1 files changed, 499 insertions, 68 deletions

diff --git a/pack-bitmap.c b/pack-bitmap.c
index bfc1014..9c666cd 100644
--- a/pack-bitmap.c
+++ b/pack-bitmap.c
@@ -13,6 +13,7 @@
 #include "repository.h"
 #include "object-store.h"
 #include "list-objects-filter-options.h"
+#include "midx.h"
 #include "config.h"
 
 /*
@@ -35,8 +36,15 @@ struct stored_bitmap {
  * the active bitmap index is the largest one.
  */
 struct bitmap_index {
-	/* Packfile to which this bitmap index belongs to */
+	/*
+	 * The pack or multi-pack index (MIDX) that this bitmap index belongs
+	 * to.
+	 *
+	 * Exactly one of these must be non-NULL; this specifies the object
+	 * order used to interpret this bitmap.
+	 */
 	struct packed_git *pack;
+	struct multi_pack_index *midx;
 
 	/*
 	 * Mark the first `reuse_objects` in the packfile as reused:
@@ -71,6 +79,9 @@ struct bitmap_index {
 	/* If not NULL, this is a name-hash cache pointing into map. */
 	uint32_t *hashes;
 
+	/* The checksum of the packfile or MIDX; points into map. */
+	const unsigned char *checksum;
+
 	/*
 	 * Extended index.
 	 *
@@ -136,6 +147,13 @@ static struct ewah_bitmap *read_bitmap_1(struct bitmap_index *index)
 	return b;
 }
 
+static uint32_t bitmap_num_objects(struct bitmap_index *index)
+{
+	if (index->midx)
+		return index->midx->num_objects;
+	return index->pack->num_objects;
+}
+
 static int load_bitmap_header(struct bitmap_index *index)
 {
 	struct bitmap_disk_header *header = (void *)index->map;
@@ -154,7 +172,7 @@ static int load_bitmap_header(struct bitmap_index *index)
 	/* Parse known bitmap format options */
 	{
 		uint32_t flags = ntohs(header->options);
-		size_t cache_size = st_mult(index->pack->num_objects, sizeof(uint32_t));
+		size_t cache_size = st_mult(bitmap_num_objects(index), sizeof(uint32_t));
 		unsigned char *index_end = index->map + index->map_size - the_hash_algo->rawsz;
 
 		if ((flags & BITMAP_OPT_FULL_DAG) == 0)
@@ -170,6 +188,7 @@ static int load_bitmap_header(struct bitmap_index *index)
 	}
 
 	index->entry_count = ntohl(header->entry_count);
+	index->checksum = header->checksum;
 	index->map_pos += header_size;
 	return 0;
 }
@@ -218,6 +237,15 @@ static inline uint8_t read_u8(const unsigned char *buffer, size_t *pos)
 
 #define MAX_XOR_OFFSET 160
 
+static int nth_bitmap_object_oid(struct bitmap_index *index,
+				 struct object_id *oid,
+				 uint32_t n)
+{
+	if (index->midx)
+		return nth_midxed_object_oid(oid, index->midx, n) ? 0 : -1;
+	return nth_packed_object_id(oid, index->pack, n);
+}
+
 static int load_bitmap_entries_v1(struct bitmap_index *index)
 {
 	uint32_t i;
@@ -237,7 +265,7 @@ static int load_bitmap_entries_v1(struct bitmap_index *index)
 		xor_offset = read_u8(index->map, &index->map_pos);
 		flags = read_u8(index->map, &index->map_pos);
 
-		if (nth_packed_object_id(&oid, index->pack, commit_idx_pos) < 0)
+		if (nth_bitmap_object_oid(index, &oid, commit_idx_pos) < 0)
 			return error("corrupt ewah bitmap: commit index %u out of range",
 				     (unsigned)commit_idx_pos);
 
@@ -262,7 +290,17 @@ static int load_bitmap_entries_v1(struct bitmap_index *index)
 	return 0;
 }
 
-static char *pack_bitmap_filename(struct packed_git *p)
+char *midx_bitmap_filename(struct multi_pack_index *midx)
+{
+	struct strbuf buf = STRBUF_INIT;
+
+	get_midx_filename(&buf, midx->object_dir);
+	strbuf_addf(&buf, "-%s.bitmap", hash_to_hex(get_midx_checksum(midx)));
+
+	return strbuf_detach(&buf, NULL);
+}
+
+char *pack_bitmap_filename(struct packed_git *p)
 {
 	size_t len;
 
@@ -271,6 +309,61 @@ static char *pack_bitmap_filename(struct packed_git *p)
 	return xstrfmt("%.*s.bitmap", (int)len, p->pack_name);
 }
 
+static int open_midx_bitmap_1(struct bitmap_index *bitmap_git,
+			      struct multi_pack_index *midx)
+{
+	struct stat st;
+	char *idx_name = midx_bitmap_filename(midx);
+	int fd = git_open(idx_name);
+
+	free(idx_name);
+
+	if (fd < 0)
+		return -1;
+
+	if (fstat(fd, &st)) {
+		close(fd);
+		return -1;
+	}
+
+	if (bitmap_git->pack || bitmap_git->midx) {
+		struct strbuf buf = STRBUF_INIT;
+		get_midx_filename(&buf, midx->object_dir);
+		/* ignore extra bitmap file; we can only handle one */
+		warning("ignoring extra bitmap file: %s", buf.buf);
+		close(fd);
+		strbuf_release(&buf);
+		return -1;
+	}
+
+	bitmap_git->midx = midx;
+	bitmap_git->map_size = xsize_t(st.st_size);
+	bitmap_git->map_pos = 0;
+	bitmap_git->map = xmmap(NULL, bitmap_git->map_size, PROT_READ,
+				MAP_PRIVATE, fd, 0);
+	close(fd);
+
+	if (load_bitmap_header(bitmap_git) < 0)
+		goto cleanup;
+
+	if (!hasheq(get_midx_checksum(bitmap_git->midx), bitmap_git->checksum))
+		goto cleanup;
+
+	if (load_midx_revindex(bitmap_git->midx) < 0) {
+		warning(_("multi-pack bitmap is missing required reverse index"));
+		goto cleanup;
+	}
+	return 0;
+
+cleanup:
+	munmap(bitmap_git->map, bitmap_git->map_size);
+	bitmap_git->map_size = 0;
+	bitmap_git->map_pos = 0;
+	bitmap_git->map = NULL;
+	bitmap_git->midx = NULL;
+	return -1;
+}
+
 static int open_pack_bitmap_1(struct bitmap_index *bitmap_git, struct packed_git *packfile)
 {
 	int fd;
@@ -292,12 +385,18 @@ static int open_pack_bitmap_1(struct bitmap_index *bitmap_git, struct packed_git
 		return -1;
 	}
 
-	if (bitmap_git->pack) {
+	if (bitmap_git->pack || bitmap_git->midx) {
+		/* ignore extra bitmap file; we can only handle one */
 		warning("ignoring extra bitmap file: %s", packfile->pack_name);
 		close(fd);
 		return -1;
 	}
 
+	if (!is_pack_valid(packfile)) {
+		close(fd);
+		return -1;
+	}
+
 	bitmap_git->pack = packfile;
 	bitmap_git->map_size = xsize_t(st.st_size);
 	bitmap_git->map = xmmap(NULL, bitmap_git->map_size, PROT_READ, MAP_PRIVATE, fd, 0);
@@ -308,19 +407,47 @@ static int open_pack_bitmap_1(struct bitmap_index *bitmap_git, struct packed_git
 		munmap(bitmap_git->map, bitmap_git->map_size);
 		bitmap_git->map = NULL;
 		bitmap_git->map_size = 0;
+		bitmap_git->map_pos = 0;
+		bitmap_git->pack = NULL;
 		return -1;
 	}
 
 	return 0;
 }
 
-static int load_pack_bitmap(struct bitmap_index *bitmap_git)
+static int load_reverse_index(struct bitmap_index *bitmap_git)
+{
+	if (bitmap_is_midx(bitmap_git)) {
+		uint32_t i;
+		int ret;
+
+		/*
+		 * The multi-pack-index's .rev file is already loaded via
+		 * open_pack_bitmap_1().
+		 *
+		 * But we still need to open the individual pack .rev files,
+		 * since we will need to make use of them in pack-objects.
+		 */
+		for (i = 0; i < bitmap_git->midx->num_packs; i++) {
+			if (prepare_midx_pack(the_repository, bitmap_git->midx, i))
+				die(_("load_reverse_index: could not open pack"));
+			ret = load_pack_revindex(bitmap_git->midx->packs[i]);
+			if (ret)
+				return ret;
+		}
+		return 0;
+	}
+	return load_pack_revindex(bitmap_git->pack);
+}
+
+static int load_bitmap(struct bitmap_index *bitmap_git)
 {
 	assert(bitmap_git->map);
 
 	bitmap_git->bitmaps = kh_init_oid_map();
 	bitmap_git->ext_index.positions = kh_init_oid_pos();
-	if (load_pack_revindex(bitmap_git->pack))
+
+	if (load_reverse_index(bitmap_git))
 		goto failed;
 
 	if (!(bitmap_git->commits = read_bitmap_1(bitmap_git)) ||
@@ -364,11 +491,46 @@ static int open_pack_bitmap(struct repository *r,
 	return ret;
 }
 
+static int open_midx_bitmap(struct repository *r,
+			    struct bitmap_index *bitmap_git)
+{
+	struct multi_pack_index *midx;
+
+	assert(!bitmap_git->map);
+
+	for (midx = get_multi_pack_index(r); midx; midx = midx->next) {
+		if (!open_midx_bitmap_1(bitmap_git, midx))
+			return 0;
+	}
+	return -1;
+}
+
+static int open_bitmap(struct repository *r,
+		       struct bitmap_index *bitmap_git)
+{
+	assert(!bitmap_git->map);
+
+	if (!open_midx_bitmap(r, bitmap_git))
+		return 0;
+	return open_pack_bitmap(r, bitmap_git);
+}
+
 struct bitmap_index *prepare_bitmap_git(struct repository *r)
 {
 	struct bitmap_index *bitmap_git = xcalloc(1, sizeof(*bitmap_git));
 
-	if (!open_pack_bitmap(r, bitmap_git) && !load_pack_bitmap(bitmap_git))
+	if (!open_bitmap(r, bitmap_git) && !load_bitmap(bitmap_git))
+		return bitmap_git;
+
+	free_bitmap_index(bitmap_git);
+	return NULL;
+}
+
+struct bitmap_index *prepare_midx_bitmap_git(struct multi_pack_index *midx)
+{
+	struct bitmap_index *bitmap_git = xcalloc(1, sizeof(*bitmap_git));
+
+	if (!open_midx_bitmap_1(bitmap_git, midx) && !load_bitmap(bitmap_git))
 		return bitmap_git;
 
 	free_bitmap_index(bitmap_git);
@@ -399,7 +561,7 @@ static inline int bitmap_position_extended(struct bitmap_index *bitmap_git,
 
 	if (pos < kh_end(positions)) {
 		int bitmap_pos = kh_value(positions, pos);
-		return bitmap_pos + bitmap_git->pack->num_objects;
+		return bitmap_pos + bitmap_num_objects(bitmap_git);
 	}
 
 	return -1;
@@ -418,10 +580,26 @@ static inline int bitmap_position_packfile(struct bitmap_index *bitmap_git,
 	return pos;
 }
 
+static int bitmap_position_midx(struct bitmap_index *bitmap_git,
+				const struct object_id *oid)
+{
+	uint32_t want, got;
+	if (!bsearch_midx(oid, bitmap_git->midx, &want))
+		return -1;
+
+	if (midx_to_pack_pos(bitmap_git->midx, want, &got) < 0)
+		return -1;
+	return got;
+}
+
 static int bitmap_position(struct bitmap_index *bitmap_git,
 			   const struct object_id *oid)
 {
-	int pos = bitmap_position_packfile(bitmap_git, oid);
+	int pos;
+	if (bitmap_is_midx(bitmap_git))
+		pos = bitmap_position_midx(bitmap_git, oid);
+	else
+		pos = bitmap_position_packfile(bitmap_git, oid);
 	return (pos >= 0) ? pos : bitmap_position_extended(bitmap_git, oid);
 }
 
@@ -451,7 +629,7 @@ static int ext_index_add_object(struct bitmap_index *bitmap_git,
 		bitmap_pos = kh_value(eindex->positions, hash_pos);
 	}
 
-	return bitmap_pos + bitmap_git->pack->num_objects;
+	return bitmap_pos + bitmap_num_objects(bitmap_git);
 }
 
 struct bitmap_show_data {
@@ -668,7 +846,7 @@ static void show_extended_objects(struct bitmap_index *bitmap_git,
 	for (i = 0; i < eindex->count; ++i) {
 		struct object *obj;
 
-		if (!bitmap_get(objects, bitmap_git->pack->num_objects + i))
+		if (!bitmap_get(objects, bitmap_num_objects(bitmap_git) + i))
 			continue;
 
 		obj = eindex->objects[i];
@@ -732,6 +910,7 @@ static void show_objects_for_type(
 			continue;
 
 		for (offset = 0; offset < BITS_IN_EWORD; ++offset) {
+			struct packed_git *pack;
 			struct object_id oid;
 			uint32_t hash = 0, index_pos;
 			off_t ofs;
@@ -741,14 +920,28 @@ static void show_objects_for_type(
 
 			offset += ewah_bit_ctz64(word >> offset);
 
-			index_pos = pack_pos_to_index(bitmap_git->pack, pos + offset);
-			ofs = pack_pos_to_offset(bitmap_git->pack, pos + offset);
-			nth_packed_object_id(&oid, bitmap_git->pack, index_pos);
+			if (bitmap_is_midx(bitmap_git)) {
+				struct multi_pack_index *m = bitmap_git->midx;
+				uint32_t pack_id;
+
+				index_pos = pack_pos_to_midx(m, pos + offset);
+				ofs = nth_midxed_offset(m, index_pos);
+				nth_midxed_object_oid(&oid, m, index_pos);
+
+				pack_id = nth_midxed_pack_int_id(m, index_pos);
+				pack = bitmap_git->midx->packs[pack_id];
+			} else {
+				index_pos = pack_pos_to_index(bitmap_git->pack, pos + offset);
+				ofs = pack_pos_to_offset(bitmap_git->pack, pos + offset);
+				nth_bitmap_object_oid(bitmap_git, &oid, index_pos);
+
+				pack = bitmap_git->pack;
+			}
 
 			if (bitmap_git->hashes)
 				hash = get_be32(bitmap_git->hashes + index_pos);
 
-			show_reach(&oid, object_type, 0, hash, bitmap_git->pack, ofs);
+			show_reach(&oid, object_type, 0, hash, pack, ofs);
 		}
 	}
 }
@@ -760,8 +953,13 @@ static int in_bitmapped_pack(struct bitmap_index *bitmap_git,
 		struct object *object = roots->item;
 		roots = roots->next;
 
-		if (find_pack_entry_one(object->oid.hash, bitmap_git->pack) > 0)
-			return 1;
+		if (bitmap_is_midx(bitmap_git)) {
+			if (bsearch_midx(&object->oid, bitmap_git->midx, NULL))
+				return 1;
+		} else {
+			if (find_pack_entry_one(object->oid.hash, bitmap_git->pack) > 0)
+				return 1;
+		}
 	}
 
 	return 0;
@@ -809,8 +1007,9 @@ static void filter_bitmap_exclude_type(struct bitmap_index *bitmap_git,
 	tips = find_tip_objects(bitmap_git, tip_objects, type);
 
 	/*
-	 * We can use the blob type-bitmap to work in whole words
-	 * for the objects that are actually in the bitmapped packfile.
+	 * We can use the type-level bitmap for 'type' to work in whole
+	 * words for the objects that are actually in the bitmapped
+	 * packfile.
 	 */
 	for (i = 0, init_type_iterator(&it, bitmap_git, type);
 	     i < to_filter->word_alloc && ewah_iterator_next(&mask, &it);
@@ -821,12 +1020,12 @@ static void filter_bitmap_exclude_type(struct bitmap_index *bitmap_git,
 	}
 
 	/*
-	 * Clear any blobs that weren't in the packfile (and so would not have
-	 * been caught by the loop above. We'll have to check them
-	 * individually.
+	 * Clear any objects that weren't in the packfile (and so would
+	 * not have been caught by the loop above. We'll have to check
+	 * them individually.
 	 */
 	for (i = 0; i < eindex->count; i++) {
-		uint32_t pos = i + bitmap_git->pack->num_objects;
+		uint32_t pos = i + bitmap_num_objects(bitmap_git);
 		if (eindex->objects[i]->type == type &&
 		    bitmap_get(to_filter, pos) &&
 		    !bitmap_get(tips, pos))
@@ -847,23 +1046,35 @@ static void filter_bitmap_blob_none(struct bitmap_index *bitmap_git,
 static unsigned long get_size_by_pos(struct bitmap_index *bitmap_git,
 				     uint32_t pos)
 {
-	struct packed_git *pack = bitmap_git->pack;
 	unsigned long size;
 	struct object_info oi = OBJECT_INFO_INIT;
 
 	oi.sizep = &size;
 
-	if (pos < pack->num_objects) {
-		off_t ofs = pack_pos_to_offset(pack, pos);
+	if (pos < bitmap_num_objects(bitmap_git)) {
+		struct packed_git *pack;
+		off_t ofs;
+
+		if (bitmap_is_midx(bitmap_git)) {
+			uint32_t midx_pos = pack_pos_to_midx(bitmap_git->midx, pos);
+			uint32_t pack_id = nth_midxed_pack_int_id(bitmap_git->midx, midx_pos);
+
+			pack = bitmap_git->midx->packs[pack_id];
+			ofs = nth_midxed_offset(bitmap_git->midx, midx_pos);
+		} else {
+			pack = bitmap_git->pack;
+			ofs = pack_pos_to_offset(pack, pos);
+		}
+
 		if (packed_object_info(the_repository, pack, ofs, &oi) < 0) {
 			struct object_id oid;
-			nth_packed_object_id(&oid, pack,
-					     pack_pos_to_index(pack, pos));
+			nth_bitmap_object_oid(bitmap_git, &oid,
+					      pack_pos_to_index(pack, pos));
 			die(_("unable to get size of %s"), oid_to_hex(&oid));
 		}
 	} else {
 		struct eindex *eindex = &bitmap_git->ext_index;
-		struct object *obj = eindex->objects[pos - pack->num_objects];
+		struct object *obj = eindex->objects[pos - bitmap_num_objects(bitmap_git)];
 		if (oid_object_info_extended(the_repository, &obj->oid, &oi, 0) < 0)
 			die(_("unable to get size of %s"), oid_to_hex(&obj->oid));
 	}
@@ -905,7 +1116,7 @@ static void filter_bitmap_blob_limit(struct bitmap_index *bitmap_git,
 	}
 
 	for (i = 0; i < eindex->count; i++) {
-		uint32_t pos = i + bitmap_git->pack->num_objects;
+		uint32_t pos = i + bitmap_num_objects(bitmap_git);
 		if (eindex->objects[i]->type == OBJ_BLOB &&
 		    bitmap_get(to_filter, pos) &&
 		    !bitmap_get(tips, pos) &&
@@ -1035,7 +1246,7 @@ struct bitmap_index *prepare_bitmap_walk(struct rev_info *revs,
 	/* try to open a bitmapped pack, but don't parse it yet
 	 * because we may not need to use it */
 	CALLOC_ARRAY(bitmap_git, 1);
-	if (open_pack_bitmap(revs->repo, bitmap_git) < 0)
+	if (open_bitmap(revs->repo, bitmap_git) < 0)
 		goto cleanup;
 
 	for (i = 0; i < revs->pending.nr; ++i) {
@@ -1079,7 +1290,7 @@ struct bitmap_index *prepare_bitmap_walk(struct rev_info *revs,
 	 * from disk. this is the point of no return; after this the rev_list
 	 * becomes invalidated and we must perform the revwalk through bitmaps
 	 */
-	if (load_pack_bitmap(bitmap_git) < 0)
+	if (load_bitmap(bitmap_git) < 0)
 		goto cleanup;
 
 	object_array_clear(&revs->pending);
@@ -1122,22 +1333,49 @@ cleanup:
 	return NULL;
 }
 
-static void try_partial_reuse(struct bitmap_index *bitmap_git,
-			      size_t pos,
-			      struct bitmap *reuse,
-			      struct pack_window **w_curs)
+/*
+ * -1 means "stop trying further objects"; 0 means we may or may not have
+ * reused, but you can keep feeding bits.
+ */
+static int try_partial_reuse(struct packed_git *pack,
+			     size_t pos,
+			     struct bitmap *reuse,
+			     struct pack_window **w_curs)
 {
-	off_t offset, header;
+	off_t offset, delta_obj_offset;
 	enum object_type type;
 	unsigned long size;
 
-	if (pos >= bitmap_git->pack->num_objects)
-		return; /* not actually in the pack */
+	/*
+	 * try_partial_reuse() is called either on (a) objects in the
+	 * bitmapped pack (in the case of a single-pack bitmap) or (b)
+	 * objects in the preferred pack of a multi-pack bitmap.
+	 * Importantly, the latter can pretend as if only a single pack
+	 * exists because:
+	 *
+	 *   - The first pack->num_objects bits of a MIDX bitmap are
+	 *     reserved for the preferred pack, and
+	 *
+	 *   - Ties due to duplicate objects are always resolved in
+	 *     favor of the preferred pack.
+	 *
+	 * Therefore we do not need to ever ask the MIDX for its copy of
+	 * an object by OID, since it will always select it from the
+	 * preferred pack. Likewise, the selected copy of the base
+	 * object for any deltas will reside in the same pack.
+	 *
+	 * This means that we can reuse pos when looking up the bit in
+	 * the reuse bitmap, too, since bits corresponding to the
+	 * preferred pack precede all bits from other packs.
+	 */
+
+	if (pos >= pack->num_objects)
+		return -1; /* not actually in the pack or MIDX preferred pack */
 
-	offset = header = pack_pos_to_offset(bitmap_git->pack, pos);
-	type = unpack_object_header(bitmap_git->pack, w_curs, &offset, &size);
+	offset = delta_obj_offset = pack_pos_to_offset(pack, pos);
+	type = unpack_object_header(pack, w_curs, &offset, &size);
 	if (type < 0)
-		return; /* broken packfile, punt */
+		return -1; /* broken packfile, punt */
 
 	if (type == OBJ_REF_DELTA || type == OBJ_OFS_DELTA) {
 		off_t base_offset;
@@ -1151,12 +1389,12 @@ static void try_partial_reuse(struct bitmap_index *bitmap_git,
 		 * and the normal slow path will complain about it in
 		 * more detail.
 		 */
-		base_offset = get_delta_base(bitmap_git->pack, w_curs,
-					     &offset, type, header);
+		base_offset = get_delta_base(pack, w_curs, &offset, type,
+					     delta_obj_offset);
 		if (!base_offset)
-			return;
-		if (offset_to_pack_pos(bitmap_git->pack, base_offset, &base_pos) < 0)
-			return;
+			return 0;
+		if (offset_to_pack_pos(pack, base_offset, &base_pos) < 0)
+			return 0;
 
 		/*
 		 * We assume delta dependencies always point backwards. This
@@ -1168,7 +1406,7 @@ static void try_partial_reuse(struct bitmap_index *bitmap_git,
 		 * odd parameters.
 		 */
 		if (base_pos >= pos)
-			return;
+			return 0;
 
 		/*
 		 * And finally, if we're not sending the base as part of our
@@ -1179,13 +1417,22 @@ static void try_partial_reuse(struct bitmap_index *bitmap_git,
 		 * object_entry code path handle it.
 		 */
 		if (!bitmap_get(reuse, base_pos))
-			return;
+			return 0;
 	}
 
 	/*
 	 * If we got here, then the object is OK to reuse. Mark it.
 	 */
 	bitmap_set(reuse, pos);
+	return 0;
+}
+
+uint32_t midx_preferred_pack(struct bitmap_index *bitmap_git)
+{
+	struct multi_pack_index *m = bitmap_git->midx;
+	if (!m)
+		BUG("midx_preferred_pack: requires non-empty MIDX");
+	return nth_midxed_pack_int_id(m, pack_pos_to_midx(bitmap_git->midx, 0));
 }
 
 int reuse_partial_packfile_from_bitmap(struct bitmap_index *bitmap_git,
@@ -1193,20 +1440,37 @@ int reuse_partial_packfile_from_bitmap(struct bitmap_index *bitmap_git,
 				       uint32_t *entries,
 				       struct bitmap **reuse_out)
 {
+	struct packed_git *pack;
 	struct bitmap *result = bitmap_git->result;
 	struct bitmap *reuse;
 	struct pack_window *w_curs = NULL;
 	size_t i = 0;
 	uint32_t offset;
+	uint32_t objects_nr;
 
 	assert(result);
 
+	load_reverse_index(bitmap_git);
+
+	if (bitmap_is_midx(bitmap_git))
+		pack = bitmap_git->midx->packs[midx_preferred_pack(bitmap_git)];
+	else
+		pack = bitmap_git->pack;
+	objects_nr = pack->num_objects;
+
 	while (i < result->word_alloc && result->words[i] == (eword_t)~0)
 		i++;
 
-	/* Don't mark objects not in the packfile */
-	if (i > bitmap_git->pack->num_objects / BITS_IN_EWORD)
-		i = bitmap_git->pack->num_objects / BITS_IN_EWORD;
+	/*
+	 * Don't mark objects not in the packfile or preferred pack. This bitmap
+	 * marks objects eligible for reuse, but the pack-reuse code only
+	 * understands how to reuse a single pack. Since the preferred pack is
+	 * guaranteed to have all bases for its deltas (in a multi-pack bitmap),
+	 * we use it instead of another pack. In single-pack bitmaps, the choice
+	 * is made for us.
+	 */
+	if (i > objects_nr / BITS_IN_EWORD)
+		i = objects_nr / BITS_IN_EWORD;
 
 	reuse = bitmap_word_alloc(i);
 	memset(reuse->words, 0xFF, i * sizeof(eword_t));
@@ -1220,10 +1484,23 @@ int reuse_partial_packfile_from_bitmap(struct bitmap_index *bitmap_git,
 				break;
 
 			offset += ewah_bit_ctz64(word >> offset);
-			try_partial_reuse(bitmap_git, pos + offset, reuse, &w_curs);
+			if (try_partial_reuse(pack, pos + offset,
+					      reuse, &w_curs) < 0) {
+				/*
+				 * try_partial_reuse indicated we couldn't reuse
+				 * any bits, so there is no point in trying more
+				 * bits in the current word, or any other words
+				 * in result.
+				 *
+				 * Jump out of both loops to avoid future
+				 * unnecessary calls to try_partial_reuse.
+				 */
+				goto done;
+			}
 		}
 	}
 
+done:
 	unuse_pack(&w_curs);
 
 	*entries = bitmap_popcount(reuse);
@@ -1237,7 +1514,7 @@ int reuse_partial_packfile_from_bitmap(struct bitmap_index *bitmap_git,
 	 * need to be handled separately.
 	 */
 	bitmap_and_not(result, reuse);
-	*packfile_out = bitmap_git->pack;
+	*packfile_out = pack;
 	*reuse_out = reuse;
 	return 0;
 }
@@ -1290,7 +1567,7 @@ static uint32_t count_object_type(struct bitmap_index *bitmap_git,
 
 	for (i = 0; i < eindex->count; ++i) {
 		if (eindex->objects[i]->type == type &&
-			bitmap_get(objects, bitmap_git->pack->num_objects + i))
+			bitmap_get(objects, bitmap_num_objects(bitmap_git) + i))
 			count++;
 	}
 
@@ -1319,10 +1596,52 @@ void count_bitmap_commit_list(struct bitmap_index *bitmap_git,
 struct bitmap_test_data {
 	struct bitmap_index *bitmap_git;
 	struct bitmap *base;
+	struct bitmap *commits;
+	struct bitmap *trees;
+	struct bitmap *blobs;
+	struct bitmap *tags;
 	struct progress *prg;
 	size_t seen;
 };
 
+static void test_bitmap_type(struct bitmap_test_data *tdata,
+			     struct object *obj, int pos)
+{
+	enum object_type bitmap_type = OBJ_NONE;
+	int bitmaps_nr = 0;
+
+	if (bitmap_get(tdata->commits, pos)) {
+		bitmap_type = OBJ_COMMIT;
+		bitmaps_nr++;
+	}
+	if (bitmap_get(tdata->trees, pos)) {
+		bitmap_type = OBJ_TREE;
+		bitmaps_nr++;
+	}
+	if (bitmap_get(tdata->blobs, pos)) {
+		bitmap_type = OBJ_BLOB;
+		bitmaps_nr++;
+	}
+	if (bitmap_get(tdata->tags, pos)) {
+		bitmap_type = OBJ_TAG;
+		bitmaps_nr++;
+	}
+
+	if (bitmap_type == OBJ_NONE)
+		die("object %s not found in type bitmaps",
+		    oid_to_hex(&obj->oid));
+
+	if (bitmaps_nr > 1)
+		die("object %s does not have a unique type",
+		    oid_to_hex(&obj->oid));
+
+	if (bitmap_type != obj->type)
+		die("object %s: real type %s, expected: %s",
+		    oid_to_hex(&obj->oid),
+		    type_name(obj->type),
+		    type_name(bitmap_type));
+}
+
 static void test_show_object(struct object *object, const char *name,
 			     void *data)
 {
@@ -1332,6 +1651,7 @@ static void test_show_object(struct object *object, const char *name,
 	bitmap_pos = bitmap_position(tdata->bitmap_git, &object->oid);
 	if (bitmap_pos < 0)
 		die("Object not in bitmap: %s\n", oid_to_hex(&object->oid));
+	test_bitmap_type(tdata, object, bitmap_pos);
 
 	bitmap_set(tdata->base, bitmap_pos);
 	display_progress(tdata->prg, ++tdata->seen);
@@ -1346,6 +1666,7 @@ static void test_show_commit(struct commit *commit, void *data)
 				     &commit->object.oid);
 	if (bitmap_pos < 0)
 		die("Object not in bitmap: %s\n", oid_to_hex(&commit->object.oid));
+	test_bitmap_type(tdata, &commit->object, bitmap_pos);
 
 	bitmap_set(tdata->base, bitmap_pos);
 	display_progress(tdata->prg, ++tdata->seen);
@@ -1393,6 +1714,10 @@ void test_bitmap_walk(struct rev_info *revs)
 
 	tdata.bitmap_git = bitmap_git;
 	tdata.base = bitmap_new();
+	tdata.commits = ewah_to_bitmap(bitmap_git->commits);
+	tdata.trees = ewah_to_bitmap(bitmap_git->trees);
+	tdata.blobs = ewah_to_bitmap(bitmap_git->blobs);
+	tdata.tags = ewah_to_bitmap(bitmap_git->tags);
 	tdata.prg = start_progress("Verifying bitmap entries", result_popcnt);
 	tdata.seen = 0;
 
@@ -1405,6 +1730,12 @@ void test_bitmap_walk(struct rev_info *revs)
 	else
 		die("mismatch in bitmap results");
 
+	bitmap_free(result);
+	bitmap_free(tdata.base);
+	bitmap_free(tdata.commits);
+	bitmap_free(tdata.trees);
+	bitmap_free(tdata.blobs);
+	bitmap_free(tdata.tags);
 	free_bitmap_index(bitmap_git);
 }
 
@@ -1426,6 +1757,33 @@ int test_bitmap_commits(struct repository *r)
 	return 0;
 }
 
+int test_bitmap_hashes(struct repository *r)
+{
+	struct bitmap_index *bitmap_git = prepare_bitmap_git(r);
+	struct object_id oid;
+	uint32_t i, index_pos;
+
+	if (!bitmap_git || !bitmap_git->hashes)
+		goto cleanup;
+
+	for (i = 0; i < bitmap_num_objects(bitmap_git); i++) {
+		if (bitmap_is_midx(bitmap_git))
+			index_pos = pack_pos_to_midx(bitmap_git->midx, i);
+		else
+			index_pos = pack_pos_to_index(bitmap_git->pack, i);
+
+		nth_bitmap_object_oid(bitmap_git, &oid, index_pos);
+
+		printf("%s %"PRIu32"\n",
+		       oid_to_hex(&oid), get_be32(bitmap_git->hashes + index_pos));
+	}
+
+cleanup:
+	free_bitmap_index(bitmap_git);
+
+	return 0;
+}
+
 int rebuild_bitmap(const uint32_t *reposition,
 		   struct ewah_bitmap *source,
 		   struct bitmap *dest)
@@ -1463,19 +1821,32 @@ uint32_t *create_bitmap_mapping(struct bitmap_index *bitmap_git,
 	uint32_t i, num_objects;
 	uint32_t *reposition;
 
-	num_objects = bitmap_git->pack->num_objects;
+	if (!bitmap_is_midx(bitmap_git))
+		load_reverse_index(bitmap_git);
+	else if (load_midx_revindex(bitmap_git->midx) < 0)
+		BUG("rebuild_existing_bitmaps: missing required rev-cache "
+		    "extension");
+
+	num_objects = bitmap_num_objects(bitmap_git);
 	CALLOC_ARRAY(reposition, num_objects);
 
 	for (i = 0; i < num_objects; ++i) {
 		struct object_id oid;
 		struct object_entry *oe;
+		uint32_t index_pos;
 
-		nth_packed_object_id(&oid, bitmap_git->pack,
-				     pack_pos_to_index(bitmap_git->pack, i));
+		if (bitmap_is_midx(bitmap_git))
+			index_pos = pack_pos_to_midx(bitmap_git->midx, i);
+		else
+			index_pos = pack_pos_to_index(bitmap_git->pack, i);
+		nth_bitmap_object_oid(bitmap_git, &oid, index_pos);
 		oe = packlist_find(mapping, &oid);
 
-		if (oe)
+		if (oe) {
 			reposition[i] = oe_in_pack_pos(mapping, oe) + 1;
+			if (bitmap_git->hashes && !oe->hash)
+				oe->hash = get_be32(bitmap_git->hashes + index_pos);
+		}
 	}
 
 	return reposition;
@@ -1492,11 +1863,32 @@ void free_bitmap_index(struct bitmap_index *b)
 	ewah_pool_free(b->trees);
 	ewah_pool_free(b->blobs);
 	ewah_pool_free(b->tags);
+	if (b->bitmaps) {
+		struct stored_bitmap *sb;
+		kh_foreach_value(b->bitmaps, sb, {
+			ewah_pool_free(sb->root);
+			free(sb);
+		});
+	}
 	kh_destroy_oid_map(b->bitmaps);
 	free(b->ext_index.objects);
 	free(b->ext_index.hashes);
+	kh_destroy_oid_pos(b->ext_index.positions);
 	bitmap_free(b->result);
 	bitmap_free(b->haves);
+	if (bitmap_is_midx(b)) {
+		/*
+		 * Multi-pack bitmaps need to have resources associated with
+		 * their on-disk reverse indexes unmapped so that stale .rev and
+		 * .bitmap files can be removed.
+		 *
+		 * Unlike pack-based bitmaps, multi-pack bitmaps can be read and
+		 * written in the same 'git multi-pack-index write --bitmap'
+		 * process. Close resources so they can be removed safely on
+		 * platforms like Windows.
+		 */
+		close_midx_revindex(b->midx);
+	}
 	free(b);
 }
 
@@ -1511,7 +1903,6 @@ static off_t get_disk_usage_for_type(struct bitmap_index *bitmap_git,
 				     enum object_type object_type)
 {
 	struct bitmap *result = bitmap_git->result;
-	struct packed_git *pack = bitmap_git->pack;
 	off_t total = 0;
 	struct ewah_iterator it;
 	eword_t filter;
@@ -1528,15 +1919,35 @@ static off_t get_disk_usage_for_type(struct bitmap_index *bitmap_git,
 			continue;
 
 		for (offset = 0; offset < BITS_IN_EWORD; offset++) {
-			size_t pos;
-
 			if ((word >> offset) == 0)
 				break;
 
 			offset += ewah_bit_ctz64(word >> offset);
-			pos = base + offset;
-			total += pack_pos_to_offset(pack, pos + 1) -
-				 pack_pos_to_offset(pack, pos);
+
+			if (bitmap_is_midx(bitmap_git)) {
+				uint32_t pack_pos;
+				uint32_t midx_pos = pack_pos_to_midx(bitmap_git->midx, base + offset);
+				off_t offset = nth_midxed_offset(bitmap_git->midx, midx_pos);
+
+				uint32_t pack_id = nth_midxed_pack_int_id(bitmap_git->midx, midx_pos);
+				struct packed_git *pack = bitmap_git->midx->packs[pack_id];
+
+				if (offset_to_pack_pos(pack, offset, &pack_pos) < 0) {
+					struct object_id oid;
+					nth_midxed_object_oid(&oid, bitmap_git->midx, midx_pos);
+
+					die(_("could not find %s in pack %s at offset %"PRIuMAX),
+					    oid_to_hex(&oid),
+					    pack->pack_name,
+					    (uintmax_t)offset);
+				}
+
+				total += pack_pos_to_offset(pack, pack_pos + 1) - offset;
+			} else {
+				size_t pos = base + offset;
+				total += pack_pos_to_offset(bitmap_git->pack, pos + 1) -
+					 pack_pos_to_offset(bitmap_git->pack, pos);
+			}
 		}
 	}
 
@@ -1546,7 +1957,6 @@ static off_t get_disk_usage_for_type(struct bitmap_index *bitmap_git,
 static off_t get_disk_usage_for_extended(struct bitmap_index *bitmap_git)
 {
 	struct bitmap *result = bitmap_git->result;
-	struct packed_git *pack = bitmap_git->pack;
 	struct eindex *eindex = &bitmap_git->ext_index;
 	off_t total = 0;
 	struct object_info oi = OBJECT_INFO_INIT;
@@ -1558,7 +1968,7 @@ static off_t get_disk_usage_for_extended(struct bitmap_index *bitmap_git)
 	for (i = 0; i < eindex->count; i++) {
 		struct object *obj = eindex->objects[i];
 
-		if (!bitmap_get(result, pack->num_objects + i))
+		if (!bitmap_get(result, bitmap_num_objects(bitmap_git) + i))
 			continue;
 
 		if (oid_object_info_extended(the_repository, &obj->oid, &oi, 0) < 0)
@@ -1588,7 +1998,28 @@ off_t get_disk_usage_from_bitmap(struct bitmap_index *bitmap_git,
 	return total;
 }
 
+int bitmap_is_midx(struct bitmap_index *bitmap_git)
+{
+	return !!bitmap_git->midx;
+}
+
 const struct string_list *bitmap_preferred_tips(struct repository *r)
 {
 	return repo_config_get_value_multi(r, "pack.preferbitmaptips");
 }
+
+int bitmap_is_preferred_refname(struct repository *r, const char *refname)
+{
+	const struct string_list *preferred_tips = bitmap_preferred_tips(r);
+	struct string_list_item *item;
+
+	if (!preferred_tips)
+		return 0;
+
+	for_each_string_list_item(item, preferred_tips) {
+		if (starts_with(refname, item->string))
+			return 1;
+	}
+
+	return 0;
+}