When a disk containing btrfs is overwritten with other FS, ext4
for example it doesn't overwrite 2nd and 3rd copy of the btrfs SB.
And btrfs_read_dev_super() would look for backup SB when primary
SB isn't found. This causes the problem as in the reproducer below.
In kernel we avoid this by _not_ reading backup SB implicitly,
this patch would port the same to btrfs-progs.
reproducer:
mkfs.btrfs /dev/sde
mkfs.ext4 /dev/sde
mount /dev/sde /ext4
btrfs-convert /dev/sde (is successful (bug))
with this patch
::
btrfs-convert /dev/sde
/dev/sde is mounted
Signed-off-by: Anand Jain <Anand.Jain@xxxxxxxxxx>
---
disk-io.c | 9 ++++++++-
1 file changed, 8 insertions(+), 1 deletion(-)
diff --git a/disk-io.c b/disk-io.c
index 0bd1bb0..19b95a7 100644
--- a/disk-io.c
+++ b/disk-io.c
@@ -1206,7 +1206,14 @@ int btrfs_read_dev_super(int fd, struct btrfs_super_block *sb, u64 sb_bytenr)
return 0;
}
- for (i = 0; i < BTRFS_SUPER_MIRROR_MAX; i++) {
+ /*
+ * we would like to check all the supers, but that would make
+ * a btrfs mount succeed after a mkfs from a different FS.
+ * So, we need to add a special mount option to scan for
+ * later supers, using BTRFS_SUPER_MIRROR_MAX instead
+ */
+
+ for (i = 0; i < 1; i++) {
bytenr = btrfs_sb_offset(i);
ret = pread64(fd, &buf, sizeof(buf), bytenr);
if (ret < sizeof(buf))
--
1.8.5.3
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