From mboxrd@z Thu Jan 1 00:00:00 1970 From: Hans de Goede Subject: PATCH: virtio_console: Fix poll blocking even though there is data to read Date: Wed, 15 Sep 2010 15:04:53 +0200 Message-ID: <4C90C475.4010809@redhat.com> Mime-Version: 1.0 Content-Type: multipart/mixed; boundary="------------050901040204040808020901" Cc: amit.shah@redhat.com, spice-devel@lists.freedesktop.org, rusty@rustcorp.com.au, kvm@vger.kernel.org To: virtualization@lists.linux-foundation.org Return-path: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: spice-devel-bounces+gcesd-spice-space-devel=m.gmane.org@lists.freedesktop.org Errors-To: spice-devel-bounces+gcesd-spice-space-devel=m.gmane.org@lists.freedesktop.org List-Id: kvm.vger.kernel.org This is a multi-part message in MIME format. --------------050901040204040808020901 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Hi All, I found this while working on a Linux agent for spice, the symptom I was seeing was select blocking on the spice vdagent virtio serial port even though there were messages queued up there. I found this while working on a Linux agent for spice, the symptom I was seeing was select blocking on the spice vdagent virtio serial port even though there were messages queued up there. virtio_console's port_fops_poll checks port->inbuf != NULL to determine if read won't block. However if an application reads enough bytes from inbuf through port_fops_read, to empty the current port->inbuf, port->inbuf will be NULL even though there may be buffers left in the virtqueue. This causes poll() to block even though there is data to be read, this patch fixes this by using the alredy defined will_read_block utility function instead of the port->inbuf != NULL check. Signed-off-By: Hans de Goede Regards, Hans --------------050901040204040808020901 Content-Type: text/plain; name="linux-2.6.35.4-virtio_console-fix-poll.patch" Content-Transfer-Encoding: 7bit Content-Disposition: attachment; filename="linux-2.6.35.4-virtio_console-fix-poll.patch" Subject: virtio_console: Fix poll blocking even though there is data to read From: Hans de Goede I found this while working on a Linux agent for spice, the symptom I was seeing was select blocking on the spice vdagent virtio serial port even though there were messages queued up there. virtio_console's port_fops_poll checks port->inbuf != NULL to determine if read won't block. However if an application reads enough bytes from inbuf through port_fops_read, to empty the current port->inbuf, port->inbuf will be NULL even though there may be buffers left in the virtqueue. This causes poll() to block even though there is data to be read, this patch fixes this by using the alredy defined will_read_block utility function instead of the port->inbuf != NULL check. Signed-off-By: Hans de Goede diff -up linux-2.6.35.x86_64/drivers/char/virtio_console.c~ linux-2.6.35.x86_64/drivers/char/virtio_console.c --- linux-2.6.35.x86_64/drivers/char/virtio_console.c~ 2010-08-02 00:11:14.000000000 +0200 +++ linux-2.6.35.x86_64/drivers/char/virtio_console.c 2010-09-15 13:39:29.043505000 +0200 @@ -642,7 +642,7 @@ static unsigned int port_fops_poll(struc poll_wait(filp, &port->waitqueue, wait); ret = 0; - if (port->inbuf) + if (!will_read_block(port)) ret |= POLLIN | POLLRDNORM; if (!will_write_block(port)) ret |= POLLOUT; --------------050901040204040808020901 Content-Type: text/plain; charset="us-ascii" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit Content-Disposition: inline --------------050901040204040808020901--