[CRIU] [PATCH] mnt: Use ns_mountpoint to open a mount point

[Cyrill Gorcunov]

On Mon, Oct 12, 2015 at 01:22:03PM +0300, Pavel Emelyanov wrote:
> On 10/12/2015 01:05 PM, Cyrill Gorcunov wrote:
> > On Mon, Oct 12, 2015 at 12:56:55PM +0300, Pavel Emelyanov wrote:
> >> On 10/09/2015 06:59 PM, Cyrill Gorcunov wrote:
> >>> From: Andrew Vagin <avagin at openvz.org>
> >>>
> >>> open_mountpoint helper is called when mount namespace are
> >>> already restored so we have to use local paths.
> >>
> >> 2 questions from my side:
> >>
> >> 1. How is this connected with the patch "fsnotify: save mnt_id with path"?
> > 
> > It's unconnected actually. The Andrew's patch adds mnt_id for tmpfs as far
> > as I remeeber. But my patch for "guessing" the path (which I'm still
> > working on) based on this patch. Still note that there mount.c code is
> > modified as well which is needed to fix debian-8 nested mountnamespace
> > problems.
> 
> OK, so that's the 3rd issue fixed by this patch? Let me summarize
> 
> 1. watch from another namespace (fixed, commiteed)
> 2. watch from bind mount with weird name (kernel is read for details)
> 3. this issue
> 
> Right? If yes, what are the circumstances when we face _this_ one?

Hmm. Let rather _me_ summarized all the problems.

1) We've catched a problem with restoring nested mount namespaces
   (in particular master/slave relationship) in debian8 container.
   To fix it Andrew made

	mnt: Fix slave mounts order estimation in can_mount_now

That's first bug and first part of its fix

2) Opening mountpoints should be done using @ns_mountpoint as
   a reference. This is a second part of the bug above fixed.
   That is _this_ patch.

Now once mountpoints order and their openup is fixed we faced
problems with opening watchees in fsnotify code. And here
two patches which should address it.

3) Andrew's fsnotify: save mnt_id with path (which address
   tmpfs only)

4) I need the last patch which would address case when name
   of watchee is mangled via bindmount. And for this
   we've at moment two patches

	a) fsnotify: Use longest mount point for inotify watchee
	b) fsnotify: Guess the path to open if multiple mount namespace are present

   Both address same problem, but I aimed for b) mostly. Both are
   under review. And I need to find out if there some better way
   than guessing the path.

That said, namepsace wide watchees are still pain and under
investigation but THIS particular patch is rather addressing
mountnamespace issue, unrelated to fsnotify and should be
merged, because fsnotify gonna rely on it.