[CRIU] Checkpointing LXC with external bind mount plugin

[Yuto KAWAMURA]

2014-08-08 23:54 GMT+09:00 Cyrill Gorcunov <gorcunov at gmail.com>:
> On Thu, Aug 07, 2014 at 10:07:43PM +0900, Yuto KAWAMURA wrote:
>> Hi,
>>
>> I'm doing little experiment of checkpointing a lxc container which has
>> bind mounted pty from the host inside of it.
>> As already noted somewhere, I know that the external bind mount of the
>> lxc container can't be dumped without a plugin.
>> I wrote a plugin handles paths which has major number UNIX98_PTY_SLAVE_MAJOR.
>> After introduced this plugin, I'm not seeing an error such as
>> "/dev/ttyX doesn't have a proper root mount" anymore, but still I'm
>> getting an error:
>>
>>   Error (tty.c:222): tty: Unexpected format on path /dev/tty1
>>
>
> Not sure about mount points, hopefully Andrew answer this part,
> but for tty -- we expect pty to live on
>
> #define PTS_FMT"/dev/pts/%d"
>
> iirc lxc containers require special tricks for console. Take a look on
>
> http://criu.org/LXC
> https://lists.linuxcontainers.org/pipermail/lxc-devel/2013-November/006329.html
>
> would it help?
>

Right, I know this restriction for the LXC container, but in my
understanding it is possible to dump a pts bind mount inside a
container if I provide a proper plugin which handles it.
WRT example of external bind mount
plugin(http://git.criu.org/?p=criu.git;a=blob;f=test/mounts/ext/ext-mount.c;h=3ad3b25b4ce377189e9f0b9f4c1c44bc6684fdcd;hb=HEAD),
seems it has the responsibility to restore the mountpoint for the
mount that will be restored, so the criu does not have to dump/restore
the path of an external bind mountpoint.
I think we need to provide a function to prevent dumping a path which
was handled by a plugin, so then we could leave the responsibility of
managing these files to the plugin.

I still need more advanced advice, but thanks anyway :)

>> I think this is because the path /dev/tty1 is still mounted after the
>> plugin handled it, and judged as a character device in
>> dump_one_file at files.c.
>> The question is, how to avoid this error? or am I understanding
>> something incorrect? or should I consider to make some changes to
>> criu?
>>
>> I'm using the version HEAD of the criu git repository.