[CRIU] [PATCH v3 1/2] restore: don't pass cgroup nsroot= option to mount()

[Tycho Andersen]

On Mon, Mar 28, 2016 at 10:57:36AM +0300, Pavel Emelyanov wrote:
> On 03/25/2016 10:26 PM, Tycho Andersen wrote:
> > https://lkml.org/lkml/2016/3/21/777 introduces a new cgroup mount option
> > called nsroot, but doesn't allow you to pass it to mount() to actually
> > mount it. Let's chop this option off so that we don't get errors from
> > mount().
> > 
> > There may be better places to chop this off (e.g. perhaps on dump),
> > although I think it is useful to have it in there for debugging purposes,
> > and only costs us a few extra bytes to keep it in the images since we're
> > going to have other cgroup options anyways.
> > 
> > v2: handle the case where nsroot= is not the last mount option
> > 
> > Signed-off-by: Tycho Andersen <tycho.andersen at canonical.com>
> > ---
> >  criu/mount.c | 20 ++++++++++++++++++++
> >  1 file changed, 20 insertions(+)
> > 
> > diff --git a/criu/mount.c b/criu/mount.c
> > index a425828..eb8d058 100644
> > --- a/criu/mount.c
> > +++ b/criu/mount.c
> > @@ -2866,6 +2866,26 @@ static int collect_mnt_from_image(struct mount_info **pms, struct ns_id *nsid)
> >  		/* FIXME: abort unsupported early */
> >  		pm->fstype = decode_fstype(me->fstype, me->fsname);
> >  
> > +		if (pm->fstype->code == FSTYPE__CGROUP) {
> 
> Can we fix the pm->options in the ->munge callback as well? To keep the generic
> code clean...

Sadly no :(. We need nsroot= to distinguish between bind mounts of
cgfs from the host, and mounts from a cgroup ns inside the container.
Without this, CRIU's bind mount autodetection matches them because the
superblock options are the same.

Tycho

> -- Pavel
> 
> > +			char *start;
> > +
> > +			start = strstr(pm->options, "nsroot=");
> > +			if (start) {
> > +				char *next = strchr(start, ',');
> > +
> > +				if (next) {
> > +					/* skip the `,' but include the terminating \0 */
> > +					memmove(start, next+1, strlen(next+1)+1);
> > +				} else {
> > +					if (start > pm->options && *(start-1) == ',')
> > +						start--;
> > +					*start = 0;
> > +				}
> > +
> > +				pr_info("trimmed nsroot option from cgroup mount, opts now: %s\n", pm->options);
> > +			}
> > +		}
> > +
> >  		if (get_mp_root(me, pm))
> >  			goto err;
> >  
> > 
>