v4l2: v4l2_compat: Add eventfd signaling to support polling

To support polling, we need to be able to signal when data is
available to be read (POLLIN), as well as events (POLLPRI). Add the
necessary calls to eventfd to allow signaling POLLIN. We signal POLLIN
by writing writing to the eventfd, and clear it by reading from the
eventfd, upon VIDIOC_DQBUF.

Note that eventfd does not support signaling POLLPRI, so we don't yet
support V4L2 events.

Signed-off-by: Paul Elder <paul.elder@ideasonboard.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>

1 files changed, 6 insertions, 1 deletions

diff --git a/src/v4l2/v4l2_compat_manager.cpp b/src/v4l2/v4l2_compat_manager.cpp
index 2338a0ee..56533c4f 100644
--- a/src/v4l2/v4l2_compat_manager.cpp
+++ b/src/v4l2/v4l2_compat_manager.cpp
@@ -155,12 +155,17 @@ int V4L2CompatManager::openat(int dirfd, const char *path, int oflag, mode_t mod
 	if (ret < 0)
 		return ret;
 
-	int efd = eventfd(0, oflag & (O_CLOEXEC | O_NONBLOCK));
+	int efd = eventfd(0, EFD_SEMAPHORE |
+			     ((oflag & O_CLOEXEC) ? EFD_CLOEXEC : 0) |
+			     ((oflag & O_NONBLOCK) ? EFD_NONBLOCK : 0));
 	if (efd < 0) {
+		int err = errno;
 		proxy->close();
+		errno = err;
 		return efd;
 	}
 
+	proxy->bind(efd);
 	devices_.emplace(efd, proxy);
 
 	return efd;