[libcamera-devel] [PATCH v3 16/30] 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>
Reviewed-by: Jean-Michel Hautbois <jeanmichel.hautbois at ideasonboard.com>
Reviewed-by: Hirokazu Honda <hiroh at chromium.org>
---
Changes since v1:

- Return buffer with state set to FrameError on error
---
 src/libcamera/framebuffer.cpp      |  2 ++
 src/libcamera/v4l2_videodevice.cpp | 10 +++++-----
 2 files changed, 7 insertions(+), 5 deletions(-)

diff --git a/src/libcamera/framebuffer.cpp b/src/libcamera/framebuffer.cpp
index e71c2ffae034..e4f8419a9063 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;
 	bool isContiguous = true;
 	ino_t inode = 0;
diff --git a/src/libcamera/v4l2_videodevice.cpp b/src/libcamera/v4l2_videodevice.cpp
index 281f3f13fc9c..81209e485c24 100644
--- a/src/libcamera/v4l2_videodevice.cpp
+++ b/src/libcamera/v4l2_videodevice.cpp
@@ -1675,7 +1675,6 @@ FrameBuffer *V4L2VideoDevice::dequeueBuffer()
 
 	unsigned int numV4l2Planes = multiPlanar ? buf.length : 1;
 	FrameMetadata &metadata = buffer->metadata_;
-	metadata.planes.clear();
 
 	if (numV4l2Planes != buffer->planes().size()) {
 		/*
@@ -1705,8 +1704,9 @@ FrameBuffer *V4L2VideoDevice::dequeueBuffer()
 				return buffer;
 			}
 
-			metadata.planes.push_back({ std::min(plane.length, bytesused) });
-			bytesused -= metadata.planes.back().bytesused;
+			metadata.planes[i].bytesused =
+				std::min(plane.length, bytesused);
+			bytesused -= metadata.planes[i].bytesused;
 		}
 	} else if (multiPlanar) {
 		/*
@@ -1715,9 +1715,9 @@ FrameBuffer *V4L2VideoDevice::dequeueBuffer()
 		 * V4L2 buffer is guaranteed to be equal at this point.
 		 */
 		for (unsigned int i = 0; i < numV4l2Planes; ++i)
-			metadata.planes.push_back({ planes[i].bytesused });
+			metadata.planes[i].bytesused = planes[i].bytesused;
 	} else {
-		metadata.planes.push_back({ buf.bytesused });
+		metadata.planes[0].bytesused = buf.bytesused;
 	}
 
 	return buffer;
-- 
Regards,

Laurent Pinchart