[libcamera-devel] [RFC PATCH v1 07/12] libcamera: framebuffer: Allocate metadata planes at construction time

[Laurent Pinchart]

The metadata planes are allocated by V4L2VideoDevice when dequeuing a
buffer. This causes the metadata planes to only be allocated after a
buffer gets dequeued, and doesn't provide any strong guarantee that
their number matches the number of FrameBuffer planes. The lack of this
invariant makes the FrameBuffer class fragile.

As a first step towards fixing this, allocate the metadata planes when
the FrameBuffer is constructed. The FrameMetadata API should be further
improved by preventing a change in the number of planes.

Signed-off-by: Laurent Pinchart <laurent.pinchart at ideasonboard.com>
---
 src/libcamera/framebuffer.cpp      |  2 ++
 src/libcamera/v4l2_videodevice.cpp | 12 +++++++++---
 2 files changed, 11 insertions(+), 3 deletions(-)

diff --git a/src/libcamera/framebuffer.cpp b/src/libcamera/framebuffer.cpp
index 99265b44da43..c1529dfb0ad1 100644
--- a/src/libcamera/framebuffer.cpp
+++ b/src/libcamera/framebuffer.cpp
@@ -210,6 +210,8 @@ FrameBuffer::FrameBuffer(const std::vector<Plane> &planes, unsigned int cookie)
 	: Extensible(std::make_unique<Private>()), planes_(planes),
 	  cookie_(cookie)
 {
+	metadata_.planes.resize(planes_.size());
+
 	unsigned int offset = 0;
 
 	/* \todo Remove the assertions after sufficient testing */
diff --git a/src/libcamera/v4l2_videodevice.cpp b/src/libcamera/v4l2_videodevice.cpp
index adabd4720668..a51971879e75 100644
--- a/src/libcamera/v4l2_videodevice.cpp
+++ b/src/libcamera/v4l2_videodevice.cpp
@@ -1586,12 +1586,18 @@ FrameBuffer *V4L2VideoDevice::dequeueBuffer()
 	buffer->metadata_.timestamp = buf.timestamp.tv_sec * 1000000000ULL
 				    + buf.timestamp.tv_usec * 1000ULL;
 
-	buffer->metadata_.planes.clear();
 	if (multiPlanar) {
+		if (buf.length > buffer->metadata_.planes.size()) {
+			LOG(V4L2, Error)
+				<< "Invalid number of planes (" << buf.length
+				<< " != " << buffer->metadata_.planes.size() << ")";
+			return nullptr;
+		}
+
 		for (unsigned int nplane = 0; nplane < buf.length; nplane++)
-			buffer->metadata_.planes.push_back({ planes[nplane].bytesused });
+			buffer->metadata_.planes[nplane].bytesused = planes[nplane].bytesused;
 	} else {
-		buffer->metadata_.planes.push_back({ buf.bytesused });
+		buffer->metadata_.planes[0].bytesused = buf.bytesused;
 	}
 
 	return buffer;
-- 
Regards,

Laurent Pinchart