media: v4l2-dev: add EPOLLPRI in v4l2_poll() when dev is unregistered

If the V4L2 device was unregistered, then add EPOLLPRI to
the poll mask. Otherwise a select() that only waits for
exceptions will not wake up. A select() that waits for
read and/or write events *will* wake up on an EPOLLERR, but
not (for some reason) if it just waits for exceptions.

Strangly the epoll functionality will wakeup on EPOLLERR if
you just wait for an exception, so in this respect select()
and epoll differ.

In the end it doesn't really matter, what matters is that
polling file handles are woken up on device unregistration.

It also improves the code a bit if vdev->fops->poll is NULL:
this didn't check for device unregistration.

Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>

diff --git a/drivers/media/v4l2-core/v4l2-dev.c b/drivers/media/v4l2-core/v4l2-dev.c
index 0ddc3554f1a4cb5778cc8d2737c5449e27fb746c..f9cff033d0dc86d7fbd426ec9a03303be5d6cc7e 100644 (file)
--- a/drivers/media/v4l2-core/v4l2-dev.c
+++ b/drivers/media/v4l2-core/v4l2-dev.c
@@ -339,12 +339,14 @@ static ssize_t v4l2_write(struct file *filp, const char __user *buf,
 static __poll_t v4l2_poll(struct file *filp, struct poll_table_struct *poll)
 {
        struct video_device *vdev = video_devdata(filp);
-       __poll_t res = EPOLLERR | EPOLLHUP;
+       __poll_t res = EPOLLERR | EPOLLHUP | EPOLLPRI;
 
-       if (!vdev->fops->poll)
-               return DEFAULT_POLLMASK;
-       if (video_is_registered(vdev))
-               res = vdev->fops->poll(filp, poll);
+       if (video_is_registered(vdev)) {
+               if (!vdev->fops->poll)
+                       res = DEFAULT_POLLMASK;
+               else
+                       res = vdev->fops->poll(filp, poll);
+       }
        if (vdev->dev_debug & V4L2_DEV_DEBUG_POLL)
                dprintk("%s: poll: %08x\n",
                        video_device_node_name(vdev), res);