[PATCH] Add git-verify-pack command.

Given a list of <pack>.idx files, this command validates the
index file and the corresponding .pack file for consistency.

This patch also uses the same validation mechanism in fsck-cache
when the --full flag is used.

During normal operation, sha1_file.c verifies that a given .idx
file matches the .pack file by comparing the SHA1 checksum
stored in .idx file and .pack file as a minimum sanity check.
We may further want to check the pack signature and version when
we map the pack, but that would be a separate patch.

Earlier, errors to map a pack file was not flagged fatal but led
to a random fatal error later.  This version explicitly die()s
when such an error is detected.

Signed-off-by: Junio C Hamano <junkio@cox.net>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

verify-pack.c

@@ -0,0 +1,26 @@
+#include "cache.h"
+#include "pack.h"
+
+static int verify_one_pack(char *arg)
+{
+	struct packed_git *g = add_packed_git(arg, strlen(arg));
+	if (!g)
+		return -1;
+	return verify_pack(g);
+}
+
+int main(int ac, char **av)
+{
+	int errs = 0;
+
+	while (1 < ac) {
+		char path[PATH_MAX];
+		strcpy(path, av[1]);
+		if (verify_one_pack(path))
+			errs++;
+		else
+			printf("%s: OK\n", av[1]);
+		ac--; av++;
+	}
+	return !!errs;
+}