config: create core.multiPackIndex setting

The core.multiPackIndex config setting controls the multi-pack-
index (MIDX) feature. If false, the setting will disable all reads
from the multi-pack-index file.

Read this config setting in the new prepare_multi_pack_index_one()
which is called during prepare_packed_git(). This check is run once
per repository.

Add comparison commands in t5319-multi-pack-index.sh to check
typical Git behavior remains the same as the config setting is turned
on and off. This currently includes 'git rev-list' and 'git log'
commands to trigger several object database reads. Currently, these
would only catch an error in the prepare_multi_pack_index_one(), but
with later commits will catch errors in object lookups, abbreviations,
and approximate object counts.

Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 25 insertions, 0 deletions

diff --git a/midx.c b/midx.c
index e83110a..4090cf4 100644
--- a/midx.c
+++ b/midx.c
@@ -1,4 +1,5 @@
 #include "cache.h"
+#include "config.h"
 #include "csum-file.h"
 #include "dir.h"
 #include "lockfile.h"
@@ -177,6 +178,30 @@ cleanup_fail:
 	return NULL;
 }
 
+int prepare_multi_pack_index_one(struct repository *r, const char *object_dir)
+{
+	struct multi_pack_index *m = r->objects->multi_pack_index;
+	struct multi_pack_index *m_search;
+	int config_value;
+
+	if (repo_config_get_bool(r, "core.multipackindex", &config_value) ||
+	    !config_value)
+		return 0;
+
+	for (m_search = m; m_search; m_search = m_search->next)
+		if (!strcmp(object_dir, m_search->object_dir))
+			return 1;
+
+	r->objects->multi_pack_index = load_multi_pack_index(object_dir);
+
+	if (r->objects->multi_pack_index) {
+		r->objects->multi_pack_index->next = m;
+		return 1;
+	}
+
+	return 0;
+}
+
 static size_t write_midx_header(struct hashfile *f,
 				unsigned char num_chunks,
 				uint32_t num_packs)