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Subject: virtio_console: Fix poll blocking even though there is data to read
From: Hans de Goede <hdegoede@redhat.com>

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 <hdegoede@redhat.com>
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;