[libcamera-devel] [PATCH v1] v4l2: V4L2CameraProxy: Add support for PREPARE_BUF as one of the supported ioctl

[Vedant Paranjape]

Add support for PREPARE_BUF as one of the ioctl. Since this is a compat
layer, there doesn't seem to be an equivalent to the "transfer ownership
of the buffer to kernel driver" in V4L2Camera class.

To match the error checks done by kernel implementation, we'd have to
check if dmabuf fd is valid and that the buffer size is large enough.
Doing so will not add any particular value to the program as
applications don't depend on these conditions being handled correctly.

Signed-off-by: Vedant Paranjape <vedantparanjape160201 at gmail.com>
---
Source builds and tests fine, also passes the v4l2-compliance

<snip>
vedant at pc ~/libcamera$ ./test/v4l2_compat/v4l2_compat_test.py ./build/src/v4l2/v4l2-compat.so
Testing /dev/video0 with uvcvideo driver... success
</snip>

Still figuring out how to test this with v4l2-ctl, if you have hints
please let me know :)
---
src/v4l2/v4l2_camera_proxy.cpp | 28 ++++++++++++++++++++++++++++
 src/v4l2/v4l2_camera_proxy.h   |  1 +
 2 files changed, 29 insertions(+)

diff --git a/src/v4l2/v4l2_camera_proxy.cpp b/src/v4l2/v4l2_camera_proxy.cpp
index 4d529bc29a4d..8c28e8738a06 100644
--- a/src/v4l2/v4l2_camera_proxy.cpp
+++ b/src/v4l2/v4l2_camera_proxy.cpp
@@ -544,6 +544,33 @@ int V4L2CameraProxy::vidioc_querybuf(V4L2CameraFile *file, struct v4l2_buffer *a
 	return 0;
 }
 
+int V4L2CameraProxy::vidioc_prepare_buf(V4L2CameraFile *file, struct v4l2_buffer *arg)
+{
+	LOG(V4L2Compat, Debug) << "Servicing vidioc_prepare_buf, index = "
+			       << arg->index << " fd = " << file->efd();
+
+	if (!hasOwnership(file))
+		return -EBUSY;
+
+	if (arg->index >= bufferCount_)
+		return -EINVAL;
+
+	if (buffers_[arg->index].flags & V4L2_BUF_FLAG_REQUEST_FD ||
+	    buffers_[arg->index].flags & V4L2_BUF_FLAG_PREPARED)
+		return -EINVAL;
+
+	if (buffers_[arg->index].flags & V4L2_BUF_FLAG_QUEUED ||
+	    !validateBufferType(arg->type) ||
+	    !validateMemoryType(arg->memory))
+		return -EINVAL;
+
+	buffers_[arg->index].flags |= V4L2_BUF_FLAG_PREPARED;
+
+	arg->flags = buffers_[arg->index].flags;
+
+	return 0;
+}
+
 int V4L2CameraProxy::vidioc_qbuf(V4L2CameraFile *file, struct v4l2_buffer *arg)
 {
 	LOG(V4L2Compat, Debug) << "Servicing vidioc_qbuf, index = "
@@ -709,6 +736,7 @@ const std::set<unsigned long> V4L2CameraProxy::supportedIoctls_ = {
 	VIDIOC_S_INPUT,
 	VIDIOC_REQBUFS,
 	VIDIOC_QUERYBUF,
+	VIDIOC_PREPARE_BUF,
 	VIDIOC_QBUF,
 	VIDIOC_DQBUF,
 	VIDIOC_EXPBUF,
diff --git a/src/v4l2/v4l2_camera_proxy.h b/src/v4l2/v4l2_camera_proxy.h
index 14e027c3e7d1..6baba94262a9 100644
--- a/src/v4l2/v4l2_camera_proxy.h
+++ b/src/v4l2/v4l2_camera_proxy.h
@@ -57,6 +57,7 @@ private:
 	int vidioc_s_input(V4L2CameraFile *file, int *arg);
 	int vidioc_reqbufs(V4L2CameraFile *file, struct v4l2_requestbuffers *arg);
 	int vidioc_querybuf(V4L2CameraFile *file, struct v4l2_buffer *arg);
+	int vidioc_prepare_buf(V4L2CameraFile *file, struct v4l2_buffer *arg);
 	int vidioc_qbuf(V4L2CameraFile *file, struct v4l2_buffer *arg);
 	int vidioc_dqbuf(V4L2CameraFile *file, struct v4l2_buffer *arg,
 			 libcamera::Mutex *lock) LIBCAMERA_TSA_REQUIRES(*lock);
-- 
2.25.1