file_system_session: add modification time

* add modification_time member
* add WRITE_TIMESTAMP packet

repos/os/include/file_system_session/file_system_session.h

@@ -71,6 +71,26 @@ namespace File_system {
 	typedef Genode::uint64_t seek_off_t;
 	typedef Genode::uint64_t file_size_t;
 
+	struct Timestamp
+	{
+		/*
+		 * The INVALID value is used whenever the underlying file system
+		 * session does not support modification timestamps. The value is
+		 * chosen such that it is unlikely to occur, instead of simply '0',
+		 * which would correspond to plausible time (see comment below).
+		 * This allows for handling this case explicitly. In any case, an
+		 * invalid timestamp should not be used for doing any calculations.
+		 */
+		static constexpr Genode::int64_t INVALID = 0x7fffffffffffffffLL;
+
+		/*
+		 * The 'value' member contains the modification timestamp in seconds.
+		 * Value '0' is defined as 1970-01-01T00:00:00Z, where a positive value
+		 * covers all seconds after this date and a negative one all before.
+		 */
+		Genode::int64_t value;
+	};
+
 	typedef Genode::Out_of_ram  Out_of_ram;
 	typedef Genode::Out_of_caps Out_of_caps;
 
@@ -127,6 +147,7 @@ class File_system::Packet_descriptor : public Genode::Packet_descriptor
 		enum Opcode {
 			READ,
 			WRITE,
+			WRITE_TIMESTAMP,
 			CONTENT_CHANGED,
 			READ_READY,
 
@@ -143,9 +164,16 @@ class File_system::Packet_descriptor : public Genode::Packet_descriptor
 
 		Node_handle _handle { 0 };   /* node handle */
 		Opcode      _op;             /* requested operation */
-		seek_off_t  _position;       /* file seek offset in bytes */
-		size_t      _length;         /* transaction length in bytes */
 		bool        _success;        /* indicates success of operation */
+		union
+		{
+			struct
+			{
+				seek_off_t  _position;       /* file seek offset in bytes */
+				size_t      _length;         /* transaction length in bytes */
+			};
+			Timestamp _modification_time;    /* seconds since the Unix epoch */
+		};
 
 	public:
 
@@ -156,7 +184,7 @@ class File_system::Packet_descriptor : public Genode::Packet_descriptor
 		                  Genode::size_t buf_size   = 0)
 		:
 			Genode::Packet_descriptor(buf_offset, buf_size),
-			_op(READ), _position(0), _length(0), _success(false) { }
+			_op(READ), _success(false), _position(0), _length(0) { }
 
 		/**
 		 * Constructor
@@ -172,8 +200,8 @@ class File_system::Packet_descriptor : public Genode::Packet_descriptor
 		                  seek_off_t position = SEEK_TAIL)
 		:
 			Genode::Packet_descriptor(p.offset(), p.size()),
-			_handle(handle), _op(op),
-			_position(position), _length(length), _success(false)
+			_handle(handle), _op(op), _success(false),
+			_position(position), _length(length)
 		{ }
 
 		/**
@@ -185,16 +213,33 @@ class File_system::Packet_descriptor : public Genode::Packet_descriptor
 		Packet_descriptor(Node_handle handle, Opcode op)
 		:
 			Genode::Packet_descriptor(0, 0),
-			_handle(handle), _op(op),
-			_position(0), _length(0), _success(true)
+			_handle(handle), _op(op), _success(true),
+			_position(0), _length(0)
+		{ }
+
+		/**
+		 * Constructor
+		 */
+		Packet_descriptor(Packet_descriptor p, Node_handle handle, Opcode op, Timestamp const &mtime)
+		:
+			Genode::Packet_descriptor(p.offset(), p.size()),
+			_handle(handle), _op(op), _success(false),
+			_modification_time(mtime)
 		{ }
 
 		Node_handle handle()    const { return _handle;   }
 		Opcode      operation() const { return _op;       }
-		seek_off_t  position()  const { return _position; }
-		size_t      length()    const { return _length;   }
+		seek_off_t  position()  const { return _op != Opcode::WRITE_TIMESTAMP ? _position : 0; }
+		size_t      length()    const { return _op != Opcode::WRITE_TIMESTAMP ? _length : 0;   }
 		bool        succeeded() const { return _success;  }
 
+		template <typename FN>
+		void with_timestamp(FN const &fn) const
+		{
+			if (_op == Opcode::WRITE_TIMESTAMP)
+				fn(_modification_time);
+		}
+
 		/*
 		 * Accessors called at the server side
 		 */
@@ -212,13 +257,13 @@ struct File_system::Status
 	};
 
 	/*
-	 * XXX  add access time
 	 * XXX  add executable bit
 	 */
 
 	file_size_t   size;
 	unsigned      mode;
 	unsigned long inode;
+	Timestamp     modification_time;
 
 	/**
 	 * Return true if node is a directory

repos/os/src/server/ram_fs/directory.h

@@ -228,6 +228,7 @@ class Ram_fs::Directory : public Node
 			s.inode = inode();
 			s.size = _num_entries * sizeof(File_system::Directory_entry);
 			s.mode = File_system::Status::MODE_DIRECTORY;
+			s.modification_time = modification_time();
 			return s;
 		}
 };

repos/os/src/server/ram_fs/file.h

@@ -112,10 +112,11 @@ class Ram_fs::File : public Node
 
 		Status status() override
 		{
-			Status s;
+			Status s { };
 			s.inode = inode();
 			s.size = _length;
 			s.mode = File_system::Status::MODE_FILE;
+			s.modification_time = modification_time();
 			return s;
 		}
 

repos/os/src/server/ram_fs/main.cc

@@ -108,6 +108,18 @@ class Ram_fs::Session_component : public File_system::Session_rpc_object
 				open_node.mark_as_written();
 				break;
 
+			case Packet_descriptor::WRITE_TIMESTAMP: {
+				Locked_ptr<Node> node { open_node.node() };
+				if (!node.valid())
+					break;
+
+				packet.with_timestamp([&] (File_system::Timestamp const time) {
+					node->update_modification_time(time);
+					succeeded = true;
+				});
+				break;
+			}
+
 			case Packet_descriptor::CONTENT_CHANGED:
 				Genode::error("CONTENT_CHANGED packets from clients have no effect");
 				return;

repos/os/src/server/ram_fs/node.h

@@ -23,6 +23,7 @@ namespace Ram_fs {
 	using namespace Genode;
 	using File_system::seek_off_t;
 	using File_system::Status;
+	using File_system::Timestamp;
 	class Node;
 	class File;
 	class Symlink;
@@ -48,6 +49,7 @@ class Ram_fs::Node : public  File_system::Node_base,
 		int                 _ref_count;
 		Name                _name;
 		unsigned long const _inode;
+		Timestamp           _modification_time { };
 
 		/**
 		 * Generate unique inode number
@@ -62,7 +64,10 @@ class Ram_fs::Node : public  File_system::Node_base,
 
 		Node()
 		: _ref_count(0), _inode(_unique_inode())
-		{ _name[0] = 0; }
+		{
+			_name[0] = 0;
+			_modification_time.value = File_system::Timestamp::INVALID;
+		}
 
 		virtual ~Node() { lock_for_destruction(); }
 
@@ -74,6 +79,13 @@ class Ram_fs::Node : public  File_system::Node_base,
 		 */
 		void name(char const *name) { strncpy(_name, name, sizeof(_name)); }
 
+		void update_modification_time(Timestamp const time)
+		{
+			_modification_time = time;
+		}
+
+		Timestamp modification_time() const { return _modification_time; }
+
 		virtual size_t read(char *dst, size_t len, seek_off_t) = 0;
 		virtual size_t write(char const *src, size_t len, seek_off_t) = 0;
 

repos/os/src/server/ram_fs/symlink.h

@@ -71,6 +71,7 @@ class Ram_fs::Symlink : public Node
 			s.inode = inode();
 			s.size = _len;
 			s.mode = File_system::Status::MODE_SYMLINK;
+			s.modification_time = modification_time();
 			return s;
 		}
 };