Re: [PATCH][RESEND] vfs: allow /proc/PID/maps to get device from stat

[Mark Fasheh <mfasheh@suse.de>]

On Mon, Aug 12, 2013 at 04:47:52AM -0700, Christoph Hellwig wrote:
> On Thu, Aug 08, 2013 at 11:44:54AM -0400, Josef Bacik wrote:
> > On Thu, Aug 08, 2013 at 06:48:05AM -0700, Christoph Hellwig wrote:
> > > On Thu, Aug 08, 2013 at 09:02:07AM -0400, Josef Bacik wrote:
> > > > This won't work, try having 10000 subvolumes with dirty inodes and do sync then
> > > > go skiing, you'll have time :).  Thanks,
> > > 
> > > Why would the dirty inodes make any difference?  If you share the bdi
> > > between the subvolumes the sync workflow should be exactly the same
> > > still.
> > > 
> > 
> > If we could dis-entangle vfsmounts from sb's and have it so you could have
> > multiple vfsmounts with just one sb that would solve at least the in-kernel
> > confusion, but I think we still have the userspace confusion.  Thanks,
> 
> I think it would mostly solve userspace confusion, as userspace only
> sees mounts and the device names.
> 
> But please fix this up properly instead of propagating the effects of
> the nasty btrfs hack that should never have been merged in that form
> further up the stack.

Can one of you explain how this solves the problem that userspace is getting
different devices for the same inode?

Seriously, I've been looking into it and I'm a bit lost. I followed the
converstaion until here but I don't see how any of the proposed changes
actually *fix* anything? Also, what is the relationship between vfsmounts
and sb today? Wouldn't a bind mount produce the situation of more than 1
vfsmount per sb that is described above?

Sincerely, someone who would like to fix this ABI breakage that has been
going on for years.
	--Mark

--
Mark Fasheh