[libcamera-devel] [PATCH v2 6/7] v4l2: v4l2_compat: Add eventfd signaling to support polling

[Paul Elder]

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 at ideasonboard.com>

---
Changes in v2: use eventfd instead of socket
---
 src/v4l2/v4l2_camera.cpp         |  9 +++++++++
 src/v4l2/v4l2_camera.h           |  3 +++
 src/v4l2/v4l2_camera_proxy.cpp   | 10 ++++++++++
 src/v4l2/v4l2_camera_proxy.h     |  4 ++++
 src/v4l2/v4l2_compat_manager.cpp |  7 ++++++-
 5 files changed, 32 insertions(+), 1 deletion(-)

diff --git a/src/v4l2/v4l2_camera.cpp b/src/v4l2/v4l2_camera.cpp
index 4da01a45..3c369328 100644
--- a/src/v4l2/v4l2_camera.cpp
+++ b/src/v4l2/v4l2_camera.cpp
@@ -8,6 +8,7 @@
 #include "v4l2_camera.h"
 
 #include <errno.h>
+#include <unistd.h>
 
 #include "libcamera/internal/log.h"
 
@@ -53,6 +54,11 @@ void V4L2Camera::close()
 	camera_->release();
 }
 
+void V4L2Camera::bind(int efd)
+{
+	efd_ = efd;
+}
+
 void V4L2Camera::getStreamConfig(StreamConfiguration *streamConfig)
 {
 	*streamConfig = config_->at(0);
@@ -84,6 +90,9 @@ void V4L2Camera::requestComplete(Request *request)
 	completedBuffers_.push_back(std::move(metadata));
 	bufferLock_.unlock();
 
+	uint64_t data = 1;
+	::write(efd_, &data, sizeof(data));
+
 	bufferSema_.release();
 }
 
diff --git a/src/v4l2/v4l2_camera.h b/src/v4l2/v4l2_camera.h
index 303eda44..33f5eb02 100644
--- a/src/v4l2/v4l2_camera.h
+++ b/src/v4l2/v4l2_camera.h
@@ -39,6 +39,7 @@ public:
 
 	int open();
 	void close();
+	void bind(int efd);
 	void getStreamConfig(StreamConfiguration *streamConfig);
 	std::vector<Buffer> completedBuffers();
 
@@ -70,6 +71,8 @@ private:
 
 	std::deque<std::unique_ptr<Request>> pendingRequests_;
 	std::deque<std::unique_ptr<Buffer>> completedBuffers_;
+
+	int efd_;
 };
 
 #endif /* __V4L2_CAMERA_H__ */
diff --git a/src/v4l2/v4l2_camera_proxy.cpp b/src/v4l2/v4l2_camera_proxy.cpp
index cbe9e026..7ee4c0cb 100644
--- a/src/v4l2/v4l2_camera_proxy.cpp
+++ b/src/v4l2/v4l2_camera_proxy.cpp
@@ -13,6 +13,7 @@
 #include <linux/videodev2.h>
 #include <string.h>
 #include <sys/mman.h>
+#include <unistd.h>
 
 #include <libcamera/camera.h>
 #include <libcamera/object.h>
@@ -451,6 +452,9 @@ int V4L2CameraProxy::vidioc_dqbuf(struct v4l2_buffer *arg)
 
 	currentBuf_ = (currentBuf_ + 1) % bufferCount_;
 
+	uint64_t data;
+	::read(efd_, &data, sizeof(data));
+
 	return 0;
 }
 
@@ -529,6 +533,12 @@ int V4L2CameraProxy::ioctl(unsigned long request, void *arg)
 	return ret;
 }
 
+void V4L2CameraProxy::bind(int fd)
+{
+	efd_ = fd;
+	vcam_->bind(fd);
+}
+
 struct PixelFormatPlaneInfo {
 	unsigned int bitsPerPixel;
 	unsigned int hSubSampling;
diff --git a/src/v4l2/v4l2_camera_proxy.h b/src/v4l2/v4l2_camera_proxy.h
index af9f9bbe..7c65c886 100644
--- a/src/v4l2/v4l2_camera_proxy.h
+++ b/src/v4l2/v4l2_camera_proxy.h
@@ -33,6 +33,8 @@ public:
 
 	int ioctl(unsigned long request, void *arg);
 
+	void bind(int fd);
+
 private:
 	bool validateBufferType(uint32_t type);
 	bool validateMemoryType(uint32_t memory);
@@ -77,6 +79,8 @@ private:
 	std::map<void *, unsigned int> mmaps_;
 
 	std::unique_ptr<V4L2Camera> vcam_;
+
+	int efd_;
 };
 
 #endif /* __V4L2_CAMERA_PROXY_H__ */
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;
-- 
2.20.1