<maybe a little more commit log would be good?>
So here is what confuses me now. :)
*every* caller of btrfs_read_dev_super() is now called with
0 for the flags variable, so it never reads the backup
under any circumstance.
If it's always called w/ 0, what is the point of the argument?
Is there another patch you have planned that would use this argument
later?
Thanks for the review. yes true. as of now it (BTRFS_SCAN_BACKUP_SB)
only serves the purpose if in future should we need it.
purpose is something like a user initiated thread which
should to go to the backup-SB if primary-SB is not found ?.
Or I can drop BTRFS_SCAN_BACKUP_SB idea depending on how
it is convenient as a whole.
See what others think, perhaps, but if nobody is using it, I think
it should just go away. I'd call it "dead code." :)
But I am surprised that none of the commands which accept alternate
superblock locations find their way into btrfs_read_dev_super() -
that seems odd to me. Is it re-implemented or open-coded in other
places?
So to be clearer, rather than removing the code right away, maybe
it's worth a look to see if the other commands which *want* backup
superblocks should be using this same code. Then you'd have a reason
for your new flag. :)
when non primary SB (sb_bytenr) is specified in btrfs_read_dev_super()
(that is when user is involved) it would directly fetch it. so its
not a problem when we know which SB to read other than the primary SB.
However when primary SB is specified it would look for only primary SB
unless BTRFS_SCAN_BACKUP_SB flag is set (with the patch). Now, do we
need this flag ? looks like Yes ! (sorry to change my opinion here
though) and as below..
In some cases when user is _not_ involved. Like in
check_mounted().
In a multi dev btrfs mounted fs. If by any chance the primary SB
is corrupted then we would say the device is NOT mounted even
if it is mounted.
eg:
# mkfs.btrfs /dev/sdb /dev/sdc -f && mount /dev/sdb /btrfs
# ./check-mounted /dev/sdc
its btrfs
/dev/sdc is currently mounted. Aborting.
# dd if=/dev/zero of=/dev/sdc count=8 seek=$(((64 * 1024)/512))
# ./check-mounted /dev/sdc
Not mounted
# cat /proc/mounts | egrep btrfs
/dev/sdb /btrfs btrfs rw,seclabel,relatime,noacl,space_cache 0 0
So we have to set BTRFS_SCAN_BACKUP_SB for check_mounted()
But the above scenario is not simple enough to be practical though.
-Anand
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