Hi,
On 09/15/2010 03:25 PM, Amit Shah wrote:
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.
That certainly works for me (as in will still fix the bug I'm hitting), but
quoting from "man 2 select":
Three independent sets of file descriptors are watched. Those listed
in readfds will be watched to see if characters become available for
reading (more precisely, to see if a read will not block; in particu‐
lar, a file descriptor is also ready on end-of-file)
Notice the "a file descriptor is also ready on end-of-file", and
port_fops_read treats the host not being connected as eof (it returns 0
in that case). So from an API pov I'm not sure what is correct.
Regards,
Hans
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