Re: [PATCH] btrfs: indicate iversion option in show_options

[Eric Sandeen <sandeen@redhat.com>]

On 7/29/20 10:47 AM, Josef Bacik wrote:
> On 7/29/20 1:42 PM, Eric Sandeen wrote:
>> On 7/29/20 9:46 AM, Josef Bacik wrote:
>>> Eric reported a problem where if you did
>>>
>>> mount -o remount /some/btrfs/fs
>>>
>>> you would lose SB_I_VERSION on the mountpoint.  After a very convoluted
>>> search I discovered this is because the remount infrastructure doesn't
>>> just say "change these things specifically", but it actually depends on
>>> userspace to tell it fucking everything that needs to be set on the
>>> mountpoint.  This led to the fucking horrifying discovery that
>>> util-linux actually has to parse /proc/mounts to figure out what the
>>> fuck is set on the mount point in order to preserve any of the options
>>> it's not actually fucking with, so in this case iversion.  If we don't
>>> indicate iversion is set, then we get iversion cleared on the mount,
>>> because util-linux doesn't pass in MS_I_VERSION as it's mount flags.
>>>
>>> So work around this fucking insanity by spitting out iversion in
>>> /proc/mounts so we get the correct flags passed to us in remount.
>>
>> Hmmm:
>>
>> # mount -o loop,noiversion btrfsfile mnt
>> # grep btrfs /proc/mounts
>> /dev/loop0 /tmp/mnt btrfs rw,seclabel,relatime,iversion,space_cache,subvolid=5,subvol=/ 0 0
>> #
>>
> 
> Ugh that's because we just set it unconditionally like XFS does, but don't actually pay attention to noiversion otherwise.  I'll fix that separately.  Thanks,

FWIW,

# mount -o remount,noiversion mnt
# grep btrfs /proc/mounts
/dev/loop0 /tmp/mnt btrfs rw,seclabel,relatime,noiversion,space_cache,subvolid=5,subvol=/ 0 0

-Eric