Re: "Btrfs: device_list_add() should not update list when mounted" breaks subvol mount

["xavier.gnata@gmail.com" <xavier.gnata@gmail.com>]

The way an encrypted home is mounted is based on links as described here:
https://help.ubuntu.com/community/EncryptedPrivateDirectory
It used to be ok before 3.17-rc3 and df -h shows:
/dev/sda5             363G  128G  217G  38% /
/home/gnata/.Private  363G  128G  217G  38% /home/gnata

It is suppose to work with a kernel >3.17-rc3 when "home" btrfs is a 
subvolume?
Does it make sense to test "[PATCH] btrfs-progs: canonicalize pathnames 
for device commands" or it is premature?

Xavier
>
> Hi Xavier,
>
>  Thanks for the report.
>
>  I got this reproduced: its a very corner case, it depends on the
>  device path given in the subsequent subvol mounts, the fix appear
>  to be outside of this patch at this moment and I am digging to know
>  if we need to normalize the device path before using it in the btrfs
>  kernel, just like btrfs-progs did recently.
>
>
>  reproducer:
>  ls -l /root/dev/sde-link
>    /root/dev/sde-link -> /dev/sde
>
>  mount -o device=/root/dev/sde-link /dev/sdd /btrfs1
>  btrfs fi show
>  Label: none  uuid: 943bf422-998c-4640-9d7f-d49f17b782ce
>     Total devices 2 FS bytes used 272.00KiB
>     devid    1 size 1.52GiB used 339.50MiB path /dev/sdd
>     devid    2 size 1.52GiB used 319.50MiB path /root/dev/sde-link
>
>  mount -o subvol=sv1,device=/dev/sde /dev/sdd /btrfs <-shouldn't fail.
>   mount: /dev/sdd already mounted or /btrfs busy
>   mount: according to mtab, /dev/sdd is mounted on /btrfs1
>
>  mount -o device=/root/dev/sde-link /dev/sdd /btrfs
>   echo $?
>   0
>
>
> Xavier, Johannes,
>
>     The quickest workaround for you will be to try to match
>  the device path as in the btrfs fi show -m </mnt> output to
>  your probably fstab/mnttab entry.
>
>
> Anand
>
> On 09/13/2014 04:43 AM, xavier.gnata@gmail.com wrote:
>> Hi,
>>
>> On standard ubuntu 14.04 a with an encrypted (cryptsetup) /home as brtfs
>> subvolume we have the following results:
>> 3.17-rc2 : Ok.
>> 3.17-rc3 and 3.17-rc4 :  /home fails to mount on boot. If one try mount
>> -a then the system tells that the partition is already mounted according
>> to matab.
>
>
>>
>> On a 3.17-rc4, btrfs fi sh returns nothing special:
>> "
>> Label: none  uuid: f4f554bb-57d9-4647-ab14-ea978c9e7e9f
>>          Total devices 1 FS bytes used 131.41GiB
>>          devid    1 size 173.31GiB used 134.03GiB path /dev/sda5
>>
>> Btrfs v3.12
>> "
>>
>> I'm not sure if it has something to do with cryptsetup...
>>
>>
>> Xavier
>>
>>> Hi Johannes,
>>>
>>>> I've two more systems with kernel version >3.17-rc3
>>>> running and no problem like this.
>>>
>>>  Does this 3.17-rc3 also has the same type of subvol config
>>>  and it mount operation/sequence as you mentioned ?
>>>
>>> > - one hdd with btrfs
>>> > - default subvolume (rootfs) is different from subovlid=0
>>> > - at boot, several subvols are mounted at /home/$DIR
>>>
>>>  I ran a few tests, on our mainline
>>>  ----
>>>  mount -o subvol=sv1 /dev/sdh1 /btrfs
>>>  mount /dev/sdh1 /btrfs
>>>   mount: /dev/sdh1 already mounted or /btrfs busy [*]
>>>  mount /dev/sdh1 /btrfs1
>>>  echo $?
>>>  0
>>>  -----
>>>
>>>  [*] hope this isn't the problem you are mentioning.
>>>
>>> Thanks, Anand