[libcamera-devel] [PATCH v2 5/8] libcamera: v4l2_videodevice: Prevent queueing buffers without a cache

[Kieran Bingham]

The v4l2 buffer cache allows us to map incoming buffers to an instance
of the V4L2 Buffer required to actually queue.

If the cache_ is not available, then the buffers required to allow
queuing to a device have been released, and this indicates an issue at
the pipeline handler.

This could be a common mistake, as it could happen if a pipeline handler
always requeues buffers to the device after they complete, without
checking if they are cancelled.

That can then lead to trying to queue a buffer to a device which no
longer expects buffers, so add a loud message to indicate what has
happened but return an error without fatally crashing.

Signed-off-by: Kieran Bingham <kieran.bingham at ideasonboard.com>
---
 src/libcamera/v4l2_videodevice.cpp | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/src/libcamera/v4l2_videodevice.cpp b/src/libcamera/v4l2_videodevice.cpp
index cb52d4cea3f6..12c09dc7578d 100644
--- a/src/libcamera/v4l2_videodevice.cpp
+++ b/src/libcamera/v4l2_videodevice.cpp
@@ -1391,6 +1391,16 @@ int V4L2VideoDevice::queueBuffer(FrameBuffer *buffer)
 	struct v4l2_buffer buf = {};
 	int ret;
 
+	/*
+	 * Pipeline handlers should not requeue buffers after releasing the
+	 * buffers on the device. Any occurence of this error should be fixed
+	 * in the pipeline handler directly.
+	 */
+	if (!cache_) {
+		LOG(V4L2, Fatal) << "No BufferCache available to queue.";
+		return -ENOENT;
+	}
+
 	ret = cache_->get(*buffer);
 	if (ret < 0)
 		return ret;
-- 
2.25.1