[CRIU] [PATCH] criu: Add exec-cmd option (v2)

[Pavel Emelyanov]

On 03/20/2014 08:40 PM, Christopher Covington wrote:
> Hi Deyan,
> 
> On 03/20/2014 12:24 PM, Deyan Doychev wrote:
>> From: Deyan Doychev <deyandoichev at gmail.com>
>>
>> The --exec-cmd option specifies a command that will be execvp()-ed on successful
>> restore. This way the command specified here will become the parent process of
>> the restored process tree.
>>
>> When this option is specified criu will fork to become a daemon before it starts
>> restoring the processes. It also implies the -d option so waiting for the
>> restored processes to finish is responsibility of the command specified here.
>>
>> This option will be used when restoring LinuX Containers and it seems helpful
>> for perf or other use cases when restored processes must be supervised by a
>> parent.
>>
>> Two directions were researched in order to integrate CRIU and LXC:
>>
>> 1. We tell to CRIU, that after restoring container is should execve()
>>    lxc properly explaining to it that there's a new container hanging
>>    around.
>>
>> 2. We make LXC set himself as child subreaper, then fork() criu and ask
>>    it to detach (-d) from restore container afterwards. Being a subreaper,
>>    it should get the container's init into his child list after it.
>>
>> The main reason for choosing the first option is that the second one can't work
>> with the RPC service. If we call restore via the service then criu service will
>> be the top-most task in the hierarchy and will not be able to reparent the
>> restore trees to any other task in the system. Calling execve from service
>> worker sub-task (and daemonizing it) should solve this.
> 
> Looks good overall. On the subject of file descriptor sharing, I wonder if all
> of the CRIU open, dup, etc. calls should also be changed to use the O_CLOEXEC
> flag?

Presumably they should. There're quite a few of them, I'm pretty sure
that the main criu task only uses some service fds. By the way, what do
you think about redirecting the logfd into 1 and 2 before exec()-ing?


Thanks,
Pavel