Re: [PATCH] btrfs-progs: a copy of superblock is zero may not mean btrfs is not there

[Anand Jain <Anand.Jain@oracle.com>]

On 04/16/2013 07:57 PM, David Sterba wrote:
> On Fri, Apr 12, 2013 at 03:55:06PM +0800, Anand Jain wrote:
>> If one of the copy of the superblock is zero it does not
>> confirm to us that btrfs isn't there on that disk. When
>> we are having more than one copy of superblock we should
>> rather let the for loop to continue to check other copies.
>>
>> the following test case and results would justify the
>> fix
>>
>> mkfs.btrfs /dev/sdb /dev/sdc -f
>> mount /dev/sdb /btrfs
>> dd if=/dev/zero bs=1 count=8 of=/dev/sdc seek=$((64*1024+64))
>> ~/before/btrfs-select-super -s 1 /dev/sdc
>> using SB copy 1, bytenr 67108864
>>
>> here btrfs-select-super just wrote superblock to a mounted btrfs
>
> Why does not check_mounted() catch this in the first place? Ie. based on
> the status in /proc/mounts not on random bytes in the superblock.

  the reason is, as of now /proc/mounts just knows about the devid 1.

Thanks, Anand