Re: [RFC][PATCH v2] mount.btrfs helper

[David Sterba <dsterba@suse.cz>]

On Fri, Dec 05, 2014 at 04:01:37PM +0000, Dimitri John Ledkov wrote:
> On 5 December 2014 at 15:32, Chris Mason <clm@fb.com> wrote:
> > On Sun, Nov 30, 2014 at 5:57 PM, Dimitri John Ledkov <xnox@debian.org>
> > wrote:
> >>
> >> On 30 November 2014 at 22:31, cwillu <cwillu@cwillu.com> wrote:
> >>>
> >>>
> >>>  In ubuntu, the initfs runs a btrfs dev scan, which should catch
> >>>  anything that would be missed there.
> >>>
> >>
> >> I'm sorry, udev rule(s) is not sufficient in the initramfs-less case,
> >> as outlined.
> >>
> >> In case of booting with initramfs, indeed, both Debian & Ubuntu
> >> include snippets there to run btrfs scan.
> >
> >
> > In an initramfs-less system, the root filesystem mount is done by the
> > kernel, without calling any mount.btrfs.  The mount helper has all the same
> > problems that calling btrfs dev scan does, it's just being run by mount.
> >
> 
> Sure. in my initramfs-less system case the root filesystem was not
> btrfs. Simply there was a btrfs filesystem defined in /etc/fstab.

So you could add a 'btrfs dev scan' before the fstab is going to be
mounted. Either a local boot script or via some unit file. We're looking
for good reasons to justify the existence of the helper, but this is
still not enough IMHO. I can see the convenience to do it automatically,
but this assumes no udev available which is probably rare these days.