Re: PATCH: virtio_console: Fix poll blocking even though there is data to read

[Amit Shah <amit.shah@redhat.com>]

On (Wed) Sep 15 2010 [15:04:53], Hans de Goede wrote:
> 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 <hdegoede@redhat.com>
> 
> Regards,
> 
> Hans

> 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))

Looks correct, but this should be

	if (port_has_data(port))

instead.

will_read_block() also tests if the host is connected, which is not what
we want for POLLIN to be set.

		Amit