Re: [PATCH 19/41] union-mount: Introduce MNT_UNION and MS_UNION flags

[Valerie Aurora <vaurora@redhat.com>]

On Mon, Nov 30, 2009 at 03:02:44AM -0500, Erez Zadok wrote:
> In message <1256152779-10054-20-git-send-email-vaurora@redhat.com>, Valerie Aurora writes:
> > From: Jan Blunck <jblunck@suse.de>
> > 
> > Add per mountpoint flag for Union Mount support. You need additional patches
> > to util-linux for that to work - see:
> > 
> > git://git.kernel.org/pub/scm/utils/util-linux-ng/val/util-linux-ng.git
> > 
> > Signed-off-by: Jan Blunck <jblunck@suse.de>
> > Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
> > Signed-off-by: Valerie Aurora <vaurora@redhat.com>
> > ---
> >  fs/namespace.c        |    5 ++++-
> >  include/linux/fs.h    |    1 +
> >  include/linux/mount.h |    1 +
> >  3 files changed, 6 insertions(+), 1 deletions(-)
> [...]
> 
> > diff --git a/include/linux/mount.h b/include/linux/mount.h
> > index 5d52753..e175c47 100644
> > --- a/include/linux/mount.h
> > +++ b/include/linux/mount.h
> > @@ -35,6 +35,7 @@ struct mnt_namespace;
> >  #define MNT_SHARED	0x1000	/* if the vfsmount is a shared mount */
> >  #define MNT_UNBINDABLE	0x2000	/* if the vfsmount is a unbindable mount */
> >  #define MNT_PNODE_MASK	0x3000	/* propagation flag mask */
> > +#define MNT_UNION	0x4000	/* if the vfsmount is a union mount */
> 
> I it correct to just add another flag here?  How does it relate to this
> 'propagation mask' right above it?  If there's some code out there which
> masks out which MNT flags get propagated and which don't, then you need to
> make a decision whether MNT_UNION needs to be propagated as well.  Either
> way, please document your decision in a comment here so no one will have to
> ask the same question again.

I sat down and puzzled this out and sent a separate patch to clean up
and comment this part of the code.

-VAL