From f57a739691e2efa1d71851cd725154a5a760d8f4 Mon Sep 17 00:00:00 2001 From: Taylor Blau Date: Wed, 1 Sep 2021 16:34:01 -0400 Subject: midx: avoid opening multiple MIDXs when writing Opening multiple instance of the same MIDX can lead to problems like two separate packed_git structures which represent the same pack being added to the repository's object store. The above scenario can happen because prepare_midx_pack() checks if `m->packs[pack_int_id]` is NULL in order to determine if a pack has been opened and installed in the repository before. But a caller can construct two copies of the same MIDX by calling get_multi_pack_index() and load_multi_pack_index() since the former manipulates the object store directly but the latter is a lower-level routine which allocates a new MIDX for each call. So if prepare_midx_pack() is called on multiple MIDXs with the same pack_int_id, then that pack will be installed twice in the object store's packed_git pointer. This can lead to problems in, for e.g., the pack-bitmap code, which does something like the following (in pack-bitmap.c:open_pack_bitmap()): struct bitmap_index *bitmap_git = ...; for (p = get_all_packs(r); p; p = p->next) { if (open_pack_bitmap_1(bitmap_git, p) == 0) ret = 0; } which is a problem if two copies of the same pack exist in the packed_git list because pack-bitmap.c:open_pack_bitmap_1() contains a conditional like the following: 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; } Avoid this scenario by not letting write_midx_internal() open a MIDX that isn't also pointed at by the object store. So long as this is the case, other routines should prefer to open MIDXs with get_multi_pack_index() or reprepare_packed_git() instead of creating instances on their own. Because get_multi_pack_index() returns `r->object_store->multi_pack_index` if it is non-NULL, we'll only have one instance of a MIDX open at one time, avoiding these problems. To encourage this, drop the `struct multi_pack_index *` parameter from `write_midx_internal()`, and rely instead on the `object_dir` to find (or initialize) the correct MIDX instance. Likewise, replace the call to `close_midx()` with `close_object_store()`, since we're about to replace the MIDX with a new one and should invalidate the object store's memory of any MIDX that might have existed beforehand. Note that this now forbids passing object directories that don't belong to alternate repositories over `--object-dir`, since before we would have happily opened a MIDX in any directory, but now restrict ourselves to only those reachable by `r->objects->multi_pack_index` (and alternate MIDXs that we can see by walking the `next` pointer). As far as I can tell, supporting arbitrary directories with `--object-dir` was a historical accident, since even the documentation says `` when referring to the value passed to this option. Signed-off-by: Taylor Blau Signed-off-by: Junio C Hamano --- object-file.c | 21 +++++++++++++++++++++ 1 file changed, 21 insertions(+) (limited to 'object-file.c') diff --git a/object-file.c b/object-file.c index a8be899481..a4d720b4f5 100644 --- a/object-file.c +++ b/object-file.c @@ -820,6 +820,27 @@ out: return ref_git; } +struct object_directory *find_odb(struct repository *r, const char *obj_dir) +{ + struct object_directory *odb; + char *obj_dir_real = real_pathdup(obj_dir, 1); + struct strbuf odb_path_real = STRBUF_INIT; + + prepare_alt_odb(r); + for (odb = r->objects->odb; odb; odb = odb->next) { + strbuf_realpath(&odb_path_real, odb->path, 1); + if (!strcmp(obj_dir_real, odb_path_real.buf)) + break; + } + + free(obj_dir_real); + strbuf_release(&odb_path_real); + + if (!odb) + die(_("could not find object directory matching %s"), obj_dir); + return odb; +} + static void fill_alternate_refs_command(struct child_process *cmd, const char *repo_path) { -- cgit v1.2.3