[4.2.y-ckt stable] Patch "[media] vb2: fix a regression in poll() behavior for output, streams" has been added to the 4.2.y-ckt tree

[Kamal Mostafa]

This is a note to let you know that I have just added a patch titled

    [media] vb2: fix a regression in poll() behavior for output,streams

to the linux-4.2.y-queue branch of the 4.2.y-ckt extended stable tree 
which can be found at:

    http://kernel.ubuntu.com/git/ubuntu/linux.git/log/?h=linux-4.2.y-queue

This patch is scheduled to be released in version 4.2.8-ckt3.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 4.2.y-ckt tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Kamal

---8<------------------------------------------------------------

>From 168889e823cd4112eb3f10439f6abc6cab9cb304 Mon Sep 17 00:00:00 2001
From: Hans Verkuil <hverkuil at xs4all.nl>
Date: Thu, 29 Oct 2015 03:02:06 -0200
Subject: [media] vb2: fix a regression in poll() behavior for output,streams

commit 4623e5967448444a4ea1e77beb58898c4af48693 upstream.

In the 3.17 kernel the poll() behavior changed for output streams:
as long as not all buffers were queued up poll() would return that
userspace can write. This is fine for the write() call, but when
using stream I/O this changed the behavior since the expectation
was that it would wait for buffers to become available for dequeuing.

This patch only enables the check whether you can queue buffers
for file I/O only, and skips it for stream I/O.

Signed-off-by: Hans Verkuil <hans.verkuil at cisco.com>
Acked-by: Laurent Pinchart <laurent.pinchart at ideasonboard.com>
Signed-off-by: Hans Verkuil <hans.verkuil at cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab at osg.samsung.com>
[ kamal: backport to 4.2-stable: file rename; context ]
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
---
 drivers/media/v4l2-core/videobuf2-core.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/drivers/media/v4l2-core/videobuf2-core.c b/drivers/media/v4l2-core/videobuf2-core.c
index a14c428..340f9ff 100644
--- a/drivers/media/v4l2-core/videobuf2-core.c
+++ b/drivers/media/v4l2-core/videobuf2-core.c
@@ -2686,10 +2686,10 @@ unsigned int vb2_poll(struct vb2_queue *q, struct file *file, poll_table *wait)
 		return res | POLLERR;

 	/*
-	 * For output streams you can write as long as there are fewer buffers
-	 * queued than there are buffers available.
+	 * For output streams you can call write() as long as there are fewer
+	 * buffers queued than there are buffers available.
 	 */
-	if (V4L2_TYPE_IS_OUTPUT(q->type) && q->queued_count < q->num_buffers)
+	if (V4L2_TYPE_IS_OUTPUT(q->type) && q->fileio && q->queued_count < q->num_buffers)
 		return res | POLLOUT | POLLWRNORM;

 	if (list_empty(&q->done_list)) {
--
1.9.1