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 <hdego...@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
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