thodg/libgit2/src/pack-objects.c

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• Hash : 0f35efeb
  Author :
  Date : 2020-05-23T10:15:51
  

  git_pool_init: handle failure cases Propagate failures caused by pool initialization errors.

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• src/pack-objects.c

• /*
   * Copyright (C) the libgit2 contributors. All rights reserved.
   *
   * This file is part of libgit2, distributed under the GNU GPL v2 with
   * a Linking Exception. For full terms see the included COPYING file.
   */
  
  #include "pack-objects.h"
  
  #include "zstream.h"
  #include "delta.h"
  #include "iterator.h"
  #include "netops.h"
  #include "pack.h"
  #include "thread-utils.h"
  #include "tree.h"
  #include "util.h"
  #include "revwalk.h"
  #include "commit_list.h"
  
  #include "git2/pack.h"
  #include "git2/commit.h"
  #include "git2/tag.h"
  #include "git2/indexer.h"
  #include "git2/config.h"
  
  struct unpacked {
  	git_pobject *object;
  	void *data;
  	struct git_delta_index *index;
  	size_t depth;
  };
  
  struct tree_walk_context {
  	git_packbuilder *pb;
  	git_buf buf;
  };
  
  struct pack_write_context {
  	git_indexer *indexer;
  	git_indexer_progress *stats;
  };
  
  struct walk_object {
  	git_oid id;
  	unsigned int uninteresting:1,
  		seen:1;
  };
  
  #ifdef GIT_THREADS
  
  #define GIT_PACKBUILDER__MUTEX_OP(pb, mtx, op) do { \
  		int result = git_mutex_##op(&(pb)->mtx); \
  		assert(!result); \
  		GIT_UNUSED(result); \
  	} while (0)
  
  #else
  
  #define GIT_PACKBUILDER__MUTEX_OP(pb,mtx,op) GIT_UNUSED(pb)
  
  #endif /* GIT_THREADS */
  
  #define git_packbuilder__cache_lock(pb) GIT_PACKBUILDER__MUTEX_OP(pb, cache_mutex, lock)
  #define git_packbuilder__cache_unlock(pb) GIT_PACKBUILDER__MUTEX_OP(pb, cache_mutex, unlock)
  #define git_packbuilder__progress_lock(pb) GIT_PACKBUILDER__MUTEX_OP(pb, progress_mutex, lock)
  #define git_packbuilder__progress_unlock(pb) GIT_PACKBUILDER__MUTEX_OP(pb, progress_mutex, unlock)
  
  /* The minimal interval between progress updates (in seconds). */
  #define MIN_PROGRESS_UPDATE_INTERVAL 0.5
  
  /* Size of the buffer to feed to zlib */
  #define COMPRESS_BUFLEN (1024 * 1024)
  
  static unsigned name_hash(const char *name)
  {
  	unsigned c, hash = 0;
  
  	if (!name)
  		return 0;
  
  	/*
  	 * This effectively just creates a sortable number from the
  	 * last sixteen non-whitespace characters. Last characters
  	 * count "most", so things that end in ".c" sort together.
  	 */
  	while ((c = *name++) != 0) {
  		if (git__isspace(c))
  			continue;
  		hash = (hash >> 2) + (c << 24);
  	}
  	return hash;
  }
  
  static int packbuilder_config(git_packbuilder *pb)
  {
  	git_config *config;
  	int ret = 0;
  	int64_t val;
  
  	if ((ret = git_repository_config_snapshot(&config, pb->repo)) < 0)
  		return ret;
  
  #define config_get(KEY,DST,DFLT) do { \
  	ret = git_config_get_int64(&val, config, KEY); \
  	if (!ret) { \
  		if (!git__is_sizet(val)) { \
  			git_error_set(GIT_ERROR_CONFIG, \
  				"configuration value '%s' is too large", KEY); \
  			ret = -1; \
  			goto out; \
  		} \
  		(DST) = (size_t)val; \
  	} else if (ret == GIT_ENOTFOUND) { \
  	    (DST) = (DFLT); \
  	    ret = 0; \
  	} else if (ret < 0) goto out; } while (0)
  
  	config_get("pack.deltaCacheSize", pb->max_delta_cache_size,
  		   GIT_PACK_DELTA_CACHE_SIZE);
  	config_get("pack.deltaCacheLimit", pb->cache_max_small_delta_size,
  		   GIT_PACK_DELTA_CACHE_LIMIT);
  	config_get("pack.deltaCacheSize", pb->big_file_threshold,
  		   GIT_PACK_BIG_FILE_THRESHOLD);
  	config_get("pack.windowMemory", pb->window_memory_limit, 0);
  
  #undef config_get
  
  out:
  	git_config_free(config);
  
  	return ret;
  }
  
  int git_packbuilder_new(git_packbuilder **out, git_repository *repo)
  {
  	git_packbuilder *pb;
  
  	*out = NULL;
  
  	pb = git__calloc(1, sizeof(*pb));
  	GIT_ERROR_CHECK_ALLOC(pb);
  
  	if (git_oidmap_new(&pb->object_ix) < 0 ||
  	    git_oidmap_new(&pb->walk_objects) < 0 ||
  	    git_pool_init(&pb->object_pool, sizeof(struct walk_object)) < 0)
  		goto on_error;
  
  	pb->repo = repo;
  	pb->nr_threads = 1; /* do not spawn any thread by default */
  
  	if (git_hash_ctx_init(&pb->ctx) < 0 ||
  		git_zstream_init(&pb->zstream, GIT_ZSTREAM_DEFLATE) < 0 ||
  		git_repository_odb(&pb->odb, repo) < 0 ||
  		packbuilder_config(pb) < 0)
  		goto on_error;
  
  #ifdef GIT_THREADS
  
  	if (git_mutex_init(&pb->cache_mutex) ||
  		git_mutex_init(&pb->progress_mutex) ||
  		git_cond_init(&pb->progress_cond))
  	{
  		git_error_set(GIT_ERROR_OS, "failed to initialize packbuilder mutex");
  		goto on_error;
  	}
  
  #endif
  
  	*out = pb;
  	return 0;
  
  on_error:
  	git_packbuilder_free(pb);
  	return -1;
  }
  
  unsigned int git_packbuilder_set_threads(git_packbuilder *pb, unsigned int n)
  {
  	assert(pb);
  
  #ifdef GIT_THREADS
  	pb->nr_threads = n;
  #else
  	GIT_UNUSED(n);
  	assert(1 == pb->nr_threads);
  #endif
  
  	return pb->nr_threads;
  }
  
  static int rehash(git_packbuilder *pb)
  {
  	git_pobject *po;
  	size_t i;
  
  	git_oidmap_clear(pb->object_ix);
  
  	for (i = 0, po = pb->object_list; i < pb->nr_objects; i++, po++) {
  		if (git_oidmap_set(pb->object_ix, &po->id, po) < 0)
  			return -1;
  	}
  
  	return 0;
  }
  
  int git_packbuilder_insert(git_packbuilder *pb, const git_oid *oid,
  			   const char *name)
  {
  	git_pobject *po;
  	size_t newsize;
  	int ret;
  
  	assert(pb && oid);
  
  	/* If the object already exists in the hash table, then we don't
  	 * have any work to do */
  	if (git_oidmap_exists(pb->object_ix, oid))
  		return 0;
  
  	if (pb->nr_objects >= pb->nr_alloc) {
  		GIT_ERROR_CHECK_ALLOC_ADD(&newsize, pb->nr_alloc, 1024);
  		GIT_ERROR_CHECK_ALLOC_MULTIPLY(&newsize, newsize / 2, 3);
  
  		if (!git__is_uint32(newsize)) {
  			git_error_set(GIT_ERROR_NOMEMORY, "packfile too large to fit in memory.");
  			return -1;
  		}
  
  		pb->nr_alloc = newsize;
  
  		pb->object_list = git__reallocarray(pb->object_list,
  			pb->nr_alloc, sizeof(*po));
  		GIT_ERROR_CHECK_ALLOC(pb->object_list);
  
  		if (rehash(pb) < 0)
  			return -1;
  	}
  
  	po = pb->object_list + pb->nr_objects;
  	memset(po, 0x0, sizeof(*po));
  
  	if ((ret = git_odb_read_header(&po->size, &po->type, pb->odb, oid)) < 0)
  		return ret;
  
  	pb->nr_objects++;
  	git_oid_cpy(&po->id, oid);
  	po->hash = name_hash(name);
  
  	if (git_oidmap_set(pb->object_ix, &po->id, po) < 0) {
  		git_error_set_oom();
  		return -1;
  	}
  
  	pb->done = false;
  
  	if (pb->progress_cb) {
  		double current_time = git__timer();
  		double elapsed = current_time - pb->last_progress_report_time;
  
  		if (elapsed >= MIN_PROGRESS_UPDATE_INTERVAL) {
  			pb->last_progress_report_time = current_time;
  
  			ret = pb->progress_cb(
  				GIT_PACKBUILDER_ADDING_OBJECTS,
  				pb->nr_objects, 0, pb->progress_cb_payload);
  
  			if (ret)
  				return git_error_set_after_callback(ret);
  		}
  	}
  
  	return 0;
  }
  
  static int get_delta(void **out, git_odb *odb, git_pobject *po)
  {
  	git_odb_object *src = NULL, *trg = NULL;
  	size_t delta_size;
  	void *delta_buf;
  	int error;
  
  	*out = NULL;
  
  	if (git_odb_read(&src, odb, &po->delta->id) < 0 ||
  	    git_odb_read(&trg, odb, &po->id) < 0)
  		goto on_error;
  
  	error = git_delta(&delta_buf, &delta_size,
  		git_odb_object_data(src), git_odb_object_size(src),
  		git_odb_object_data(trg), git_odb_object_size(trg),
  		0);
  
  	if (error < 0 && error != GIT_EBUFS)
  		goto on_error;
  
  	if (error == GIT_EBUFS || delta_size != po->delta_size) {
  		git_error_set(GIT_ERROR_INVALID, "delta size changed");
  		goto on_error;
  	}
  
  	*out = delta_buf;
  
  	git_odb_object_free(src);
  	git_odb_object_free(trg);
  	return 0;
  
  on_error:
  	git_odb_object_free(src);
  	git_odb_object_free(trg);
  	return -1;
  }
  
  static int write_object(
  	git_packbuilder *pb,
  	git_pobject *po,
  	int (*write_cb)(void *buf, size_t size, void *cb_data),
  	void *cb_data)
  {
  	git_odb_object *obj = NULL;
  	git_object_t type;
  	unsigned char hdr[10], *zbuf = NULL;
  	void *data = NULL;
  	size_t hdr_len, zbuf_len = COMPRESS_BUFLEN, data_len;
  	int error;
  
  	/*
  	 * If we have a delta base, let's use the delta to save space.
  	 * Otherwise load the whole object. 'data' ends up pointing to
  	 * whatever data we want to put into the packfile.
  	 */
  	if (po->delta) {
  		if (po->delta_data)
  			data = po->delta_data;
  		else if ((error = get_delta(&data, pb->odb, po)) < 0)
  				goto done;
  
  		data_len = po->delta_size;
  		type = GIT_OBJECT_REF_DELTA;
  	} else {
  		if ((error = git_odb_read(&obj, pb->odb, &po->id)) < 0)
  			goto done;
  
  		data = (void *)git_odb_object_data(obj);
  		data_len = git_odb_object_size(obj);
  		type = git_odb_object_type(obj);
  	}
  
  	/* Write header */
  	hdr_len = git_packfile__object_header(hdr, data_len, type);
  
  	if ((error = write_cb(hdr, hdr_len, cb_data)) < 0 ||
  		(error = git_hash_update(&pb->ctx, hdr, hdr_len)) < 0)
  		goto done;
  
  	if (type == GIT_OBJECT_REF_DELTA) {
  		if ((error = write_cb(po->delta->id.id, GIT_OID_RAWSZ, cb_data)) < 0 ||
  			(error = git_hash_update(&pb->ctx, po->delta->id.id, GIT_OID_RAWSZ)) < 0)
  			goto done;
  	}
  
  	/* Write data */
  	if (po->z_delta_size) {
  		data_len = po->z_delta_size;
  
  		if ((error = write_cb(data, data_len, cb_data)) < 0 ||
  			(error = git_hash_update(&pb->ctx, data, data_len)) < 0)
  			goto done;
  	} else {
  		zbuf = git__malloc(zbuf_len);
  		GIT_ERROR_CHECK_ALLOC(zbuf);
  
  		git_zstream_reset(&pb->zstream);
  
  		if ((error = git_zstream_set_input(&pb->zstream, data, data_len)) < 0)
  			goto done;
  
  		while (!git_zstream_done(&pb->zstream)) {
  			if ((error = git_zstream_get_output(zbuf, &zbuf_len, &pb->zstream)) < 0 ||
  				(error = write_cb(zbuf, zbuf_len, cb_data)) < 0 ||
  				(error = git_hash_update(&pb->ctx, zbuf, zbuf_len)) < 0)
  				goto done;
  
  			zbuf_len = COMPRESS_BUFLEN; /* reuse buffer */
  		}
  	}
  
  	/*
  	 * If po->delta is true, data is a delta and it is our
  	 * responsibility to free it (otherwise it's a git_object's
  	 * data). We set po->delta_data to NULL in case we got the
  	 * data from there instead of get_delta(). If we didn't,
  	 * there's no harm.
  	 */
  	if (po->delta) {
  		git__free(data);
  		po->delta_data = NULL;
  	}
  
  	pb->nr_written++;
  
  done:
  	git__free(zbuf);
  	git_odb_object_free(obj);
  	return error;
  }
  
  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 int write_one(
  	enum write_one_status *status,
  	git_packbuilder *pb,
  	git_pobject *po,
  	int (*write_cb)(void *buf, size_t size, void *cb_data),
  	void *cb_data)
  {
  	int error;
  
  	if (po->recursing) {
  		*status = WRITE_ONE_RECURSIVE;
  		return 0;
  	} else if (po->written) {
  		*status = WRITE_ONE_SKIP;
  		return 0;
  	}
  
  	if (po->delta) {
  		po->recursing = 1;
  
  		if ((error = write_one(status, pb, po->delta, write_cb, cb_data)) < 0)
  			return error;
  
  		/* we cannot depend on this one */
  		if (*status == WRITE_ONE_RECURSIVE)
  			po->delta = NULL;
  	}
  
  	*status = WRITE_ONE_WRITTEN;
  	po->written = 1;
  	po->recursing = 0;
  
  	return write_object(pb, po, write_cb, cb_data);
  }
  
  GIT_INLINE(void) add_to_write_order(git_pobject **wo, size_t *endp,
  	git_pobject *po)
  {
  	if (po->filled)
  		return;
  	wo[(*endp)++] = po;
  	po->filled = 1;
  }
  
  static void add_descendants_to_write_order(git_pobject **wo, size_t *endp,
  	git_pobject *po)
  {
  	int add_to_order = 1;
  	while (po) {
  		if (add_to_order) {
  			git_pobject *s;
  			/* add this node... */
  			add_to_write_order(wo, endp, po);
  			/* all its siblings... */
  			for (s = po->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 (po->delta_child) {
  			add_to_order = 1;
  			po = po->delta_child;
  		} else {
  			add_to_order = 0;
  			/* our sibling might have some children, it is next */
  			if (po->delta_sibling) {
  				po = po->delta_sibling;
  				continue;
  			}
  			/* go back to our parent node */
  			po = po->delta;
  			while (po && !po->delta_sibling) {
  				/* we're on the right side of a subtree, keep
  				 * going up until we can go right again */
  				po = po->delta;
  			}
  			if (!po) {
  				/* done- we hit our original root node */
  				return;
  			}
  			/* pass it off to sibling at this level */
  			po = po->delta_sibling;
  		}
  	};
  }
  
  static void add_family_to_write_order(git_pobject **wo, size_t *endp,
  	git_pobject *po)
  {
  	git_pobject *root;
  
  	for (root = po; root->delta; root = root->delta)
  		; /* nothing */
  	add_descendants_to_write_order(wo, endp, root);
  }
  
  static int cb_tag_foreach(const char *name, git_oid *oid, void *data)
  {
  	git_packbuilder *pb = data;
  	git_pobject *po;
  
  	GIT_UNUSED(name);
  
  	if ((po = git_oidmap_get(pb->object_ix, oid)) == NULL)
  		return 0;
  
  	po->tagged = 1;
  
  	/* TODO: peel objects */
  
  	return 0;
  }
  
  static git_pobject **compute_write_order(git_packbuilder *pb)
  {
  	size_t i, wo_end, last_untagged;
  	git_pobject **wo;
  
  	if ((wo = git__mallocarray(pb->nr_objects, sizeof(*wo))) == NULL)
  		return NULL;
  
  	for (i = 0; i < pb->nr_objects; i++) {
  		git_pobject *po = pb->object_list + i;
  		po->tagged = 0;
  		po->filled = 0;
  		po->delta_child = NULL;
  		po->delta_sibling = NULL;
  	}
  
  	/*
  	 * Fully connect delta_child/delta_sibling network.
  	 * Make sure delta_sibling is sorted in the original
  	 * recency order.
  	 */
  	for (i = pb->nr_objects; i > 0;) {
  		git_pobject *po = &pb->object_list[--i];
  		if (!po->delta)
  			continue;
  		/* Mark me as the first child */
  		po->delta_sibling = po->delta->delta_child;
  		po->delta->delta_child = po;
  	}
  
  	/*
  	 * Mark objects that are at the tip of tags.
  	 */
  	if (git_tag_foreach(pb->repo, &cb_tag_foreach, pb) < 0) {
  		git__free(wo);
  		return NULL;
  	}
  
  	/*
  	 * Give the objects in the original recency order until
  	 * we see a tagged tip.
  	 */
  	for (i = wo_end = 0; i < pb->nr_objects; i++) {
  		git_pobject *po = pb->object_list + i;
  		if (po->tagged)
  			break;
  		add_to_write_order(wo, &wo_end, po);
  	}
  	last_untagged = i;
  
  	/*
  	 * Then fill all the tagged tips.
  	 */
  	for (; i < pb->nr_objects; i++) {
  		git_pobject *po = pb->object_list + i;
  		if (po->tagged)
  			add_to_write_order(wo, &wo_end, po);
  	}
  
  	/*
  	 * And then all remaining commits and tags.
  	 */
  	for (i = last_untagged; i < pb->nr_objects; i++) {
  		git_pobject *po = pb->object_list + i;
  		if (po->type != GIT_OBJECT_COMMIT &&
  		    po->type != GIT_OBJECT_TAG)
  			continue;
  		add_to_write_order(wo, &wo_end, po);
  	}
  
  	/*
  	 * And then all the trees.
  	 */
  	for (i = last_untagged; i < pb->nr_objects; i++) {
  		git_pobject *po = pb->object_list + i;
  		if (po->type != GIT_OBJECT_TREE)
  			continue;
  		add_to_write_order(wo, &wo_end, po);
  	}
  
  	/*
  	 * Finally all the rest in really tight order
  	 */
  	for (i = last_untagged; i < pb->nr_objects; i++) {
  		git_pobject *po = pb->object_list + i;
  		if (!po->filled)
  			add_family_to_write_order(wo, &wo_end, po);
  	}
  
  	if (wo_end != pb->nr_objects) {
  		git__free(wo);
  		git_error_set(GIT_ERROR_INVALID, "invalid write order");
  		return NULL;
  	}
  
  	return wo;
  }
  
  static int write_pack(git_packbuilder *pb,
  	int (*write_cb)(void *buf, size_t size, void *cb_data),
  	void *cb_data)
  {
  	git_pobject **write_order;
  	git_pobject *po;
  	enum write_one_status status;
  	struct git_pack_header ph;
  	git_oid entry_oid;
  	size_t i = 0;
  	int error = 0;
  
  	write_order = compute_write_order(pb);
  	if (write_order == NULL)
  		return -1;
  
  	if (!git__is_uint32(pb->nr_objects)) {
  		git_error_set(GIT_ERROR_INVALID, "too many objects");
  		return -1;
  	}
  
  	/* Write pack header */
  	ph.hdr_signature = htonl(PACK_SIGNATURE);
  	ph.hdr_version = htonl(PACK_VERSION);
  	ph.hdr_entries = htonl(pb->nr_objects);
  
  	if ((error = write_cb(&ph, sizeof(ph), cb_data)) < 0 ||
  		(error = git_hash_update(&pb->ctx, &ph, sizeof(ph))) < 0)
  		goto done;
  
  	pb->nr_remaining = pb->nr_objects;
  	do {
  		pb->nr_written = 0;
  		for ( ; i < pb->nr_objects; ++i) {
  			po = write_order[i];
  
  			if ((error = write_one(&status, pb, po, write_cb, cb_data)) < 0)
  				goto done;
  		}
  
  		pb->nr_remaining -= pb->nr_written;
  	} while (pb->nr_remaining && i < pb->nr_objects);
  
  	if ((error = git_hash_final(&entry_oid, &pb->ctx)) < 0)
  		goto done;
  
  	error = write_cb(entry_oid.id, GIT_OID_RAWSZ, cb_data);
  
  done:
  	/* if callback cancelled writing, we must still free delta_data */
  	for ( ; i < pb->nr_objects; ++i) {
  		po = write_order[i];
  		if (po->delta_data) {
  			git__free(po->delta_data);
  			po->delta_data = NULL;
  		}
  	}
  
  	git__free(write_order);
  	return error;
  }
  
  static int write_pack_buf(void *buf, size_t size, void *data)
  {
  	git_buf *b = (git_buf *)data;
  	return git_buf_put(b, buf, size);
  }
  
  static int type_size_sort(const void *_a, const void *_b)
  {
  	const git_pobject *a = (git_pobject *)_a;
  	const git_pobject *b = (git_pobject *)_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;
  	/*
  	 * TODO
  	 *
  	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 */
  }
  
  static int delta_cacheable(
  	git_packbuilder *pb,
  	size_t src_size,
  	size_t trg_size,
  	size_t delta_size)
  {
  	size_t new_size;
  
  	if (git__add_sizet_overflow(&new_size, pb->delta_cache_size, delta_size))
  		return 0;
  
  	if (pb->max_delta_cache_size && new_size > pb->max_delta_cache_size)
  		return 0;
  
  	if (delta_size < pb->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;
  }
  
  static int try_delta(git_packbuilder *pb, struct unpacked *trg,
  		     struct unpacked *src, size_t max_depth,
  			 size_t *mem_usage, int *ret)
  {
  	git_pobject *trg_object = trg->object;
  	git_pobject *src_object = src->object;
  	git_odb_object *obj;
  	size_t trg_size, src_size, delta_size, sizediff, max_size, sz;
  	size_t ref_depth;
  	void *delta_buf;
  
  	/* Don't bother doing diffs between different types */
  	if (trg_object->type != src_object->type) {
  		*ret = -1;
  		return 0;
  	}
  
  	*ret = 0;
  
  	/* TODO: support reuse-delta */
  
  	/* Let's not bust the allowed depth. */
  	if (src->depth >= max_depth)
  		return 0;
  
  	/* Now some size filtering heuristics. */
  	trg_size = trg_object->size;
  	if (!trg_object->delta) {
  		max_size = trg_size/2 - 20;
  		ref_depth = 1;
  	} else {
  		max_size = trg_object->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_object->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) {
  		if (git_odb_read(&obj, pb->odb, &trg_object->id) < 0)
  			return -1;
  
  		sz = git_odb_object_size(obj);
  		trg->data = git__malloc(sz);
  		GIT_ERROR_CHECK_ALLOC(trg->data);
  		memcpy(trg->data, git_odb_object_data(obj), sz);
  
  		git_odb_object_free(obj);
  
  		if (sz != trg_size) {
  			git_error_set(GIT_ERROR_INVALID,
  				   "inconsistent target object length");
  			return -1;
  		}
  
  		*mem_usage += sz;
  	}
  	if (!src->data) {
  		size_t obj_sz;
  
  		if (git_odb_read(&obj, pb->odb, &src_object->id) < 0 ||
  			!git__is_ulong(obj_sz = git_odb_object_size(obj)))
  			return -1;
  
  		sz = obj_sz;
  		src->data = git__malloc(sz);
  		GIT_ERROR_CHECK_ALLOC(src->data);
  		memcpy(src->data, git_odb_object_data(obj), sz);
  
  		git_odb_object_free(obj);
  
  		if (sz != src_size) {
  			git_error_set(GIT_ERROR_INVALID,
  				   "inconsistent source object length");
  			return -1;
  		}
  
  		*mem_usage += sz;
  	}
  	if (!src->index) {
  		if (git_delta_index_init(&src->index, src->data, src_size) < 0)
  			return 0; /* suboptimal pack - out of memory */
  
  		*mem_usage += git_delta_index_size(src->index);
  	}
  
  	if (git_delta_create_from_index(&delta_buf, &delta_size, src->index, trg->data, trg_size,
  		max_size) < 0)
  		return 0;
  
  	if (trg_object->delta) {
  		/* Prefer only shallower same-sized deltas. */
  		if (delta_size == trg_object->delta_size &&
  		    src->depth + 1 >= trg->depth) {
  			git__free(delta_buf);
  			return 0;
  		}
  	}
  
  	git_packbuilder__cache_lock(pb);
  	if (trg_object->delta_data) {
  		git__free(trg_object->delta_data);
  		assert(pb->delta_cache_size >= trg_object->delta_size);
  		pb->delta_cache_size -= trg_object->delta_size;
  		trg_object->delta_data = NULL;
  	}
  	if (delta_cacheable(pb, src_size, trg_size, delta_size)) {
  		bool overflow = git__add_sizet_overflow(
  			&pb->delta_cache_size, pb->delta_cache_size, delta_size);
  
  		git_packbuilder__cache_unlock(pb);
  
  		if (overflow) {
  			git__free(delta_buf);
  			return -1;
  		}
  
  		trg_object->delta_data = git__realloc(delta_buf, delta_size);
  		GIT_ERROR_CHECK_ALLOC(trg_object->delta_data);
  	} else {
  		/* create delta when writing the pack */
  		git_packbuilder__cache_unlock(pb);
  		git__free(delta_buf);
  	}
  
  	trg_object->delta = src_object;
  	trg_object->delta_size = delta_size;
  	trg->depth = src->depth + 1;
  
  	*ret = 1;
  	return 0;
  }
  
  static size_t check_delta_limit(git_pobject *me, size_t n)
  {
  	git_pobject *child = me->delta_child;
  	size_t m = n;
  
  	while (child) {
  		size_t c = check_delta_limit(child, n + 1);
  		if (m < c)
  			m = c;
  		child = child->delta_sibling;
  	}
  	return m;
  }
  
  static size_t free_unpacked(struct unpacked *n)
  {
  	size_t freed_mem = 0;
  
  	if (n->index) {
  		freed_mem += git_delta_index_size(n->index);
  		git_delta_index_free(n->index);
  	}
  	n->index = NULL;
  
  	if (n->data) {
  		freed_mem += n->object->size;
  		git__free(n->data);
  		n->data = NULL;
  	}
  	n->object = NULL;
  	n->depth = 0;
  	return freed_mem;
  }
  
  static int report_delta_progress(
  	git_packbuilder *pb, uint32_t count, bool force)
  {
  	int ret;
  
  	if (pb->progress_cb) {
  		double current_time = git__timer();
  		double elapsed = current_time - pb->last_progress_report_time;
  
  		if (force || elapsed >= MIN_PROGRESS_UPDATE_INTERVAL) {
  			pb->last_progress_report_time = current_time;
  
  			ret = pb->progress_cb(
  				GIT_PACKBUILDER_DELTAFICATION,
  				count, pb->nr_objects, pb->progress_cb_payload);
  
  			if (ret)
  				return git_error_set_after_callback(ret);
  		}
  	}
  
  	return 0;
  }
  
  static int find_deltas(git_packbuilder *pb, git_pobject **list,
  	size_t *list_size, size_t window, size_t depth)
  {
  	git_pobject *po;
  	git_buf zbuf = GIT_BUF_INIT;
  	struct unpacked *array;
  	size_t idx = 0, count = 0;
  	size_t mem_usage = 0;
  	size_t i;
  	int error = -1;
  
  	array = git__calloc(window, sizeof(struct unpacked));
  	GIT_ERROR_CHECK_ALLOC(array);
  
  	for (;;) {
  		struct unpacked *n = array + idx;
  		size_t max_depth, j, best_base = SIZE_MAX;
  
  		git_packbuilder__progress_lock(pb);
  		if (!*list_size) {
  			git_packbuilder__progress_unlock(pb);
  			break;
  		}
  
  		pb->nr_deltified += 1;
  		report_delta_progress(pb, pb->nr_deltified, false);
  
  		po = *list++;
  		(*list_size)--;
  		git_packbuilder__progress_unlock(pb);
  
  		mem_usage -= free_unpacked(n);
  		n->object = po;
  
  		while (pb->window_memory_limit &&
  		       mem_usage > pb->window_memory_limit &&
  		       count > 1) {
  			size_t tail = (idx + window - count) % window;
  			mem_usage -= free_unpacked(array + tail);
  			count--;
  		}
  
  		/*
  		 * 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 (po->delta_child) {
  			size_t delta_limit = check_delta_limit(po, 0);
  
  			if (delta_limit > max_depth)
  				goto next;
  
  			max_depth -= delta_limit;
  		}
  
  		j = window;
  		while (--j > 0) {
  			int ret;
  			size_t other_idx = idx + j;
  			struct unpacked *m;
  
  			if (other_idx >= window)
  				other_idx -= window;
  
  			m = array + other_idx;
  			if (!m->object)
  				break;
  
  			if (try_delta(pb, n, m, max_depth, &mem_usage, &ret) < 0)
  				goto on_error;
  			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 (po->delta_data) {
  			if (git_zstream_deflatebuf(&zbuf, po->delta_data, po->delta_size) < 0)
  				goto on_error;
  
  			git__free(po->delta_data);
  			po->delta_data = git__malloc(zbuf.size);
  			GIT_ERROR_CHECK_ALLOC(po->delta_data);
  
  			memcpy(po->delta_data, zbuf.ptr, zbuf.size);
  			po->z_delta_size = zbuf.size;
  			git_buf_clear(&zbuf);
  
  			git_packbuilder__cache_lock(pb);
  			pb->delta_cache_size -= po->delta_size;
  			pb->delta_cache_size += po->z_delta_size;
  			git_packbuilder__cache_unlock(pb);
  		}
  
  		/*
  		 * 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 (po->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 (po->delta) {
  			struct unpacked swap = array[best_base];
  			size_t dist = (window + idx - best_base) % window;
  			size_t dst = best_base;
  			while (dist--) {
  				size_t 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;
  	}
  	error = 0;
  
  on_error:
  	for (i = 0; i < window; ++i) {
  		git__free(array[i].index);
  		git__free(array[i].data);
  	}
  	git__free(array);
  	git_buf_dispose(&zbuf);
  
  	return error;
  }
  
  #ifdef GIT_THREADS
  
  struct thread_params {
  	git_thread thread;
  	git_packbuilder *pb;
  
  	git_pobject **list;
  
  	git_cond cond;
  	git_mutex mutex;
  
  	size_t list_size;
  	size_t remaining;
  
  	size_t window;
  	size_t depth;
  	size_t working;
  	size_t data_ready;
  };
  
  static void *threaded_find_deltas(void *arg)
  {
  	struct thread_params *me = arg;
  
  	while (me->remaining) {
  		if (find_deltas(me->pb, me->list, &me->remaining,
  				me->window, me->depth) < 0) {
  			; /* TODO */
  		}
  
  		git_packbuilder__progress_lock(me->pb);
  		me->working = 0;
  		git_cond_signal(&me->pb->progress_cond);
  		git_packbuilder__progress_unlock(me->pb);
  
  		if (git_mutex_lock(&me->mutex)) {
  			git_error_set(GIT_ERROR_THREAD, "unable to lock packfile condition mutex");
  			return NULL;
  		}
  
  		while (!me->data_ready)
  			git_cond_wait(&me->cond, &me->mutex);
  
  		/*
  		 * 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.
  		 */
  		me->data_ready = 0;
  		git_mutex_unlock(&me->mutex);
  	}
  	/* leave ->working 1 so that this doesn't get more work assigned */
  	return NULL;
  }
  
  static int ll_find_deltas(git_packbuilder *pb, git_pobject **list,
  			  size_t list_size, size_t window, size_t depth)
  {
  	struct thread_params *p;
  	size_t i;
  	int ret, active_threads = 0;
  
  	if (!pb->nr_threads)
  		pb->nr_threads = git_online_cpus();
  
  	if (pb->nr_threads <= 1) {
  		find_deltas(pb, list, &list_size, window, depth);
  		return 0;
  	}
  
  	p = git__mallocarray(pb->nr_threads, sizeof(*p));
  	GIT_ERROR_CHECK_ALLOC(p);
  
  	/* Partition the work among the threads */
  	for (i = 0; i < pb->nr_threads; ++i) {
  		size_t sub_size = list_size / (pb->nr_threads - i);
  
  		/* don't use too small segments or no deltas will be found */
  		if (sub_size < 2*window && i+1 < pb->nr_threads)
  			sub_size = 0;
  
  		p[i].pb = pb;
  		p[i].window = window;
  		p[i].depth = depth;
  		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 < pb->nr_threads; ++i) {
  		if (!p[i].list_size)
  			continue;
  
  		git_mutex_init(&p[i].mutex);
  		git_cond_init(&p[i].cond);
  
  		ret = git_thread_create(&p[i].thread,
  					threaded_find_deltas, &p[i]);
  		if (ret) {
  			git_error_set(GIT_ERROR_THREAD, "unable to create thread");
  			return -1;
  		}
  		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;
  		size_t sub_size = 0;
  
  		/* Start by locating a thread that has transitioned its
  		 * 'working' flag from 1 -> 0. This indicates that it is
  		 * ready to receive more work using our work-stealing
  		 * algorithm. */
  		git_packbuilder__progress_lock(pb);
  		for (;;) {
  			for (i = 0; !target && i < pb->nr_threads; i++)
  				if (!p[i].working)
  					target = &p[i];
  			if (target)
  				break;
  			git_cond_wait(&pb->progress_cond, &pb->progress_mutex);
  		}
  
  		/* At this point we hold the progress lock and have located
  		 * a thread to receive more work. We still need to locate a
  		 * thread from which to steal work (the victim). */
  		for (i = 0; i < pb->nr_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;
  		git_packbuilder__progress_unlock(pb);
  
  		if (git_mutex_lock(&target->mutex)) {
  			git_error_set(GIT_ERROR_THREAD, "unable to lock packfile condition mutex");
  			git__free(p);
  			return -1;
  		}
  
  		target->data_ready = 1;
  		git_cond_signal(&target->cond);
  		git_mutex_unlock(&target->mutex);
  
  		if (!sub_size) {
  			git_thread_join(&target->thread, NULL);
  			git_cond_free(&target->cond);
  			git_mutex_free(&target->mutex);
  			active_threads--;
  		}
  	}
  
  	git__free(p);
  	return 0;
  }
  
  #else
  #define ll_find_deltas(pb, l, ls, w, d) find_deltas(pb, l, &ls, w, d)
  #endif
  
  static int prepare_pack(git_packbuilder *pb)
  {
  	git_pobject **delta_list;
  	size_t i, n = 0;
  
  	if (pb->nr_objects == 0 || pb->done)
  		return 0; /* nothing to do */
  
  	/*
  	 * Although we do not report progress during deltafication, we
  	 * at least report that we are in the deltafication stage
  	 */
  	if (pb->progress_cb)
  			pb->progress_cb(GIT_PACKBUILDER_DELTAFICATION, 0, pb->nr_objects, pb->progress_cb_payload);
  
  	delta_list = git__mallocarray(pb->nr_objects, sizeof(*delta_list));
  	GIT_ERROR_CHECK_ALLOC(delta_list);
  
  	for (i = 0; i < pb->nr_objects; ++i) {
  		git_pobject *po = pb->object_list + i;
  
  		/* Make sure the item is within our size limits */
  		if (po->size < 50 || po->size > pb->big_file_threshold)
  			continue;
  
  		delta_list[n++] = po;
  	}
  
  	if (n > 1) {
  		git__tsort((void **)delta_list, n, type_size_sort);
  		if (ll_find_deltas(pb, delta_list, n,
  				   GIT_PACK_WINDOW + 1,
  				   GIT_PACK_DEPTH) < 0) {
  			git__free(delta_list);
  			return -1;
  		}
  	}
  
  	report_delta_progress(pb, pb->nr_objects, true);
  
  	pb->done = true;
  	git__free(delta_list);
  	return 0;
  }
  
  #define PREPARE_PACK if (prepare_pack(pb) < 0) { return -1; }
  
  int git_packbuilder_foreach(git_packbuilder *pb, int (*cb)(void *buf, size_t size, void *payload), void *payload)
  {
  	PREPARE_PACK;
  	return write_pack(pb, cb, payload);
  }
  
  int git_packbuilder_write_buf(git_buf *buf, git_packbuilder *pb)
  {
  	PREPARE_PACK;
  	git_buf_sanitize(buf);
  	return write_pack(pb, &write_pack_buf, buf);
  }
  
  static int write_cb(void *buf, size_t len, void *payload)
  {
  	struct pack_write_context *ctx = payload;
  	return git_indexer_append(ctx->indexer, buf, len, ctx->stats);
  }
  
  int git_packbuilder_write(
  	git_packbuilder *pb,
  	const char *path,
  	unsigned int mode,
  	git_indexer_progress_cb progress_cb,
  	void *progress_cb_payload)
  {
  	git_indexer_options opts = GIT_INDEXER_OPTIONS_INIT;
  	git_indexer *indexer;
  	git_indexer_progress stats;
  	struct pack_write_context ctx;
  	int t;
  
  	PREPARE_PACK;
  
  	opts.progress_cb = progress_cb;
  	opts.progress_cb_payload = progress_cb_payload;
  
  	if (git_indexer_new(
  		&indexer, path, mode, pb->odb, &opts) < 0)
  		return -1;
  
  	if (!git_repository__configmap_lookup(&t, pb->repo, GIT_CONFIGMAP_FSYNCOBJECTFILES) && t)
  		git_indexer__set_fsync(indexer, 1);
  
  	ctx.indexer = indexer;
  	ctx.stats = &stats;
  
  	if (git_packbuilder_foreach(pb, write_cb, &ctx) < 0 ||
  		git_indexer_commit(indexer, &stats) < 0) {
  		git_indexer_free(indexer);
  		return -1;
  	}
  
  	git_oid_cpy(&pb->pack_oid, git_indexer_hash(indexer));
  
  	git_indexer_free(indexer);
  	return 0;
  }
  
  #undef PREPARE_PACK
  
  const git_oid *git_packbuilder_hash(git_packbuilder *pb)
  {
  	return &pb->pack_oid;
  }
  
  
  static int cb_tree_walk(
  	const char *root, const git_tree_entry *entry, void *payload)
  {
  	int error;
  	struct tree_walk_context *ctx = payload;
  
  	/* A commit inside a tree represents a submodule commit and should be skipped. */
  	if (git_tree_entry_type(entry) == GIT_OBJECT_COMMIT)
  		return 0;
  
  	if (!(error = git_buf_sets(&ctx->buf, root)) &&
  		!(error = git_buf_puts(&ctx->buf, git_tree_entry_name(entry))))
  		error = git_packbuilder_insert(
  			ctx->pb, git_tree_entry_id(entry), git_buf_cstr(&ctx->buf));
  
  	return error;
  }
  
  int git_packbuilder_insert_commit(git_packbuilder *pb, const git_oid *oid)
  {
  	git_commit *commit;
  
  	if (git_commit_lookup(&commit, pb->repo, oid) < 0 ||
  		git_packbuilder_insert(pb, oid, NULL) < 0)
  		return -1;
  
  	if (git_packbuilder_insert_tree(pb, git_commit_tree_id(commit)) < 0)
  		return -1;
  
  	git_commit_free(commit);
  	return 0;
  }
  
  int git_packbuilder_insert_tree(git_packbuilder *pb, const git_oid *oid)
  {
  	int error;
  	git_tree *tree = NULL;
  	struct tree_walk_context context = { pb, GIT_BUF_INIT };
  
  	if (!(error = git_tree_lookup(&tree, pb->repo, oid)) &&
  	    !(error = git_packbuilder_insert(pb, oid, NULL)))
  		error = git_tree_walk(tree, GIT_TREEWALK_PRE, cb_tree_walk, &context);
  
  	git_tree_free(tree);
  	git_buf_dispose(&context.buf);
  	return error;
  }
  
  int git_packbuilder_insert_recur(git_packbuilder *pb, const git_oid *id, const char *name)
  {
  	git_object *obj;
  	int error;
  
  	assert(pb && id);
  
  	if ((error = git_object_lookup(&obj, pb->repo, id, GIT_OBJECT_ANY)) < 0)
  		return error;
  
  	switch (git_object_type(obj)) {
  	case GIT_OBJECT_BLOB:
  		error = git_packbuilder_insert(pb, id, name);
  		break;
  	case GIT_OBJECT_TREE:
  		error = git_packbuilder_insert_tree(pb, id);
  		break;
  	case GIT_OBJECT_COMMIT:
  		error = git_packbuilder_insert_commit(pb, id);
  		break;
  	case GIT_OBJECT_TAG:
  		if ((error = git_packbuilder_insert(pb, id, name)) < 0)
  			goto cleanup;
  		error = git_packbuilder_insert_recur(pb, git_tag_target_id((git_tag *) obj), NULL);
  		break;
  
  	default:
  		git_error_set(GIT_ERROR_INVALID, "unknown object type");
  		error = -1;
  	}
  
  cleanup:
  	git_object_free(obj);
  	return error;
  }
  
  size_t git_packbuilder_object_count(git_packbuilder *pb)
  {
  	return pb->nr_objects;
  }
  
  size_t git_packbuilder_written(git_packbuilder *pb)
  {
  	return pb->nr_written;
  }
  
  static int lookup_walk_object(struct walk_object **out, git_packbuilder *pb, const git_oid *id)
  {
  	struct walk_object *obj;
  
  	obj = git_pool_mallocz(&pb->object_pool, 1);
  	if (!obj) {
  		git_error_set_oom();
  		return -1;
  	}
  
  	git_oid_cpy(&obj->id, id);
  
  	*out = obj;
  	return 0;
  }
  
  static int retrieve_object(struct walk_object **out, git_packbuilder *pb, const git_oid *id)
  {
  	struct walk_object *obj;
  	int error;
  
  	if ((obj = git_oidmap_get(pb->walk_objects, id)) == NULL) {
  		if ((error = lookup_walk_object(&obj, pb, id)) < 0)
  			return error;
  
  		if ((error = git_oidmap_set(pb->walk_objects, &obj->id, obj)) < 0)
  			return error;
  	}
  
  	*out = obj;
  	return 0;
  }
  
  static int mark_blob_uninteresting(git_packbuilder *pb, const git_oid *id)
  {
  	int error;
  	struct walk_object *obj;
  
  	if ((error = retrieve_object(&obj, pb, id)) < 0)
  		return error;
  
  	obj->uninteresting = 1;
  
  	return 0;
  }
  
  static int mark_tree_uninteresting(git_packbuilder *pb, const git_oid *id)
  {
  	struct walk_object *obj;
  	git_tree *tree;
  	int error;
  	size_t i;
  
  	if ((error = retrieve_object(&obj, pb, id)) < 0)
  		return error;
  
  	if (obj->uninteresting)
  		return 0;
  
  	obj->uninteresting = 1;
  
  	if ((error = git_tree_lookup(&tree, pb->repo, id)) < 0)
  		return error;
  
  	for (i = 0; i < git_tree_entrycount(tree); i++) {
  		const git_tree_entry *entry = git_tree_entry_byindex(tree, i);
  		const git_oid *entry_id = git_tree_entry_id(entry);
  		switch (git_tree_entry_type(entry)) {
  		case GIT_OBJECT_TREE:
  			if ((error = mark_tree_uninteresting(pb, entry_id)) < 0)
  				goto cleanup;
  			break;
  		case GIT_OBJECT_BLOB:
  			if ((error = mark_blob_uninteresting(pb, entry_id)) < 0)
  				goto cleanup;
  			break;
  		default:
  			/* it's a submodule or something unknown, we don't want it */
  			;
  		}
  	}
  
  cleanup:
  	git_tree_free(tree);
  	return error;
  }
  
  /*
   * Mark the edges of the graph uninteresting. Since we start from a
   * git_revwalk, the commits are already uninteresting, but we need to
   * mark the trees and blobs.
   */
  static int mark_edges_uninteresting(git_packbuilder *pb, git_commit_list *commits)
  {
  	int error;
  	git_commit_list *list;
  	git_commit *commit;
  
  	for (list = commits; list; list = list->next) {
  		if (!list->item->uninteresting)
  			continue;
  
  		if ((error = git_commit_lookup(&commit, pb->repo, &list->item->oid)) < 0)
  			return error;
  
  		error = mark_tree_uninteresting(pb, git_commit_tree_id(commit));
  		git_commit_free(commit);
  
  		if (error < 0)
  			return error;
  	}
  
  	return 0;
  }
  
  int insert_tree(git_packbuilder *pb, git_tree *tree)
  {
  	size_t i;
  	int error;
  	git_tree *subtree;
  	struct walk_object *obj;
  	const char *name;
  
  	if ((error = retrieve_object(&obj, pb, git_tree_id(tree))) < 0)
  		return error;
  
  	if (obj->seen || obj->uninteresting)
  		return 0;
  
  	obj->seen = 1;
  
  	if ((error = git_packbuilder_insert(pb, &obj->id, NULL)))
  		return error;
  
  	for (i = 0; i < git_tree_entrycount(tree); i++) {
  		const git_tree_entry *entry = git_tree_entry_byindex(tree, i);
  		const git_oid *entry_id = git_tree_entry_id(entry);
  		switch (git_tree_entry_type(entry)) {
  		case GIT_OBJECT_TREE:
  			if ((error = git_tree_lookup(&subtree, pb->repo, entry_id)) < 0)
  				return error;
  
  			error = insert_tree(pb, subtree);
  			git_tree_free(subtree);
  
  			if (error < 0)
  				return error;
  
  			break;
  		case GIT_OBJECT_BLOB:
  			if ((error = retrieve_object(&obj, pb, entry_id)) < 0)
  				return error;
  			if (obj->uninteresting)
  				continue;
  			name = git_tree_entry_name(entry);
  			if ((error = git_packbuilder_insert(pb, entry_id, name)) < 0)
  				return error;
  			break;
  		default:
  			/* it's a submodule or something unknown, we don't want it */
  			;
  		}
  	}
  
  
  	return error;
  }
  
  int insert_commit(git_packbuilder *pb, struct walk_object *obj)
  {
  	int error;
  	git_commit *commit = NULL;
  	git_tree *tree = NULL;
  
  	obj->seen = 1;
  
  	if ((error = git_packbuilder_insert(pb, &obj->id, NULL)) < 0)
  		return error;
  
  	if ((error = git_commit_lookup(&commit, pb->repo, &obj->id)) < 0)
  		return error;
  
  	if ((error = git_tree_lookup(&tree, pb->repo, git_commit_tree_id(commit))) < 0)
  		goto cleanup;
  
  	if ((error = insert_tree(pb, tree)) < 0)
  		goto cleanup;
  
  cleanup:
  	git_commit_free(commit);
  	git_tree_free(tree);
  	return error;
  }
  
  int git_packbuilder_insert_walk(git_packbuilder *pb, git_revwalk *walk)
  {
  	int error;
  	git_oid id;
  	struct walk_object *obj;
  
  	assert(pb && walk);
  
  	if ((error = mark_edges_uninteresting(pb, walk->user_input)) < 0)
  		return error;
  
  	/*
  	 * TODO: git marks the parents of the edges
  	 * uninteresting. This may provide a speed advantage, but does
  	 * seem to assume the remote does not have a single-commit
  	 * history on the other end.
  	 */
  
  	/* walk down each tree up to the blobs and insert them, stopping when uninteresting */
  	while ((error = git_revwalk_next(&id, walk)) == 0) {
  		if ((error = retrieve_object(&obj, pb, &id)) < 0)
  			return error;
  
  		if (obj->seen || obj->uninteresting)
  			continue;
  
  		if ((error = insert_commit(pb, obj)) < 0)
  			return error;
  	}
  
  	if (error == GIT_ITEROVER)
  		error = 0;
  
  	return error;
  }
  
  int git_packbuilder_set_callbacks(git_packbuilder *pb, git_packbuilder_progress progress_cb, void *progress_cb_payload)
  {
  	if (!pb)
  		return -1;
  
  	pb->progress_cb = progress_cb;
  	pb->progress_cb_payload = progress_cb_payload;
  
  	return 0;
  }
  
  void git_packbuilder_free(git_packbuilder *pb)
  {
  	if (pb == NULL)
  		return;
  
  #ifdef GIT_THREADS
  
  	git_mutex_free(&pb->cache_mutex);
  	git_mutex_free(&pb->progress_mutex);
  	git_cond_free(&pb->progress_cond);
  
  #endif
  
  	if (pb->odb)
  		git_odb_free(pb->odb);
  
  	if (pb->object_ix)
  		git_oidmap_free(pb->object_ix);
  
  	if (pb->object_list)
  		git__free(pb->object_list);
  
  	git_oidmap_free(pb->walk_objects);
  	git_pool_clear(&pb->object_pool);
  
  	git_hash_ctx_cleanup(&pb->ctx);
  	git_zstream_free(&pb->zstream);
  
  	git__free(pb);
  }
  

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