libcamera: buffer: Store Request reference in Buffer

Add to the Buffer class methods to set and retrieve a reference to the
Request instance the buffer is part of.

As buffers outlive the Request they are associated with, the reference
is only temporary valid during the buffer completion interval (from when
the buffer gets queued to Camera for processing, until it gets marked as
completed).

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

include/libcamera/buffer.h

@@ -13,6 +13,7 @@
 namespace libcamera {
 
 class BufferPool;
+class Request;
 
 class Plane final
 {
@@ -52,14 +53,18 @@ public:
 	unsigned int sequence() const { return sequence_; }
 	Status status() const { return status_; }
 	std::vector<Plane> &planes() { return planes_; }
+	Request *request() const { return request_; }
 
 private:
 	friend class BufferPool;
 	friend class PipelineHandler;
+	friend class Request;
 	friend class V4L2Device;
 
 	void cancel();
 
+	void setRequest(Request *request) { request_ = request; }
+
 	unsigned int index_;
 	unsigned int bytesused_;
 	uint64_t timestamp_;
@@ -67,6 +72,7 @@ private:
 	Status status_;
 
 	std::vector<Plane> planes_;
+	Request *request_;
 };
 
 class BufferPool final

src/libcamera/buffer.cpp

@@ -196,7 +196,7 @@ void *Plane::mem()
  */
 
 Buffer::Buffer()
-	: index_(-1)
+	: index_(-1), request_(nullptr)
 {
 }
 
@@ -248,6 +248,22 @@ Buffer::Buffer()
  * \return The buffer status
  */
 
+/**
+ * \fn Buffer::request()
+ * \brief Retrieve the request this buffer belongs to
+ *
+ * The intended callers of this method are buffer completion handlers that
+ * need to associate a buffer to the request it belongs to.
+ *
+ * A Buffer is associated to a request by Request::prepare() and the
+ * association is valid until the buffer completes. The returned request
+ * pointer is valid only during that interval.
+ *
+ * \return The Request the Buffer belongs to, or nullptr if the buffer is
+ * either completed or not associated with a request
+ * \sa Buffer::setRequest()
+ */
+
 /**
  * \brief Mark a buffer as cancel by setting its status to BufferCancelled
  */
@@ -259,6 +275,13 @@ void Buffer::cancel()
 	status_ = BufferCancelled;
 }
 
+/**
+ * \fn Buffer::setRequest()
+ * \brief Set the request this buffer belongs to
+ *
+ * The intended callers are Request::prepare() and Request::completeBuffer().
+ */
+
 /**
  * \class BufferPool
  * \brief A pool of buffers

src/libcamera/request.cpp

@@ -141,6 +141,7 @@ int Request::prepare()
 
 	for (auto const &pair : bufferMap_) {
 		Buffer *buffer = pair.second;
+		buffer->setRequest(this);
 		pending_.insert(buffer);
 	}
 
@@ -177,6 +178,8 @@ bool Request::completeBuffer(Buffer *buffer)
 	int ret = pending_.erase(buffer);
 	ASSERT(ret == 1);
 
+	buffer->setRequest(nullptr);
+
 	return !hasPendingBuffers();
 }