X-Git-Url: https://git.verplant.org/?a=blobdiff_plain;f=read-cache.c;h=2ee96bc92c37a204a844afb3354483b733db0c4e;hb=5c2a7fbc362e4227ced84c32c3fdc9682d085962;hp=54536944648c166008f06d29f65314b58b0c3988;hpb=4bb04f2190d526f8917663f0be62d8026e1ed100;p=git.git

diff --git a/read-cache.c b/read-cache.c
index 54536944..2ee96bc9 100644
--- a/read-cache.c
+++ b/read-cache.c
@@ -216,8 +216,25 @@ int write_sha1_buffer(const unsigned char *sha1, void *buf, unsigned int size)
 	int fd;
 
 	fd = open(filename, O_WRONLY | O_CREAT | O_EXCL, 0666);
-	if (fd < 0)
-		return (errno == EEXIST) ? 0 : -1;
+	if (fd < 0) {
+		void *map;
+		static int error(const char * string);
+
+		if (errno != EEXIST)
+			return -1;
+#ifndef COLLISION_CHECK
+		fd = open(filename, O_RDONLY);
+		if (fd < 0)
+			return -1;
+		map = mmap(NULL, size, PROT_READ, MAP_PRIVATE, fd, 0);
+		if (map == MAP_FAILED)
+			return -1;
+		if (memcmp(buf, map, size))
+			return error("SHA1 collision detected!"
+					" This is bad, bad, BAD!\a\n");
+#endif
+		return 0;
+	}
 	write(fd, buf, size);
 	close(fd);
 	return 0;