[CRIU] Restore CRIU image across a host

[Tycho Andersen]

On Tue, Aug 04, 2015 at 05:01:14PM -0400, Hui Kang wrote:
> Hi,
> I am trying to restore the process on a different criu host by transferring
> the CRIU images. The checkpointed criu images are scp-ed to a different
> host; however the restore fails. The restore.log shows that
> 
> (00.075765)      1: nr_restored_pages: 66
> (00.075772)      1: nr_shared_pages:   0
> (00.075779)      1: nr_droped_pages:   0
> (00.075829)      1: Found fd 1 (id pipe:[13922]) in inherit fd list (caller
> close_old_fds)
> (00.075841)      1: Found fd 2 (id pipe:[13923]) in inherit fd list (caller
> close_old_fds)
> (00.075859)      1: cg: Move into 2
>  1: cg:   `-> blkio//[PID]/tasks
> (00.075906)      1: cg:   `-> cpu//[PID]/tasks
> (00.075946)      1: cg:   `-> cpuacct//[PID]/tasks
> (00.075967)      1: cg:   `-> cpuset//[PID]/tasks
> (00.076008)      1: Error (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.
> 
> Note that the process being migrated has its cgroup directory in the source
> node, which apparently does not exist in the destination host. So I first
> mkdir /sys/fs/cgroup/cpu/PID .... and copy the content from the source to
> destination.

You might want to use one of the new `--manage-cgroups full` mode to
do this for you. That said, moving something into cpuset's tasks fails
with ENOSPC for the following reasons (from cpuset(7)):

       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.

So depending on what you copied over, it can cause some problems. In
`--manage-cgroups full` mode, criu's code should be smart enough to handle
things, though.

Tycho

> Is there anything wrong in these steps? Thanks.
> 
> - Hui

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