Re: booting btrfs

[Vladimir 'φ-coder/phcoder' Serbinenko]

On 16.10.2013 05:37, Chris Murphy wrote:
> 
> On Oct 15, 2013, at 8:50 PM, Andrey Borzenkov <address@hidden> wrote:
> 
>> В Mon, 14 Oct 2013 14:20:14 -0600
>> Chris Murphy <address@hidden> пишет:
>>
>>>
>>>> Is there a way to detect that mountinfo gives garbage and somehow get
>>>> where the real root points?
>>>
>>> I don't know. I've asked on address@hidden Instead of rebooting, I merely 
>>> tried mounting without options after changing the default subvolume to a 
>>> nested subvolume (one attempt subvolume in a subvolume, another a subvolume 
>>> in a directory): in both cases /proc/self/mountinfo reports / as the root, 
>>> not the full path or ID of the subvolume actually mounted.
>>>
>>> Somehow it seems like the mountinfo root field should return a block device 
>>> and full path to the mounted subvolume or its ID. Currently it seems like a 
>>> problem.
>>>
>>
>> To quote one of btrfs developer (I had unrelated discussion on openSUSE
>> list):
>>
>> --><--
>> This is a known problem, on my todo list, with a few non-working
>> solutions.
>>
>> If you mount via subvol=/subvol then /proc/self/mountinfo will show
>> 'subvol' as the mounted subvolume (4th column)
>>
>> 4 19 0:17 /subvol /mnt/ rw,relatime - btrfs /dev/sda15 rw,space_cache
>>
>> but if the subvolume is set-default and then implicitly mounted,
>> mountinfo will not show that (that's the bug).
> 
> If mounted with subvolid= the same thing happens. Mountinfo doesn't show the 
> subvolume name, it's just /. It's also a problem understanding from mountinfo 
> all of the devices that make up a btrfs volume. This can be learned from 
> btrfsprogs.
>> --><--
>>
>> That said, information can be obtained also using different means
>> (btrfs utility or directly btrfs IOCTL). The question is to which
>> extent we want to depend on existence of btrfsprogs.
> 
> Yeah at the moment if I use subvolid= to mount, I then have no idea how to 
> find out what subvolume is mounted. As far as I know btrfsprogs doesn't a way 
> to determine what subvols are mounted. It must be inferred (by mountpoint or 
> by contents of the mountpoint).
> 
> Anyway, as for support for subvolid in GRUB, I still think it would be nice 
> as it's shorter than full paths. But this is not an enhancement hill I'm 
> willing to die on by any means.
> 
I changed in trunk to make / refer to real root and modified
grub-mkrelpath to follow the same convention, even if disk is mounted
with subvolid.

signature.asc
Description: OpenPGP digital signature