[CRIU] --ext-mount-map auto likes MS_BIND too much

[Andrew Vagin]

On Tue, Apr 14, 2015 at 12:00:54PM -0600, Tycho Andersen wrote:
> On Tue, Apr 14, 2015 at 07:45:54PM +0200, Oleg Nesterov wrote:
> > Hi Tycho,
> > 
> > Before anything else, let me remind that I do not really understand
> > this code.
> > 
> > Not only I am very new to criu, I know almost nothing about this
> > mount black magic. I still have no idea what this slave/shared/etc
> > actually means, and I am thinking in horror that sooner or later
> > I will need to read the docs ;)
> > 
> > That said.
> > 
> > On 04/14, Tycho Andersen wrote:
> > >
> > > > Perhaps resolve_external_mounts() should skip the fsroot_mounted() mount
> > > > points at least? Although afaics this is not enough too.
> > >
> > > I think we can't do an fsroot_mounted() check as we discussed here:
> > >
> > > http://lists.openvz.org/pipermail/criu/2015-April/019744.html
> > 
> > Thanks, will read tomorrow. But yes, yes, I understand that
> > fsroot_mounted() is not an option.
> > 
> > > but yes, something does look wrong :). In this case, the mounts are
> > > actually the same mounts, just in different namespaces. Perhaps
> > > mounts_equal()
> > 
> > As you already pointed out, this can't work. But let's ignore this.
> > 
> > Afaics, we obviously need the
> > 
> > 	bool come_on_this_mount_doesn_t_need_external()
>

+1

I suggested something like this here:
http://lists.openvz.org/pipermail/criu/2015-April/019592.html

> :D
> 
> > helper called by resolve_external_mounts(). But this is not enough, the
> > problem is worse (I think).
> > 
> > What should we do with other ->external checks? Just for example, don't
> > we need to chanhge collect_shared()
> > 
> > 	- if (need_master && m->parent && !m->external)
> > 	+ if (need_master && m->parent && !m->external &&
> > 	      !come_on_this_mount_doesn_t_need_external(m))
> 
> If we have that above, I think it just won't be resolved so the
> external bit should be false here, so I think at this point we should
> still print the error.
> 
> > ?
> > 
> > And can_mount_now() looks suspicious too....
> 
> I think (?) this is only a problem if we support internal sharing of
> external mounts, which I gave up on because I didn't want to figure
> out how to fix it right now :).
> 
> Tycho
> 
> > Oleg.
> > 
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