is mounting subvolumes with a read-only root subvolume allowed?

is mounting subvolumes with a read-only root subvolume allowed?

[Zbigniew Jędrzejewski-Szmek]

Hi,
I have a box with / and /home being subvolumes from the same btrfs filesystem.

/etc/fstab:
UUID=c0686...      /      btrfs subvol=root,x-systemd.device-timeout=0 1 1
UUID=c0686...      /home  btrfs subvol=home,x-systemd.device-timeout=0 1 1
...

/ is initially mounted readonly by the initramfs, and then after switching
to the real system, /home is attempted to be mounted in parallel with /
being remounted rw. If remounting rw happens first, boot proceeds. If
mounting /home is attempted to realy, it fails.

$ /bin/mount /home
mount: /dev/mapper/luks-765... is already mounted or /home busy
       /dev/mapper/luks-765... is already mounted on /
$ /bin/mount -o remount,rw /
$ /bin/mount /home
$

So, is this expected that the other subvolume must be mounted rw?

Zbyszek

Re: [systemd-devel] is mounting subvolumes with a read-only root subvolume allowed?

[Karel Zak]

On Fri, Nov 15, 2013 at 12:32:10AM +0100, Zbigniew Jędrzejewski-Szmek wrote:
> Hi,
> I have a box with / and /home being subvolumes from the same btrfs filesystem.
> 
> /etc/fstab:
> UUID=c0686...      /      btrfs subvol=root,x-systemd.device-timeout=0 1 1
> UUID=c0686...      /home  btrfs subvol=home,x-systemd.device-timeout=0 1 1
> ...
> 
> / is initially mounted readonly by the initramfs, and then after switching
> to the real system, /home is attempted to be mounted in parallel with /
> being remounted rw. If remounting rw happens first, boot proceeds. If
> mounting /home is attempted to realy, it fails.
> 
> $ /bin/mount /home
> mount: /dev/mapper/luks-765... is already mounted or /home busy
>        /dev/mapper/luks-765... is already mounted on /
> $ /bin/mount -o remount,rw /
> $ /bin/mount /home
> $
> 
> So, is this expected that the other subvolume must be mounted rw?

 This is known and pretty stupid issue:
 http://www.spinics.net/lists/linux-btrfs/msg25502.html

 ... but it seems that btrfs guys are fine with this "feature".

    Karel

-- 
 Karel Zak  <kzak@redhat.com>
 http://karelzak.blogspot.com

Re: [systemd-devel] is mounting subvolumes with a read-only root subvolume allowed?

[Zbigniew Jędrzejewski-Szmek]

On Fri, Nov 15, 2013 at 12:43:51AM +0100, Karel Zak wrote:
> On Fri, Nov 15, 2013 at 12:32:10AM +0100, Zbigniew Jędrzejewski-Szmek wrote:
> > Hi,
> > I have a box with / and /home being subvolumes from the same btrfs filesystem.
> > 
> > /etc/fstab:
> > UUID=c0686...      /      btrfs subvol=root,x-systemd.device-timeout=0 1 1
> > UUID=c0686...      /home  btrfs subvol=home,x-systemd.device-timeout=0 1 1
> > ...
> > 
> > / is initially mounted readonly by the initramfs, and then after switching
> > to the real system, /home is attempted to be mounted in parallel with /
> > being remounted rw. If remounting rw happens first, boot proceeds. If
> > mounting /home is attempted to realy, it fails.
> > 
> > $ /bin/mount /home
> > mount: /dev/mapper/luks-765... is already mounted or /home busy
> >        /dev/mapper/luks-765... is already mounted on /
> > $ /bin/mount -o remount,rw /
> > $ /bin/mount /home
> > $
> > 
> > So, is this expected that the other subvolume must be mounted rw?
> 
>  This is known and pretty stupid issue:
>  http://www.spinics.net/lists/linux-btrfs/msg25502.html
> 
>  ... but it seems that btrfs guys are fine with this "feature".
5 months without a reply. Great.

Zbyszek