libcamera: file_descriptor: Add a function to retrieve the inode

The inode is useful to check if two file descriptors refer to the same
file. Add a function to retrieve it.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Kieran Bingham <kieran.bingham@ideasonboard.com>
Reviewed-by: Jean-Michel Hautbois <jeanmichel.hautbois@ideasonboard.com>
Reviewed-by: Paul Elder <paul.elder@ideasonboard.com>
Reviewed-by: Hirokazu Honda <hiroh@chromium.org>

include/libcamera/file_descriptor.h

@@ -8,6 +8,7 @@
 #define __LIBCAMERA_FILE_DESCRIPTOR_H__
 
 #include <memory>
+#include <sys/types.h>
 
 namespace libcamera {
 
@@ -27,6 +28,8 @@ public:
 	int fd() const { return fd_ ? fd_->fd() : -1; }
 	FileDescriptor dup() const;
 
+	ino_t inode() const;
+
 private:
 	class Descriptor
 	{