linux-kernel - Re: [PATCH] tty: Fix tcdrain hang due to tty chars_in

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Message-ID: <20090717170124.05881456@lxorguk.ukuu.org.uk>
Date:	Fri, 17 Jul 2009 17:01:24 +0100
From:	Alan Cox <alan@...rguk.ukuu.org.uk>
To:	Jeff Harris <jeff_harris@...trox.com>
Cc:	alan@...ux.intel.com, vapier@...too.org, adobriyan@...il.com,
	linux-kernel@...r.kernel.org, Jeff Harris <jeff_harris@...trox.com>
Subject: Re: [PATCH] tty: Fix tcdrain hang due to tty chars_in_buffer errors

On Fri, 17 Jul 2009 11:07:54 -0400
Jeff Harris <jeff_harris@...trox.com> wrote:

> If a tty driver's chars_in_buffer callback reports an error, the wait loop in

chars_in_buffer cannot report an error. It reports how many characters
are in the buffer.

> A process calling tcdrain will block indefinitely if it calls tcdrain when the
> device is disconnected.

Fix your chars_in_buffer. On a disconnect its quite reasonable to return
0, as they are not buffered any more.

Alan
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