Correct un-initialized fsid variable

diff --git a/disk-io.c b/disk-io.c
index b21a87f..0395205 100644 (file)
--- a/disk-io.c
+++ b/disk-io.c
@@ -910,6 +910,7 @@ struct btrfs_root *open_ctree_fd(int fp, const char *path, u64 sb_bytenr,
 int btrfs_read_dev_super(int fd, struct btrfs_super_block *sb, u64 sb_bytenr)
 {
        u8 fsid[BTRFS_FSID_SIZE];
+       int fsid_is_initialized = 0;
        struct btrfs_super_block buf;
        int i;
        int ret;
@@ -936,15 +937,26 @@ int btrfs_read_dev_super(int fd, struct btrfs_super_block *sb, u64 sb_bytenr)
                if (ret < sizeof(buf))
                        break;
 
-               if (btrfs_super_bytenr(&buf) != bytenr ||
-                   strncmp((char *)(&buf.magic), BTRFS_MAGIC,
+               if (btrfs_super_bytenr(&buf) != bytenr )
+                       continue;
+               /* if magic is NULL, the device was removed */
+               if (buf.magic == 0 && i == 0) 
+                       return -1;
+               if (strncmp((char *)(&buf.magic), BTRFS_MAGIC,
                            sizeof(buf.magic)))
                        continue;
 
-               if (i == 0)
+               if (!fsid_is_initialized) {
                        memcpy(fsid, buf.fsid, sizeof(fsid));
-               else if (memcmp(fsid, buf.fsid, sizeof(fsid)))
+                       fsid_is_initialized = 1;
+               } else if (memcmp(fsid, buf.fsid, sizeof(fsid))) {
+                       /*
+                        * the superblocks (the original one and
+                        * its backups) contain data of different
+                        * filesystems -> the super cannot be trusted
+                        */
                        continue;
+               }
 
                if (btrfs_super_generation(&buf) > transid) {
                        memcpy(sb, &buf, sizeof(*sb));