v4l2-event: Add v4l2_subscribed_event_ops

Quoted 7 lines

Review

Quoted 7 lines

(quoted diff) +7 -0

+	if (sev->ops && sev->ops->add) {
+		int ret = sev->ops->add(sev);
+		if (ret) {
+			sev->ops = NULL;
+			v4l2_event_unsubscribe(fh, sub);
+			return ret;
+		}

The problem here is that the event is basically available for use after the spin_unlock_irqrestore(), but before the sev->ops->add() call. In the past I just 'knew' that the event would never be generated by the control framework until after v4l2_ctrl_add_event was called, but this should be formalized now that these ops are added.

I see two options:

1) Have some method to mark the sev as being 'invalid' so functions sending events can skip it (needed as well for your patch 4/6).

2) Document that drivers should never be able to send an event until after the add() callback has succeeded.

I am leaning towards option 1 myself.

How about leaving sev->elems at 0 until after the add() op succeeds?

That's easy to test against and easy to implement.