[libcamera-devel] [RFC PATCH 3/5] libcamera: v4l2 device: Store buffer info in planes

[Gabby George]

To perform a memory mapping using mmap, the MappedFrameBuffer class needs the plane offset and file descriptor information of the frame buffer's plane(s). This information is provided in the response to REQBUF, which happens during buffer allocation. Store the plane offset and file descriptor information in the buffer's plane at the time of allocation.

Currently, there is a metadata buffer type (metadata format UVCH) that does not support exporting buffers using EXPBUF, so this should only be done if the buffer type is metadata capture.

Signed-off-by: Gabby George <gabbymg94 at gmail.com>
---
 src/libcamera/v4l2_videodevice.cpp | 32 ++++++++++++++++++++----------
 1 file changed, 21 insertions(+), 11 deletions(-)

diff --git a/src/libcamera/v4l2_videodevice.cpp b/src/libcamera/v4l2_videodevice.cpp
index a72ef64d..8cf427c0 100644
--- a/src/libcamera/v4l2_videodevice.cpp
+++ b/src/libcamera/v4l2_videodevice.cpp
@@ -1402,18 +1402,28 @@ std::unique_ptr<FrameBuffer> V4L2VideoDevice::createBuffer(unsigned int index)
 
 	std::vector<FrameBuffer::Plane> planes;
 	for (unsigned int nplane = 0; nplane < numPlanes; nplane++) {
-		UniqueFD fd = exportDmabufFd(buf.index, nplane);
-		if (!fd.isValid())
-			return nullptr;
-
 		FrameBuffer::Plane plane;
-		plane.fd = SharedFD(std::move(fd));
-		/*
-		 * V4L2 API doesn't provide dmabuf offset information of plane.
-		 * Set 0 as a placeholder offset.
-		 * \todo Set the right offset once V4L2 API provides a way.
-		 */
-		plane.offset = 0;
+
+		if (buf.type != V4L2_BUF_TYPE_META_CAPTURE) {
+			UniqueFD fd = exportDmabufFd(buf.index, nplane);
+			if (!fd.isValid())
+				return nullptr;
+			plane.fd = SharedFD(std::move(fd));
+
+			/*
+			* V4L2 API doesn't provide dmabuf offset information of plane.
+			* Set 0 as a placeholder offset.
+			* \todo Set the right offset once V4L2 API provides a way.
+			*/
+			plane.offset = 0;
+		} else {
+			/* Dmabuf fd is not exported for metadata, so store
+			 * the offset from the querybuf call and this device's fd.
+			 */
+			SharedFD tmp(this->fd());
+			plane.fd = tmp;
+			plane.offset = buf.m.offset;
+		}
 		plane.length = multiPlanar ? buf.m.planes[nplane].length : buf.length;
 
 		planes.push_back(std::move(plane));
-- 
2.34.1