linux-kernel - Re: [PATCH] tty: Fix async io write notifications

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Message-ID: <20081124142128.11cb3d06@lxorguk.ukuu.org.uk>
Date:	Mon, 24 Nov 2008 14:21:28 +0000
From:	Alan Cox <alan@...rguk.ukuu.org.uk>
To:	Thomas Pfaff <tpfaff@....com>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] tty: Fix async io write notifications

On Mon, 24 Nov 2008 14:40:15 +0100 (CET)
Thomas Pfaff <tpfaff@....com> wrote:

> he N_TTY ldisc layer does not send SIGIO POLL_OUTs correctly when output is 
> possible due to flawed handling of the TTY_DO_WRITE_WAKEUP bit. It will either 
> send no SIGIOs at all or on every tty wakeup.
> 
> The fix is to set the bit when the tty driver write would block and test and 
> clear it on write wakeup.
> 
> Signed-off-by: Thomas Pfaff <tpfaff@....com>

I had done a patch already but yours is somewhat nicer so I've merged
yours instead with some tweaks as it clashed with an existing N_TTY patch

I left the tty->fasync check in the if (in case the user clears async I/O
events) and I reversed the tests on the end of n_tty_write simply
because the compiler has the variables we need to check to hand but not
tty->fasync.

This all looks good to me. It breaks on ptys but that is another bug and
I'll merge a patch to fix the ptys next.

Alan
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