pack-objects: enforce --depth limit in reused deltas

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

#include "builtin.h"
#include "cache.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 "pack-objects.h"
#include "progress.h"
#include "refs.h"
#include "streaming.h"
#include "thread-utils.h"
#include "pack-bitmap.h"
#include "reachable.h"
#include "sha1-array.h"
#include "argv-array.h"
#include "mru.h"

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;

static int non_empty;
static int reuse_delta = 1, reuse_object = 1;
static int keep_unreachable, unpack_unreachable, include_tag;
static unsigned long 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;
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 num_preferred_base;
static struct progress *progress_state;
static int pack_compression_level = Z_DEFAULT_COMPRESSION;
static int pack_compression_seen;

static struct packed_git *reuse_packfile;
static uint32_t reuse_packfile_objects;
static off_t reuse_packfile_offset;

static int use_bitmap_index_default = 1;
static int use_bitmap_index = -1;
static int write_bitmap_index;
static uint16_t write_bitmap_options;

static unsigned long delta_cache_size = 0;
static unsigned long max_delta_cache_size = 256 * 1024 * 1024;
static unsigned long cache_max_small_delta_size = 1000;

static unsigned long window_memory_limit = 0;

/*
 * 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_sha1_file(entry->idx.sha1, &type, &size);
        if (!buf)
                die("unable to read %s", sha1_to_hex(entry->idx.sha1));
        base_buf = read_sha1_file(entry->delta->idx.sha1, &type, &base_size);
        if (!base_buf)
                die("unable to read %s", sha1_to_hex(entry->delta->idx.sha1));
        delta_buf = diff_delta(base_buf, base_size,
                               buf, size, &delta_size, 0);
        if (!delta_buf || delta_size != entry->delta_size)
                die("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 sha1file *f,
                                           const unsigned char *sha1)
{
        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"), sha1_to_hex(sha1));

                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);
                        sha1write(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 sha1file *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;
                sha1write(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 sha1file *f, struct object_entry *entry,
                                           unsigned long limit, int usable_delta)
{
        unsigned long size, datalen;
        unsigned char header[10], dheader[10];
        unsigned hdrlen;
        enum object_type type;
        void *buf;
        struct git_istream *st = NULL;

        if (!usable_delta) {
                if (entry->type == OBJ_BLOB &&
                    entry->size > big_file_threshold &&
                    (st = open_istream(entry->idx.sha1, &type, &size, NULL)) != NULL)
                        buf = NULL;
                else {
                        buf = read_sha1_file(entry->idx.sha1, &type, &size);
                        if (!buf)
                                die(_("unable to read %s"), sha1_to_hex(entry->idx.sha1));
                }
                /*
                 * make sure no cached delta data remains from a
                 * previous attempt before a pack split occurred.
                 */
                free(entry->delta_data);
                entry->delta_data = NULL;
                entry->z_delta_size = 0;
        } else if (entry->delta_data) {
                size = entry->delta_size;
                buf = entry->delta_data;
                entry->delta_data = NULL;
                type = (allow_ofs_delta && entry->delta->idx.offset) ?
                        OBJ_OFS_DELTA : OBJ_REF_DELTA;
        } else {
                buf = get_delta(entry);
                size = entry->delta_size;
                type = (allow_ofs_delta && entry->delta->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(type, size, header);

        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 - entry->delta->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 + 20 >= limit) {
                        if (st)
                                close_istream(st);
                        free(buf);
                        return 0;
                }
                sha1write(f, header, hdrlen);
                sha1write(f, dheader + pos, sizeof(dheader) - pos);
                hdrlen += sizeof(dheader) - pos;
        } else if (type == OBJ_REF_DELTA) {
                /*
                 * Deltas with a base reference contain
                 * an additional 20 bytes for the base sha1.
                 */
                if (limit && hdrlen + 20 + datalen + 20 >= limit) {
                        if (st)
                                close_istream(st);
                        free(buf);
                        return 0;
                }
                sha1write(f, header, hdrlen);
                sha1write(f, entry->delta->idx.sha1, 20);
                hdrlen += 20;
        } else {
                if (limit && hdrlen + datalen + 20 >= limit) {
                        if (st)
                                close_istream(st);
                        free(buf);
                        return 0;
                }
                sha1write(f, header, hdrlen);
        }
        if (st) {
                datalen = write_large_blob_data(st, f, entry->idx.sha1);
                close_istream(st);
        } else {
                sha1write(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 sha1file *f, struct object_entry *entry,
                                unsigned long limit, int usable_delta)
{
        struct packed_git *p = entry->in_pack;
        struct pack_window *w_curs = NULL;
        struct revindex_entry *revidx;
        off_t offset;
        enum object_type type = entry->type;
        off_t datalen;
        unsigned char header[10], dheader[10];
        unsigned hdrlen;

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

        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", sha1_to_hex(entry->idx.sha1));
                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", sha1_to_hex(entry->idx.sha1));
                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 - entry->delta->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 + 20 >= limit) {
                        unuse_pack(&w_curs);
                        return 0;
                }
                sha1write(f, header, hdrlen);
                sha1write(f, dheader + pos, sizeof(dheader) - pos);
                hdrlen += sizeof(dheader) - pos;
                reused_delta++;
        } else if (type == OBJ_REF_DELTA) {
                if (limit && hdrlen + 20 + datalen + 20 >= limit) {
                        unuse_pack(&w_curs);
                        return 0;
                }
                sha1write(f, header, hdrlen);
                sha1write(f, entry->delta->idx.sha1, 20);
                hdrlen += 20;
                reused_delta++;
        } else {
                if (limit && hdrlen + datalen + 20 >= limit) {
                        unuse_pack(&w_curs);
                        return 0;
                }
                sha1write(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 sha1file *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 (!entry->delta)
                usable_delta = 0;       /* no delta */
        else if (!pack_size_limit)
               usable_delta = 1;        /* unlimited packfile */
        else if (entry->delta->idx.offset == (off_t)-1)
                usable_delta = 0;       /* base was written to another pack */
        else if (entry->delta->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 (!entry->in_pack)
                to_reuse = 0;   /* can't reuse what we don't have */
        else if (entry->type == OBJ_REF_DELTA || entry->type == OBJ_OFS_DELTA)
                                /* check_object() decided it for us ... */
                to_reuse = usable_delta;
                                /* ... but pack split may override that */
        else if (entry->type != entry->in_pack_type)
                to_reuse = 0;   /* pack has delta which is unusable */
        else if (entry->delta)
                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 sha1file *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",
                        sha1_to_hex(e->idx.sha1));
                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 (e->delta) {
                e->idx.offset = 1; /* now recurse */
                switch (write_one(f, e->delta, offset)) {
                case WRITE_ONE_RECURSIVE:
                        /* we cannot depend on this one */
                        e->delta = 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)
{
        unsigned char peeled[20];
        struct object_entry *entry = packlist_find(&to_pack, oid->hash, NULL);

        if (entry)
                entry->tagged = 1;
        if (!peel_ref(path, peeled)) {
                entry = packlist_find(&to_pack, peeled, NULL);
                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)
                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 = e->delta_sibling; s; s = s->delta_sibling) {
                                add_to_write_order(wo, endp, s);
                        }
                }
                /* drop down a level to add left subtree nodes if possible */
                if (e->delta_child) {
                        add_to_order = 1;
                        e = e->delta_child;
                } else {
                        add_to_order = 0;
                        /* our sibling might have some children, it is next */
                        if (e->delta_sibling) {
                                e = e->delta_sibling;
                                continue;
                        }
                        /* go back to our parent node */
                        e = e->delta;
                        while (e && !e->delta_sibling) {
                                /* we're on the right side of a subtree, keep
                                 * going up until we can go right again */
                                e = e->delta;
                        }
                        if (!e) {
                                /* done- we hit our original root node */
                                return;
                        }
                        /* pass it off to sibling at this level */
                        e = e->delta_sibling;
                }
        };
}

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; root->delta; root = root->delta)
                ; /* nothing */
        add_descendants_to_write_order(wo, endp, root);
}

static struct object_entry **compute_write_order(void)
{
        unsigned int i, wo_end, last_untagged;

        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;
                objects[i].delta_child = NULL;
                objects[i].delta_sibling = 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 (!e->delta)
                        continue;
                /* Mark me as the first child */
                e->delta_sibling = e->delta->delta_child;
                e->delta->delta_child = e;
        }

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

        /*
         * Give the objects in the original recency order until
         * we see a tagged tip.
         */
        ALLOC_ARRAY(wo, to_pack.nr_objects);
        for (i = wo_end = 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 (objects[i].type != OBJ_COMMIT &&
                    objects[i].type != 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 (objects[i].type != 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)
                        add_family_to_write_order(wo, &wo_end, &objects[i]);
        }

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

        return wo;
}

static off_t write_reused_pack(struct sha1file *f)
{
        unsigned char buffer[8192];
        off_t to_write, total;
        int fd;

        if (!is_pack_valid(reuse_packfile))
                die("packfile is invalid: %s", reuse_packfile->pack_name);

        fd = git_open(reuse_packfile->pack_name);
        if (fd < 0)
                die_errno("unable to open packfile for reuse: %s",
                          reuse_packfile->pack_name);

        if (lseek(fd, sizeof(struct pack_header), SEEK_SET) == -1)
                die_errno("unable to seek in reused packfile");

        if (reuse_packfile_offset < 0)
                reuse_packfile_offset = reuse_packfile->pack_size - 20;

        total = to_write = reuse_packfile_offset - sizeof(struct pack_header);

        while (to_write) {
                int read_pack = xread(fd, buffer, sizeof(buffer));

                if (read_pack <= 0)
                        die_errno("unable to read from reused packfile");

                if (read_pack > to_write)
                        read_pack = to_write;

                sha1write(f, buffer, read_pack);
                to_write -= read_pack;

                /*
                 * We don't know the actual number of objects written,
                 * only how many bytes written, how many bytes total, and
                 * how many objects total. So we can fake it by pretending all
                 * objects we are writing are the same size. This gives us a
                 * smooth progress meter, and at the end it matches the true
                 * answer.
                 */
                written = reuse_packfile_objects *
                                (((double)(total - to_write)) / total);
                display_progress(progress_state, written);
        }

        close(fd);
        written = reuse_packfile_objects;
        display_progress(progress_state, written);
        return reuse_packfile_offset - sizeof(struct pack_header);
}

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 sha1file *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 {
                unsigned char sha1[20];
                char *pack_tmp_name = NULL;

                if (pack_to_stdout)
                        f = sha1fd_throughput(1, "<stdout>", progress_state);
                else
                        f = create_tmp_packfile(&pack_tmp_name);

                offset = write_pack_header(f, nr_remaining);

                if (reuse_packfile) {
                        off_t packfile_size;
                        assert(pack_to_stdout);

                        packfile_size = write_reused_pack(f);
                        offset += packfile_size;
                }

                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) {
                        sha1close(f, sha1, CSUM_CLOSE);
                } else if (nr_written == nr_remaining) {
                        sha1close(f, sha1, CSUM_FSYNC);
                } else {
                        int fd = sha1close(f, sha1, 0);
                        fixup_pack_header_footer(fd, sha1, pack_tmp_name,
                                                 nr_written, sha1, offset);
                        close(fd);
                        if (write_bitmap_index) {
                                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(sha1);
                                bitmap_writer_build_type_index(written_list, nr_written);
                        }

                        finish_tmp_packfile(&tmpname, pack_tmp_name,
                                            written_list, nr_written,
                                            &pack_idx_opts, sha1);

                        if (write_bitmap_index) {
                                strbuf_addf(&tmpname, "%s.bitmap", sha1_to_hex(sha1));

                                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(sha1_to_hex(sha1));
                }

                /* 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);
}

static void setup_delta_attr_check(struct git_attr_check *check)
{
        static struct git_attr *attr_delta;

        if (!attr_delta)
                attr_delta = git_attr("delta");

        check[0].attr = attr_delta;
}

static int no_try_delta(const char *path)
{
        struct git_attr_check check[1];

        setup_delta_attr_check(check);
        if (git_check_attr(path, ARRAY_SIZE(check), check))
                return 0;
        if (ATTR_FALSE(check->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 unsigned char *sha1,
                                int exclude,
                                uint32_t *index_pos)
{
        struct object_entry *entry;

        entry = packlist_find(&to_pack, sha1, index_pos);
        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 &&
            (!local || !have_non_local_packs))
                return 1;

        if (local && !p->pack_local)
                return 0;
        if (ignore_packed_keep && p->pack_local && p->pack_keep)
                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 unsigned char *sha1,
                               int exclude,
                               struct packed_git **found_pack,
                               off_t *found_offset)
{
        struct mru_entry *entry;
        int want;

        if (!exclude && local && has_loose_object_nonlocal(sha1))
                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 (entry = packed_git_mru->head; entry; entry = entry->next) {
                struct packed_git *p = entry->item;
                off_t offset;

                if (p == *found_pack)
                        offset = *found_offset;
                else
                        offset = find_pack_entry_one(sha1, 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)
                                mru_mark(packed_git_mru, entry);
                        if (want != -1)
                                return want;
                }
        }

        return 1;
}

static void create_object_entry(const unsigned char *sha1,
                                enum object_type type,
                                uint32_t hash,
                                int exclude,
                                int no_try_delta,
                                uint32_t index_pos,
                                struct packed_git *found_pack,
                                off_t found_offset)
{
        struct object_entry *entry;

        entry = packlist_alloc(&to_pack, sha1, index_pos);
        entry->hash = hash;
        if (type)
                entry->type = type;
        if (exclude)
                entry->preferred_base = 1;
        else
                nr_result++;
        if (found_pack) {
                entry->in_pack = 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 unsigned char *sha1, enum object_type type,
                            const char *name, int exclude)
{
        struct packed_git *found_pack = NULL;
        off_t found_offset = 0;
        uint32_t index_pos;

        if (have_duplicate_entry(sha1, exclude, &index_pos))
                return 0;

        if (!want_object_in_pack(sha1, exclude, &found_pack, &found_offset)) {
                /* The pack is missing an object, so it will not have closure */
                if (write_bitmap_index) {
                        warning(_(no_closure_warning));
                        write_bitmap_index = 0;
                }
                return 0;
        }

        create_object_entry(sha1, type, pack_name_hash(name),
                            exclude, name && no_try_delta(name),
                            index_pos, found_pack, found_offset);

        display_progress(progress_state, nr_result);
        return 1;
}

static int add_object_entry_from_bitmap(const unsigned char *sha1,
                                        enum object_type type,
                                        int flags, uint32_t name_hash,
                                        struct packed_git *pack, off_t offset)
{
        uint32_t index_pos;

        if (have_duplicate_entry(sha1, 0, &index_pos))
                return 0;

        if (!want_object_in_pack(sha1, 0, &pack, &offset))
                return 0;

        create_object_entry(sha1, type, name_hash, 0, 0, index_pos, pack, offset);

        display_progress(progress_state, nr_result);
        return 1;
}

struct pbase_tree_cache {
        unsigned char sha1[20];
        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 unsigned char *sha1)
{
        return sha1[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 unsigned char *sha1)
{
        struct pbase_tree_cache *ent, *nent;
        void *data;
        unsigned long size;
        enum object_type type;
        int neigh;
        int my_ix = pbase_tree_cache_ix(sha1);
        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 && !hashcmp(ent->sha1, sha1)) {
                        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_sha1_file(sha1, &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;
        }
        hashcpy(nent->sha1, sha1);
        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->hash,
                                         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->hash);
                        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 = (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_paths) ? -1 : 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)
                memmove(done_pbase_paths + pos + 1,
                        done_pbase_paths + pos,
                        (done_pbase_paths_num - pos - 1) * sizeof(unsigned));
        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.sha1, 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(unsigned char *sha1)
{
        struct pbase_tree *it;
        void *data;
        unsigned long size;
        unsigned char tree_sha1[20];

        if (window <= num_preferred_base++)
                return;

        data = read_object_with_reference(sha1, tree_type, &size, tree_sha1);
        if (!data)
                return;

        for (it = pbase_tree; it; it = it->next) {
                if (!hashcmp(it->pcache.sha1, tree_sha1)) {
                        free(data);
                        return;
                }
        }

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

        hashcpy(it->pcache.sha1, tree_sha1);
        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 *this = it;
                it = this->next;
                free(this->pcache.tree_data);
                free(this);
        }

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

        free(done_pbase_paths);
        done_pbase_paths = NULL;
        done_pbase_paths_num = done_pbase_paths_alloc = 0;
}

static void check_object(struct object_entry *entry)
{
        if (entry->in_pack) {
                struct packed_git *p = entry->in_pack;
                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;

                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,
                                                   &entry->in_pack_type,
                                                   &entry->size);
                if (used == 0)
                        goto give_up;

                /*
                 * 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. */
                        entry->type = entry->in_pack_type;
                        entry->in_pack_header_size = used;
                        if (entry->type < OBJ_COMMIT || entry->type > 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 + 20;
                        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",
                                              sha1_to_hex(entry->idx.sha1));
                                        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",
                                      sha1_to_hex(entry->idx.sha1));
                                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 (base_ref && (base_entry = packlist_find(&to_pack, base_ref, NULL))) {
                        /*
                         * If base_ref was set above that means we wish to
                         * reuse delta data, and we even found that base
                         * in the list of objects we want to pack. Goodie!
                         *
                         * 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.
                         */
                        entry->type = entry->in_pack_type;
                        entry->delta = base_entry;
                        entry->delta_size = entry->size;
                        entry->delta_sibling = base_entry->delta_child;
                        base_entry->delta_child = entry;
                        unuse_pack(&w_curs);
                        return;
                }

                if (entry->type) {
                        /*
                         * 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.
                         */
                        entry->size = get_size_from_delta(p, &w_curs,
                                        entry->in_pack_offset + entry->in_pack_header_size);
                        if (entry->size == 0)
                                goto give_up;
                        unuse_pack(&w_curs);
                        return;
                }

                /*
                 * No choice but to fall back to the recursive delta walk
                 * with sha1_object_info() to find about the object type
                 * at this point...
                 */
                give_up:
                unuse_pack(&w_curs);
        }

        entry->type = sha1_object_info(entry->idx.sha1, &entry->size);
        /*
         * The error condition 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;

        /* avoid filesystem trashing with loose objects */
        if (!a->in_pack && !b->in_pack)
                return hashcmp(a->idx.sha1, b->idx.sha1);

        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)
{
        struct object_entry **p = &entry->delta->delta_child;
        struct object_info oi = OBJECT_INFO_INIT;

        while (*p) {
                if (*p == entry)
                        *p = (*p)->delta_sibling;
                else
                        p = &(*p)->delta_sibling;
        }
        entry->delta = NULL;
        entry->depth = 0;

        oi.sizep = &entry->size;
        oi.typep = &entry->type;
        if (packed_object_info(entry->in_pack, entry->in_pack_offset, &oi) < 0) {
                /*
                 * We failed to get the info from this pack for some reason;
                 * fall back to sha1_object_info, which may find another copy.
                 * And if that fails, the error will be recorded in entry->type
                 * and dealt with in prepare_pack().
                 */
                entry->type = sha1_object_info(entry->idx.sha1, &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)
{
        /* If it's not a delta, it can't be part of a cycle. */
        if (!entry->delta) {
                entry->dfs_state = DFS_DONE;
                return;
        }

        switch (entry->dfs_state) {
        case DFS_NONE:
                /*
                 * This is the first time we've seen the object. We mark it as
                 * part of the active potential cycle and recurse.
                 */
                entry->dfs_state = DFS_ACTIVE;
                break_delta_chains(entry->delta);

                /*
                 * Once we've recursed, our base (if we still have one) knows
                 * its depth, so we can compute ours (and check it against
                 * the limit).
                 */
                if (entry->delta) {
                        entry->depth = entry->delta->depth + 1;
                        if (entry->depth > depth)
                                drop_reused_delta(entry);
                }

                entry->dfs_state = DFS_DONE;
                break;

        case DFS_DONE:
                /* object already examined, and not part of a cycle */
                break;

        case DFS_ACTIVE:
                /*
                 * We found a cycle that needs broken. It would be correct to
                 * break any link in the chain, but it's convenient to
                 * break this one.
                 */
                drop_reused_delta(entry);
                entry->dfs_state = DFS_DONE;
                break;
        }
}

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

        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 (big_file_threshold < entry->size)
                        entry->no_try_delta = 1;
        }

        /*
         * 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;

        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 (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;
}

#ifndef NO_PTHREADS

static pthread_mutex_t read_mutex;
#define read_lock()             pthread_mutex_lock(&read_mutex)
#define read_unlock()           pthread_mutex_unlock(&read_mutex)

static pthread_mutex_t cache_mutex;
#define cache_lock()            pthread_mutex_lock(&cache_mutex)
#define cache_unlock()          pthread_mutex_unlock(&cache_mutex)

static pthread_mutex_t progress_mutex;
#define progress_lock()         pthread_mutex_lock(&progress_mutex)
#define progress_unlock()       pthread_mutex_unlock(&progress_mutex)

#else

#define read_lock()             (void)0
#define read_unlock()           (void)0
#define cache_lock()            (void)0
#define cache_unlock()          (void)0
#define progress_lock()         (void)0
#define progress_unlock()       (void)0

#endif

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 (trg_entry->type != src_entry->type)
                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 && trg_entry->in_pack &&
            trg_entry->in_pack == src_entry->in_pack &&
            !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 = trg_entry->size;
        if (!trg_entry->delta) {
                max_size = trg_size/2 - 20;
                ref_depth = 1;
        } else {
                max_size = trg_entry->delta_size;
                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 = src_entry->size;
        sizediff = src_size < trg_size ? trg_size - src_size : 0;
        if (sizediff >= max_size)
                return 0;
        if (trg_size < src_size / 32)
                return 0;

        /* Load data if not already done */
        if (!trg->data) {
                read_lock();
                trg->data = read_sha1_file(trg_entry->idx.sha1, &type, &sz);
                read_unlock();
                if (!trg->data)
                        die("object %s cannot be read",
                            sha1_to_hex(trg_entry->idx.sha1));
                if (sz != trg_size)
                        die("object %s inconsistent object length (%lu vs %lu)",
                            sha1_to_hex(trg_entry->idx.sha1), sz, trg_size);
                *mem_usage += sz;
        }
        if (!src->data) {
                read_lock();
                src->data = read_sha1_file(src_entry->idx.sha1, &type, &sz);
                read_unlock();
                if (!src->data) {
                        if (src_entry->preferred_base) {
                                static int warned = 0;
                                if (!warned++)
                                        warning("object %s cannot be read",
                                                sha1_to_hex(src_entry->idx.sha1));
                                /*
                                 * 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",
                            sha1_to_hex(src_entry->idx.sha1));
                }
                if (sz != src_size)
                        die("object %s inconsistent object length (%lu vs %lu)",
                            sha1_to_hex(src_entry->idx.sha1), sz, 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 (trg_entry->delta) {
                /* Prefer only shallower same-sized deltas. */
                if (delta_size == trg_entry->delta_size &&
                    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 -= trg_entry->delta_size;
                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);
        }

        trg_entry->delta = src_entry;
        trg_entry->delta_size = 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 = me->delta_child;
        unsigned int m = n;
        while (child) {
                unsigned int c = check_delta_limit(child, n + 1);
                if (m < c)
                        m = c;
                child = child->delta_sibling;
        }
        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 += n->entry->size;
                free(n->data);
                n->data = NULL;
        }
        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) {
                        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 (entry->delta_child) {
                        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) {
                        entry->z_delta_size = do_compress(&entry->delta_data,
                                                          entry->delta_size);
                        cache_lock();
                        delta_cache_size -= entry->delta_size;
                        delta_cache_size += entry->z_delta_size;
                        cache_unlock();
                }

                /* 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 (entry->delta && 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 (entry->delta) {
                        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);
}

#ifndef NO_PTHREADS

static void try_to_free_from_threads(size_t size)
{
        read_lock();
        release_pack_memory(size);
        read_unlock();
}

static try_to_free_t old_try_to_free_routine;

/*
 * 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.
 */

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)
{
        init_recursive_mutex(&read_mutex);
        pthread_mutex_init(&cache_mutex, NULL);
        pthread_mutex_init(&progress_mutex, NULL);
        pthread_cond_init(&progress_cond, NULL);
        old_try_to_free_routine = set_try_to_free_routine(try_to_free_from_threads);
}

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

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

        while (me->remaining) {
                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);
        }
        /* 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(stderr, "Delta compression using up to %d threads.\n",
                                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);
}

#else
#define ll_find_deltas(l, s, w, d, p)   find_deltas(l, &s, w, d, p)
#endif

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 (packlist_find(&to_pack, oid->hash, NULL))
                return;

        tag = lookup_tag(oid->hash);
        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.hash, 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.hash)    && /* peelable? */
            packlist_find(&to_pack, peeled.hash, NULL))      /* 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;

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

                if (entry->size < 50)
                        continue;

                if (entry->no_try_delta)
                        continue;

                if (!entry->preferred_base) {
                        nr_deltas++;
                        if (entry->type < 0)
                                die("unable to get type of object %s",
                                    sha1_to_hex(entry->idx.sha1));
                } else {
                        if (entry->type < 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.compression")) {
                int level = git_config_int(k, v);
                if (level == -1)
                        level = Z_DEFAULT_COMPRESSION;
                else if (level < 0 || level > Z_BEST_COMPRESSION)
                        die("bad pack compression level %d", level);
                pack_compression_level = level;
                pack_compression_seen = 1;
                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.threads")) {
                delta_search_threads = git_config_int(k, v);
                if (delta_search_threads < 0)
                        die("invalid number of threads specified (%d)",
                            delta_search_threads);
#ifdef NO_PTHREADS
                if (delta_search_threads != 1)
                        warning("no threads support, ignoring %s", k);
#endif
                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[40 + 1 + PATH_MAX + 2];
        unsigned char sha1[20];

        for (;;) {
                if (!fgets(line, sizeof(line), stdin)) {
                        if (feof(stdin))
                                break;
                        if (!ferror(stdin))
                                die("fgets returned NULL, not EOF, not error!");
                        if (errno != EINTR)
                                die_errno("fgets");
                        clearerr(stdin);
                        continue;
                }
                if (line[0] == '-') {
                        if (get_sha1_hex(line+1, sha1))
                                die("expected edge sha1, got garbage:\n %s",
                                    line);
                        add_preferred_base(sha1);
                        continue;
                }
                if (get_sha1_hex(line, sha1))
                        die("expected sha1, got garbage:\n %s", line);

                add_preferred_base_object(line+41);
                add_object_entry(sha1, 0, line+41, 0);
        }
}

#define OBJECT_ADDED (1u<<20)

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

        if (write_bitmap_index)
                index_commit_for_bitmap(commit);
}

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

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

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

struct in_pack {
        int alloc;
        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(struct rev_info *revs)
{
        struct packed_git *p;
        struct in_pack in_pack;
        uint32_t i;

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

        for (p = packed_git; p; p = p->next) {
                const unsigned char *sha1;
                struct object *o;

                if (!p->pack_local || p->pack_keep)
                        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++) {
                        sha1 = nth_packed_object_sha1(p, i);
                        o = lookup_unknown_object(sha1);
                        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.hash, o->type, "", 0);
                }
        }
        free(in_pack.array);
}

static int add_loose_object(const unsigned char *sha1, const char *path,
                            void *data)
{
        enum object_type type = sha1_object_info(sha1, NULL);

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

        add_object_entry(sha1, 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 unsigned char *sha1)
{
        static struct packed_git *last_found = (void *)1;
        struct packed_git *p;

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

        while (p) {
                if ((!p->pack_local || p->pack_keep) &&
                        find_pack_entry_one(sha1, p)) {
                        last_found = p;
                        return 1;
                }
                if (p == last_found)
                        p = packed_git;
                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 sha1_array recent_objects;

static int loosened_object_can_be_discarded(const unsigned char *sha1,
                                            unsigned long mtime)
{
        if (!unpack_unreachable_expiration)
                return 0;
        if (mtime > unpack_unreachable_expiration)
                return 0;
        if (sha1_array_lookup(&recent_objects, sha1) >= 0)
                return 0;
        return 1;
}

static void loosen_unused_packed_objects(struct rev_info *revs)
{
        struct packed_git *p;
        uint32_t i;
        const unsigned char *sha1;

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

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

                for (i = 0; i < p->num_objects; i++) {
                        sha1 = nth_packed_object_sha1(p, i);
                        if (!packlist_find(&to_pack, sha1, NULL) &&
                            !has_sha1_pack_kept_or_nonlocal(sha1) &&
                            !loosened_object_can_be_discarded(sha1, p->mtime))
                                if (force_object_loose(sha1, 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 pack_to_stdout && allow_ofs_delta;
}

static int get_object_list_from_bitmap(struct rev_info *revs)
{
        if (prepare_bitmap_walk(revs) < 0)
                return -1;

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

        traverse_bitmap_commit_list(&add_object_entry_from_bitmap);
        return 0;
}

static void record_recent_object(struct object *obj,
                                 const char *name,
                                 void *data)
{
        sha1_array_append(&recent_objects, obj->oid.hash);
}

static void record_recent_commit(struct commit *commit, void *data)
{
        sha1_array_append(&recent_objects, commit->object.oid.hash);
}

static void get_object_list(int ac, const char **av)
{
        struct rev_info revs;
        char line[1000];
        int flags = 0;

        init_revisions(&revs, NULL);
        save_commit_buffer = 0;
        setup_revisions(ac, av, &revs, NULL);

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

        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 ")) {
                                unsigned char sha1[20];
                                if (get_sha1_hex(line + 10, sha1))
                                        die("not an SHA-1 '%s'", line + 10);
                                register_shallow(sha1);
                                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);
        }

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

        if (prepare_revision_walk(&revs))
                die("revision walk setup failed");
        mark_edges_uninteresting(&revs, show_edge);
        traverse_commit_list(&revs, show_commit, show_object, 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(&revs);
        if (pack_loose_unreachable)
                add_unreachable_loose_objects();
        if (unpack_unreachable)
                loosen_unused_packed_objects(&revs);

        sha1_array_clear(&recent_objects);
}

static int option_parse_index_version(const struct option *opt,
                                      const char *arg, int unset)
{
        char *c;
        const char *val = arg;
        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 thin = 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 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"),
                  0, 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")),
                { OPTION_SET_INT, 0, "unpacked", &rev_list_unpacked, NULL,
                  N_("limit the objects to those that are not yet packed"),
                  PARSE_OPT_NOARG | PARSE_OPT_NONEG, NULL, 1 },
                { OPTION_SET_INT, 0, "all", &rev_list_all, NULL,
                  N_("include objects reachable from any reference"),
                  PARSE_OPT_NOARG | PARSE_OPT_NONEG, NULL, 1 },
                { OPTION_SET_INT, 0, "reflog", &rev_list_reflog, NULL,
                  N_("include objects referred by reflog entries"),
                  PARSE_OPT_NOARG | PARSE_OPT_NONEG, NULL, 1 },
                { OPTION_SET_INT, 0, "indexed-objects", &rev_list_index, NULL,
                  N_("include objects referred to by the index"),
                  PARSE_OPT_NOARG | PARSE_OPT_NONEG, NULL, 1 },
                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, "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,
                         N_("ignore packs that have companion .keep file")),
                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_BOOL(0, "write-bitmap-index", &write_bitmap_index,
                         N_("write a bitmap index together with the pack index")),
                OPT_END(),
        };

        check_replace_refs = 0;

        reset_pack_idx_option(&pack_idx_opts);
        git_config(git_pack_config, NULL);
        if (!pack_compression_seen && core_compression_seen)
                pack_compression_level = core_compression_level;

        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);

        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 (!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();

#ifdef NO_PTHREADS
        if (delta_search_threads != 1)
                warning("no threads support, ignoring --threads");
#endif
        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;

        /*
         * "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())
                use_bitmap_index = 0;

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

        if (progress && all_progress_implied)
                progress = 2;

        prepare_packed_git();
        if (ignore_packed_keep) {
                struct packed_git *p;
                for (p = packed_git; p; p = p->next)
                        if (p->pack_local && p->pack_keep)
                                break;
                if (!p) /* no keep-able packs found */
                        ignore_packed_keep = 0;
        }
        if (local) {
                /*
                 * unlike ignore_packed_keep 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 = packed_git; p; p = p->next) {
                        if (!p->pack_local) {
                                have_non_local_packs = 1;
                                break;
                        }
                }
        }

        if (progress)
                progress_state = start_progress(_("Counting 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);

        if (non_empty && !nr_result)
                return 0;
        if (nr_result)
                prepare_pack(window, depth);
        write_pack_file();
        if (progress)
                fprintf(stderr, "Total %"PRIu32" (delta %"PRIu32"),"
                        " reused %"PRIu32" (delta %"PRIu32")\n",
                        written, written_delta, reused, reused_delta);
        return 0;
}