Re: [RFC v2 1/4] v4l: return POLLERR on V4L2 sub-devices if no events are subscribed

[Hans Verkuil]

On 10/02/13 15:45, Sakari Ailus wrote:

From: Teemu Tuominen <teemux.tuomi...@intel.com>

Add check and return POLLERR from subdev_poll() in case of no events
subscribed and wakeup once the last event subscription is removed.

This change is essentially done to add possibility to wakeup polling
with concurrent unsubscribe.

Signed-off-by: Teemu Tuominen <teemux.tuomi...@intel.com>

Move the check after calling poll_wait(). Otherwise it's possible that we go
to sleep without getting notified if the subscription went away between the
two.

Signed-off-by: Sakari Ailus <sakari.ai...@linux.intel.com>
Tested-by: Teemu Tuominen <teemux.tuomi...@intel.com>

Acked-by: Hans Verkuil <hans.verk...@cisco.com>

Regards,

        Hans

---
  drivers/media/v4l2-core/v4l2-event.c  | 15 +++++++++++++++
  drivers/media/v4l2-core/v4l2-subdev.c |  3 +++
  include/media/v4l2-event.h            |  1 +
  3 files changed, 19 insertions(+)

diff --git a/drivers/media/v4l2-core/v4l2-event.c 
b/drivers/media/v4l2-core/v4l2-event.c
index 86dcb54..b53897e 100644
--- a/drivers/media/v4l2-core/v4l2-event.c
+++ b/drivers/media/v4l2-core/v4l2-event.c
@@ -107,6 +107,19 @@ static struct v4l2_subscribed_event *v4l2_event_subscribed(
        return NULL;
  }

+bool v4l2_event_has_subscribed(struct v4l2_fh *fh)
+{
+       unsigned long flags;
+       bool rval;
+
+       spin_lock_irqsave(&fh->vdev->fh_lock, flags);
+       rval = !list_empty(&fh->subscribed);
+       spin_unlock_irqrestore(&fh->vdev->fh_lock, flags);
+
+       return rval;
+}
+EXPORT_SYMBOL(v4l2_event_has_subscribed);
+
  static void __v4l2_event_queue_fh(struct v4l2_fh *fh, const struct v4l2_event 
*ev,
                const struct timespec *ts)
  {
@@ -299,6 +312,8 @@ int v4l2_event_unsubscribe(struct v4l2_fh *fh,
                        fh->navailable--;
                }
                list_del(&sev->list);
+               if (list_empty(&fh->subscribed))
+                       wake_up_all(&fh->wait);
        }

        spin_unlock_irqrestore(&fh->vdev->fh_lock, flags);
diff --git a/drivers/media/v4l2-core/v4l2-subdev.c 
b/drivers/media/v4l2-core/v4l2-subdev.c
index 996c248..7d72389 100644
--- a/drivers/media/v4l2-core/v4l2-subdev.c
+++ b/drivers/media/v4l2-core/v4l2-subdev.c
@@ -382,6 +382,9 @@ static unsigned int subdev_poll(struct file *file, 
poll_table *wait)
        if (v4l2_event_pending(fh))
                return POLLPRI;

+       if (!v4l2_event_has_subscribed(fh))
+               return POLLERR | POLLPRI;
+
        return 0;
  }

diff --git a/include/media/v4l2-event.h b/include/media/v4l2-event.h
index be05d01..a9ca2b5 100644
--- a/include/media/v4l2-event.h
+++ b/include/media/v4l2-event.h
@@ -121,6 +121,7 @@ struct v4l2_subscribed_event {

  int v4l2_event_dequeue(struct v4l2_fh *fh, struct v4l2_event *event,
                       int nonblocking);
+bool v4l2_event_has_subscribed(struct v4l2_fh *fh);
  void v4l2_event_queue(struct video_device *vdev, const struct v4l2_event *ev);
  void v4l2_event_queue_fh(struct v4l2_fh *fh, const struct v4l2_event *ev);
  int v4l2_event_pending(struct v4l2_fh *fh);

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