pack-bitmap.c: open and store incremental bitmap layers

Prepare the pack-bitmap machinery to work with incremental MIDXs by
adding a new "base" field to keep track of the bitmap index associated
with the previous MIDX layer.

The changes in this commit are mostly boilerplate to open the correct
bitmap(s), add them to the chain bitmap layers along the "base" pointer,
ensures that the correct packs and their reverse indexes are loaded
across MIDX layers, etc.

While we're at it, keep track of a base_nr field to indicate how many
bitmap layers (including the current bitmap) exist. This will be used in
a future commit to allocate an array of 'struct ewah_bitmap' pointers to
collect all of the respective type bitmaps among all layers to
initialize a multi-EWAH iterator.

Subsequent commits will teach the functions within the pack-bitmap
machinery how to interact with these new fields.

Signed-off-by: Taylor Blau <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: ttaylorr

pack-bitmap.c

@@ -54,6 +54,13 @@ struct bitmap_index {
 	struct packed_git *pack;
 	struct multi_pack_index *midx;
 
+	/*
+	 * If using a multi-pack index chain, 'base' points to the
+	 * bitmap index corresponding to this bitmap's midx->base_midx.
+	 */
+	struct bitmap_index *base;
+	uint32_t base_nr;
+
 	/* mmapped buffer of the whole bitmap index */
 	unsigned char *map;
 	size_t map_size; /* size of the mmaped buffer */
@@ -377,8 +384,13 @@ static int load_bitmap_entries_v1(struct bitmap_index *index)
 char *midx_bitmap_filename(struct multi_pack_index *midx)
 {
 	struct strbuf buf = STRBUF_INIT;
-	get_midx_filename_ext(&buf, midx->object_dir, get_midx_checksum(midx),
-			      MIDX_EXT_BITMAP);
+	if (midx->has_chain)
+		get_split_midx_filename_ext(&buf, midx->object_dir,
+					    get_midx_checksum(midx),
+					    MIDX_EXT_BITMAP);
+	else
+		get_midx_filename_ext(&buf, midx->object_dir,
+				      get_midx_checksum(midx), MIDX_EXT_BITMAP);
 
 	return strbuf_detach(&buf, NULL);
 }
@@ -397,10 +409,17 @@ static int open_midx_bitmap_1(struct bitmap_index *bitmap_git,
 {
 	struct stat st;
 	char *bitmap_name = midx_bitmap_filename(midx);
-	int fd = git_open(bitmap_name);
+	int fd;
 	uint32_t i, preferred_pack;
 	struct packed_git *preferred;
 
+	fd = git_open(bitmap_name);
+	if (fd < 0 && errno == ENOENT) {
+		FREE_AND_NULL(bitmap_name);
+		bitmap_name = midx_bitmap_filename(midx);
+		fd = git_open(bitmap_name);
+	}
+
 	if (fd < 0) {
 		if (errno != ENOENT)
 			warning_errno("cannot open '%s'", bitmap_name);
@@ -446,7 +465,7 @@ static int open_midx_bitmap_1(struct bitmap_index *bitmap_git,
 		goto cleanup;
 	}
 
-	for (i = 0; i < bitmap_git->midx->num_packs; i++) {
+	for (i = 0; i < bitmap_git->midx->num_packs + bitmap_git->midx->num_packs_in_base; i++) {
 		if (prepare_midx_pack(the_repository, bitmap_git->midx, i)) {
 			warning(_("could not open pack %s"),
 				bitmap_git->midx->pack_names[i]);
@@ -459,13 +478,20 @@ static int open_midx_bitmap_1(struct bitmap_index *bitmap_git,
 		goto cleanup;
 	}
 
-	preferred = bitmap_git->midx->packs[preferred_pack];
+	preferred = nth_midxed_pack(bitmap_git->midx, preferred_pack);
 	if (!is_pack_valid(preferred)) {
 		warning(_("preferred pack (%s) is invalid"),
 			preferred->pack_name);
 		goto cleanup;
 	}
 
+	if (midx->base_midx) {
+		bitmap_git->base = prepare_midx_bitmap_git(midx->base_midx);
+		bitmap_git->base_nr = bitmap_git->base->base_nr + 1;
+	} else {
+		bitmap_git->base_nr = 1;
+	}
+
 	return 0;
 
 cleanup:
@@ -516,6 +542,7 @@ static int open_pack_bitmap_1(struct bitmap_index *bitmap_git, struct packed_git
 	bitmap_git->map_size = xsize_t(st.st_size);
 	bitmap_git->map = xmmap(NULL, bitmap_git->map_size, PROT_READ, MAP_PRIVATE, fd, 0);
 	bitmap_git->map_pos = 0;
+	bitmap_git->base_nr = 1;
 	close(fd);
 
 	if (load_bitmap_header(bitmap_git) < 0) {
@@ -535,8 +562,7 @@ static int open_pack_bitmap_1(struct bitmap_index *bitmap_git, struct packed_git
 static int load_reverse_index(struct repository *r, struct bitmap_index *bitmap_git)
 {
 	if (bitmap_is_midx(bitmap_git)) {
-		uint32_t i;
-		int ret;
+		struct multi_pack_index *m;
 
 		/*
 		 * The multi-pack-index's .rev file is already loaded via
@@ -545,10 +571,15 @@ static int load_reverse_index(struct repository *r, struct bitmap_index *bitmap_
 		 * 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++) {
-			ret = load_pack_revindex(r, bitmap_git->midx->packs[i]);
-			if (ret)
-				return ret;
+		for (m = bitmap_git->midx; m; m = m->base_midx) {
+			uint32_t i;
+			int ret;
+
+			for (i = 0; i < m->num_packs; i++) {
+				ret = load_pack_revindex(r, m->packs[i]);
+				if (ret)
+					return ret;
+			}
 		}
 		return 0;
 	}
@@ -574,6 +605,13 @@ static int load_bitmap(struct repository *r, struct bitmap_index *bitmap_git)
 	if (!bitmap_git->table_lookup && load_bitmap_entries_v1(bitmap_git) < 0)
 		goto failed;
 
+	if (bitmap_git->base) {
+		if (!bitmap_is_midx(bitmap_git))
+			BUG("non-MIDX bitmap has non-NULL base bitmap index");
+		if (load_bitmap(r, bitmap_git->base) < 0)
+			goto failed;
+	}
+
 	return 0;
 
 failed:
@@ -658,10 +696,9 @@ struct bitmap_index *prepare_bitmap_git(struct repository *r)
 
 struct bitmap_index *prepare_midx_bitmap_git(struct multi_pack_index *midx)
 {
-	struct repository *r = the_repository;
 	struct bitmap_index *bitmap_git = xcalloc(1, sizeof(*bitmap_git));
 
-	if (!open_midx_bitmap_1(bitmap_git, midx) && !load_bitmap(r, bitmap_git))
+	if (!open_midx_bitmap_1(bitmap_git, midx))
 		return bitmap_git;
 
 	free_bitmap_index(bitmap_git);