[CRIU] [PATCH v2] tty: Restore controlling terminal once per session

[Andrew Vagin]

On Fri, Nov 06, 2015 at 04:07:43PM +0300, Cyrill Gorcunov wrote:
> On Thu, Nov 05, 2015 at 08:06:48PM +0300, Cyrill Gorcunov wrote:
> > There might be several same terminals opened (say
> > tty6 or whatever) which gonna look as a seaprate
> > files but actually pointing into same tty kernel
> > instance. Moreover if it's a controlling terminal
> > we will be trying to restore it as many times as
> > find non zero sid on the peer.
> > 
> 
> An updated variant attached.

> From 64eafbd295f2e907793f81e3c7bff4904b5342c0 Mon Sep 17 00:00:00 2001
> From: Cyrill Gorcunov <gorcunov at openvz.org>
> Date: Thu, 5 Nov 2015 20:05:41 +0300
> Subject: [PATCH v2] tty: Restore controlling terminal once per session
> 
> There might be several same terminals opened (say
> tty6 or whatever) which gonna look as separate
> files but actually pointing to the same tty kernel
> instance. Moreover if it's a controlling terminal
> we will be trying to restore it as many times as
> find non zero sid on a peer.
> 
> Instead lets do a simple trick first: choose a leader
> from a terminal group and use it only for controlling
> terminal restoration.
> 
> https://jira.sw.ru/browse/PSBM-40969
>

Reviewed-by: Andrew Vagin <avagin at odin.com>

> Signed-off-by: Cyrill Gorcunov <gorcunov at openvz.org>
> ---
>  tty.c | 36 ++++++++++++++++++++++++++++++++++++
>  1 file changed, 36 insertions(+)
> 
> diff --git a/tty.c b/tty.c
> index 63a6ba24eb73..3f1bc18be664 100644
> --- a/tty.c
> +++ b/tty.c
> @@ -92,6 +92,8 @@ struct tty_info {
>  
>  	bool				create;
>  	bool				inherit;
> +
> +	struct tty_info			*ctl_tty;
>  };
>  
>  struct tty_dump_info {
> @@ -1080,6 +1082,14 @@ static int tty_find_restoring_task(struct tty_info *info)
>  		}
>  
>  		/*
> +		 * Restoring via leader only. All files
> +		 * opened over same real tty get propagated
> +		 * automatically by kernel itself.
> +		 */
> +		if (info->ctl_tty != info)
> +			return 0;
> +
> +		/*
>  		 * Find out the task which is session leader
>  		 * and it can restore the controlling terminal
>  		 * for us.
> @@ -1159,6 +1169,31 @@ int tty_setup_slavery(void)
>  {
>  	struct tty_info *info, *peer, *m;
>  
> +	/*
> +	 * The image may carry several terminals opened
> +	 * belonging to the same session, so choose the
> +	 * leader which gonna be setting up the controlling
> +	 * terminal.
> +	 */
> +	list_for_each_entry(info, &all_ttys, list) {
> +		if (!info->tie->sid || info->ctl_tty ||
> +		    info->driver->type == TTY_TYPE__CTTY)
> +			continue;
> +
> +		info->ctl_tty = info;
> +		pr_debug("ctl tty leader %x\n", info->tfe->id);
> +		peer = info;
> +		list_for_each_entry_safe_continue(peer, m, &all_ttys, list) {
> +			if (!peer->tie->sid || peer->ctl_tty ||
> +			    peer->driver->type == TTY_TYPE__CTTY)
> +				continue;
> +			if (peer->tie->sid == info->tie->sid) {
> +				pr_debug(" `- slave %x\n", peer->tfe->id);
> +				peer->ctl_tty = info;
> +			}
> +		}
> +	}
> +
>  	list_for_each_entry(info, &all_ttys, list) {
>  		if (tty_find_restoring_task(info))
>  			return -1;
> @@ -1316,6 +1351,7 @@ static int collect_one_tty(void *obj, ProtobufCMessage *msg)
>  	info->driver = get_tty_driver(major(info->tie->rdev), minor(info->tie->rdev));
>  	info->create = tty_is_master(info);
>  	info->inherit = false;
> +	info->ctl_tty = NULL;
>  
>  	if (verify_info(info))
>  		return -1;
> -- 
> 2.4.3
>