[libvirt] [PATCH RFC 2/5] lxc: make container's init process session leader

[Daniel P. Berrange]

On Thu, Jul 21, 2016 at 03:37:24PM +0000, Katerina Koukiou wrote:
> This patch forces container's init process, to become a session leader,
> that is its session ID is made the same as its process ID.
> That might seem unnecessary in general, but if we want to checkpoint a
> container with CRIU, which is needed for container migration,
> we must ensure that the SID of each process inside the container points
> to a process that lives in the same PID namespace as the container.
> Therefore, we force that the session leader is the init.
> 
> Signed-off-by: Katerina Koukiou <k.koukiou at gmail.com>
> ---
>  src/lxc/lxc_container.c | 8 ++++++++
>  1 file changed, 8 insertions(+)
> 
> diff --git a/src/lxc/lxc_container.c b/src/lxc/lxc_container.c
> index 916a37b..b857431 100644
> --- a/src/lxc/lxc_container.c
> +++ b/src/lxc/lxc_container.c
> @@ -2245,6 +2245,14 @@ static int lxcContainerChild(void *data)
>                               argv->npassFDs, argv->passFDs) < 0)
>          goto cleanup;
>  
> +    /* Make init process of the container the leader of the new session.
> +     * That is needed when checkpointing container.
> +     */
> +    if (setsid() < 0) {
> +        virReportSystemError(errno, "%s",
> +                             _("Unable to become session leader"));
> +    }

Needs a goto cleanup, otherwise the error code gets set to 0

> +
>      ret = 0;
>   cleanup:
>      VIR_FREE(ttyPath);

This is a clear bugfix we need even ignoring CRIU reqiurements, so I've
pushed this with the fix mentioned. For example, it fixes running of
a shell as pid 1 which previously reported

sh: cannot set terminal process group (-1): Inappropriate ioctl for device
sh: no job control in this shell


Regards,
Daniel
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