[libcamera-devel] [PATCH v6 7/7] libcamera: buffer: Store Request reference in Buffer

[Jacopo Mondi]

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

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

Signed-off-by: Jacopo Mondi <jacopo at jmondi.org>
---
 include/libcamera/buffer.h           |  6 +++++
 src/libcamera/buffer.cpp             | 34 +++++++++++++++++++++++++++-
 src/libcamera/pipeline/ipu3/ipu3.cpp |  2 +-
 src/libcamera/request.cpp            |  4 ++++
 4 files changed, 44 insertions(+), 2 deletions(-)

diff --git a/include/libcamera/buffer.h b/include/libcamera/buffer.h
index 0c844d126a27..8f9b42e39339 100644
--- a/include/libcamera/buffer.h
+++ b/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
diff --git a/src/libcamera/buffer.cpp b/src/libcamera/buffer.cpp
index e2d1cf04411e..550091c998a6 100644
--- a/src/libcamera/buffer.cpp
+++ b/src/libcamera/buffer.cpp
@@ -196,7 +196,7 @@ void *Plane::mem()
  */
 
 Buffer::Buffer()
-	: index_(-1)
+	: index_(-1), request_(nullptr)
 {
 }
 
@@ -248,6 +248,25 @@ 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
+ * needs to associated a buffer to the request it has been queued to.
+ *
+ * Buffers are associated to requests at Request::prepare() time and said
+ * association is valid until the buffer does not complete at
+ * Request::completeBuffer() time. Before and after the buffer completion
+ * interval (the time between when the request is queued to the Camera, and
+ * the buffer is marked as 'complete' by pipeline handlers) the reference to
+ * the request is set to nullptr.
+ *
+ * \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 +278,19 @@ void Buffer::cancel()
 	status_ = BufferCancelled;
 }
 
+/**
+ * \fn Buffer::setRequest()
+ * \brief Set the request this buffer belongs to
+ *
+ * Buffers are associated to Streams in a Request, which is then sent to the
+ * Camera for processing. This method stores in the Buffer a pointer to the
+ * Request this Buffer is part of, for later retrieval through the
+ * Buffer::request() method.
+ *
+ * The intended callers are the Request::prepare() and Request::completeBuffer()
+ * methods.
+ */
+
 /**
  * \class BufferPool
  * \brief A pool of buffers
diff --git a/src/libcamera/pipeline/ipu3/ipu3.cpp b/src/libcamera/pipeline/ipu3/ipu3.cpp
index f96e8763bce9..6f5747fb1505 100644
--- a/src/libcamera/pipeline/ipu3/ipu3.cpp
+++ b/src/libcamera/pipeline/ipu3/ipu3.cpp
@@ -633,7 +633,7 @@ void PipelineHandlerIPU3::IPU3CameraData::imguInputBufferReady(Buffer *buffer)
  */
 void PipelineHandlerIPU3::IPU3CameraData::imguOutputBufferReady(Buffer *buffer)
 {
-	Request *request = queuedRequests_.front();
+	Request *request = buffer->request();
 
 	pipe_->completeBuffer(camera_, request, buffer);
 	pipe_->completeRequest(camera_, request);
diff --git a/src/libcamera/request.cpp b/src/libcamera/request.cpp
index 1946845b91f4..9ae62f632308 100644
--- a/src/libcamera/request.cpp
+++ b/src/libcamera/request.cpp
@@ -144,6 +144,8 @@ int Request::prepare()
 
 	for (auto const &pair : bufferMap_) {
 		Buffer *buffer = pair.second;
+
+		buffer->setRequest(this);
 		pending_.insert(buffer);
 	}
 
@@ -180,6 +182,8 @@ bool Request::completeBuffer(Buffer *buffer)
 	int ret = pending_.erase(buffer);
 	ASSERT(ret == 1);
 
+	buffer->setRequest(nullptr);
+
 	return !hasPendingBuffers();
 }
 
-- 
2.21.0