[CRIU] Restore CRIU image across a host

[Hui Kang]

Hi, Tycho

On Wed, Aug 5, 2015 at 9:39 AM, Tycho Andersen <tycho.andersen at canonical.com
> wrote:

> Hi Hui,
>
> On Tue, Aug 04, 2015 at 11:15:25PM -0400, Hui Kang wrote:
> > Hi, Tycho
> > I created a patch
> > (http://lists.openvz.org/pipermail/criu/2015-August/021576.html) and
> > pass cgrou_manage as CG_MODE_FULL to the criu service. From the
> > restore.log, I can see that criu will smartly create all the cgroup
> > directories. However, the restore still fails at this cpu of wrting to
> >
> > (cgroup.c:901): cg: Can't move into cpuset//[PID]/tasks (-1/0): No
> > space left on device
> > (00.082249) Error (cr-restore.c:1919): Restoring FAILED.
> >
> > As Tycho pointed that:
> >
> > >> >        ENOSPC Attempted to write(2) the process ID (PID) of  a
> process
> > >> > to  a  cpuset
> > >> >               tasks file when the cpuset had an empty cpuset.cpus
> or empty
> > >> > cpuset.mems
> > >> >               setting.
> > >> >
> > >> >        ENOSPC Attempted to write(2) an empty cpuset.cpus or
> cpuset.mems
> > >> > setting  to  a
> > >> >               cpuset that has tasks attached.
>
> There are a few different things going on here,
>
> > I verify that cpuset.cpus (created by CRIU full cg manage) in the
> > destination host is empty, while cpuset.cpus in the source host is
> > "0-3".
> >
> > Further, when I attemped to write "0-3" to the cpuset.cpus in the
> > destination host before restoring, it gave permission error.
> >
> > echo "0-3" > /sys/fs/cgroup/cpuset/[PID]/cpuset.cpus
> > -bash: echo: write error: Permission denied
>
> You're probably not root here, so you need to do something like:
>
> $ echo "0-3" | sudo tee /sys/fs/cgroup/cpuset/foo/cpuset.cpus
> 0-3
>
> otherwise you'll get EPERM.
>

I tried both sudo and root to restore and write to the cpuset.cpus file;
both failed and gave me the error

tee: /sys/fs/cgroup/cpuset/foo/cpuset.cpus: Permission denied


>
> > Should CRIU write some default value to the cpuset.cpus file when
> > creating the director? This could help restoring processes with cgroup
> > across host. If so, I would be more than happy to work on a patch.
> > Thanks.


> It should already try to do this in restore_special_cpuset_props(),
> although it seems that bit isn't working for you. If you want to
> debug, that's probably a good place to start.
>

In fact the restoration of cgroup on a different host fails in the function
restore_cgroup_prop. The error message I got is

prepare_cgroup_dirs
(00.001362) cg: Created cgroup dir cpuset/foo
(00.001429) Error (cgroup.c:978): cg: Failed closing
cpuset/foo/cpuset.cpus: Permission denied
(00.001441) Error (cgroup.c:1085): cg: Restoring special cpuset props
failed!

 Then I changed chmod 777 to cpuset/foot and got those "permission denied"
or "no space left" error.


I am guessing that current criu implementation failed to propogate the
cgroup dir across host. Have you ever test this? Thanks.

- Hui


> Tycho
>
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