vfs: add Rtc_file_system

The Rtc_file_system reads the current time from a Rtc_session and
provides the time as '%Y-%m-%d %H:%M\n' to all users of the vfs
node.

Fixes #1238.

repos/os/include/vfs/rtc_file_system.h

@@ -0,0 +1,79 @@
+/*
+ * \brief  Rtc file system
+ * \author Josef Soentgen
+ * \date   2014-08-20
+ */
+
+/*
+ * Copyright (C) 2014 Genode Labs GmbH
+ *
+ * This file is part of the Genode OS framework, which is distributed
+ * under the terms of the GNU General Public License version 2.
+ */
+
+#ifndef _INCLUDE__VFS__RTC_FILE_SYSTEM_H_
+#define _INCLUDE__VFS__RTC_FILE_SYSTEM_H_
+
+/* Genode includes */
+#include <rtc_session/connection.h>
+#include <vfs/file_system.h>
+
+/* libc includes */
+#include <time.h>
+
+namespace Vfs { class Rtc_file_system; }
+
+
+class Vfs::Rtc_file_system : public Single_file_system
+{
+	private:
+
+		Rtc::Connection _rtc;
+
+	public:
+
+		Rtc_file_system(Xml_node config)
+		:
+			Single_file_system(NODE_TYPE_CHAR_DEVICE, name(), config)
+		{ }
+
+		static char const *name() { return "rtc"; }
+
+
+		/********************************
+		 ** File I/O service interface **
+		 ********************************/
+
+		Write_result write(Vfs_handle *, char const *, size_t count, size_t &count_out) override
+		{
+			return WRITE_ERR_IO;
+		}
+
+		/**
+		 * Read the current time from the RTC
+		 *
+		 * On each read the current time is queried and afterwards formated
+		 * as '%Y-%m-%d %H:%M\n'.
+		 */
+		Read_result read(Vfs_handle *vfs_handle, char *dst, size_t count, size_t &out_count) override
+		{
+			time_t t = _rtc.get_current_time() / 1000000ULL;
+
+			struct tm *tm = localtime(&t);
+
+			char buf[16 + 1 + 1];
+			Genode::snprintf(buf, sizeof(buf), "%04d-%02d-%02d %02d:%02d\n",
+			                 1900 + tm->tm_year, /* years since 1900 */
+			                 1 + tm->tm_mon,     /* months since January [0-11] */
+			                 tm->tm_mday, tm->tm_hour, tm->tm_min);
+
+			size_t len = count > sizeof(buf) ? sizeof(buf) : count;
+			Genode::memcpy(dst, buf, len);
+
+			out_count = len;
+
+			return READ_OK;
+		}
+};
+
+#endif /* _INCLUDE__VFS__RTC_FILE_SYSTEM_H_ */