libcamera: base: Introduce UniqueFD

This introduces UniqueFD. It acts like unique_ptr to a file descriptor.

Signed-off-by: Hirokazu Honda <hiroh@chromium.org>
Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Hirokazu Honda <hiroh@chromium.org>

include/libcamera/base/meson.build

@@ -24,6 +24,7 @@ libcamera_base_headers = files([
     'thread.h',
     'thread_annotations.h',
     'timer.h',
+    'unique_fd.h',
     'utils.h',
 ])
 

include/libcamera/base/unique_fd.h

@@ -0,0 +1,69 @@
+/* SPDX-License-Identifier: LGPL-2.1-or-later */
+/*
+ * Copyright (C) 2021, Google Inc.
+ *
+ * unique_fd.h - File descriptor wrapper that owns a file descriptor.
+ */
+
+#pragma once
+
+#include <utility>
+
+#include <libcamera/base/class.h>
+#include <libcamera/base/compiler.h>
+
+namespace libcamera {
+
+class UniqueFD final
+{
+public:
+	UniqueFD()
+		: fd_(-1)
+	{
+	}
+
+	explicit UniqueFD(int fd)
+		: fd_(fd)
+	{
+	}
+
+	UniqueFD(UniqueFD &&other)
+		: fd_(other.release())
+	{
+	}
+
+	~UniqueFD()
+	{
+		reset();
+	}
+
+	UniqueFD &operator=(UniqueFD &&other)
+	{
+		reset(other.release());
+		return *this;
+	}
+
+	__nodiscard int release()
+	{
+		int fd = fd_;
+		fd_ = -1;
+		return fd;
+	}
+
+	void reset(int fd = -1);
+
+	void swap(UniqueFD &other)
+	{
+		std::swap(fd_, other.fd_);
+	}
+
+	int get() const { return fd_; }
+	bool isValid() const { return fd_ >= 0; }
+
+private:
+	LIBCAMERA_DISABLE_COPY(UniqueFD)
+
+	int fd_;
+};
+
+} /* namespace libcamera */