vfs: add modification time member to directory_service

Issue #1784.

repos/os/include/vfs/dir_file_system.h

@@ -462,6 +462,7 @@ class Vfs::Dir_file_system : public File_system
 				out.gid    = 0;
 				out.inode  = 1;
 				out.device = (Genode::addr_t)this;
+				out.modification_time = { Vfs::Timestamp::INVALID };
 				return STAT_OK;
 			}
 

repos/os/include/vfs/directory_service.h

@@ -160,6 +160,7 @@ struct Vfs::Directory_service : Interface
 		unsigned      gid    = 0;
 		unsigned long inode  = 0;
 		unsigned long device = 0;
+		Timestamp     modification_time { Timestamp::INVALID };
 	};
 
 	enum Stat_result { STAT_ERR_NO_ENTRY = NUM_GENERAL_ERRORS,

repos/os/include/vfs/file_io_service.h

@@ -172,6 +172,20 @@ struct Vfs::File_io_service : Interface
 	virtual bool queue_sync(Vfs_handle *) { return true; }
 
 	virtual Sync_result complete_sync(Vfs_handle *) { return SYNC_OK; }
+
+	/***********************
+	 ** Modification time **
+	 ***********************/
+
+	/**
+	 * Update the modification time of a file
+	 *
+	 * \return true if update attempt was successful
+	 */
+	virtual bool update_modification_timestamp(Vfs_handle *, Vfs::Timestamp)
+	{
+		return true;
+	}
 };
 
 #endif /* _INCLUDE__VFS__FILE_IO_SERVICE_H_ */

repos/os/include/vfs/types.h

@@ -49,6 +49,12 @@ namespace Vfs {
 	using Genode::Interface;
 	using Genode::String;
 
+	struct Timestamp
+	{
+		static constexpr long long INVALID = (1LL << 63) + 1;
+		long long value;
+	};
+
 	typedef Genode::Path<MAX_PATH_LEN> Absolute_path;
 }