linux-kernel - Re: Q.: Why does tty_ioctl.c: set_termios return EINTR instead of ERESTARTSYS?

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Message-ID: <4E994A65.7000509@suse.cz>
Date:	Sat, 15 Oct 2011 10:55:01 +0200
From:	Jiri Slaby <jslaby@...e.cz>
To:	Godmar Back <godmar@...il.com>
CC:	linux-kernel@...r.kernel.org, Alan Cox <alan@...rguk.ukuu.org.uk>,
	Greg KH <gregkh@...e.de>
Subject: Re: Q.: Why does tty_ioctl.c: set_termios return EINTR instead of
 ERESTARTSYS?

On 10/14/2011 06:52 PM, Godmar Back wrote:
> A student in my OS class noticed during their shell assignment that
> tcsetattr() is being interrupted with EINTR even though they had set
> SA_RESTART.
> 
> Upon taking a closer look, I noticed that
> drivers/char/tty_ioctl.c:set_termios(), which lies on the code path
> for the POSIX tcsetattr() function, returns -EINTR when a signal is
> pending. Consequently, the SA_RESTART flag is not honored and user
> code must check for and handle EINTR.
> 
> I don't immediately see what would prevent this system call from being
> restartable.
> 
> Is there a particular reason why it cannot be made restartable?

EINTR is used when there is no way to rollback already performed
actions. In this case, a flush could be performed. (This holds only for
TCSETSF, TCSETSF2 and similar.) So I think this is the reason we cannot
return ERESTARTSYS.

However I CCed tty fellows, they may have a different opinion.

regards,
-- 
js
suse labs
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