
                 * base from this object's position in the pack.
                 */
                off_t ofs = entry->idx.offset - DELTA(entry)->idx.offset;
                unsigned pos = sizeof(dheader) - 1;
                dheader[pos] = ofs & 127;
                while (ofs >>= 7)
                        dheader[--pos] = 128 | (--ofs & 127);
                if (limit && hdrlen + sizeof(dheader) - pos + datalen + hashsz >= limit) {
                        if (st)
                                close_istream(st);
                        free(buf);
                        return 0;
                }
                hashwrite(f, header, hdrlen);
                hashwrite(f, dheader + pos, sizeof(dheader) - pos);
                hdrlen += sizeof(dheader) - pos;
        } else if (type == OBJ_REF_DELTA) {
                /*
                 * Deltas with a base reference contain
                 * additional bytes for the base object ID.
                 */
                if (limit && hdrlen + hashsz + datalen + hashsz >= limit) {
                        if (st)
                                close_istream(st);
                        free(buf);
                        return 0;
                }
                hashwrite(f, header, hdrlen);
                hashwrite(f, DELTA(entry)->idx.oid.hash, hashsz);
                hdrlen += hashsz;
        } else {
                if (limit && hdrlen + datalen + hashsz >= limit) {
                        if (st)
                                close_istream(st);
                        free(buf);
                        return 0;
                }
                hashwrite(f, header, hdrlen);
        }
        if (st) {
                datalen = write_large_blob_data(st, f, &entry->idx.oid);
                close_istream(st);
        } else {
                hashwrite(f, buf, datalen);
                free(buf);
        }

        return hdrlen + datalen;
}

/* Return 0 if we will bust the pack-size limit */
static off_t write_reuse_object(struct hashfile *f, struct object_entry *entry,
                                unsigned long limit, int usable_delta)
{
        struct packed_git *p = IN_PACK(entry);
        struct pack_window *w_curs = NULL;
        struct revindex_entry *revidx;
        off_t offset;
        enum object_type type = oe_type(entry);
        off_t datalen;
        unsigned char header[MAX_PACK_OBJECT_HEADER],
                      dheader[MAX_PACK_OBJECT_HEADER];
        unsigned hdrlen;
        const unsigned hashsz = the_hash_algo->rawsz;
        unsigned long entry_size = SIZE(entry);

        if (DELTA(entry))
                type = (allow_ofs_delta && DELTA(entry)->idx.offset) ?
                        OBJ_OFS_DELTA : OBJ_REF_DELTA;
        hdrlen = encode_in_pack_object_header(header, sizeof(header),
                                              type, entry_size);

        offset = entry->in_pack_offset;
        revidx = find_pack_revindex(p, offset);
        datalen = revidx[1].offset - offset;
        if (!pack_to_stdout && p->index_version > 1 &&
            check_pack_crc(p, &w_curs, offset, datalen, revidx->nr)) {
                error(_("bad packed object CRC for %s"),
                      oid_to_hex(&entry->idx.oid));
                unuse_pack(&w_curs);
                return write_no_reuse_object(f, entry, limit, usable_delta);
        }

        offset += entry->in_pack_header_size;
        datalen -= entry->in_pack_header_size;

        if (!pack_to_stdout && p->index_version == 1 &&
            check_pack_inflate(p, &w_curs, offset, datalen, entry_size)) {
                error(_("corrupt packed object for %s"),
                      oid_to_hex(&entry->idx.oid));
                unuse_pack(&w_curs);
                return write_no_reuse_object(f, entry, limit, usable_delta);
        }

        if (type == OBJ_OFS_DELTA) {
                off_t ofs = entry->idx.offset - DELTA(entry)->idx.offset;
                unsigned pos = sizeof(dheader) - 1;
                dheader[pos] = ofs & 127;
                while (ofs >>= 7)
                        dheader[--pos] = 128 | (--ofs & 127);
                if (limit && hdrlen + sizeof(dheader) - pos + datalen + hashsz >= limit) {
                        unuse_pack(&w_curs);
                        return 0;
                }
                hashwrite(f, header, hdrlen);
                hashwrite(f, dheader + pos, sizeof(dheader) - pos);
                hdrlen += sizeof(dheader) - pos;
                reused_delta++;
        } else if (type == OBJ_REF_DELTA) {
                if (limit && hdrlen + hashsz + datalen + hashsz >= limit) {
                        unuse_pack(&w_curs);
                        return 0;
                }
                hashwrite(f, header, hdrlen);
                hashwrite(f, DELTA(entry)->idx.oid.hash, hashsz);
                hdrlen += hashsz;
                reused_delta++;
        } else {
                if (limit && hdrlen + datalen + hashsz >= limit) {
                        unuse_pack(&w_curs);
                        return 0;
                }
                hashwrite(f, header, hdrlen);
        }
        copy_pack_data(f, p, &w_curs, offset, datalen);
        unuse_pack(&w_curs);
        reused++;
        return hdrlen + datalen;
}

/* Return 0 if we will bust the pack-size limit */
static off_t write_object(struct hashfile *f,
                          struct object_entry *entry,
                          off_t write_offset)
{
        unsigned long limit;
        off_t len;
        int usable_delta, to_reuse;

        if (!pack_to_stdout)
                crc32_begin(f);

        /* apply size limit if limited packsize and not first object */
        if (!pack_size_limit || !nr_written)
                limit = 0;
        else if (pack_size_limit <= write_offset)
                /*
                 * the earlier object did not fit the limit; avoid
                 * mistaking this with unlimited (i.e. limit = 0).
                 */
                limit = 1;
        else
                limit = pack_size_limit - write_offset;

        if (!DELTA(entry))
                usable_delta = 0;       /* no delta */
        else if (!pack_size_limit)
               usable_delta = 1;        /* unlimited packfile */
        else if (DELTA(entry)->idx.offset == (off_t)-1)
                usable_delta = 0;       /* base was written to another pack */
        else if (DELTA(entry)->idx.offset)
                usable_delta = 1;       /* base already exists in this pack */
        else
                usable_delta = 0;       /* base could end up in another pack */

        if (!reuse_object)
                to_reuse = 0;   /* explicit */
        else if (!IN_PACK(entry))
                to_reuse = 0;   /* can't reuse what we don't have */
        else if (oe_type(entry) == OBJ_REF_DELTA ||
                 oe_type(entry) == OBJ_OFS_DELTA)
                                /* check_object() decided it for us ... */
                to_reuse = usable_delta;
                                /* ... but pack split may override that */
        else if (oe_type(entry) != entry->in_pack_type)
                to_reuse = 0;   /* pack has delta which is unusable */
        else if (DELTA(entry))
                to_reuse = 0;   /* we want to pack afresh */
        else
                to_reuse = 1;   /* we have it in-pack undeltified,
                                 * and we do not need to deltify it.
                                 */

        if (!to_reuse)
                len = write_no_reuse_object(f, entry, limit, usable_delta);
        else
                len = write_reuse_object(f, entry, limit, usable_delta);
        if (!len)
                return 0;

        if (usable_delta)
                written_delta++;
        written++;
        if (!pack_to_stdout)
                entry->idx.crc32 = crc32_end(f);
        return len;
}

enum write_one_status {
        WRITE_ONE_SKIP = -1, /* already written */
        WRITE_ONE_BREAK = 0, /* writing this will bust the limit; not written */
        WRITE_ONE_WRITTEN = 1, /* normal */
        WRITE_ONE_RECURSIVE = 2 /* already scheduled to be written */
};

static enum write_one_status write_one(struct hashfile *f,
                                       struct object_entry *e,
                                       off_t *offset)
{
        off_t size;
        int recursing;

        /*
         * we set offset to 1 (which is an impossible value) to mark
         * the fact that this object is involved in "write its base
         * first before writing a deltified object" recursion.
         */
        recursing = (e->idx.offset == 1);
        if (recursing) {
                warning(_("recursive delta detected for object %s"),
                        oid_to_hex(&e->idx.oid));
                return WRITE_ONE_RECURSIVE;
        } else if (e->idx.offset || e->preferred_base) {
                /* offset is non zero if object is written already. */
                return WRITE_ONE_SKIP;
        }

        /* if we are deltified, write out base object first. */
        if (DELTA(e)) {
                e->idx.offset = 1; /* now recurse */
                switch (write_one(f, DELTA(e), offset)) {
                case WRITE_ONE_RECURSIVE:
                        /* we cannot depend on this one */
                        SET_DELTA(e, NULL);
                        break;
                default:
                        break;
                case WRITE_ONE_BREAK:
                        e->idx.offset = recursing;
                        return WRITE_ONE_BREAK;
                }
        }

        e->idx.offset = *offset;
        size = write_object(f, e, *offset);
        if (!size) {
                e->idx.offset = recursing;
                return WRITE_ONE_BREAK;
        }
        written_list[nr_written++] = &e->idx;

        /* make sure off_t is sufficiently large not to wrap */
        if (signed_add_overflows(*offset, size))
                die(_("pack too large for current definition of off_t"));
        *offset += size;
        return WRITE_ONE_WRITTEN;
}

static int mark_tagged(const char *path, const struct object_id *oid, int flag,
                       void *cb_data)
{
        struct object_id peeled;
        struct object_entry *entry = packlist_find(&to_pack, oid);

        if (entry)
                entry->tagged = 1;
        if (!peel_ref(path, &peeled)) {
                entry = packlist_find(&to_pack, &peeled);
                if (entry)
                        entry->tagged = 1;
        }
        return 0;
}

static inline void add_to_write_order(struct object_entry **wo,
                               unsigned int *endp,
                               struct object_entry *e)
{
        if (e->filled || oe_layer(&to_pack, e) != write_layer)
                return;
        wo[(*endp)++] = e;
        e->filled = 1;
}

static void add_descendants_to_write_order(struct object_entry **wo,
                                           unsigned int *endp,
                                           struct object_entry *e)
{
        int add_to_order = 1;
        while (e) {
                if (add_to_order) {
                        struct object_entry *s;
                        /* add this node... */
                        add_to_write_order(wo, endp, e);
                        /* all its siblings... */
                        for (s = DELTA_SIBLING(e); s; s = DELTA_SIBLING(s)) {
                                add_to_write_order(wo, endp, s);
                        }
                }
                /* drop down a level to add left subtree nodes if possible */
                if (DELTA_CHILD(e)) {
                        add_to_order = 1;
                        e = DELTA_CHILD(e);
                } else {
                        add_to_order = 0;
                        /* our sibling might have some children, it is next */
                        if (DELTA_SIBLING(e)) {
                                e = DELTA_SIBLING(e);
                                continue;
                        }
                        /* go back to our parent node */
                        e = DELTA(e);
                        while (e && !DELTA_SIBLING(e)) {
                                /* we're on the right side of a subtree, keep
                                 * going up until we can go right again */
                                e = DELTA(e);
                        }
                        if (!e) {
                                /* done- we hit our original root node */
                                return;
                        }
                        /* pass it off to sibling at this level */
                        e = DELTA_SIBLING(e);
                }
        };
}

static void add_family_to_write_order(struct object_entry **wo,
                                      unsigned int *endp,
                                      struct object_entry *e)
{
        struct object_entry *root;

        for (root = e; DELTA(root); root = DELTA(root))
                ; /* nothing */
        add_descendants_to_write_order(wo, endp, root);
}

static void compute_layer_order(struct object_entry **wo, unsigned int *wo_end)
{
        unsigned int i, last_untagged;
        struct object_entry *objects = to_pack.objects;

        for (i = 0; i < to_pack.nr_objects; i++) {
                if (objects[i].tagged)
                        break;
                add_to_write_order(wo, wo_end, &objects[i]);
        }
        last_untagged = i;

        /*
         * Then fill all the tagged tips.
         */
        for (; i < to_pack.nr_objects; i++) {
                if (objects[i].tagged)
                        add_to_write_order(wo, wo_end, &objects[i]);
        }

        /*
         * And then all remaining commits and tags.
         */
        for (i = last_untagged; i < to_pack.nr_objects; i++) {
                if (oe_type(&objects[i]) != OBJ_COMMIT &&
                    oe_type(&objects[i]) != OBJ_TAG)
                        continue;
                add_to_write_order(wo, wo_end, &objects[i]);
        }

        /*
         * And then all the trees.
         */
        for (i = last_untagged; i < to_pack.nr_objects; i++) {
                if (oe_type(&objects[i]) != OBJ_TREE)
                        continue;
                add_to_write_order(wo, wo_end, &objects[i]);
        }

        /*
         * Finally all the rest in really tight order
         */
        for (i = last_untagged; i < to_pack.nr_objects; i++) {
                if (!objects[i].filled && oe_layer(&to_pack, &objects[i]) == write_layer)
                        add_family_to_write_order(wo, wo_end, &objects[i]);
        }
}

static struct object_entry **compute_write_order(void)
{
        uint32_t max_layers = 1;
        unsigned int i, wo_end;

        struct object_entry **wo;
        struct object_entry *objects = to_pack.objects;

        for (i = 0; i < to_pack.nr_objects; i++) {
                objects[i].tagged = 0;
                objects[i].filled = 0;
                SET_DELTA_CHILD(&objects[i], NULL);
                SET_DELTA_SIBLING(&objects[i], NULL);
        }

        /*
         * Fully connect delta_child/delta_sibling network.
         * Make sure delta_sibling is sorted in the original
         * recency order.
         */
        for (i = to_pack.nr_objects; i > 0;) {
                struct object_entry *e = &objects[--i];
                if (!DELTA(e))
                        continue;
                /* Mark me as the first child */
                e->delta_sibling_idx = DELTA(e)->delta_child_idx;
                SET_DELTA_CHILD(DELTA(e), e);
        }

        /*
         * Mark objects that are at the tip of tags.
         */
        for_each_tag_ref(mark_tagged, NULL);

        if (use_delta_islands)
                max_layers = compute_pack_layers(&to_pack);

        ALLOC_ARRAY(wo, to_pack.nr_objects);
        wo_end = 0;

        for (; write_layer < max_layers; ++write_layer)
                compute_layer_order(wo, &wo_end);

        if (wo_end != to_pack.nr_objects)
                die(_("ordered %u objects, expected %"PRIu32),
                    wo_end, to_pack.nr_objects);

        return wo;
}


/*
 * A reused set of objects. All objects in a chunk have the same
 * relative position in the original packfile and the generated
 * packfile.
 */

static struct reused_chunk {
        /* The offset of the first object of this chunk in the original
         * packfile. */
        off_t original;
        /* The offset of the first object of this chunk in the generated
         * packfile minus "original". */
        off_t difference;
} *reused_chunks;
static int reused_chunks_nr;
static int reused_chunks_alloc;

static void record_reused_object(off_t where, off_t offset)
{
        if (reused_chunks_nr && reused_chunks[reused_chunks_nr-1].difference == offset)
                return;

        ALLOC_GROW(reused_chunks, reused_chunks_nr + 1,
                   reused_chunks_alloc);
        reused_chunks[reused_chunks_nr].original = where;
        reused_chunks[reused_chunks_nr].difference = offset;
        reused_chunks_nr++;
}

/*
 * Binary search to find the chunk that "where" is in. Note
 * that we're not looking for an exact match, just the first
 * chunk that contains it (which implicitly ends at the start
 * of the next chunk.
 */
static off_t find_reused_offset(off_t where)
{
        int lo = 0, hi = reused_chunks_nr;
        while (lo < hi) {
                int mi = lo + ((hi - lo) / 2);
                if (where == reused_chunks[mi].original)
                        return reused_chunks[mi].difference;
                if (where < reused_chunks[mi].original)
                        hi = mi;
                else
                        lo = mi + 1;
        }

        /*
         * The first chunk starts at zero, so we can't have gone below
         * there.
         */
        assert(lo);
        return reused_chunks[lo-1].difference;
}

static void write_reused_pack_one(size_t pos, struct hashfile *out,
                                  struct pack_window **w_curs)
{
        off_t offset, next, cur;
        enum object_type type;
        unsigned long size;

        offset = reuse_packfile->revindex[pos].offset;
        next = reuse_packfile->revindex[pos + 1].offset;

        record_reused_object(offset, offset - hashfile_total(out));

        cur = offset;
        type = unpack_object_header(reuse_packfile, w_curs, &cur, &size);
        assert(type >= 0);

        if (type == OBJ_OFS_DELTA) {
                off_t base_offset;
                off_t fixup;

                unsigned char header[MAX_PACK_OBJECT_HEADER];
                unsigned len;

                base_offset = get_delta_base(reuse_packfile, w_curs, &cur, type, offset);
                assert(base_offset != 0);

                /* Convert to REF_DELTA if we must... */
                if (!allow_ofs_delta) {
                        int base_pos = find_revindex_position(reuse_packfile, base_offset);
                        const unsigned char *base_sha1 =
                                nth_packed_object_sha1(reuse_packfile,
                                                       reuse_packfile->revindex[base_pos].nr);

                        len = encode_in_pack_object_header(header, sizeof(header),
                                                           OBJ_REF_DELTA, size);
                        hashwrite(out, header, len);
                        hashwrite(out, base_sha1, 20);
                        copy_pack_data(out, reuse_packfile, w_curs, cur, next - cur);
                        return;
                }

                /* Otherwise see if we need to rewrite the offset... */
                fixup = find_reused_offset(offset) -
                        find_reused_offset(base_offset);
                if (fixup) {
                        unsigned char ofs_header[10];
                        unsigned i, ofs_len;
                        off_t ofs = offset - base_offset - fixup;

                        len = encode_in_pack_object_header(header, sizeof(header),
                                                           OBJ_OFS_DELTA, size);

                        i = sizeof(ofs_header) - 1;
                        ofs_header[i] = ofs & 127;
                        while (ofs >>= 7)
                                ofs_header[--i] = 128 | (--ofs & 127);

                        ofs_len = sizeof(ofs_header) - i;

                        hashwrite(out, header, len);
                        hashwrite(out, ofs_header + sizeof(ofs_header) - ofs_len, ofs_len);
                        copy_pack_data(out, reuse_packfile, w_curs, cur, next - cur);
                        return;
                }

                /* ...otherwise we have no fixup, and can write it verbatim */
        }

        copy_pack_data(out, reuse_packfile, w_curs, offset, next - offset);
}

static size_t write_reused_pack_verbatim(struct hashfile *out,
                                         struct pack_window **w_curs)
{
        size_t pos = 0;

        while (pos < reuse_packfile_bitmap->word_alloc &&
                        reuse_packfile_bitmap->words[pos] == (eword_t)~0)
                pos++;

        if (pos) {
                off_t to_write;

                written = (pos * BITS_IN_EWORD);
                to_write = reuse_packfile->revindex[written].offset
                        - sizeof(struct pack_header);

                /* We're recording one chunk, not one object. */
                record_reused_object(sizeof(struct pack_header), 0);
                hashflush(out);
                copy_pack_data(out, reuse_packfile, w_curs,
                        sizeof(struct pack_header), to_write);

                display_progress(progress_state, written);
        }
        return pos;
}

static void write_reused_pack(struct hashfile *f)
{
        size_t i = 0;
        uint32_t offset;
        struct pack_window *w_curs = NULL;

        if (allow_ofs_delta)
                i = write_reused_pack_verbatim(f, &w_curs);

        for (; i < reuse_packfile_bitmap->word_alloc; ++i) {
                eword_t word = reuse_packfile_bitmap->words[i];
                size_t pos = (i * BITS_IN_EWORD);

                for (offset = 0; offset < BITS_IN_EWORD; ++offset) {
                        if ((word >> offset) == 0)
                                break;

                        offset += ewah_bit_ctz64(word >> offset);
                        write_reused_pack_one(pos + offset, f, &w_curs);
                        display_progress(progress_state, ++written);
                }
        }

        unuse_pack(&w_curs);
}

static const char no_split_warning[] = N_(
"disabling bitmap writing, packs are split due to pack.packSizeLimit"
);

static void write_pack_file(void)
{
        uint32_t i = 0, j;
        struct hashfile *f;
        off_t offset;
        uint32_t nr_remaining = nr_result;
        time_t last_mtime = 0;
        struct object_entry **write_order;

        if (progress > pack_to_stdout)
                progress_state = start_progress(_("Writing objects"), nr_result);
        ALLOC_ARRAY(written_list, to_pack.nr_objects);
        write_order = compute_write_order();

        do {
                struct object_id oid;
                char *pack_tmp_name = NULL;

                if (pack_to_stdout)
                        f = hashfd_throughput(1, "<stdout>", progress_state);
                else
                        f = create_tmp_packfile(&pack_tmp_name);

                offset = write_pack_header(f, nr_remaining);

                if (reuse_packfile) {
                        assert(pack_to_stdout);
                        write_reused_pack(f);
                        offset = hashfile_total(f);
                }

                nr_written = 0;
                for (; i < to_pack.nr_objects; i++) {
                        struct object_entry *e = write_order[i];
                        if (write_one(f, e, &offset) == WRITE_ONE_BREAK)
                                break;
                        display_progress(progress_state, written);
                }

                /*
                 * Did we write the wrong # entries in the header?
                 * If so, rewrite it like in fast-import
                 */
                if (pack_to_stdout) {
                        finalize_hashfile(f, oid.hash, CSUM_HASH_IN_STREAM | CSUM_CLOSE);
                } else if (nr_written == nr_remaining) {
                        finalize_hashfile(f, oid.hash, CSUM_HASH_IN_STREAM | CSUM_FSYNC | CSUM_CLOSE);
                } else {
                        int fd = finalize_hashfile(f, oid.hash, 0);
                        fixup_pack_header_footer(fd, oid.hash, pack_tmp_name,
                                                 nr_written, oid.hash, offset);
                        close(fd);
                        if (write_bitmap_index) {
                                if (write_bitmap_index != WRITE_BITMAP_QUIET)
                                        warning(_(no_split_warning));
                                write_bitmap_index = 0;
                        }
                }

                if (!pack_to_stdout) {
                        struct stat st;
                        struct strbuf tmpname = STRBUF_INIT;

                        /*
                         * Packs are runtime accessed in their mtime
                         * order since newer packs are more likely to contain
                         * younger objects.  So if we are creating multiple
                         * packs then we should modify the mtime of later ones
                         * to preserve this property.
                         */
                        if (stat(pack_tmp_name, &st) < 0) {
                                warning_errno(_("failed to stat %s"), pack_tmp_name);
                        } else if (!last_mtime) {
                                last_mtime = st.st_mtime;
                        } else {
                                struct utimbuf utb;
                                utb.actime = st.st_atime;
                                utb.modtime = --last_mtime;
                                if (utime(pack_tmp_name, &utb) < 0)
                                        warning_errno(_("failed utime() on %s"), pack_tmp_name);
                        }

                        strbuf_addf(&tmpname, "%s-", base_name);

                        if (write_bitmap_index) {
                                bitmap_writer_set_checksum(oid.hash);
                                bitmap_writer_build_type_index(
                                        &to_pack, written_list, nr_written);
                        }

                        finish_tmp_packfile(&tmpname, pack_tmp_name,
                                            written_list, nr_written,
                                            &pack_idx_opts, oid.hash);

                        if (write_bitmap_index) {
                                strbuf_addf(&tmpname, "%s.bitmap", oid_to_hex(&oid));

                                stop_progress(&progress_state);

                                bitmap_writer_show_progress(progress);
                                bitmap_writer_reuse_bitmaps(&to_pack);
                                bitmap_writer_select_commits(indexed_commits, indexed_commits_nr, -1);
                                bitmap_writer_build(&to_pack);
                                bitmap_writer_finish(written_list, nr_written,
                                                     tmpname.buf, write_bitmap_options);
                                write_bitmap_index = 0;
                        }

                        strbuf_release(&tmpname);
                        free(pack_tmp_name);
                        puts(oid_to_hex(&oid));
                }

                /* mark written objects as written to previous pack */
                for (j = 0; j < nr_written; j++) {
                        written_list[j]->offset = (off_t)-1;
                }
                nr_remaining -= nr_written;
        } while (nr_remaining && i < to_pack.nr_objects);

        free(written_list);
        free(write_order);
        stop_progress(&progress_state);
        if (written != nr_result)
                die(_("wrote %"PRIu32" objects while expecting %"PRIu32),
                    written, nr_result);
        trace2_data_intmax("pack-objects", the_repository,
                           "write_pack_file/wrote", nr_result);
}

static int no_try_delta(const char *path)
{
        static struct attr_check *check;

        if (!check)
                check = attr_check_initl("delta", NULL);
        git_check_attr(the_repository->index, path, check);
        if (ATTR_FALSE(check->items[0].value))
                return 1;
        return 0;
}

/*
 * When adding an object, check whether we have already added it
 * to our packing list. If so, we can skip. However, if we are
 * being asked to excludei t, but the previous mention was to include
 * it, make sure to adjust its flags and tweak our numbers accordingly.
 *
 * As an optimization, we pass out the index position where we would have
 * found the item, since that saves us from having to look it up again a
 * few lines later when we want to add the new entry.
 */
static int have_duplicate_entry(const struct object_id *oid,
                                int exclude)
{
        struct object_entry *entry;

        if (reuse_packfile_bitmap &&
            bitmap_walk_contains(bitmap_git, reuse_packfile_bitmap, oid))
                return 1;

        entry = packlist_find(&to_pack, oid);
        if (!entry)
                return 0;

        if (exclude) {
                if (!entry->preferred_base)
                        nr_result--;
                entry->preferred_base = 1;
        }

        return 1;
}

static int want_found_object(int exclude, struct packed_git *p)
{
        if (exclude)
                return 1;
        if (incremental)
                return 0;

        /*
         * When asked to do --local (do not include an object that appears in a
         * pack we borrow from elsewhere) or --honor-pack-keep (do not include
         * an object that appears in a pack marked with .keep), finding a pack
         * that matches the criteria is sufficient for us to decide to omit it.
         * However, even if this pack does not satisfy the criteria, we need to
         * make sure no copy of this object appears in _any_ pack that makes us
         * to omit the object, so we need to check all the packs.
         *
         * We can however first check whether these options can possible matter;
         * if they do not matter we know we want the object in generated pack.
         * Otherwise, we signal "-1" at the end to tell the caller that we do
         * not know either way, and it needs to check more packs.
         */
        if (!ignore_packed_keep_on_disk &&
            !ignore_packed_keep_in_core &&
            (!local || !have_non_local_packs))
                return 1;

        if (local && !p->pack_local)
                return 0;
        if (p->pack_local &&
            ((ignore_packed_keep_on_disk && p->pack_keep) ||
             (ignore_packed_keep_in_core && p->pack_keep_in_core)))
                return 0;

        /* we don't know yet; keep looking for more packs */
        return -1;
}

/*
 * Check whether we want the object in the pack (e.g., we do not want
 * objects found in non-local stores if the "--local" option was used).
 *
 * If the caller already knows an existing pack it wants to take the object
 * from, that is passed in *found_pack and *found_offset; otherwise this
 * function finds if there is any pack that has the object and returns the pack
 * and its offset in these variables.
 */
static int want_object_in_pack(const struct object_id *oid,
                               int exclude,
                               struct packed_git **found_pack,
                               off_t *found_offset)
{
        int want;
        struct list_head *pos;
        struct multi_pack_index *m;

        if (!exclude && local && has_loose_object_nonlocal(oid))
                return 0;

        /*
         * If we already know the pack object lives in, start checks from that
         * pack - in the usual case when neither --local was given nor .keep files
         * are present we will determine the answer right now.
         */
        if (*found_pack) {
                want = want_found_object(exclude, *found_pack);
                if (want != -1)
                        return want;
        }

        for (m = get_multi_pack_index(the_repository); m; m = m->next) {
                struct pack_entry e;
                if (fill_midx_entry(the_repository, oid, &e, m)) {
                        struct packed_git *p = e.p;
                        off_t offset;

                        if (p == *found_pack)
                                offset = *found_offset;
                        else
                                offset = find_pack_entry_one(oid->hash, p);

                        if (offset) {
                                if (!*found_pack) {
                                        if (!is_pack_valid(p))
                                                continue;
                                        *found_offset = offset;
                                        *found_pack = p;
                                }
                                want = want_found_object(exclude, p);
                                if (want != -1)
                                        return want;
                        }
                }
        }

        list_for_each(pos, get_packed_git_mru(the_repository)) {
                struct packed_git *p = list_entry(pos, struct packed_git, mru);
                off_t offset;

                if (p == *found_pack)
                        offset = *found_offset;
                else
                        offset = find_pack_entry_one(oid->hash, p);

                if (offset) {
                        if (!*found_pack) {
                                if (!is_pack_valid(p))
                                        continue;
                                *found_offset = offset;
                                *found_pack = p;
                        }
                        want = want_found_object(exclude, p);
                        if (!exclude && want > 0)
                                list_move(&p->mru,
                                          get_packed_git_mru(the_repository));
                        if (want != -1)
                                return want;
                }
        }

        return 1;
}

static void create_object_entry(const struct object_id *oid,
                                enum object_type type,
                                uint32_t hash,
                                int exclude,
                                int no_try_delta,
                                struct packed_git *found_pack,
                                off_t found_offset)
{
        struct object_entry *entry;

        entry = packlist_alloc(&to_pack, oid);
        entry->hash = hash;
        oe_set_type(entry, type);
        if (exclude)
                entry->preferred_base = 1;
        else
                nr_result++;
        if (found_pack) {
                oe_set_in_pack(&to_pack, entry, found_pack);
                entry->in_pack_offset = found_offset;
        }

        entry->no_try_delta = no_try_delta;
}

static const char no_closure_warning[] = N_(
"disabling bitmap writing, as some objects are not being packed"
);

static int add_object_entry(const struct object_id *oid, enum object_type type,
                            const char *name, int exclude)
{
        struct packed_git *found_pack = NULL;
        off_t found_offset = 0;

        display_progress(progress_state, ++nr_seen);

        if (have_duplicate_entry(oid, exclude))
                return 0;

        if (!want_object_in_pack(oid, exclude, &found_pack, &found_offset)) {
                /* The pack is missing an object, so it will not have closure */
                if (write_bitmap_index) {
                        if (write_bitmap_index != WRITE_BITMAP_QUIET)
                                warning(_(no_closure_warning));
                        write_bitmap_index = 0;
                }
                return 0;
        }

        create_object_entry(oid, type, pack_name_hash(name),
                            exclude, name && no_try_delta(name),
                            found_pack, found_offset);
        return 1;
}

static int add_object_entry_from_bitmap(const struct object_id *oid,
                                        enum object_type type,
                                        int flags, uint32_t name_hash,
                                        struct packed_git *pack, off_t offset)
{
        display_progress(progress_state, ++nr_seen);

        if (have_duplicate_entry(oid, 0))
                return 0;

        if (!want_object_in_pack(oid, 0, &pack, &offset))
                return 0;

        create_object_entry(oid, type, name_hash, 0, 0, pack, offset);
        return 1;
}

struct pbase_tree_cache {
        struct object_id oid;
        int ref;
        int temporary;
        void *tree_data;
        unsigned long tree_size;
};

static struct pbase_tree_cache *(pbase_tree_cache[256]);
static int pbase_tree_cache_ix(const struct object_id *oid)
{
        return oid->hash[0] % ARRAY_SIZE(pbase_tree_cache);
}
static int pbase_tree_cache_ix_incr(int ix)
{
        return (ix+1) % ARRAY_SIZE(pbase_tree_cache);
}

static struct pbase_tree {
        struct pbase_tree *next;
        /* This is a phony "cache" entry; we are not
         * going to evict it or find it through _get()
         * mechanism -- this is for the toplevel node that
         * would almost always change with any commit.
         */
        struct pbase_tree_cache pcache;
} *pbase_tree;

static struct pbase_tree_cache *pbase_tree_get(const struct object_id *oid)
{
        struct pbase_tree_cache *ent, *nent;
        void *data;
        unsigned long size;
        enum object_type type;
        int neigh;
        int my_ix = pbase_tree_cache_ix(oid);
        int available_ix = -1;

        /* pbase-tree-cache acts as a limited hashtable.
         * your object will be found at your index or within a few
         * slots after that slot if it is cached.
         */
        for (neigh = 0; neigh < 8; neigh++) {
                ent = pbase_tree_cache[my_ix];
                if (ent && oideq(&ent->oid, oid)) {
                        ent->ref++;
                        return ent;
                }
                else if (((available_ix < 0) && (!ent || !ent->ref)) ||
                         ((0 <= available_ix) &&
                          (!ent && pbase_tree_cache[available_ix])))
                        available_ix = my_ix;
                if (!ent)
                        break;
                my_ix = pbase_tree_cache_ix_incr(my_ix);
        }

        /* Did not find one.  Either we got a bogus request or
         * we need to read and perhaps cache.
         */
        data = read_object_file(oid, &type, &size);
        if (!data)
                return NULL;
        if (type != OBJ_TREE) {
                free(data);
                return NULL;
        }

        /* We need to either cache or return a throwaway copy */

        if (available_ix < 0)
                ent = NULL;
        else {
                ent = pbase_tree_cache[available_ix];
                my_ix = available_ix;
        }

        if (!ent) {
                nent = xmalloc(sizeof(*nent));
                nent->temporary = (available_ix < 0);
        }
        else {
                /* evict and reuse */
                free(ent->tree_data);
                nent = ent;
        }
        oidcpy(&nent->oid, oid);
        nent->tree_data = data;
        nent->tree_size = size;
        nent->ref = 1;
        if (!nent->temporary)
                pbase_tree_cache[my_ix] = nent;
        return nent;
}

static void pbase_tree_put(struct pbase_tree_cache *cache)
{
        if (!cache->temporary) {
                cache->ref--;
                return;
        }
        free(cache->tree_data);
        free(cache);
}

static int name_cmp_len(const char *name)
{
        int i;
        for (i = 0; name[i] && name[i] != '\n' && name[i] != '/'; i++)
                ;
        return i;
}

static void add_pbase_object(struct tree_desc *tree,
                             const char *name,
                             int cmplen,
                             const char *fullname)
{
        struct name_entry entry;
        int cmp;

        while (tree_entry(tree,&entry)) {
                if (S_ISGITLINK(entry.mode))
                        continue;
                cmp = tree_entry_len(&entry) != cmplen ? 1 :
                      memcmp(name, entry.path, cmplen);
                if (cmp > 0)
                        continue;
                if (cmp < 0)
                        return;
                if (name[cmplen] != '/') {
                        add_object_entry(&entry.oid,
                                         object_type(entry.mode),
                                         fullname, 1);
                        return;
                }
                if (S_ISDIR(entry.mode)) {
                        struct tree_desc sub;
                        struct pbase_tree_cache *tree;
                        const char *down = name+cmplen+1;
                        int downlen = name_cmp_len(down);

                        tree = pbase_tree_get(&entry.oid);
                        if (!tree)
                                return;
                        init_tree_desc(&sub, tree->tree_data, tree->tree_size);

                        add_pbase_object(&sub, down, downlen, fullname);
                        pbase_tree_put(tree);
                }
        }
}

static unsigned *done_pbase_paths;
static int done_pbase_paths_num;
static int done_pbase_paths_alloc;
static int done_pbase_path_pos(unsigned hash)
{
        int lo = 0;
        int hi = done_pbase_paths_num;
        while (lo < hi) {
                int mi = lo + (hi - lo) / 2;
                if (done_pbase_paths[mi] == hash)
                        return mi;
                if (done_pbase_paths[mi] < hash)
                        hi = mi;
                else
                        lo = mi + 1;
        }
        return -lo-1;
}

static int check_pbase_path(unsigned hash)
{
        int pos = done_pbase_path_pos(hash);
        if (0 <= pos)
                return 1;
        pos = -pos - 1;
        ALLOC_GROW(done_pbase_paths,
                   done_pbase_paths_num + 1,
                   done_pbase_paths_alloc);
        done_pbase_paths_num++;
        if (pos < done_pbase_paths_num)
                MOVE_ARRAY(done_pbase_paths + pos + 1, done_pbase_paths + pos,
                           done_pbase_paths_num - pos - 1);
        done_pbase_paths[pos] = hash;
        return 0;
}

static void add_preferred_base_object(const char *name)
{
        struct pbase_tree *it;
        int cmplen;
        unsigned hash = pack_name_hash(name);

        if (!num_preferred_base || check_pbase_path(hash))
                return;

        cmplen = name_cmp_len(name);
        for (it = pbase_tree; it; it = it->next) {
                if (cmplen == 0) {
                        add_object_entry(&it->pcache.oid, OBJ_TREE, NULL, 1);
                }
                else {
                        struct tree_desc tree;
                        init_tree_desc(&tree, it->pcache.tree_data, it->pcache.tree_size);
                        add_pbase_object(&tree, name, cmplen, name);
                }
        }
}

static void add_preferred_base(struct object_id *oid)
{
        struct pbase_tree *it;
        void *data;
        unsigned long size;
        struct object_id tree_oid;

        if (window <= num_preferred_base++)
                return;

        data = read_object_with_reference(the_repository, oid,
                                          tree_type, &size, &tree_oid);
        if (!data)
                return;

        for (it = pbase_tree; it; it = it->next) {
                if (oideq(&it->pcache.oid, &tree_oid)) {
                        free(data);
                        return;
                }
        }

        it = xcalloc(1, sizeof(*it));
        it->next = pbase_tree;
        pbase_tree = it;

        oidcpy(&it->pcache.oid, &tree_oid);
        it->pcache.tree_data = data;
        it->pcache.tree_size = size;
}

static void cleanup_preferred_base(void)
{
        struct pbase_tree *it;
        unsigned i;

        it = pbase_tree;
        pbase_tree = NULL;
        while (it) {
                struct pbase_tree *tmp = it;
                it = tmp->next;
                free(tmp->pcache.tree_data);
                free(tmp);
        }

        for (i = 0; i < ARRAY_SIZE(pbase_tree_cache); i++) {
                if (!pbase_tree_cache[i])
                        continue;
                free(pbase_tree_cache[i]->tree_data);
                FREE_AND_NULL(pbase_tree_cache[i]);
        }

        FREE_AND_NULL(done_pbase_paths);
        done_pbase_paths_num = done_pbase_paths_alloc = 0;
}

/*
 * Return 1 iff the object specified by "delta" can be sent
 * literally as a delta against the base in "base_sha1". If
 * so, then *base_out will point to the entry in our packing
 * list, or NULL if we must use the external-base list.
 *
 * Depth value does not matter - find_deltas() will
 * never consider reused delta as the base object to
 * deltify other objects against, in order to avoid
 * circular deltas.
 */
static int can_reuse_delta(const unsigned char *base_sha1,
                           struct object_entry *delta,
                           struct object_entry **base_out)
{
        struct object_entry *base;
        struct object_id base_oid;

        if (!base_sha1)
                return 0;

        oidread(&base_oid, base_sha1);

        /*
         * First see if we're already sending the base (or it's explicitly in
         * our "excluded" list).
         */
        base = packlist_find(&to_pack, &base_oid);
        if (base) {
                if (!in_same_island(&delta->idx.oid, &base->idx.oid))
                        return 0;
                *base_out = base;
                return 1;
        }

        /*
         * Otherwise, reachability bitmaps may tell us if the receiver has it,
         * even if it was buried too deep in history to make it into the
         * packing list.
         */
        if (thin && bitmap_has_oid_in_uninteresting(bitmap_git, &base_oid)) {
                if (use_delta_islands) {
                        if (!in_same_island(&delta->idx.oid, &base_oid))
                                return 0;
                }
                *base_out = NULL;
                return 1;
        }

        return 0;
}

static void check_object(struct object_entry *entry)
{
        unsigned long canonical_size;

        if (IN_PACK(entry)) {
                struct packed_git *p = IN_PACK(entry);
                struct pack_window *w_curs = NULL;
                const unsigned char *base_ref = NULL;
                struct object_entry *base_entry;
                unsigned long used, used_0;
                unsigned long avail;
                off_t ofs;
                unsigned char *buf, c;
                enum object_type type;
                unsigned long in_pack_size;

                buf = use_pack(p, &w_curs, entry->in_pack_offset, &avail);

                /*
                 * We want in_pack_type even if we do not reuse delta
                 * since non-delta representations could still be reused.
                 */
                used = unpack_object_header_buffer(buf, avail,
                                                   &type,
                                                   &in_pack_size);
                if (used == 0)
                        goto give_up;

                if (type < 0)
                        BUG("invalid type %d", type);
                entry->in_pack_type = type;

                /*
                 * Determine if this is a delta and if so whether we can
                 * reuse it or not.  Otherwise let's find out as cheaply as
                 * possible what the actual type and size for this object is.
                 */
                switch (entry->in_pack_type) {
                default:
                        /* Not a delta hence we've already got all we need. */
                        oe_set_type(entry, entry->in_pack_type);
                        SET_SIZE(entry, in_pack_size);
                        entry->in_pack_header_size = used;
                        if (oe_type(entry) < OBJ_COMMIT || oe_type(entry) > OBJ_BLOB)
                                goto give_up;
                        unuse_pack(&w_curs);
                        return;
                case OBJ_REF_DELTA:
                        if (reuse_delta && !entry->preferred_base)
                                base_ref = use_pack(p, &w_curs,
                                                entry->in_pack_offset + used, NULL);
                        entry->in_pack_header_size = used + the_hash_algo->rawsz;
                        break;
                case OBJ_OFS_DELTA:
                        buf = use_pack(p, &w_curs,
                                       entry->in_pack_offset + used, NULL);
                        used_0 = 0;
                        c = buf[used_0++];
                        ofs = c & 127;
                        while (c & 128) {
                                ofs += 1;
                                if (!ofs || MSB(ofs, 7)) {
                                        error(_("delta base offset overflow in pack for %s"),
                                              oid_to_hex(&entry->idx.oid));
                                        goto give_up;
                                }
                                c = buf[used_0++];
                                ofs = (ofs << 7) + (c & 127);
                        }
                        ofs = entry->in_pack_offset - ofs;
                        if (ofs <= 0 || ofs >= entry->in_pack_offset) {
                                error(_("delta base offset out of bound for %s"),
                                      oid_to_hex(&entry->idx.oid));
                                goto give_up;
                        }
                        if (reuse_delta && !entry->preferred_base) {
                                struct revindex_entry *revidx;
                                revidx = find_pack_revindex(p, ofs);
                                if (!revidx)
                                        goto give_up;
                                base_ref = nth_packed_object_sha1(p, revidx->nr);
                        }
                        entry->in_pack_header_size = used + used_0;
                        break;
                }

                if (can_reuse_delta(base_ref, entry, &base_entry)) {
                        oe_set_type(entry, entry->in_pack_type);
                        SET_SIZE(entry, in_pack_size); /* delta size */
                        SET_DELTA_SIZE(entry, in_pack_size);

                        if (base_entry) {
                                SET_DELTA(entry, base_entry);
                                entry->delta_sibling_idx = base_entry->delta_child_idx;
                                SET_DELTA_CHILD(base_entry, entry);
                        } else {
                                SET_DELTA_EXT(entry, base_ref);
                        }

                        unuse_pack(&w_curs);
                        return;
                }

                if (oe_type(entry)) {
                        off_t delta_pos;

                        /*
                         * This must be a delta and we already know what the
                         * final object type is.  Let's extract the actual
                         * object size from the delta header.
                         */
                        delta_pos = entry->in_pack_offset + entry->in_pack_header_size;
                        canonical_size = get_size_from_delta(p, &w_curs, delta_pos);
                        if (canonical_size == 0)
                                goto give_up;
                        SET_SIZE(entry, canonical_size);
                        unuse_pack(&w_curs);
                        return;
                }

                /*
                 * No choice but to fall back to the recursive delta walk
                 * with oid_object_info() to find about the object type
                 * at this point...
                 */
                give_up:
                unuse_pack(&w_curs);
        }

        oe_set_type(entry,
                    oid_object_info(the_repository, &entry->idx.oid, &canonical_size));
        if (entry->type_valid) {
                SET_SIZE(entry, canonical_size);
        } else {
                /*
                 * Bad object type is checked in prepare_pack().  This is
                 * to permit a missing preferred base object to be ignored
                 * as a preferred base.  Doing so can result in a larger
                 * pack file, but the transfer will still take place.
                 */
        }
}

static int pack_offset_sort(const void *_a, const void *_b)
{
        const struct object_entry *a = *(struct object_entry **)_a;
        const struct object_entry *b = *(struct object_entry **)_b;
        const struct packed_git *a_in_pack = IN_PACK(a);
        const struct packed_git *b_in_pack = IN_PACK(b);

        /* avoid filesystem trashing with loose objects */
        if (!a_in_pack && !b_in_pack)
                return oidcmp(&a->idx.oid, &b->idx.oid);

        if (a_in_pack < b_in_pack)
                return -1;
        if (a_in_pack > b_in_pack)
                return 1;
        return a->in_pack_offset < b->in_pack_offset ? -1 :
                        (a->in_pack_offset > b->in_pack_offset);
}

/*
 * Drop an on-disk delta we were planning to reuse. Naively, this would
 * just involve blanking out the "delta" field, but we have to deal
 * with some extra book-keeping:
 *
 *   1. Removing ourselves from the delta_sibling linked list.
 *
 *   2. Updating our size/type to the non-delta representation. These were
 *      either not recorded initially (size) or overwritten with the delta type
 *      (type) when check_object() decided to reuse the delta.
 *
 *   3. Resetting our delta depth, as we are now a base object.
 */
static void drop_reused_delta(struct object_entry *entry)
{
        unsigned *idx = &to_pack.objects[entry->delta_idx - 1].delta_child_idx;
        struct object_info oi = OBJECT_INFO_INIT;
        enum object_type type;
        unsigned long size;

        while (*idx) {
                struct object_entry *oe = &to_pack.objects[*idx - 1];

                if (oe == entry)
                        *idx = oe->delta_sibling_idx;
                else
                        idx = &oe->delta_sibling_idx;
        }
        SET_DELTA(entry, NULL);
        entry->depth = 0;

        oi.sizep = &size;
        oi.typep = &type;
        if (packed_object_info(the_repository, IN_PACK(entry), entry->in_pack_offset, &oi) < 0) {
                /*
                 * We failed to get the info from this pack for some reason;
                 * fall back to oid_object_info, which may find another copy.
                 * And if that fails, the error will be recorded in oe_type(entry)
                 * and dealt with in prepare_pack().
                 */
                oe_set_type(entry,
                            oid_object_info(the_repository, &entry->idx.oid, &size));
        } else {
                oe_set_type(entry, type);
        }
        SET_SIZE(entry, size);
}

/*
 * Follow the chain of deltas from this entry onward, throwing away any links
 * that cause us to hit a cycle (as determined by the DFS state flags in
 * the entries).
 *
 * We also detect too-long reused chains that would violate our --depth
 * limit.
 */
static void break_delta_chains(struct object_entry *entry)
{
        /*
         * The actual depth of each object we will write is stored as an int,
         * as it cannot exceed our int "depth" limit. But before we break
         * changes based no that limit, we may potentially go as deep as the
         * number of objects, which is elsewhere bounded to a uint32_t.
         */
        uint32_t total_depth;
        struct object_entry *cur, *next;

        for (cur = entry, total_depth = 0;
             cur;
             cur = DELTA(cur), total_depth++) {
                if (cur->dfs_state == DFS_DONE) {
                        /*
                         * We've already seen this object and know it isn't
                         * part of a cycle. We do need to append its depth
                         * to our count.
                         */
                        total_depth += cur->depth;
                        break;
                }

                /*
                 * We break cycles before looping, so an ACTIVE state (or any
                 * other cruft which made its way into the state variable)
                 * is a bug.
                 */
                if (cur->dfs_state != DFS_NONE)
                        BUG("confusing delta dfs state in first pass: %d",
                            cur->dfs_state);

                /*
                 * Now we know this is the first time we've seen the object. If
                 * it's not a delta, we're done traversing, but we'll mark it
                 * done to save time on future traversals.
                 */
                if (!DELTA(cur)) {
                        cur->dfs_state = DFS_DONE;
                        break;
                }

                /*
                 * Mark ourselves as active and see if the next step causes
                 * us to cycle to another active object. It's important to do
                 * this _before_ we loop, because it impacts where we make the
                 * cut, and thus how our total_depth counter works.
                 * E.g., We may see a partial loop like:
                 *
                 *   A -> B -> C -> D -> B
                 *
                 * Cutting B->C breaks the cycle. But now the depth of A is
                 * only 1, and our total_depth counter is at 3. The size of the
                 * error is always one less than the size of the cycle we
                 * broke. Commits C and D were "lost" from A's chain.
                 *
                 * If we instead cut D->B, then the depth of A is correct at 3.
                 * We keep all commits in the chain that we examined.
                 */
                cur->dfs_state = DFS_ACTIVE;
                if (DELTA(cur)->dfs_state == DFS_ACTIVE) {
                        drop_reused_delta(cur);
                        cur->dfs_state = DFS_DONE;
                        break;
                }
        }

        /*
         * And now that we've gone all the way to the bottom of the chain, we
         * need to clear the active flags and set the depth fields as
         * appropriate. Unlike the loop above, which can quit when it drops a
         * delta, we need to keep going to look for more depth cuts. So we need
         * an extra "next" pointer to keep going after we reset cur->delta.
         */
        for (cur = entry; cur; cur = next) {
                next = DELTA(cur);

                /*
                 * We should have a chain of zero or more ACTIVE states down to
                 * a final DONE. We can quit after the DONE, because either it
                 * has no bases, or we've already handled them in a previous
                 * call.
                 */
                if (cur->dfs_state == DFS_DONE)
                        break;
                else if (cur->dfs_state != DFS_ACTIVE)
                        BUG("confusing delta dfs state in second pass: %d",
                            cur->dfs_state);

                /*
                 * If the total_depth is more than depth, then we need to snip
                 * the chain into two or more smaller chains that don't exceed
                 * the maximum depth. Most of the resulting chains will contain
                 * (depth + 1) entries (i.e., depth deltas plus one base), and
                 * the last chain (i.e., the one containing entry) will contain
                 * whatever entries are left over, namely
                 * (total_depth % (depth + 1)) of them.
                 *
                 * Since we are iterating towards decreasing depth, we need to
                 * decrement total_depth as we go, and we need to write to the
                 * entry what its final depth will be after all of the
                 * snipping. Since we're snipping into chains of length (depth
                 * + 1) entries, the final depth of an entry will be its
                 * original depth modulo (depth + 1). Any time we encounter an
                 * entry whose final depth is supposed to be zero, we snip it
                 * from its delta base, thereby making it so.
                 */
                cur->depth = (total_depth--) % (depth + 1);
                if (!cur->depth)
                        drop_reused_delta(cur);

                cur->dfs_state = DFS_DONE;
        }
}

static void get_object_details(void)
{
        uint32_t i;
        struct object_entry **sorted_by_offset;

        if (progress)
                progress_state = start_progress(_("Counting objects"),
                                                to_pack.nr_objects);

        sorted_by_offset = xcalloc(to_pack.nr_objects, sizeof(struct object_entry *));
        for (i = 0; i < to_pack.nr_objects; i++)
                sorted_by_offset[i] = to_pack.objects + i;
        QSORT(sorted_by_offset, to_pack.nr_objects, pack_offset_sort);

        for (i = 0; i < to_pack.nr_objects; i++) {
                struct object_entry *entry = sorted_by_offset[i];
                check_object(entry);
                if (entry->type_valid &&
                    oe_size_greater_than(&to_pack, entry, big_file_threshold))
                        entry->no_try_delta = 1;
                display_progress(progress_state, i + 1);
        }
        stop_progress(&progress_state);

        /*
         * This must happen in a second pass, since we rely on the delta
         * information for the whole list being completed.
         */
        for (i = 0; i < to_pack.nr_objects; i++)
                break_delta_chains(&to_pack.objects[i]);

        free(sorted_by_offset);
}

/*
 * We search for deltas in a list sorted by type, by filename hash, and then
 * by size, so that we see progressively smaller and smaller files.
 * That's because we prefer deltas to be from the bigger file
 * to the smaller -- deletes are potentially cheaper, but perhaps
 * more importantly, the bigger file is likely the more recent
 * one.  The deepest deltas are therefore the oldest objects which are
 * less susceptible to be accessed often.
 */
static int type_size_sort(const void *_a, const void *_b)
{
        const struct object_entry *a = *(struct object_entry **)_a;
        const struct object_entry *b = *(struct object_entry **)_b;
        const enum object_type a_type = oe_type(a);
        const enum object_type b_type = oe_type(b);
        const unsigned long a_size = SIZE(a);
        const unsigned long b_size = SIZE(b);

        if (a_type > b_type)
                return -1;
        if (a_type < b_type)
                return 1;
        if (a->hash > b->hash)
                return -1;
        if (a->hash < b->hash)
                return 1;
        if (a->preferred_base > b->preferred_base)
                return -1;
        if (a->preferred_base < b->preferred_base)
                return 1;
        if (use_delta_islands) {
                const int island_cmp = island_delta_cmp(&a->idx.oid, &b->idx.oid);
                if (island_cmp)
                        return island_cmp;
        }
        if (a_size > b_size)
                return -1;
        if (a_size < b_size)
                return 1;
        return a < b ? -1 : (a > b);  /* newest first */
}

struct unpacked {
        struct object_entry *entry;
        void *data;
        struct delta_index *index;
        unsigned depth;
};

static int delta_cacheable(unsigned long src_size, unsigned long trg_size,
                           unsigned long delta_size)
{
        if (max_delta_cache_size && delta_cache_size + delta_size > max_delta_cache_size)
                return 0;

        if (delta_size < cache_max_small_delta_size)
                return 1;

        /* cache delta, if objects are large enough compared to delta size */
        if ((src_size >> 20) + (trg_size >> 21) > (delta_size >> 10))
                return 1;

        return 0;
}

/* Protect delta_cache_size */
static pthread_mutex_t cache_mutex;
#define cache_lock()            pthread_mutex_lock(&cache_mutex)
#define cache_unlock()          pthread_mutex_unlock(&cache_mutex)

/*
 * Protect object list partitioning (e.g. struct thread_param) and
 * progress_state
 */
static pthread_mutex_t progress_mutex;
#define progress_lock()         pthread_mutex_lock(&progress_mutex)
#define progress_unlock()       pthread_mutex_unlock(&progress_mutex)

/*
 * Access to struct object_entry is unprotected since each thread owns
 * a portion of the main object list. Just don't access object entries
 * ahead in the list because they can be stolen and would need
 * progress_mutex for protection.
 */

/*
 * Return the size of the object without doing any delta
 * reconstruction (so non-deltas are true object sizes, but deltas
 * return the size of the delta data).
 */
unsigned long oe_get_size_slow(struct packing_data *pack,
                               const struct object_entry *e)
{
        struct packed_git *p;
        struct pack_window *w_curs;
        unsigned char *buf;
        enum object_type type;
        unsigned long used, avail, size;

        if (e->type_ != OBJ_OFS_DELTA && e->type_ != OBJ_REF_DELTA) {
                packing_data_lock(&to_pack);
                if (oid_object_info(the_repository, &e->idx.oid, &size) < 0)
                        die(_("unable to get size of %s"),
                            oid_to_hex(&e->idx.oid));
                packing_data_unlock(&to_pack);
                return size;
        }

        p = oe_in_pack(pack, e);
        if (!p)
                BUG("when e->type is a delta, it must belong to a pack");

        packing_data_lock(&to_pack);
        w_curs = NULL;
        buf = use_pack(p, &w_curs, e->in_pack_offset, &avail);
        used = unpack_object_header_buffer(buf, avail, &type, &size);
        if (used == 0)
                die(_("unable to parse object header of %s"),
                    oid_to_hex(&e->idx.oid));

        unuse_pack(&w_curs);
        packing_data_unlock(&to_pack);
        return size;
}

static int try_delta(struct unpacked *trg, struct unpacked *src,
                     unsigned max_depth, unsigned long *mem_usage)
{
        struct object_entry *trg_entry = trg->entry;
        struct object_entry *src_entry = src->entry;
        unsigned long trg_size, src_size, delta_size, sizediff, max_size, sz;
        unsigned ref_depth;
        enum object_type type;
        void *delta_buf;

        /* Don't bother doing diffs between different types */
        if (oe_type(trg_entry) != oe_type(src_entry))
                return -1;

        /*
         * We do not bother to try a delta that we discarded on an
         * earlier try, but only when reusing delta data.  Note that
         * src_entry that is marked as the preferred_base should always
         * be considered, as even if we produce a suboptimal delta against
         * it, we will still save the transfer cost, as we already know
         * the other side has it and we won't send src_entry at all.
         */
        if (reuse_delta && IN_PACK(trg_entry) &&
            IN_PACK(trg_entry) == IN_PACK(src_entry) &&
            !src_entry->preferred_base &&
            trg_entry->in_pack_type != OBJ_REF_DELTA &&
            trg_entry->in_pack_type != OBJ_OFS_DELTA)
                return 0;

        /* Let's not bust the allowed depth. */
        if (src->depth >= max_depth)
                return 0;

        /* Now some size filtering heuristics. */
        trg_size = SIZE(trg_entry);
        if (!DELTA(trg_entry)) {
                max_size = trg_size/2 - the_hash_algo->rawsz;
                ref_depth = 1;
        } else {
                max_size = DELTA_SIZE(trg_entry);
                ref_depth = trg->depth;
        }
        max_size = (uint64_t)max_size * (max_depth - src->depth) /
                                                (max_depth - ref_depth + 1);
        if (max_size == 0)
                return 0;
        src_size = SIZE(src_entry);
        sizediff = src_size < trg_size ? trg_size - src_size : 0;
        if (sizediff >= max_size)
                return 0;
        if (trg_size < src_size / 32)
                return 0;

        if (!in_same_island(&trg->entry->idx.oid, &src->entry->idx.oid))
                return 0;

        /* Load data if not already done */
        if (!trg->data) {
                packing_data_lock(&to_pack);
                trg->data = read_object_file(&trg_entry->idx.oid, &type, &sz);
                packing_data_unlock(&to_pack);
                if (!trg->data)
                        die(_("object %s cannot be read"),
                            oid_to_hex(&trg_entry->idx.oid));
                if (sz != trg_size)
                        die(_("object %s inconsistent object length (%"PRIuMAX" vs %"PRIuMAX")"),
                            oid_to_hex(&trg_entry->idx.oid), (uintmax_t)sz,
                            (uintmax_t)trg_size);
                *mem_usage += sz;
        }
        if (!src->data) {
                packing_data_lock(&to_pack);
                src->data = read_object_file(&src_entry->idx.oid, &type, &sz);
                packing_data_unlock(&to_pack);
                if (!src->data) {
                        if (src_entry->preferred_base) {
                                static int warned = 0;
                                if (!warned++)
                                        warning(_("object %s cannot be read"),
                                                oid_to_hex(&src_entry->idx.oid));
                                /*
                                 * Those objects are not included in the
                                 * resulting pack.  Be resilient and ignore
                                 * them if they can't be read, in case the
                                 * pack could be created nevertheless.
                                 */
                                return 0;
                        }
                        die(_("object %s cannot be read"),
                            oid_to_hex(&src_entry->idx.oid));
                }
                if (sz != src_size)
                        die(_("object %s inconsistent object length (%"PRIuMAX" vs %"PRIuMAX")"),
                            oid_to_hex(&src_entry->idx.oid), (uintmax_t)sz,
                            (uintmax_t)src_size);
                *mem_usage += sz;
        }
        if (!src->index) {
                src->index = create_delta_index(src->data, src_size);
                if (!src->index) {
                        static int warned = 0;
                        if (!warned++)
                                warning(_("suboptimal pack - out of memory"));
                        return 0;
                }
                *mem_usage += sizeof_delta_index(src->index);
        }

        delta_buf = create_delta(src->index, trg->data, trg_size, &delta_size, max_size);
        if (!delta_buf)
                return 0;

        if (DELTA(trg_entry)) {
                /* Prefer only shallower same-sized deltas. */
                if (delta_size == DELTA_SIZE(trg_entry) &&
                    src->depth + 1 >= trg->depth) {
                        free(delta_buf);
                        return 0;
                }
        }

        /*
         * Handle memory allocation outside of the cache
         * accounting lock.  Compiler will optimize the strangeness
         * away when NO_PTHREADS is defined.
         */
        free(trg_entry->delta_data);
        cache_lock();
        if (trg_entry->delta_data) {
                delta_cache_size -= DELTA_SIZE(trg_entry);
                trg_entry->delta_data = NULL;
        }
        if (delta_cacheable(src_size, trg_size, delta_size)) {
                delta_cache_size += delta_size;
                cache_unlock();
                trg_entry->delta_data = xrealloc(delta_buf, delta_size);
        } else {
                cache_unlock();
                free(delta_buf);
        }

        SET_DELTA(trg_entry, src_entry);
        SET_DELTA_SIZE(trg_entry, delta_size);
        trg->depth = src->depth + 1;

        return 1;
}

static unsigned int check_delta_limit(struct object_entry *me, unsigned int n)
{
        struct object_entry *child = DELTA_CHILD(me);
        unsigned int m = n;
        while (child) {
                const unsigned int c = check_delta_limit(child, n + 1);
                if (m < c)
                        m = c;
                child = DELTA_SIBLING(child);
        }
        return m;
}

static unsigned long free_unpacked(struct unpacked *n)
{
        unsigned long freed_mem = sizeof_delta_index(n->index);
        free_delta_index(n->index);
        n->index = NULL;
        if (n->data) {
                freed_mem += SIZE(n->entry);
                FREE_AND_NULL(n->data);
        }
        n->entry = NULL;
        n->depth = 0;
        return freed_mem;
}

static void find_deltas(struct object_entry **list, unsigned *list_size,
                        int window, int depth, unsigned *processed)
{
        uint32_t i, idx = 0, count = 0;
        struct unpacked *array;
        unsigned long mem_usage = 0;

        array = xcalloc(window, sizeof(struct unpacked));

        for (;;) {
                struct object_entry *entry;
                struct unpacked *n = array + idx;
                int j, max_depth, best_base = -1;

                progress_lock();
                if (!*list_size) {
                        progress_unlock();
                        break;
                }
                entry = *list++;
                (*list_size)--;
                if (!entry->preferred_base) {
                        (*processed)++;
                        display_progress(progress_state, *processed);
                }
                progress_unlock();

                mem_usage -= free_unpacked(n);
                n->entry = entry;

                while (window_memory_limit &&
                       mem_usage > window_memory_limit &&
                       count > 1) {
                        const uint32_t tail = (idx + window - count) % window;
                        mem_usage -= free_unpacked(array + tail);
                        count--;
                }

                /* We do not compute delta to *create* objects we are not
                 * going to pack.
                 */
                if (entry->preferred_base)
                        goto next;

                /*
                 * If the current object is at pack edge, take the depth the
                 * objects that depend on the current object into account
                 * otherwise they would become too deep.
                 */
                max_depth = depth;
                if (DELTA_CHILD(entry)) {
                        max_depth -= check_delta_limit(entry, 0);
                        if (max_depth <= 0)
                                goto next;
                }

                j = window;
                while (--j > 0) {
                        int ret;
                        uint32_t other_idx = idx + j;
                        struct unpacked *m;
                        if (other_idx >= window)
                                other_idx -= window;
                        m = array + other_idx;
                        if (!m->entry)
                                break;
                        ret = try_delta(n, m, max_depth, &mem_usage);
                        if (ret < 0)
                                break;
                        else if (ret > 0)
                                best_base = other_idx;
                }

                /*
                 * If we decided to cache the delta data, then it is best
                 * to compress it right away.  First because we have to do
                 * it anyway, and doing it here while we're threaded will
                 * save a lot of time in the non threaded write phase,
                 * as well as allow for caching more deltas within
                 * the same cache size limit.
                 * ...
                 * But only if not writing to stdout, since in that case
                 * the network is most likely throttling writes anyway,
                 * and therefore it is best to go to the write phase ASAP
                 * instead, as we can afford spending more time compressing
                 * between writes at that moment.
                 */
                if (entry->delta_data && !pack_to_stdout) {
                        unsigned long size;

                        size = do_compress(&entry->delta_data, DELTA_SIZE(entry));
                        if (size < (1U << OE_Z_DELTA_BITS)) {
                                entry->z_delta_size = size;
                                cache_lock();
                                delta_cache_size -= DELTA_SIZE(entry);
                                delta_cache_size += entry->z_delta_size;
                                cache_unlock();
                        } else {
                                FREE_AND_NULL(entry->delta_data);
                                entry->z_delta_size = 0;
                        }
                }

                /* if we made n a delta, and if n is already at max
                 * depth, leaving it in the window is pointless.  we
                 * should evict it first.
                 */
                if (DELTA(entry) && max_depth <= n->depth)
                        continue;

                /*
                 * Move the best delta base up in the window, after the
                 * currently deltified object, to keep it longer.  It will
                 * be the first base object to be attempted next.
                 */
                if (DELTA(entry)) {
                        struct unpacked swap = array[best_base];
                        int dist = (window + idx - best_base) % window;
                        int dst = best_base;
                        while (dist--) {
                                int src = (dst + 1) % window;
                                array[dst] = array[src];
                                dst = src;
                        }
                        array[dst] = swap;
                }

                next:
                idx++;
                if (count + 1 < window)
                        count++;
                if (idx >= window)
                        idx = 0;
        }

        for (i = 0; i < window; ++i) {
                free_delta_index(array[i].index);
                free(array[i].data);
        }
        free(array);
}

/*
 * The main object list is split into smaller lists, each is handed to
 * one worker.
 *
 * The main thread waits on the condition that (at least) one of the workers
 * has stopped working (which is indicated in the .working member of
 * struct thread_params).
 *
 * When a work thread has completed its work, it sets .working to 0 and
 * signals the main thread and waits on the condition that .data_ready
 * becomes 1.
 *
 * The main thread steals half of the work from the worker that has
 * most work left to hand it to the idle worker.
 */

struct thread_params {
        pthread_t thread;
        struct object_entry **list;
        unsigned list_size;
        unsigned remaining;
        int window;
        int depth;
        int working;
        int data_ready;
        pthread_mutex_t mutex;
        pthread_cond_t cond;
        unsigned *processed;
};

static pthread_cond_t progress_cond;

/*
 * Mutex and conditional variable can't be statically-initialized on Windows.
 */
static void init_threaded_search(void)
{
        pthread_mutex_init(&cache_mutex, NULL);
        pthread_mutex_init(&progress_mutex, NULL);
        pthread_cond_init(&progress_cond, NULL);
}

static void cleanup_threaded_search(void)
{
        pthread_cond_destroy(&progress_cond);
        pthread_mutex_destroy(&cache_mutex);
        pthread_mutex_destroy(&progress_mutex);
}

static void *threaded_find_deltas(void *arg)
{
        struct thread_params *me = arg;

        progress_lock();
        while (me->remaining) {
                progress_unlock();

                find_deltas(me->list, &me->remaining,
                            me->window, me->depth, me->processed);

                progress_lock();
                me->working = 0;
                pthread_cond_signal(&progress_cond);
                progress_unlock();

                /*
                 * We must not set ->data_ready before we wait on the
                 * condition because the main thread may have set it to 1
                 * before we get here. In order to be sure that new
                 * work is available if we see 1 in ->data_ready, it
                 * was initialized to 0 before this thread was spawned
                 * and we reset it to 0 right away.
                 */
                pthread_mutex_lock(&me->mutex);
                while (!me->data_ready)
                        pthread_cond_wait(&me->cond, &me->mutex);
                me->data_ready = 0;
                pthread_mutex_unlock(&me->mutex);

                progress_lock();
        }
        progress_unlock();
        /* leave ->working 1 so that this doesn't get more work assigned */
        return NULL;
}

static void ll_find_deltas(struct object_entry **list, unsigned list_size,
                           int window, int depth, unsigned *processed)
{
        struct thread_params *p;
        int i, ret, active_threads = 0;

        init_threaded_search();

        if (delta_search_threads <= 1) {
                find_deltas(list, &list_size, window, depth, processed);
                cleanup_threaded_search();
                return;
        }
        if (progress > pack_to_stdout)
                fprintf_ln(stderr, _("Delta compression using up to %d threads"),
                           delta_search_threads);
        p = xcalloc(delta_search_threads, sizeof(*p));

        /* Partition the work amongst work threads. */
        for (i = 0; i < delta_search_threads; i++) {
                unsigned sub_size = list_size / (delta_search_threads - i);

                /* don't use too small segments or no deltas will be found */
                if (sub_size < 2*window && i+1 < delta_search_threads)
                        sub_size = 0;

                p[i].window = window;
                p[i].depth = depth;
                p[i].processed = processed;
                p[i].working = 1;
                p[i].data_ready = 0;

                /* try to split chunks on "path" boundaries */
                while (sub_size && sub_size < list_size &&
                       list[sub_size]->hash &&
                       list[sub_size]->hash == list[sub_size-1]->hash)
                        sub_size++;

                p[i].list = list;
                p[i].list_size = sub_size;
                p[i].remaining = sub_size;

                list += sub_size;
                list_size -= sub_size;
        }

        /* Start work threads. */
        for (i = 0; i < delta_search_threads; i++) {
                if (!p[i].list_size)
                        continue;
                pthread_mutex_init(&p[i].mutex, NULL);
                pthread_cond_init(&p[i].cond, NULL);
                ret = pthread_create(&p[i].thread, NULL,
                                     threaded_find_deltas, &p[i]);
                if (ret)
                        die(_("unable to create thread: %s"), strerror(ret));
                active_threads++;
        }

        /*
         * Now let's wait for work completion.  Each time a thread is done
         * with its work, we steal half of the remaining work from the
         * thread with the largest number of unprocessed objects and give
         * it to that newly idle thread.  This ensure good load balancing
         * until the remaining object list segments are simply too short
         * to be worth splitting anymore.
         */
        while (active_threads) {
                struct thread_params *target = NULL;
                struct thread_params *victim = NULL;
                unsigned sub_size = 0;

                progress_lock();
                for (;;) {
                        for (i = 0; !target && i < delta_search_threads; i++)
                                if (!p[i].working)
                                        target = &p[i];
                        if (target)
                                break;
                        pthread_cond_wait(&progress_cond, &progress_mutex);
                }

                for (i = 0; i < delta_search_threads; i++)
                        if (p[i].remaining > 2*window &&
                            (!victim || victim->remaining < p[i].remaining))
                                victim = &p[i];
                if (victim) {
                        sub_size = victim->remaining / 2;
                        list = victim->list + victim->list_size - sub_size;
                        while (sub_size && list[0]->hash &&
                               list[0]->hash == list[-1]->hash) {
                                list++;
                                sub_size--;
                        }
                        if (!sub_size) {
                                /*
                                 * It is possible for some "paths" to have
                                 * so many objects that no hash boundary
                                 * might be found.  Let's just steal the
                                 * exact half in that case.
                                 */
                                sub_size = victim->remaining / 2;
                                list -= sub_size;
                        }
                        target->list = list;
                        victim->list_size -= sub_size;
                        victim->remaining -= sub_size;
                }
                target->list_size = sub_size;
                target->remaining = sub_size;
                target->working = 1;
                progress_unlock();

                pthread_mutex_lock(&target->mutex);
                target->data_ready = 1;
                pthread_cond_signal(&target->cond);
                pthread_mutex_unlock(&target->mutex);

                if (!sub_size) {
                        pthread_join(target->thread, NULL);
                        pthread_cond_destroy(&target->cond);
                        pthread_mutex_destroy(&target->mutex);
                        active_threads--;
                }
        }
        cleanup_threaded_search();
        free(p);
}

static int obj_is_packed(const struct object_id *oid)
{
        return packlist_find(&to_pack, oid) ||
                (reuse_packfile_bitmap &&
                 bitmap_walk_contains(bitmap_git, reuse_packfile_bitmap, oid));
}

static void add_tag_chain(const struct object_id *oid)
{
        struct tag *tag;

        /*
         * We catch duplicates already in add_object_entry(), but we'd
         * prefer to do this extra check to avoid having to parse the
         * tag at all if we already know that it's being packed (e.g., if
         * it was included via bitmaps, we would not have parsed it
         * previously).
         */
        if (obj_is_packed(oid))
                return;

        tag = lookup_tag(the_repository, oid);
        while (1) {
                if (!tag || parse_tag(tag) || !tag->tagged)
                        die(_("unable to pack objects reachable from tag %s"),
                            oid_to_hex(oid));

                add_object_entry(&tag->object.oid, OBJ_TAG, NULL, 0);

                if (tag->tagged->type != OBJ_TAG)
                        return;

                tag = (struct tag *)tag->tagged;
        }
}

static int add_ref_tag(const char *path, const struct object_id *oid, int flag, void *cb_data)
{
        struct object_id peeled;

        if (starts_with(path, "refs/tags/") && /* is a tag? */
            !peel_ref(path, &peeled)    && /* peelable? */
            obj_is_packed(&peeled)) /* object packed? */
                add_tag_chain(oid);
        return 0;
}

static void prepare_pack(int window, int depth)
{
        struct object_entry **delta_list;
        uint32_t i, nr_deltas;
        unsigned n;

        if (use_delta_islands)
                resolve_tree_islands(the_repository, progress, &to_pack);

        get_object_details();

        /*
         * If we're locally repacking then we need to be doubly careful
         * from now on in order to make sure no stealth corruption gets
         * propagated to the new pack.  Clients receiving streamed packs
         * should validate everything they get anyway so no need to incur
         * the additional cost here in that case.
         */
        if (!pack_to_stdout)
                do_check_packed_object_crc = 1;

        if (!to_pack.nr_objects || !window || !depth)
                return;

        ALLOC_ARRAY(delta_list, to_pack.nr_objects);
        nr_deltas = n = 0;

        for (i = 0; i < to_pack.nr_objects; i++) {
                struct object_entry *entry = to_pack.objects + i;

                if (DELTA(entry))
                        /* This happens if we decided to reuse existing
                         * delta from a pack.  "reuse_delta &&" is implied.
                         */
                        continue;

                if (!entry->type_valid ||
                    oe_size_less_than(&to_pack, entry, 50))
                        continue;

                if (entry->no_try_delta)
                        continue;

                if (!entry->preferred_base) {
                        nr_deltas++;
                        if (oe_type(entry) < 0)
                                die(_("unable to get type of object %s"),
                                    oid_to_hex(&entry->idx.oid));
                } else {
                        if (oe_type(entry) < 0) {
                                /*
                                 * This object is not found, but we
                                 * don't have to include it anyway.
                                 */
                                continue;
                        }
                }

                delta_list[n++] = entry;
        }

        if (nr_deltas && n > 1) {
                unsigned nr_done = 0;

                if (progress)
                        progress_state = start_progress(_("Compressing objects"),
                                                        nr_deltas);
                QSORT(delta_list, n, type_size_sort);
                ll_find_deltas(delta_list, n, window+1, depth, &nr_done);
                stop_progress(&progress_state);
                if (nr_done != nr_deltas)
                        die(_("inconsistency with delta count"));
        }
        free(delta_list);
}

static int git_pack_config(const char *k, const char *v, void *cb)
{
        if (!strcmp(k, "pack.window")) {
                window = git_config_int(k, v);
                return 0;
        }
        if (!strcmp(k, "pack.windowmemory")) {
                window_memory_limit = git_config_ulong(k, v);
                return 0;
        }
        if (!strcmp(k, "pack.depth")) {
                depth = git_config_int(k, v);
                return 0;
        }
        if (!strcmp(k, "pack.deltacachesize")) {
                max_delta_cache_size = git_config_int(k, v);
                return 0;
        }
        if (!strcmp(k, "pack.deltacachelimit")) {
                cache_max_small_delta_size = git_config_int(k, v);
                return 0;
        }
        if (!strcmp(k, "pack.writebitmaphashcache")) {
                if (git_config_bool(k, v))
                        write_bitmap_options |= BITMAP_OPT_HASH_CACHE;
                else
                        write_bitmap_options &= ~BITMAP_OPT_HASH_CACHE;
        }
        if (!strcmp(k, "pack.usebitmaps")) {
                use_bitmap_index_default = git_config_bool(k, v);
                return 0;
        }
        if (!strcmp(k, "pack.allowpackreuse")) {
                allow_pack_reuse = git_config_bool(k, v);
                return 0;
        }
        if (!strcmp(k, "pack.threads")) {
                delta_search_threads = git_config_int(k, v);
                if (delta_search_threads < 0)
                        die(_("invalid number of threads specified (%d)"),
                            delta_search_threads);
                if (!HAVE_THREADS && delta_search_threads != 1) {
                        warning(_("no threads support, ignoring %s"), k);
                        delta_search_threads = 0;
                }
                return 0;
        }
        if (!strcmp(k, "pack.indexversion")) {
                pack_idx_opts.version = git_config_int(k, v);
                if (pack_idx_opts.version > 2)
                        die(_("bad pack.indexversion=%"PRIu32),
                            pack_idx_opts.version);
                return 0;
        }
        return git_default_config(k, v, cb);
}

static void read_object_list_from_stdin(void)
{
        char line[GIT_MAX_HEXSZ + 1 + PATH_MAX + 2];
        struct object_id oid;
        const char *p;

        for (;;) {
                if (!fgets(line, sizeof(line), stdin)) {
                        if (feof(stdin))
                                break;
                        if (!ferror(stdin))
                                die("BUG: fgets returned NULL, not EOF, not error!");
                        if (errno != EINTR)
                                die_errno("fgets");
                        clearerr(stdin);
                        continue;
                }
                if (line[0] == '-') {
                        if (get_oid_hex(line+1, &oid))
                                die(_("expected edge object ID, got garbage:\n %s"),
                                    line);
                        add_preferred_base(&oid);
                        continue;
                }
                if (parse_oid_hex(line, &oid, &p))
                        die(_("expected object ID, got garbage:\n %s"), line);

                add_preferred_base_object(p + 1);
                add_object_entry(&oid, OBJ_NONE, p + 1, 0);
        }
}

/* Remember to update object flag allocation in object.h */
#define OBJECT_ADDED (1u<<20)

static void show_commit(struct commit *commit, void *data)
{
        add_object_entry(&commit->object.oid, OBJ_COMMIT, NULL, 0);
        commit->object.flags |= OBJECT_ADDED;

        if (write_bitmap_index)
                index_commit_for_bitmap(commit);

        if (use_delta_islands)
                propagate_island_marks(commit);
}

static void show_object(struct object *obj, const char *name, void *data)
{
        add_preferred_base_object(name);
        add_object_entry(&obj->oid, obj->type, name, 0);
        obj->flags |= OBJECT_ADDED;

        if (use_delta_islands) {
                const char *p;
                unsigned depth;
                struct object_entry *ent;

                /* the empty string is a root tree, which is depth 0 */
                depth = *name ? 1 : 0;
                for (p = strchr(name, '/'); p; p = strchr(p + 1, '/'))
                        depth++;

                ent = packlist_find(&to_pack, &obj->oid);
                if (ent && depth > oe_tree_depth(&to_pack, ent))
                        oe_set_tree_depth(&to_pack, ent, depth);
        }
}

static void show_object__ma_allow_any(struct object *obj, const char *name, void *data)
{
        assert(arg_missing_action == MA_ALLOW_ANY);

        /*
         * Quietly ignore ALL missing objects.  This avoids problems with
         * staging them now and getting an odd error later.
         */
        if (!has_object_file(&obj->oid))
                return;

        show_object(obj, name, data);
}

static void show_object__ma_allow_promisor(struct object *obj, const char *name, void *data)
{
        assert(arg_missing_action == MA_ALLOW_PROMISOR);

        /*
         * Quietly ignore EXPECTED missing objects.  This avoids problems with
         * staging them now and getting an odd error later.
         */
        if (!has_object_file(&obj->oid) && is_promisor_object(&obj->oid))
                return;

        show_object(obj, name, data);
}

static int option_parse_missing_action(const struct option *opt,
                                       const char *arg, int unset)
{
        assert(arg);
        assert(!unset);

        if (!strcmp(arg, "error")) {
                arg_missing_action = MA_ERROR;
                fn_show_object = show_object;
                return 0;
        }

        if (!strcmp(arg, "allow-any")) {
                arg_missing_action = MA_ALLOW_ANY;
                fetch_if_missing = 0;
                fn_show_object = show_object__ma_allow_any;
                return 0;
        }

        if (!strcmp(arg, "allow-promisor")) {
                arg_missing_action = MA_ALLOW_PROMISOR;
                fetch_if_missing = 0;
                fn_show_object = show_object__ma_allow_promisor;
                return 0;
        }

        die(_("invalid value for --missing"));
        return 0;
}

static void show_edge(struct commit *commit)
{
        add_preferred_base(&commit->object.oid);
}

struct in_pack_object {
        off_t offset;
        struct object *object;
};

struct in_pack {
        unsigned int alloc;
        unsigned int nr;
        struct in_pack_object *array;
};

static void mark_in_pack_object(struct object *object, struct packed_git *p, struct in_pack *in_pack)
{
        in_pack->array[in_pack->nr].offset = find_pack_entry_one(object->oid.hash, p);
        in_pack->array[in_pack->nr].object = object;
        in_pack->nr++;
}

/*
 * Compare the objects in the offset order, in order to emulate the
 * "git rev-list --objects" output that produced the pack originally.
 */
static int ofscmp(const void *a_, const void *b_)
{
        struct in_pack_object *a = (struct in_pack_object *)a_;
        struct in_pack_object *b = (struct in_pack_object *)b_;

        if (a->offset < b->offset)
                return -1;
        else if (a->offset > b->offset)
                return 1;
        else
                return oidcmp(&a->object->oid, &b->object->oid);
}

static void add_objects_in_unpacked_packs(void)
{
        struct packed_git *p;
        struct in_pack in_pack;
        uint32_t i;

        memset(&in_pack, 0, sizeof(in_pack));

        for (p = get_all_packs(the_repository); p; p = p->next) {
                struct object_id oid;
                struct object *o;

                if (!p->pack_local || p->pack_keep || p->pack_keep_in_core)
                        continue;
                if (open_pack_index(p))
                        die(_("cannot open pack index"));

                ALLOC_GROW(in_pack.array,
                           in_pack.nr + p->num_objects,
                           in_pack.alloc);

                for (i = 0; i < p->num_objects; i++) {
                        nth_packed_object_oid(&oid, p, i);
                        o = lookup_unknown_object(&oid);
                        if (!(o->flags & OBJECT_ADDED))
                                mark_in_pack_object(o, p, &in_pack);
                        o->flags |= OBJECT_ADDED;
                }
        }

        if (in_pack.nr) {
                QSORT(in_pack.array, in_pack.nr, ofscmp);
                for (i = 0; i < in_pack.nr; i++) {
                        struct object *o = in_pack.array[i].object;
                        add_object_entry(&o->oid, o->type, "", 0);
                }
        }
        free(in_pack.array);
}

static int add_loose_object(const struct object_id *oid, const char *path,
                            void *data)
{
        enum object_type type = oid_object_info(the_repository, oid, NULL);

        if (type < 0) {
                warning(_("loose object at %s could not be examined"), path);
                return 0;
        }

        add_object_entry(oid, type, "", 0);
        return 0;
}

/*
 * We actually don't even have to worry about reachability here.
 * add_object_entry will weed out duplicates, so we just add every
 * loose object we find.
 */
static void add_unreachable_loose_objects(void)
{
        for_each_loose_file_in_objdir(get_object_directory(),
                                      add_loose_object,
                                      NULL, NULL, NULL);
}

static int has_sha1_pack_kept_or_nonlocal(const struct object_id *oid)
{
        static struct packed_git *last_found = (void *)1;
        struct packed_git *p;

        p = (last_found != (void *)1) ? last_found :
                                        get_all_packs(the_repository);

        while (p) {
                if ((!p->pack_local || p->pack_keep ||
                                p->pack_keep_in_core) &&
                        find_pack_entry_one(oid->hash, p)) {
                        last_found = p;
                        return 1;
                }
                if (p == last_found)
                        p = get_all_packs(the_repository);
                else
                        p = p->next;
                if (p == last_found)
                        p = p->next;
        }
        return 0;
}

/*
 * Store a list of sha1s that are should not be discarded
 * because they are either written too recently, or are
 * reachable from another object that was.
 *
 * This is filled by get_object_list.
 */
static struct oid_array recent_objects;

static int loosened_object_can_be_discarded(const struct object_id *oid,
                                            timestamp_t mtime)
{
        if (!unpack_unreachable_expiration)
                return 0;
        if (mtime > unpack_unreachable_expiration)
                return 0;
        if (oid_array_lookup(&recent_objects, oid) >= 0)
                return 0;
        return 1;
}

static void loosen_unused_packed_objects(void)
{
        struct packed_git *p;
        uint32_t i;
        struct object_id oid;

        for (p = get_all_packs(the_repository); p; p = p->next) {
                if (!p->pack_local || p->pack_keep || p->pack_keep_in_core)
                        continue;

                if (open_pack_index(p))
                        die(_("cannot open pack index"));

                for (i = 0; i < p->num_objects; i++) {
                        nth_packed_object_oid(&oid, p, i);
                        if (!packlist_find(&to_pack, &oid) &&
                            !has_sha1_pack_kept_or_nonlocal(&oid) &&
                            !loosened_object_can_be_discarded(&oid, p->mtime))
                                if (force_object_loose(&oid, p->mtime))
                                        die(_("unable to force loose object"));
                }
        }
}

/*
 * This tracks any options which pack-reuse code expects to be on, or which a
 * reader of the pack might not understand, and which would therefore prevent
 * blind reuse of what we have on disk.
 */
static int pack_options_allow_reuse(void)
{
        return allow_pack_reuse &&
               pack_to_stdout &&
               !ignore_packed_keep_on_disk &&
               !ignore_packed_keep_in_core &&
               (!local || !have_non_local_packs) &&
               !incremental;
}

static int get_object_list_from_bitmap(struct rev_info *revs)
{
        if (!(bitmap_git = prepare_bitmap_walk(revs)))
                return -1;

        if (pack_options_allow_reuse() &&
            !reuse_partial_packfile_from_bitmap(
                        bitmap_git,
                        &reuse_packfile,
                        &reuse_packfile_objects,
                        &reuse_packfile_bitmap)) {
                assert(reuse_packfile_objects);
                nr_result += reuse_packfile_objects;
                display_progress(progress_state, nr_result);
        }

        traverse_bitmap_commit_list(bitmap_git, &add_object_entry_from_bitmap);
        return 0;
}

static void record_recent_object(struct object *obj,
                                 const char *name,
                                 void *data)
{
        oid_array_append(&recent_objects, &obj->oid);
}

static void record_recent_commit(struct commit *commit, void *data)
{
        oid_array_append(&recent_objects, &commit->object.oid);
}

static void get_object_list(int ac, const char **av)
{
        struct rev_info revs;
        struct setup_revision_opt s_r_opt = {
                .allow_exclude_promisor_objects = 1,
        };
        char line[1000];
        int flags = 0;
        int save_warning;

        repo_init_revisions(the_repository, &revs, NULL);
        save_commit_buffer = 0;
        setup_revisions(ac, av, &revs, &s_r_opt);

        /* make sure shallows are read */
        is_repository_shallow(the_repository);

        save_warning = warn_on_object_refname_ambiguity;
        warn_on_object_refname_ambiguity = 0;

        while (fgets(line, sizeof(line), stdin) != NULL) {
                int len = strlen(line);
                if (len && line[len - 1] == '\n')
                        line[--len] = 0;
                if (!len)
                        break;
                if (*line == '-') {
                        if (!strcmp(line, "--not")) {
                                flags ^= UNINTERESTING;
                                write_bitmap_index = 0;
                                continue;
                        }
                        if (starts_with(line, "--shallow ")) {
                                struct object_id oid;
                                if (get_oid_hex(line + 10, &oid))
                                        die("not an SHA-1 '%s'", line + 10);
                                register_shallow(the_repository, &oid);
                                use_bitmap_index = 0;
                                continue;
                        }
                        die(_("not a rev '%s'"), line);
                }
                if (handle_revision_arg(line, &revs, flags, REVARG_CANNOT_BE_FILENAME))
                        die(_("bad revision '%s'"), line);
        }

        warn_on_object_refname_ambiguity = save_warning;

        if (use_bitmap_index && !get_object_list_from_bitmap(&revs))
                return;

        if (use_delta_islands)
                load_delta_islands(the_repository, progress);

        if (prepare_revision_walk(&revs))
                die(_("revision walk setup failed"));
        mark_edges_uninteresting(&revs, show_edge, sparse);

        if (!fn_show_object)
                fn_show_object = show_object;
        traverse_commit_list_filtered(&filter_options, &revs,
                                      show_commit, fn_show_object, NULL,
                                      NULL);

        if (unpack_unreachable_expiration) {
                revs.ignore_missing_links = 1;
                if (add_unseen_recent_objects_to_traversal(&revs,
                                unpack_unreachable_expiration))
                        die(_("unable to add recent objects"));
                if (prepare_revision_walk(&revs))
                        die(_("revision walk setup failed"));
                traverse_commit_list(&revs, record_recent_commit,
                                     record_recent_object, NULL);
        }

        if (keep_unreachable)
                add_objects_in_unpacked_packs();
        if (pack_loose_unreachable)
                add_unreachable_loose_objects();
        if (unpack_unreachable)
                loosen_unused_packed_objects();

        oid_array_clear(&recent_objects);
}

static void add_extra_kept_packs(const struct string_list *names)
{
        struct packed_git *p;

        if (!names->nr)
                return;

        for (p = get_all_packs(the_repository); p; p = p->next) {
                const char *name = basename(p->pack_name);
                int i;

                if (!p->pack_local)
                        continue;

                for (i = 0; i < names->nr; i++)
                        if (!fspathcmp(name, names->items[i].string))
                                break;

                if (i < names->nr) {
                        p->pack_keep_in_core = 1;
                        ignore_packed_keep_in_core = 1;
                        continue;
                }
        }
}

static int option_parse_index_version(const struct option *opt,
                                      const char *arg, int unset)
{
        char *c;
        const char *val = arg;

        BUG_ON_OPT_NEG(unset);

        pack_idx_opts.version = strtoul(val, &c, 10);
        if (pack_idx_opts.version > 2)
                die(_("unsupported index version %s"), val);
        if (*c == ',' && c[1])
                pack_idx_opts.off32_limit = strtoul(c+1, &c, 0);
        if (*c || pack_idx_opts.off32_limit & 0x80000000)
                die(_("bad index version '%s'"), val);
        return 0;
}

static int option_parse_unpack_unreachable(const struct option *opt,
                                           const char *arg, int unset)
{
        if (unset) {
                unpack_unreachable = 0;
                unpack_unreachable_expiration = 0;
        }
        else {
                unpack_unreachable = 1;
                if (arg)
                        unpack_unreachable_expiration = approxidate(arg);
        }
        return 0;
}

int cmd_pack_objects(int argc, const char **argv, const char *prefix)
{
        int use_internal_rev_list = 0;
        int shallow = 0;
        int all_progress_implied = 0;
        struct argv_array rp = ARGV_ARRAY_INIT;
        int rev_list_unpacked = 0, rev_list_all = 0, rev_list_reflog = 0;
        int rev_list_index = 0;
        struct string_list keep_pack_list = STRING_LIST_INIT_NODUP;
        struct option pack_objects_options[] = {
                OPT_SET_INT('q', "quiet", &progress,
                            N_("do not show progress meter"), 0),
                OPT_SET_INT(0, "progress", &progress,
                            N_("show progress meter"), 1),
                OPT_SET_INT(0, "all-progress", &progress,
                            N_("show progress meter during object writing phase"), 2),
                OPT_BOOL(0, "all-progress-implied",
                         &all_progress_implied,
                         N_("similar to --all-progress when progress meter is shown")),
                { OPTION_CALLBACK, 0, "index-version", NULL, N_("<version>[,<offset>]"),
                  N_("write the pack index file in the specified idx format version"),
                  PARSE_OPT_NONEG, option_parse_index_version },
                OPT_MAGNITUDE(0, "max-pack-size", &pack_size_limit,
                              N_("maximum size of each output pack file")),
                OPT_BOOL(0, "local", &local,
                         N_("ignore borrowed objects from alternate object store")),
                OPT_BOOL(0, "incremental", &incremental,
                         N_("ignore packed objects")),
                OPT_INTEGER(0, "window", &window,
                            N_("limit pack window by objects")),
                OPT_MAGNITUDE(0, "window-memory", &window_memory_limit,
                              N_("limit pack window by memory in addition to object limit")),
                OPT_INTEGER(0, "depth", &depth,
                            N_("maximum length of delta chain allowed in the resulting pack")),
                OPT_BOOL(0, "reuse-delta", &reuse_delta,
                         N_("reuse existing deltas")),
                OPT_BOOL(0, "reuse-object", &reuse_object,
                         N_("reuse existing objects")),
                OPT_BOOL(0, "delta-base-offset", &allow_ofs_delta,
                         N_("use OFS_DELTA objects")),
                OPT_INTEGER(0, "threads", &delta_search_threads,
                            N_("use threads when searching for best delta matches")),
                OPT_BOOL(0, "non-empty", &non_empty,
                         N_("do not create an empty pack output")),
                OPT_BOOL(0, "revs", &use_internal_rev_list,
                         N_("read revision arguments from standard input")),
                OPT_SET_INT_F(0, "unpacked", &rev_list_unpacked,
                              N_("limit the objects to those that are not yet packed"),
                              1, PARSE_OPT_NONEG),
                OPT_SET_INT_F(0, "all", &rev_list_all,
                              N_("include objects reachable from any reference"),
                              1, PARSE_OPT_NONEG),
                OPT_SET_INT_F(0, "reflog", &rev_list_reflog,
                              N_("include objects referred by reflog entries"),
                              1, PARSE_OPT_NONEG),
                OPT_SET_INT_F(0, "indexed-objects", &rev_list_index,
                              N_("include objects referred to by the index"),
                              1, PARSE_OPT_NONEG),
                OPT_BOOL(0, "stdout", &pack_to_stdout,
                         N_("output pack to stdout")),
                OPT_BOOL(0, "include-tag", &include_tag,
                         N_("include tag objects that refer to objects to be packed")),
                OPT_BOOL(0, "keep-unreachable", &keep_unreachable,
                         N_("keep unreachable objects")),
                OPT_BOOL(0, "pack-loose-unreachable", &pack_loose_unreachable,
                         N_("pack loose unreachable objects")),
                { OPTION_CALLBACK, 0, "unpack-unreachable", NULL, N_("time"),
                  N_("unpack unreachable objects newer than <time>"),
                  PARSE_OPT_OPTARG, option_parse_unpack_unreachable },
                OPT_BOOL(0, "sparse", &sparse,
                         N_("use the sparse reachability algorithm")),
                OPT_BOOL(0, "thin", &thin,
                         N_("create thin packs")),
                OPT_BOOL(0, "shallow", &shallow,
                         N_("create packs suitable for shallow fetches")),
                OPT_BOOL(0, "honor-pack-keep", &ignore_packed_keep_on_disk,
                         N_("ignore packs that have companion .keep file")),
                OPT_STRING_LIST(0, "keep-pack", &keep_pack_list, N_("name"),
                                N_("ignore this pack")),
                OPT_INTEGER(0, "compression", &pack_compression_level,
                            N_("pack compression level")),
                OPT_SET_INT(0, "keep-true-parents", &grafts_replace_parents,
                            N_("do not hide commits by grafts"), 0),
                OPT_BOOL(0, "use-bitmap-index", &use_bitmap_index,
                         N_("use a bitmap index if available to speed up counting objects")),
                OPT_SET_INT(0, "write-bitmap-index", &write_bitmap_index,
                            N_("write a bitmap index together with the pack index"),
                            WRITE_BITMAP_TRUE),
                OPT_SET_INT_F(0, "write-bitmap-index-quiet",
                              &write_bitmap_index,
                              N_("write a bitmap index if possible"),
                              WRITE_BITMAP_QUIET, PARSE_OPT_HIDDEN),
                OPT_PARSE_LIST_OBJECTS_FILTER(&filter_options),
                { OPTION_CALLBACK, 0, "missing", NULL, N_("action"),
                  N_("handling for missing objects"), PARSE_OPT_NONEG,
                  option_parse_missing_action },
                OPT_BOOL(0, "exclude-promisor-objects", &exclude_promisor_objects,
                         N_("do not pack objects in promisor packfiles")),
                OPT_BOOL(0, "delta-islands", &use_delta_islands,
                         N_("respect islands during delta compression")),
                OPT_END(),
        };

        if (DFS_NUM_STATES > (1 << OE_DFS_STATE_BITS))
                BUG("too many dfs states, increase OE_DFS_STATE_BITS");

        read_replace_refs = 0;

        sparse = git_env_bool("GIT_TEST_PACK_SPARSE", 0);
        prepare_repo_settings(the_repository);
        if (!sparse && the_repository->settings.pack_use_sparse != -1)
                sparse = the_repository->settings.pack_use_sparse;

        reset_pack_idx_option(&pack_idx_opts);
        git_config(git_pack_config, NULL);

        progress = isatty(2);
        argc = parse_options(argc, argv, prefix, pack_objects_options,
                             pack_usage, 0);

        if (argc) {
                base_name = argv[0];
                argc--;
        }
        if (pack_to_stdout != !base_name || argc)
                usage_with_options(pack_usage, pack_objects_options);

        if (depth >= (1 << OE_DEPTH_BITS)) {
                warning(_("delta chain depth %d is too deep, forcing %d"),
                        depth, (1 << OE_DEPTH_BITS) - 1);
                depth = (1 << OE_DEPTH_BITS) - 1;
        }
        if (cache_max_small_delta_size >= (1U << OE_Z_DELTA_BITS)) {
                warning(_("pack.deltaCacheLimit is too high, forcing %d"),
                        (1U << OE_Z_DELTA_BITS) - 1);
                cache_max_small_delta_size = (1U << OE_Z_DELTA_BITS) - 1;
        }

        argv_array_push(&rp, "pack-objects");
        if (thin) {
                use_internal_rev_list = 1;
                argv_array_push(&rp, shallow
                                ? "--objects-edge-aggressive"
                                : "--objects-edge");
        } else
                argv_array_push(&rp, "--objects");

        if (rev_list_all) {
                use_internal_rev_list = 1;
                argv_array_push(&rp, "--all");
        }
        if (rev_list_reflog) {
                use_internal_rev_list = 1;
                argv_array_push(&rp, "--reflog");
        }
        if (rev_list_index) {
                use_internal_rev_list = 1;
                argv_array_push(&rp, "--indexed-objects");
        }
        if (rev_list_unpacked) {
                use_internal_rev_list = 1;
                argv_array_push(&rp, "--unpacked");
        }

        if (exclude_promisor_objects) {
                use_internal_rev_list = 1;
                fetch_if_missing = 0;
                argv_array_push(&rp, "--exclude-promisor-objects");
        }
        if (unpack_unreachable || keep_unreachable || pack_loose_unreachable)
                use_internal_rev_list = 1;

        if (!reuse_object)
                reuse_delta = 0;
        if (pack_compression_level == -1)
                pack_compression_level = Z_DEFAULT_COMPRESSION;
        else if (pack_compression_level < 0 || pack_compression_level > Z_BEST_COMPRESSION)
                die(_("bad pack compression level %d"), pack_compression_level);

        if (!delta_search_threads)      /* --threads=0 means autodetect */
                delta_search_threads = online_cpus();

        if (!HAVE_THREADS && delta_search_threads != 1)
                warning(_("no threads support, ignoring --threads"));
        if (!pack_to_stdout && !pack_size_limit)
                pack_size_limit = pack_size_limit_cfg;
        if (pack_to_stdout && pack_size_limit)
                die(_("--max-pack-size cannot be used to build a pack for transfer"));
        if (pack_size_limit && pack_size_limit < 1024*1024) {
                warning(_("minimum pack size limit is 1 MiB"));
                pack_size_limit = 1024*1024;
        }

        if (!pack_to_stdout && thin)
                die(_("--thin cannot be used to build an indexable pack"));

        if (keep_unreachable && unpack_unreachable)
                die(_("--keep-unreachable and --unpack-unreachable are incompatible"));
        if (!rev_list_all || !rev_list_reflog || !rev_list_index)
                unpack_unreachable_expiration = 0;

        if (filter_options.choice) {
                if (!pack_to_stdout)
                        die(_("cannot use --filter without --stdout"));
                use_bitmap_index = 0;
        }

        /*
         * "soft" reasons not to use bitmaps - for on-disk repack by default we want
         *
         * - to produce good pack (with bitmap index not-yet-packed objects are
         *   packed in suboptimal order).
         *
         * - to use more robust pack-generation codepath (avoiding possible
         *   bugs in bitmap code and possible bitmap index corruption).
         */
        if (!pack_to_stdout)
                use_bitmap_index_default = 0;

        if (use_bitmap_index < 0)
                use_bitmap_index = use_bitmap_index_default;

        /* "hard" reasons not to use bitmaps; these just won't work at all */
        if (!use_internal_rev_list || (!pack_to_stdout && write_bitmap_index) || is_repository_shallow(the_repository))
                use_bitmap_index = 0;

        if (pack_to_stdout || !rev_list_all)
                write_bitmap_index = 0;

        if (use_delta_islands)
                argv_array_push(&rp, "--topo-order");

        if (progress && all_progress_implied)
                progress = 2;

        add_extra_kept_packs(&keep_pack_list);
        if (ignore_packed_keep_on_disk) {
                struct packed_git *p;
                for (p = get_all_packs(the_repository); p; p = p->next)
                        if (p->pack_local && p->pack_keep)
                                break;
                if (!p) /* no keep-able packs found */
                        ignore_packed_keep_on_disk = 0;
        }
        if (local) {
                /*
                 * unlike ignore_packed_keep_on_disk above, we do not
                 * want to unset "local" based on looking at packs, as
                 * it also covers non-local objects
                 */
                struct packed_git *p;
                for (p = get_all_packs(the_repository); p; p = p->next) {
                        if (!p->pack_local) {
                                have_non_local_packs = 1;
                                break;
                        }
                }
        }

        trace2_region_enter("pack-objects", "enumerate-objects",
                            the_repository);
        prepare_packing_data(the_repository, &to_pack);

        if (progress)
                progress_state = start_progress(_("Enumerating objects"), 0);
        if (!use_internal_rev_list)
                read_object_list_from_stdin();
        else {
                get_object_list(rp.argc, rp.argv);
                argv_array_clear(&rp);
        }
        cleanup_preferred_base();
        if (include_tag && nr_result)
                for_each_ref(add_ref_tag, NULL);
        stop_progress(&progress_state);
        trace2_region_leave("pack-objects", "enumerate-objects",
                            the_repository);

        if (non_empty && !nr_result)
                return 0;
        if (nr_result) {
                trace2_region_enter("pack-objects", "prepare-pack",
                                    the_repository);
                prepare_pack(window, depth);
                trace2_region_leave("pack-objects", "prepare-pack",
                                    the_repository);
        }

        trace2_region_enter("pack-objects", "write-pack-file", the_repository);
        write_pack_file();
        trace2_region_leave("pack-objects", "write-pack-file", the_repository);

        if (progress)
                fprintf_ln(stderr,
                           _("Total %"PRIu32" (delta %"PRIu32"),"
                             " reused %"PRIu32" (delta %"PRIu32"),"
                             " pack-reused %"PRIu32),
                           written, written_delta, reused, reused_delta,
                           reuse_packfile_objects);
        return 0;
}