libcamera: sysfs: Add helper to lookup sysfs path of a character device

Add a helper function to lookup the sysfs path of a character device.
Store the function in a new libcamera::sysfs namespace as there is not
class to host it.

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

include/libcamera/internal/meson.build

@@ -25,6 +25,7 @@ libcamera_internal_headers = files([
     'process.h',
     'pub_key.h',
     'semaphore.h',
+    'sysfs.h',
     'thread.h',
     'utils.h',
     'v4l2_controls.h',

include/libcamera/internal/sysfs.h

@@ -0,0 +1,22 @@
+/* SPDX-License-Identifier: LGPL-2.1-or-later */
+/*
+ * Copyright (C) 2020, Google Inc.
+ *
+ * sysfs.h - Miscellaneous utility functions to access sysfs
+ */
+#ifndef __LIBCAMERA_INTERNAL_SYSFS_H__
+#define __LIBCAMERA_INTERNAL_SYSFS_H__
+
+#include <string>
+
+namespace libcamera {
+
+namespace sysfs {
+
+std::string charDevPath(const std::string &deviceNode);
+
+} /* namespace sysfs */
+
+} /* namespace libcamera */
+
+#endif /* __LIBCAMERA_INTERNAL_SYSFS_H__ */