[CRIU] Podman container migration

[Andrei Vagin]

On Wed, Jan 09, 2019 at 03:16:38PM +0100, Adrian Reber wrote:
> I started to look into migrating containers with Podman and I am
> currently stuck at files which are bind-mounted into the container:
> 
> If I checkpoint a container and restore it, it works.
> 
> If I checkpoint a container and transfer the checkpoint to another
> container it only works if the previous container is running, as
> CRIU fails to mount the file into the container.
> 
> Following is from the checkpointed container:
> 
>         {
>             "fstype": 5, 
>             "mnt_id": 368, 
>             "root_dev": "0:20", 
>             "parent_mnt_id": 367, 
>             "flags": "0x1000006", 
>             "root": "/containers/storage/overlay-containers/43d02fb390d236ec42c5119b6655be44157e4a61103bc827db3b0718feecc898/userdata/run/secrets", 
>             "mountpoint": "/run/secrets", 
>             "source": "tmpfs", 
>             "options": "size=2899748k,nr_inodes=724937,mode=755", 
>             "shared_id": 0, 
>             "master_id": 0, 
>             "sb_flags": "0x0", 
>             "ext_key": "/run/secrets"
>         }, 
> 
> 
> The main problem I see is that the storage location of the checkpointed
> container is part of "root".
> 
> Or do I have to make sure that the migrated container is using the same
> paths as the restored container.
> 
> I get the following error during restore, if I copy the checkpoint to another
> container.
> 
> (00.009274)      1: mnt: Start with 0:/tmp/.criu.mntns.d6UW28
> (00.009279)      1: mnt: 	Mounting overlay @/tmp/.criu.mntns.d6UW28/12-0000000000/ (0)
> (00.009285)      1: mnt: 367:/tmp/.criu.mntns.d6UW28/12-0000000000/ private 1 shared 0 slave 0
> (00.009295)      1: mnt: 	Mounting tmpfs @/tmp/.criu.mntns.d6UW28/12-0000000000/run/secrets (0)
> (00.009297)      1: mnt: 	Bind /var/run/containers/storage/overlay-containers/43d02fb390d236ec42c5119b6655be44157e4a61103bc827db3b0718feecc898/userdata/run/secrets to /tmp/.criu.mntns.d6UW28/12-0000000000/run/secrets
> (00.009326)      1: Error (criu/mount.c:2279): mnt: Can't mount at /tmp/.criu.mntns.d6UW28/12-0000000000/run/secrets: No such file or directory

runsc creates a destination directory for external mounts:
https://github.com/opencontainers/runc/blob/master/libcontainer/rootfs_linux.go#L278

when a container is restored, destination directories for external
mounts are not created, because we suppose that the container rootfs
will be restored or migrated too. CRIU and runsc doesn't handle a
container rootfs, so you need to do this in podman.


> (00.009331)      1: mnt: Start with 0:/tmp/.criu.mntns.d6UW28
> (00.027848) Error (criu/mount.c:3274): mnt: Can't remove the directory /tmp/.criu.mntns.d6UW28: No such file or directory
> (00.027860) Error (criu/cr-restore.c:2300): Restoring FAILED.
> 
> The checkpointed container has the ID 43d02fb390d236ec42c5119b6655be44157e4a61103bc827db3b0718feecc898
> and the restored container has the ID 5ff14ac246ec6624c9667767532436d6fa5e3abda2b4437dc4b0db2ff1ff661a
> 
> How do I tell CRIU to use another directory for the bind mount?
> 
> 		Adrian