Re: booting btrfs

[Andrey Borzenkov <arvidjaar@gmail.com>]

В Mon, 14 Oct 2013 14:20:14 -0600
Chris Murphy <lists@colorremedies.com> 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 linux-btrfs@. 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).
--><--

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.