Loop over pack_windows when inflating/accessing data.

When multiple mmaps start getting used for all pack file access it
is not possible to get all data associated with a specific object
in one contiguous memory region.  This limitation prevents simply
passing a single address and length to SHA1_Update or to inflate.

Instead we need to loop until we have processed all data of interest.

As we loop over the data we are always interested in reusing the same
window 'cursor', as the prior window will no longer be of any use
to us.  This allows the use_pack() call to automatically decrement
the use count of the prior window before setting up access for us
to the next window.

Within each loop we need to make use of the available length output
parameter of use_pack() to tell us how many bytes are available in
the current memory region, as we cannot tell otherwise.

Signed-off-by: Shawn O. Pearce <spearce@spearce.org>
Signed-off-by: Junio C Hamano <junkio@cox.net>

1 files changed, 20 insertions, 26 deletions

diff --git a/pack-check.c b/pack-check.c
index 972916f..08a9fd8 100644
--- a/pack-check.c
+++ b/pack-check.c
@@ -8,39 +8,38 @@ static int verify_packfile(struct packed_git *p,
 	void *index_base = p->index_base;
 	SHA_CTX ctx;
 	unsigned char sha1[20];
-	unsigned long pack_size = p->pack_size;
-	void *pack_base;
-	struct pack_header *hdr;
+	unsigned long offset = 0, pack_sig = p->pack_size - 20;
 	int nr_objects, err, i;
 
-	/* Header consistency check */
-	pack_base = use_pack(p, w_curs, 0, NULL);
-	hdr = (struct pack_header*)pack_base;
-	if (hdr->hdr_signature != htonl(PACK_SIGNATURE))
-		return error("Packfile %s signature mismatch", p->pack_name);
-	if (!pack_version_ok(hdr->hdr_version))
-		return error("Packfile version %d unsupported",
-			     ntohl(hdr->hdr_version));
-	nr_objects = ntohl(hdr->hdr_entries);
-	if (num_packed_objects(p) != nr_objects)
-		return error("Packfile claims to have %d objects, "
-			     "while idx size expects %d", nr_objects,
-			     num_packed_objects(p));
+	/* Note that the pack header checks are actually performed by
+	 * use_pack when it first opens the pack file.  If anything
+	 * goes wrong during those checks then the call will die out
+	 * immediately.
+	 */
 
 	SHA1_Init(&ctx);
-	SHA1_Update(&ctx, pack_base, pack_size - 20);
+	while (offset < pack_sig) {
+		unsigned int remaining;
+		unsigned char *in = use_pack(p, w_curs, offset, &remaining);
+		offset += remaining;
+		if (offset > pack_sig)
+			remaining -= offset - pack_sig;
+		SHA1_Update(&ctx, in, remaining);
+	}
 	SHA1_Final(sha1, &ctx);
-	if (hashcmp(sha1, (unsigned char *)pack_base + pack_size - 20))
+	if (hashcmp(sha1, use_pack(p, w_curs, pack_sig, NULL)))
 		return error("Packfile %s SHA1 mismatch with itself",
 			     p->pack_name);
 	if (hashcmp(sha1, (unsigned char *)index_base + index_size - 40))
 		return error("Packfile %s SHA1 mismatch with idx",
 			     p->pack_name);
+	unuse_pack(w_curs);
 
 	/* Make sure everything reachable from idx is valid.  Since we
 	 * have verified that nr_objects matches between idx and pack,
 	 * we do not do scan-streaming check on the pack file.
 	 */
+	nr_objects = num_packed_objects(p);
 	for (i = err = 0; i < nr_objects; i++) {
 		unsigned char sha1[20];
 		void *data;
@@ -73,15 +72,12 @@ static int verify_packfile(struct packed_git *p,
 
 #define MAX_CHAIN 40
 
-static void show_pack_info(struct packed_git *p,
-		struct pack_window **w_curs)
+static void show_pack_info(struct packed_git *p)
 {
-	struct pack_header *hdr;
 	int nr_objects, i;
 	unsigned int chain_histogram[MAX_CHAIN];
 
-	hdr = (struct pack_header*)use_pack(p, w_curs, 0, NULL);
-	nr_objects = ntohl(hdr->hdr_entries);
+	nr_objects = num_packed_objects(p);
 	memset(chain_histogram, 0, sizeof(chain_histogram));
 
 	for (i = 0; i < nr_objects; i++) {
@@ -153,9 +149,7 @@ int verify_pack(struct packed_git *p, int verbose)
 		if (ret)
 			printf("%s: bad\n", p->pack_name);
 		else {
-			struct pack_window *w_curs = NULL;
-			show_pack_info(p, &w_curs);
-			unuse_pack(&w_curs);
+			show_pack_info(p);
 			printf("%s: ok\n", p->pack_name);
 		}
 	}