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Date: Tue, 29 Jul 2003 10:36:30 -0700
From: Andrew Morton <akpm@osdl.org>
To: Andries.Brouwer@cwi.nl
Cc: torvalds@osdl.org, linux-kernel@vger.kernel.org,
       Manfred Spraul <manfred@colorfullife.com>
Subject: Re: [PATCH] select fix
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Andries.Brouwer@cwi.nl wrote:
>
> Recently people complained on lk about a problem: one sees
> 
> select(2, NULL, [1], NULL, NULL)        = 1 (out [1])
> write(1, "hi\n", 3)                     = -1 EAGAIN (Resource temporarily unavailable)
> 
> for a stopped tty opened with O_NONBLOCK. This violates POSIX,
> and the 100% CPU use in a select loop does not look pretty either.
> The below fixes this.
> ...
>
> -	if (tty->driver->chars_in_buffer(tty) < WAKEUP_CHARS)
> +	if (!tty->stopped && tty->driver->chars_in_buffer(tty) < WAKEUP_CHARS)
>  		mask |= POLLOUT | POLLWRNORM;

Manfred sent a patch through esterday which addresses it this way:

-	if (tty->driver->chars_in_buffer(tty) < WAKEUP_CHARS)
+	if (tty->driver->chars_in_buffer(tty) < WAKEUP_CHARS &&
+			tty->driver->write_room(tty) > 0)

Any preferences?