On 16.10.2013 05:37, Chris Murphy wrote: > > On Oct 15, 2013, at 8:50 PM, Andrey Borzenkov <arvidj...@gmail.com> wrote: > >> В Mon, 14 Oct 2013 14:20:14 -0600 >> Chris Murphy <li...@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). > > 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.
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