libcamera: camera: Validate Request before queueing it

Extend the Request::prepare() operation to validate the request before
preparing it. Return an error if the request is invalid, which for now
is limited to ensuring that the request contains at least one buffer.

Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Jacopo Mondi <jacopo@jmondi.org>

2 files changed, 19 insertions, 4 deletions

diff --git a/src/libcamera/camera.cpp b/src/libcamera/camera.cpp
index 2d0a8066..75a21008 100644
--- a/src/libcamera/camera.cpp
+++ b/src/libcamera/camera.cpp
@@ -713,9 +713,14 @@ Request *Camera::createRequest()
  * \brief Queue a request to the camera
  * \param[in] request The request to queue to the camera
  *
- * This method queues a \a request allocated with createRequest() to the camera
- * for capture. Once the request has been queued, the camera will notify its
- * completion through the \ref requestCompleted signal.
+ * This method queues a \a request to the camera for capture.
+ *
+ * After allocating the request with createRequest(), the application shall
+ * fill it with at least one capture buffer before queuing it. Requests that
+ * contain no buffers are invalid and are rejected without being queued.
+ *
+ * Once the request has been queued, the camera will notify its completion
+ * through the \ref requestCompleted signal.
  *
  * Ownership of the request is transferred to the camera. It will be deleted
  * automatically after it completes.
diff --git a/src/libcamera/request.cpp b/src/libcamera/request.cpp
index e5c25d2c..95818a26 100644
--- a/src/libcamera/request.cpp
+++ b/src/libcamera/request.cpp
@@ -115,10 +115,20 @@ Buffer *Request::findBuffer(Stream *stream) const
  */
 
 /**
- * \brief Prepare the resources for the completion handler
+ * \brief Validate the request and prepare it for the completion handler
+ *
+ * Requests that contain no buffers are invalid and are rejected.
+ *
+ * \return 0 on success or a negative error code otherwise
+ * \retval -EINVAL The request is invalid
  */
 int Request::prepare()
 {
+	if (bufferMap_.empty()) {
+		LOG(Request, Error) << "Invalid request due to missing buffers";
+		return -EINVAL;
+	}
+
 	for (auto const &pair : bufferMap_) {
 		Buffer *buffer = pair.second;
 		pending_.insert(buffer);