[CRIU] [PATCH] criu: tty -- Restore tty params synchronously

[Cyrill Gorcunov]

On Thu, Apr 21, 2016 at 9:02 PM, Cyrill Gorcunov <gorcunov at gmail.com> wrote:
> On Thu, Apr 21, 2016 at 08:48:49PM +0300, Pavel Emelyanov wrote:
>> >>
>> >> But the restore fails anyway, so we do we care?
>> >
>> > Yes we care. The restoration of params must be done on alive terminals.
>>
>> OK, but if terminal is dead, then the restore is failing. So why not
>> have one more failure in logs?
>
> Because in this case we don't control when real async ioctl is called,
> as far as I understand we may hit it earlier and hide real case of
> problem.
>
> After all your questions, I started doubting if the changelog is correct.
> For sure the reason of failure is async ioctl call over terminal
> which is not alive (since with the patch container passes this point
> of restore) but maybe I've overlooked something. Gimme some time...

You know, we may fail inbetween, having restore-tty-params request in the fly.
Imagine

pty_open_unpaired_slave
pty_open_slaves
  ...
  fd = open_tty_reg()
  restore_tty_params --> sends request
  send_fd_to_peer(fd) -> it fails
  close_safe(&fd);
  return -1;
now pty_open_unpaired_slave will close the master but then in-flight
request may start and will exit with error.
Moreover I think we should not call userns_call if there is no p.has
set. I will optimize it on top.
So please merge this patch.