fs/adfs: map: fix map scanning

When scanning the map for a fragment id, we need to keep track of the
free space links, so we don't inadvertently believe that the freespace
link is a valid fragment id.
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

fs/adfs/map.c

@@ -72,9 +72,12 @@ static int lookup_zone(const struct adfs_discmap *dm, const unsigned int idlen,
 	const u32 idmask = (1 << idlen) - 1;
 	unsigned char *map = dm->dm_bh->b_data;
 	unsigned int start = dm->dm_startbit;
-	unsigned int fragend;
+	unsigned int freelink, fragend;
 	u32 frag;
 
+	frag = GET_FRAG_ID(map, 8, idmask & 0x7fff);
+	freelink = frag ? 8 + frag : 0;
+
 	do {
 		frag = GET_FRAG_ID(map, start, idmask);
 
@@ -82,7 +85,9 @@ static int lookup_zone(const struct adfs_discmap *dm, const unsigned int idlen,
 		if (fragend >= endbit)
 			goto error;
 
-		if (frag == frag_id) {
+		if (start == freelink) {
+			freelink += frag & 0x7fff;
+		} else if (frag == frag_id) {
 			unsigned int length = fragend + 1 - start;
 
 			if (*offset < length)