From mboxrd@z Thu Jan  1 00:00:00 1970
Received: from mailman by lists.gnu.org with tmda-scanned (Exim 4.43)
	id 1NyzQb-0003Se-P0
	for qemu-devel@nongnu.org; Mon, 05 Apr 2010 23:26:13 -0400
Received: from [140.186.70.92] (port=54887 helo=eggs.gnu.org)
	by lists.gnu.org with esmtp (Exim 4.43) id 1NyzQZ-0003SN-KW
	for qemu-devel@nongnu.org; Mon, 05 Apr 2010 23:26:12 -0400
Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.69)
	(envelope-from <amit.shah@redhat.com>) id 1NyzQX-0007sl-Mj
	for qemu-devel@nongnu.org; Mon, 05 Apr 2010 23:26:11 -0400
Received: from mx1.redhat.com ([209.132.183.28]:25076)
	by eggs.gnu.org with esmtp (Exim 4.69)
	(envelope-from <amit.shah@redhat.com>) id 1NyzQX-0007sR-EG
	for qemu-devel@nongnu.org; Mon, 05 Apr 2010 23:26:09 -0400
Date: Tue, 6 Apr 2010 08:54:29 +0530
From: Amit Shah <amit.shah@redhat.com>
Subject: Re: [Qemu-devel] [PATCH 1/5] char: Let the caller know how many
	bytes were written in case of incomplete writes
Message-ID: <20100406032429.GB4135@amit-x200.redhat.com>
References: <1270471538-31275-1-git-send-email-amit.shah@redhat.com>
	<1270471538-31275-2-git-send-email-amit.shah@redhat.com>
	<201004051733.38629.paul@codesourcery.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <201004051733.38629.paul@codesourcery.com>
List-Id: qemu-devel.nongnu.org
List-Unsubscribe: <http://lists.nongnu.org/mailman/listinfo/qemu-devel>,
	<mailto:qemu-devel-request@nongnu.org?subject=unsubscribe>
List-Archive: <http://lists.gnu.org/pipermail/qemu-devel>
List-Post: <mailto:qemu-devel@nongnu.org>
List-Help: <mailto:qemu-devel-request@nongnu.org?subject=help>
List-Subscribe: <http://lists.nongnu.org/mailman/listinfo/qemu-devel>,
	<mailto:qemu-devel-request@nongnu.org?subject=subscribe>
To: Paul Brook <paul@codesourcery.com>
Cc: Juan Quintela <quintela@redhat.com>, qemu-devel@nongnu.org, Gerd Hoffmann <kraxel@redhat.com>

On (Mon) Apr 05 2010 [17:33:38], Paul Brook wrote:
> > There might be cases where a few bytes would have been sent out to char
> > devices and some not. Currently the return values from qemu_chr_write()
> > to char devs are only -1, indicating an error, or the complete length
> > of the string passed.
> > 
> > Make 'len' a pointer instead, and indicate how much of the string was
> > written. The return value will either be the same as 'len' or a negative
> > number indicating an error condition.
> 
> This seems wrong. We should not be getting recoverable errors.

I was thinking of adding a bool to CharDriverState to indicate if EAGAIN
should be reported to the writer. This can be conveyed at the time of
doing qemu_chr_add_handlers().

It would certainly be beneficial for consumers of virtio-serial to be
notified of -EAGAIN so that the guest can be throttled till the chardev
catches up with the data being sent.

		Amit