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btrfs-progs: avoid implicit scan for backup SB 

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@oracle.com>
Signed-off-by: Chris Mason <clm@fb.com>
master
Anand Jain 2014-03-17 19:59:01 +08:00 committed by Chris Mason
parent bf357ff320
commit a062ffd74d
1 changed files with 8 additions and 1 deletions
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9
disk-io.c
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@ -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))