pack-objects.c

#include "builtin.h"
#include "cache.h"
#include "config.h"
#include "attr.h"
#include "object.h"
#include "blob.h"
#include "commit.h"
#include "tag.h"
#include "tree.h"
#include "delta.h"
#include "pack.h"
#include "pack-revindex.h"
#include "csum-file.h"
#include "tree-walk.h"
#include "diff.h"
#include "revision.h"
#include "list-objects.h"
#include "list-objects-filter.h"
#include "list-objects-filter-options.h"
#include "pack-objects.h"
#include "progress.h"
#include "refs.h"
#include "streaming.h"
#include "thread-utils.h"
#include "pack-bitmap.h"
#include "reachable.h"
#include "sha1-array.h"
#include "argv-array.h"
#include "mru.h"
#include "packfile.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 timestamp_t unpack_unreachable_expiration;
static int pack_loose_unreachable;
static int local;
static int have_non_local_packs;
static int incremental;
static int ignore_packed_keep;
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 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 int exclude_promisor_objects;

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;

static struct list_objects_filter_options filter_options;

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

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

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

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

	indexed_commits[indexed_commits_nr++] = commit;
}

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

	buf = read_sha1_file(entry->idx.oid.hash, &type, &size);
	if (!buf)
		die("unable to read %s", oid_to_hex(&entry->idx.oid));
	base_buf = read_sha1_file(entry->delta->idx.oid.hash, &type,
				  &base_size);
	if (!base_buf)
		die("unable to read %s",
		    oid_to_hex(&entry->delta->idx.oid));
	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[MAX_PACK_OBJECT_HEADER],
		      dheader[MAX_PACK_OBJECT_HEADER];
	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.oid.hash, &type, &size, NULL)) != NULL)
			buf = NULL;
		else {
			buf = read_sha1_file(entry->idx.oid.hash, &type,
					     &size);
			if (!buf)
				die(_("unable to read %s"),
				    oid_to_hex(&entry->idx.oid));
		}
		/*
		 * make sure no cached delta data remains from a
		 * previous attempt before a pack split occurred.
		 */
		FREE_AND_NULL(entry->delta_data);
		entry->z_delta_size = 0;
	} else if (entry->delta_data) {
		size = 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(header, sizeof(header),
					      type, size);

	if (type == OBJ_OFS_DELTA) {
		/*
		 * Deltas with relative base contain an additional
		 * encoding of the relative offset for the delta
		 * base from this object's position in the pack.
		 */
		off_t ofs = entry->idx.offset - 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.oid.hash, 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.oid.hash);
		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[MAX_PACK_OBJECT_HEADER],
		      dheader[MAX_PACK_OBJECT_HEADER];
	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(header, sizeof(header),
					      type, entry->size);

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

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

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

	if (type == OBJ_OFS_DELTA) {
		off_t ofs = entry->idx.offset - 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.oid.hash, 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",
			oid_to_hex(&e->idx.oid));
		return WRITE_ONE_RECURSIVE;
	} else if (e->idx.offset || e->preferred_base) {
		/* offset is non zero if object is written already. */
		return WRITE_ONE_SKIP;
	}

	/* if we are deltified, write out base object first. */
	if (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 int no_try_delta(const char *path)
{
	static struct attr_check *check;

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

/*
 * When adding an object, check whether we have already added it
 * to our packing list. If so, we can skip. However, if we are
 * being asked to excludei t, but the previous mention was to include
 * it, make sure to adjust its flags and tweak our numbers accordingly.
 *
 * As an optimization, we pass out the index position where we would have
 * found the item, since that saves us from having to look it up again a
 * few lines later when we want to add the new entry.
 */
static int have_duplicate_entry(const 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 = lo + (hi - lo) / 2;
		if (done_pbase_paths[mi] == hash)
			return mi;
		if (done_pbase_paths[mi] < hash)
			hi = mi;
		else
			lo = mi + 1;
	}
	return -lo-1;
}

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

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

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

	cmplen = name_cmp_len(name);
	for (it = pbase_tree; it; it = it->next) {
		if (cmplen == 0) {
			add_object_entry(it->pcache.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_AND_NULL(pbase_tree_cache[i]);
	}

	FREE_AND_NULL(done_pbase_paths);
	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",
					      oid_to_hex(&entry->idx.oid));
					goto give_up;
				}
				c = buf[used_0++];
				ofs = (ofs << 7) + (c & 127);
			}
			ofs = entry->in_pack_offset - ofs;
			if (ofs <= 0 || ofs >= entry->in_pack_offset) {
				error("delta base offset out of bound for %s",
				      oid_to_hex(&entry->idx.oid));
				goto give_up;
			}
			if (reuse_delta && !entry->preferred_base) {
				struct revindex_entry *revidx;
				revidx = find_pack_revindex(p, ofs);
				if (!revidx)
					goto give_up;
				base_ref = nth_packed_object_sha1(p, revidx->nr);
			}
			entry->in_pack_header_size = used + used_0;
			break;
		}

		if (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.oid.hash, &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 oidcmp(&a->idx.oid, &b->idx.oid);

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

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

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

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

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

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

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

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

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

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

		cur->dfs_state = DFS_DONE;
	}
}

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

	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.oid.hash, &type,
					   &sz);
		read_unlock();
		if (!trg->data)
			die("object %s cannot be read",
			    oid_to_hex(&trg_entry->idx.oid));
		if (sz != trg_size)
			die("object %s inconsistent object length (%lu vs %lu)",
			    oid_to_hex(&trg_entry->idx.oid), sz,
			    trg_size);
		*mem_usage += sz;
	}
	if (!src->data) {
		read_lock();
		src->data = read_sha1_file(src_entry->idx.oid.hash, &type,
					   &sz);
		read_unlock();
		if (!src->data) {
			if (src_entry->preferred_base) {
				static int warned = 0;
				if (!warned++)
					warning("object %s cannot be read",
						oid_to_hex(&src_entry->idx.oid));
				/*
				 * Those objects are not included in the
				 * resulting pack.  Be resilient and ignore
				 * them if they can't be read, in case the
				 * pack could be created nevertheless.
				 */
				return 0;
			}
			die("object %s cannot be read",
			    oid_to_hex(&src_entry->idx.oid));
		}
		if (sz != src_size)
			die("object %s inconsistent object length (%lu vs %lu)",
			    oid_to_hex(&src_entry->idx.oid), 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_AND_NULL(n->data);
	}
	n->entry = NULL;
	n->depth = 0;
	return freed_mem;
}

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

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

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

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

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

		while (window_memory_limit &&
		       mem_usage > window_memory_limit &&
		       count > 1) {
			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;

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

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

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

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

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

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

	init_threaded_search();

	if (delta_search_threads <= 1) {
		find_deltas(list, &list_size, window, depth, processed);
		cleanup_threaded_search();
		return;
	}
	if (progress > pack_to_stdout)
		fprintf(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);
	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",
				    oid_to_hex(&entry->idx.oid));
		} 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.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);
			delta_search_threads = 0;
		}
#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_object__ma_allow_any(struct object *obj, const char *name, void *data)
{
	assert(arg_missing_action == MA_ALLOW_ANY);

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

	show_object(obj, name, data);
}

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

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

	show_object(obj, name, data);
}

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

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

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

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

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

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

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

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

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

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

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

static void add_objects_in_unpacked_packs(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 struct object_id *oid, const char *path,
			    void *data)
{
	enum object_type type = sha1_object_info(oid->hash, NULL);

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

	add_object_entry(oid->hash, 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 oid_array recent_objects;

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

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

	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++) {
			nth_packed_object_oid(&oid, p, i);
			if (!packlist_find(&to_pack, oid.hash, NULL) &&
			    !has_sha1_pack_kept_or_nonlocal(oid.hash) &&
			    !loosened_object_can_be_discarded(&oid, p->mtime))
				if (force_object_loose(oid.hash, 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 &&
	       !ignore_packed_keep &&
	       (!local || !have_non_local_packs) &&
	       !incremental;
}

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)
{
	oid_array_append(&recent_objects, &obj->oid);
}

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

static void get_object_list(int ac, const char **av)
{
	struct rev_info revs;
	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 ")) {
				struct object_id oid;
				if (get_oid_hex(line + 10, &oid))
					die("not an SHA-1 '%s'", line + 10);
				register_shallow(&oid);
				use_bitmap_index = 0;
				continue;
			}
			die("not a rev '%s'", line);
		}
		if (handle_revision_arg(line, &revs, flags, REVARG_CANNOT_BE_FILENAME))
			die("bad revision '%s'", line);
	}

	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);

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

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

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

	oid_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_PARSE_LIST_OBJECTS_FILTER(&filter_options),
		{ OPTION_CALLBACK, 0, "missing", NULL, N_("action"),
		  N_("handling for missing objects"), PARSE_OPT_NONEG,
		  option_parse_missing_action },
		OPT_BOOL(0, "exclude-promisor-objects", &exclude_promisor_objects,
			 N_("do not pack objects in promisor packfiles")),
		OPT_END(),
	};

	check_replace_refs = 0;

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

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

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

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

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

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

	if (!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;

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

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

	if (use_bitmap_index < 0)
		use_bitmap_index = use_bitmap_index_default;

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