pack-bitmap: introduce function to open bitmap for a single source

The function `prepare_bitmap_git()` opens the first bitmap it can find
in any of the object sources connected to the repository. In a
subsequent commit, the "packed" object database backend will learn to
use bitmaps to answer object filters when enumerating objects. That
backend operates on a single object source though, so using a bitmap
that potentially belongs to a different source would be wrong:

  - The source would yield objects that are not part of the source
    itself.

  - The object source info would be attributed to the wrong source.

  - With multiple sources, each source would enumerate the same bitmap
    another time.

Introduce a new function `prepare_bitmap_git_for_source()` that only
opens bitmaps belonging to the given object source.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

2 files changed, 14 insertions, 0 deletions

diff --git a/pack-bitmap.c b/pack-bitmap.c
index 72c8ae3228..09ba15d26b 100644
--- a/pack-bitmap.c
+++ b/pack-bitmap.c
@@ -753,6 +753,18 @@ struct bitmap_index *prepare_midx_bitmap_git(struct multi_pack_index *midx)
 	return NULL;
 }
 
+struct bitmap_index *prepare_bitmap_git_for_source(struct odb_source_packed *source)
+{
+	struct bitmap_index *bitmap_git = xcalloc(1, sizeof(*bitmap_git));
+
+	if (!open_bitmap_for_source(source, bitmap_git) &&
+	    !load_bitmap(source->base.odb->repo, bitmap_git, 0))
+		return bitmap_git;
+
+	free_bitmap_index(bitmap_git);
+	return NULL;
+}
+
 int bitmap_index_contains_pack(struct bitmap_index *bitmap, struct packed_git *pack)
 {
 	for (; bitmap; bitmap = bitmap->base) {
diff --git a/pack-bitmap.h b/pack-bitmap.h
index ae8dc491ac..9f20fb6e56 100644
--- a/pack-bitmap.h
+++ b/pack-bitmap.h
@@ -9,6 +9,7 @@
 #include "string-list.h"
 
 struct commit;
+struct odb_source_packed;
 struct repository;
 struct rev_info;
 
@@ -68,6 +69,7 @@ struct bitmapped_pack {
 
 struct bitmap_index *prepare_bitmap_git(struct repository *r);
 struct bitmap_index *prepare_midx_bitmap_git(struct multi_pack_index *midx);
+struct bitmap_index *prepare_bitmap_git_for_source(struct odb_source_packed *source);
 
 /*
  * Given a bitmap index, determine whether it contains the pack either directly