[CRIU] [PATCH] fsmptify: Filter out internal inotify bits when restoring marks

[Cyrill Gorcunov]

On Mon, Oct 12, 2015 at 01:27:12PM +0300, Pavel Emelyanov wrote:
> On 09/22/2015 12:48 AM, Cyrill Gorcunov wrote:
> > The kernel prior 4.3 is exporting FS_EVENT_ON_CHILD
> > bit via procfs fdinfo interface. This bit is kernel's
> > internal and should not be passed in inotify_add_watch
> > call. Thus simply filter it out when obtain from old
> > images for backward compatibility reason.
> > 
> > More details here https://lkml.org/lkml/2015/9/21/680
> > 
> > Signed-off-by: Cyrill Gorcunov <gorcunov at openvz.org>
> > ---
> >  fsnotify.c | 10 ++++++++++
> >  1 file changed, 10 insertions(+)
> > 
> > diff --git a/fsnotify.c b/fsnotify.c
> > index 9b1323363457..17abd499c337 100644
> > --- a/fsnotify.c
> > +++ b/fsnotify.c
> > @@ -801,6 +801,16 @@ static int collect_one_inotify_mark(void *o, ProtobufCMessage *msg)
> >  	INIT_LIST_HEAD(&mark->list);
> >  	mark->remap = NULL;
> >  
> > +	/*
> > +	 * The kernel prior 4.3 might export internal event
> > +	 * mask bits which are not part of user-space API. It
> > +	 * is fixed in kernel but we have to keep backward
> > +	 * compatibility with old images. So mask out
> > +	 * inappropriate bits (in particular fdinfo might
> > +	 * have FS_EVENT_ON_CHILD bit set).
> > +	 */
> > +	mark->iwe->mask &= IN_ALL_EVENTS;
> 
> OK, so after thinking about it more, here's what seems correct to me:
> 
> 1. On restore drop the FS_EVENT_ON_CHILD from image unconditionally.

We can't: this bit is internal kernel bit and may be a valid one in
a future (exported into userspace). So what we need is to simply
filter out all unsupported bits I think.

> 2. On dump check for this bit and pr_warn if present.