pack-bitmap.c: support bitmap pack-reuse with incremental MIDXs

In a similar fashion as previous commits in the first phase of
incremental MIDXs, enumerate not just the packs in the current
incremental MIDX layer, but previous ones as well.

Likewise, in reuse_partial_packfile_from_bitmap(), when reusing only a
single pack from a MIDX, use the oldest layer's preferred pack as it is
likely to contain the most amount of reusable sections.

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

Author: ttaylorr

pack-bitmap.c

@@ -2320,7 +2320,8 @@ void reuse_partial_packfile_from_bitmap(struct bitmap_index *bitmap_git,
 		multi_pack_reuse = 0;
 
 	if (multi_pack_reuse) {
-		for (i = 0; i < bitmap_git->midx->num_packs; i++) {
+		struct multi_pack_index *m = bitmap_git->midx;
+		for (i = 0; i < m->num_packs + m->num_packs_in_base; i++) {
 			struct bitmapped_pack pack;
 			if (nth_bitmapped_pack(r, bitmap_git->midx, &pack, i) < 0) {
 				warning(_("unable to load pack: '%s', disabling pack-reuse"),
@@ -2344,14 +2345,18 @@ void reuse_partial_packfile_from_bitmap(struct bitmap_index *bitmap_git,
 		uint32_t pack_int_id;
 
 		if (bitmap_is_midx(bitmap_git)) {
+			struct multi_pack_index *m = bitmap_git->midx;
 			uint32_t preferred_pack_pos;
 
-			if (midx_preferred_pack(bitmap_git->midx, &preferred_pack_pos) < 0) {
+			while (m->base_midx)
+				m = m->base_midx;
+
+			if (midx_preferred_pack(m, &preferred_pack_pos) < 0) {
 				warning(_("unable to compute preferred pack, disabling pack-reuse"));
 				return;
 			}
 
-			pack = bitmap_git->midx->packs[preferred_pack_pos];
+			pack = nth_midxed_pack(m, preferred_pack_pos);
 			pack_int_id = preferred_pack_pos;
 		} else {
 			pack = bitmap_git->pack;