[libvirt] [PATCH] LXC: create a bind mount for sysfs when enable userns but disable netns

Daniel P. Berrange berrange at redhat.com
Thu Mar 19 17:28:27 UTC 2015


On Thu, Mar 19, 2015 at 06:04:57PM +0100, Richard Weinberger wrote:
> Am 19.03.2015 um 17:58 schrieb Daniel P. Berrange:
> > On Thu, Mar 19, 2015 at 05:54:32PM +0100, Richard Weinberger wrote:
> >> Am 11.03.2015 um 10:36 schrieb Richard Weinberger:
> >>> Am 11.03.2015 um 03:30 schrieb Chen, Hanxiao:
> >>>>>> @@ -826,8 +829,25 @@ static int lxcContainerMountBasicFS(bool userns_enabled)
> >>>>>>          bool bindOverReadonly;
> >>>>>>          virLXCBasicMountInfo const *mnt = &lxcBasicMounts[i];
> >>>>>>
> >>>>>> +        /* When enable userns but disable netns, kernel will
> >>>>>> +         * forbid us doing a new fresh mount for sysfs.
> >>>>>> +         * So we had to do a bind mount for sysfs instead.
> >>>>>> +         */
> >>>>>> +        if (userns_enabled && netns_disabled &&
> >>>>>> +            STREQ(mnt->src, "sysfs")) {
> >>>>>> +            if (VIR_STRDUP(mnt_src, "/sys") < 0) {
> >>>>>> +                goto cleanup;
> >>>>>> +            }
> >>>>>
> >>>>> This is clearly broken and looks very untested to me.
> >>>>>
> >>>> It's broken now.
> >>>> But when I submitted this patch last year, it's not.
> >>>
> >>> Are you sure?
> >>> Just built libvirt v1.2.6-222-ga86b621, head is
> >>> commit a86b6215a74b1feb2667204e214fbfd2f7decc5c
> >>> Author: Chen Hanxiao <chenhanxiao at cn.fujitsu.com>
> >>> Date:   Mon Jul 14 18:01:51 2014 +0800
> >>>
> >>>     LXC: create a bind mount for sysfs when enable userns but disable netns
> >>>
> >>> /sys is still an empty directory but as at this time (most likely due to another bug)
> >>> libvirt was able to create /sys/fs/cgroup and mounted groups there.
> >>> But no sysfs at all is at /sys.
> >>>
> >>> I mean, how is this supposed to work? You bind mount /sys over /sys...
> >>
> >> Any further comments on that?
> > 
> > It just looks impossible for it to work in this way
> 
> That's also my impression.
> 
> Therefore containers without their own network namespace currently don't work
> and have never worked as expected.

No, it is only a problem if userns is used. If userns is not used then
they do work

> Shall we revert commit a86b6215a74b and try to bind mount
> before the pivot_root()?

Not sure if that works with userns is active either.

Regards,
Daniel
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