[CRIU] Sync TODO-s for mount.c work

[Tycho Andersen]

On Thu, Apr 23, 2015 at 07:15:47PM +0300, Pavel Emelyanov wrote:
> On 04/23/2015 07:05 PM, Tycho Andersen wrote:
> > On Thu, Apr 23, 2015 at 06:51:26PM +0300, Pavel Emelyanov wrote:
> >> On 04/23/2015 06:09 PM, Tycho Andersen wrote:
> >>> On Thu, Apr 23, 2015 at 06:04:35PM +0300, Pavel Emelyanov wrote:
> >>>> On 04/23/2015 05:31 PM, Tycho Andersen wrote:
> >>>>> On Thu, Apr 23, 2015 at 02:52:35PM +0300, Pavel Emelyanov wrote:
> >>>>>> On 04/23/2015 02:17 PM, Oleg Nesterov wrote:
> >>>>>>
> >>>>>>> Now what? Obviously we can't just add
> >>>>>>>
> >>>>>>> 	if (is_not_external_mount(m))
> >>>>>>> 		continue;
> >>>>>>
> >>>>>> Why not? The is_not_external_mount() is
> >>>>>>
> >>>>>> fsroot_mounted(m) || /* mount's root is visible from chroot */
> >>>>>
> >>>>> But what if the mount's root is /? e.g with pstore in lxc, the
> >>>>> mountinfo from inside looks like:
> >>>>>
> >>>>> 110 104 0:23 / /sys/fs/pstore rw,nosuid,nodev,noexec,relatime master:11 - pstore pstore rw
> >>>>>
> >>>>> which is a bind mount from the host's:
> >>>>>
> >>>>> 29 17 0:23 / /sys/fs/pstore rw,nosuid,nodev,noexec,relatime shared:11 - pstore pstore rw
> >>>>
> >>>> Ah, so sharing takes place. OK, then (sorry, maybe I'm replaying your
> >>>> conversation again, but I'm still blind about it) the check should be
> >>>>
> >>>>    (fsroot_mounted(m) || root_is_visible(m)) && master_is_external(m)
> >>>
> >>> I think not, because if we didn't have this as a shared mount it would
> >>> still be an external bind mount, just without sharing. An external
> >>> master peer is an indication that it's a bind mount, but if we don't
> >>> have one of those, it could still be a bind mount.
> >>
> >> Ah, sure. It should be NOT before master_is_external, like this
> >>
> >>    (fsroot_mounted(m) || root_is_visible(m)) && !master_is_external()
> >>
> >> Provided master_is_external() is false for private mounts, this should
> >> handle Oleg's case with mount --make-rprivate, but in suboptimal way --
> >> all mountpoints will be bind-mounted from host with MS_SLAVE flag.
> > 
> > But this only works for mounts that have external masters. Doesn't it
> > fail to exclude mounts which aren't in a peer group at all (since
> > !master_is_external() will always be true for them)?
> 
> Yes, !master_is_external() will be true and then the 2nd part of the
> check will take place -- fsroot || root_is_visible. If _this_ will be
> false then mountpoint will be still considered to be external.

Oh, sorry, I was off by one in my negation :). Doesn't this exclude my
pstore example if the mounts are all private?

Tycho

> -- Pavel