libcamera: v4l2_device: Update dequeued buffer information

Copy the information from the struct v4l2_buffer when dequeueing the
buffer as applications need this information to make sense of the
captured data.

Signed-off-by: Niklas Söderlund <niklas.soderlund@ragnatech.se>
Signed-off-by: Jacopo Mondi <jacopo@jmondi.org>
Signed-off-by: Kieran Bingham <kieran.bingham@ideasonboard.com>
Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>

src/libcamera/buffer.cpp

@@ -203,6 +203,32 @@ Buffer::Buffer()
  * \brief A Signal to provide notifications that the specific Buffer is ready
  */
 
+/**
+ * \fn Buffer::bytesused()
+ * \brief Retrieve the number of bytes occupied by the data in the buffer
+ * \return Number of bytes occupied in the buffer
+ */
+
+/**
+ * \fn Buffer::timestamp()
+ * \brief Retrieve the time when the buffer was processed
+ *
+ * The timestamp is expressed as a number number of nanoseconds since the epoch.
+ *
+ * \return Timestamp when the buffer was processed
+ */
+
+/**
+ * \fn Buffer::sequence()
+ * \brief Retrieve the buffer sequence number
+ *
+ * The sequence number is a monotonically increasing number assigned to the
+ * buffer processed by the stream. Gaps in the sequence numbers indicate
+ * dropped frames.
+ *
+ * \return Sequence number of the buffer
+ */
+
 /**
  * \class BufferPool
  * \brief A pool of buffers

src/libcamera/v4l2_device.cpp

@@ -9,6 +9,7 @@
 #include <string.h>
 #include <sys/ioctl.h>
 #include <sys/mman.h>
+#include <sys/time.h>
 #include <unistd.h>
 #include <vector>
 
@@ -723,7 +724,14 @@ Buffer *V4L2Device::dequeueBuffer()
 	if (--queuedBuffersCount_ == 0)
 		fdEvent_->setEnabled(false);
 
-	return &bufferPool_->buffers()[buf.index];
+	Buffer *buffer = &bufferPool_->buffers()[buf.index];
+
+	buffer->bytesused_ = buf.bytesused;
+	buffer->timestamp_ = buf.timestamp.tv_sec * 1000000000ULL
+			   + buf.timestamp.tv_usec * 1000ULL;
+	buffer->sequence_ = buf.sequence;
+
+	return buffer;
 }
 
 /**