[CRIU] [PATCH 1/2] mnt: do_new_mount should restore sharing

[Tycho Andersen]

On Mon, Apr 20, 2015 at 06:52:59PM +0300, Andrew Vagin wrote:
> On Fri, Apr 17, 2015 at 11:07:49AM -0600, Tycho Andersen wrote:
> > On Fri, Apr 17, 2015 at 06:58:34PM +0300, Andrew Vagin wrote:
> > > On Wed, Apr 15, 2015 at 01:17:40PM -0600, Tycho Andersen wrote:
> > > > The function masks off sharing in the initial setting, but doesn't correctly
> > > > reset the flags afterwards.
> > > > 
> > > > CC: Oleg Nesterov <oleg at redhat.com>
> > > > Signed-off-by: Tycho Andersen <tycho.andersen at canonical.com>
> > > > ---
> > > >  mount.c | 4 +++-
> > > >  1 file changed, 3 insertions(+), 1 deletion(-)
> > > > 
> > > > diff --git a/mount.c b/mount.c
> > > > index 1d8f486..17f97a2 100644
> > > > --- a/mount.c
> > > > +++ b/mount.c
> > > > @@ -1789,7 +1789,9 @@ static int do_new_mount(struct mount_info *mi)
> > > >  		return -1;
> > > >  	}
> > > >  
> > > > -	if (restore_shared_options(mi, 0, mi->shared_id, 0))
> > > > +	if (restore_shared_options(mi, !mi->shared_id && !mi->master_id,
> > > 
> > > Could you explain this? If we talk about external mount, we need to give
> > > true here if host_mi->shared_id isn't equal to mi->shared_id.
> > 
> > All external mounts are restored via do_bind_mount(), so the sharing
> > here is all internal.
> 
> I mean auto external mounts.
> 
> Lets imagine that we dump a mount point and find a pair on the host.
> On restore we bind-mount the host point into a restored point and a new
> mount point will inherit the host group. We know that these groups were
> different on dump, so we need to reset a group in the new mount point.
> For that we need to remount it as private and then as shared.

Yes, that's what force_private_remount in do_bind_mount() is for.
Autodetected external mounts aren't restored via do_new_mount().

> > 
> > However, I think if this mi->shared_id differs from
> > mi->parent->shared_id we do need to remount private first, since the
> > internal sharing is different. I can resend with this change if it
> > makes sense.
> 
> There is no correlation between mi->shared_id and mi->parent->shared_id.

A mount inherits its parent's sharing when initially mounted, so if
the IDs differ, don't we need to re-mount private to get a new id?

Tycho

> > 
> > Tycho
> > 
> > > > +					mi->shared_id,
> > > > +					mi->master_id))
> > > >  		return -1;
> > > >  
> > > >  	mi->mounted = true;
> > > > -- 
> > > > 2.1.4
> > > > 
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