From mboxrd@z Thu Jan  1 00:00:00 1970
Received: from [140.186.70.92] (port=38452 helo=eggs.gnu.org)
	by lists.gnu.org with esmtp (Exim 4.43) id 1PNlBA-0003Hq-ID
	for qemu-devel@nongnu.org; Wed, 01 Dec 2010 06:48:58 -0500
Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71)
	(envelope-from <amit.shah@redhat.com>) id 1PNlB8-00022N-Ne
	for qemu-devel@nongnu.org; Wed, 01 Dec 2010 06:48:56 -0500
Received: from mx1.redhat.com ([209.132.183.28]:39559)
	by eggs.gnu.org with esmtp (Exim 4.71)
	(envelope-from <amit.shah@redhat.com>) id 1PNlB8-000227-Gz
	for qemu-devel@nongnu.org; Wed, 01 Dec 2010 06:48:54 -0500
Date: Wed, 1 Dec 2010 17:18:37 +0530
From: Amit Shah <amit.shah@redhat.com>
Subject: Re: [Qemu-devel] [PATCH v8 7/7] virtio-console: Enable port
	throttling when chardev is slow to consume data
Message-ID: <20101201114837.GB2962@amit-x200.redhat.com>
References: <cover.1291196789.git.amit.shah@redhat.com>
	<90e8c0b7db1086c38283f684a159a892b4a66228.1291196789.git.amit.shah@redhat.com>
	<201012011130.58630.paul@codesourcery.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <201012011130.58630.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.nongnu.org/archive/html/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 (Wed) Dec 01 2010 [11:30:58], Paul Brook wrote:
> >  /* Callback function that's called when the guest sends us data */
> >  static void flush_buf(VirtIOSerialPort *port, const uint8_t *buf, size_t
> > len) {
> >      VirtConsole *vcon = DO_UPCAST(VirtConsole, port, port);
> > +    int ret;
> > 
> > -    qemu_chr_write(vcon->chr, buf, len);
> > +    ret = qemu_chr_write(vcon->chr, buf, len);
> > +    if (ret == -EAGAIN) {
> > +        virtio_serial_throttle_port(port, true);
> > +    }
> >  }
> 
> This looks wrong. It will loose data in the case of a partial write
> (i.e. ret < len)

That doesn't happen currently (qemu_chr_write doesn't return a value > 0
but < len).

I had code in there to handle it, but that would change behaviour for
current users of qemu_chr_write(), which is a risk.

		Amit