libcamera: buffer: Create a MappedBuffer

Provide a MappedFrameBuffer helper class which will map
all of the Planes within a FrameBuffer and provide CPU addressable
pointers for those planes.

The MappedFrameBuffer implements the interface of the MappedBuffer
allowing other buffer types to be constructed of the same form, with a
common interface and cleanup.

This allows MappedBuffer instances to be created from Camera3Buffer types.

Mappings are removed upon destruction.

Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Kieran Bingham <kieran.bingham@ideasonboard.com>

include/libcamera/internal/buffer.h

@@ -0,0 +1,47 @@
+/* SPDX-License-Identifier: LGPL-2.1-or-later */
+/*
+ * Copyright (C) 2020, Google Inc.
+ *
+ * buffer.h - Internal buffer handling
+ */
+#ifndef __LIBCAMERA_INTERNAL_BUFFER_H__
+#define __LIBCAMERA_INTERNAL_BUFFER_H__
+
+#include <sys/mman.h>
+#include <vector>
+
+#include <libcamera/buffer.h>
+#include <libcamera/span.h>
+
+namespace libcamera {
+
+class MappedBuffer
+{
+public:
+	using Plane = Span<uint8_t>;
+
+	~MappedBuffer();
+
+	MappedBuffer(MappedBuffer &&other);
+	MappedBuffer &operator=(MappedBuffer &&other);
+
+	bool isValid() const { return error_ == 0; }
+	int error() const { return error_; }
+	const std::vector<Plane> &maps() const { return maps_; }
+
+protected:
+	MappedBuffer();
+
+	int error_;
+	std::vector<Plane> maps_;
+};
+
+class MappedFrameBuffer : public MappedBuffer
+{
+public:
+	MappedFrameBuffer(const FrameBuffer *buffer, int flags);
+};
+
+} /* namespace libcamera */
+
+#endif /* __LIBCAMERA_INTERNAL_BUFFER_H__ */