pack: make packed_git_mru global a value instead of a pointer

The MRU cache that keeps track of recently used packs is represented
using two global variables:

	struct mru packed_git_mru_storage;
	struct mru *packed_git_mru = &packed_git_mru_storage;

Callers never assign to the packed_git_mru pointer, though, so we can
simplify by eliminating it and using &packed_git_mru_storage (renamed
to &packed_git_mru) directly.  This variable is only used by the
packfile subsystem, making this a relatively uninvasive change (and
any new unadapted callers would trigger a compile error).

Noticed while moving these globals to the object_store struct.

Signed-off-by: Stefan Beller <sbeller@google.com>
Signed-off-by: Jonathan Nieder <jrnieder@gmail.com>
Acked-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/pack-objects.c

@@ -1012,7 +1012,7 @@ static int want_object_in_pack(const unsigned char *sha1,
 			return want;
 	}
 
-	for (entry = packed_git_mru->head; entry; entry = entry->next) {
+	for (entry = packed_git_mru.head; entry; entry = entry->next) {
 		struct packed_git *p = entry->item;
 		off_t offset;
 
@@ -1030,7 +1030,7 @@ static int want_object_in_pack(const unsigned char *sha1,
 			}
 			want = want_found_object(exclude, p);
 			if (!exclude && want > 0)
-				mru_mark(packed_git_mru, entry);
+				mru_mark(&packed_git_mru, entry);
 			if (want != -1)
 				return want;
 		}

cache.h

@@ -4,6 +4,7 @@
 #include "git-compat-util.h"
 #include "strbuf.h"
 #include "hashmap.h"
+#include "mru.h"
 #include "advice.h"
 #include "gettext.h"
 #include "convert.h"
@@ -1589,8 +1590,7 @@ extern struct packed_git {
  * A most-recently-used ordered version of the packed_git list, which can
  * be iterated instead of packed_git (and marked via mru_mark).
  */
-struct mru;
-extern struct mru *packed_git_mru;
+extern struct mru packed_git_mru;
 
 struct pack_entry {
 	off_t offset;

packfile.c

@@ -40,9 +40,7 @@ static unsigned int pack_max_fds;
 static size_t peak_pack_mapped;
 static size_t pack_mapped;
 struct packed_git *packed_git;
-
-static struct mru packed_git_mru_storage;
-struct mru *packed_git_mru = &packed_git_mru_storage;
+struct mru packed_git_mru;
 
 #define SZ_FMT PRIuMAX
 static inline uintmax_t sz_fmt(size_t s) { return s; }
@@ -861,9 +859,9 @@ static void prepare_packed_git_mru(void)
 {
 	struct packed_git *p;
 
-	mru_clear(packed_git_mru);
+	mru_clear(&packed_git_mru);
 	for (p = packed_git; p; p = p->next)
-		mru_append(packed_git_mru, p);
+		mru_append(&packed_git_mru, p);
 }
 
 static int prepare_packed_git_run_once = 0;
@@ -1832,9 +1830,9 @@ int find_pack_entry(const unsigned char *sha1, struct pack_entry *e)
 	if (!packed_git)
 		return 0;
 
-	for (p = packed_git_mru->head; p; p = p->next) {
+	for (p = packed_git_mru.head; p; p = p->next) {
 		if (fill_pack_entry(sha1, e, p->item)) {
-			mru_mark(packed_git_mru, p);
+			mru_mark(&packed_git_mru, p);
 			return 1;
 		}
 	}