linux-kernel - Re: [PATCH resend v2] tty: n_tty -- Add new TIOCPEEKRAW ioctl to peek unread data

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Date:	Thu, 26 May 2016 22:32:52 +0300
From:	Cyrill Gorcunov <gorcunov@...il.com>
To:	Peter Hurley <peter@...leysoftware.com>
Cc:	LKML <linux-kernel@...r.kernel.org>, Jiri Slaby <jslaby@...e.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Andrey Vagin <avagin@...tuozzo.com>,
	Pavel Emelianov <xemul@...tuozzo.com>,
	Vladimir Davydov <vdavydov@...tuozzo.com>,
	Konstantin Khorenko <khorenko@...tuozzo.com>
Subject: Re: [PATCH resend v2] tty: n_tty -- Add new TIOCPEEKRAW ioctl to
 peek unread data

On Tue, Apr 12, 2016 at 12:42:11AM +0300, Cyrill Gorcunov wrote:
...
> I think so. At least this gives some kind of consistensy while we're
> fetching data. Something close to peeking data from pipes/sockets.
> 
> > In that case, I think just write trylocking the termios rwsem should
> > prevent any parallel i/o, at least for the N_TTY line discipline.
> > 
> > This should only interfere with processes not being dumped because
> > ptrace signalling should have ejected any process to be dumped out
> > of their i/o loops (readers or writers).
> > 
> > Also, I think we should further limit the interface based on what is
> > supported currently; IOW, check that the driver is either pty or vt,
> > assert that the line discipline is N_TTY at both ends, etc.
> 
> Thats a good idea, thanks, will do!

It's almost a month passed, so I'm really sorry for delay in response
(been trying to implement pty c/r on userspace level together with
other stuff). Peter, I believe your initial idea of fetching data
via native read inside criu works well for us so far. We've been
playing with tests and they are passing just fine. Thanks a huge
for all your comments and overall help!

	Cyrill