Add a service to log into a file

Original version by Alexander Tarasikov, refined by Norman Feske.

Fixes #736

doc/components.txt

@@ -314,6 +314,9 @@ Separate components:
 :'os/src/server/terminal_log':
   Adapter for forwarding LOG messages to a terminal session.
 
+:'libports/src/server/fs_log':
+  Adapter that writes LOG messages to files on a file system.
+
 :'demo/src/server/nitlog':
   Provides a LOG session, printing log output on screen via a nitpicker
   session.

libports/src/server/fs_log/README

@@ -0,0 +1,18 @@
+LOG server that writes log messages onto a file system.
+
+Using this component, log messages of different processes can be redirected
+to files on a file-system service. The assignment of processes to files can
+be expressed in the configuration as follows:
+
+! <start name="fs_log">
+!   <resource name="RAM" quantum="2M"/>
+!   <provides><service name="LOG"/></provides>
+!   <config>
+!     <policy label="noux"    file="/noux.log" />
+!     <policy label="noux ->" file="/noux_process.log" />
+!   </config>
+! </start>
+
+In this example, all messages originating from the noux process are directed
+to the file '/noux.log'. All messages originating from children of the noux
+process end up in the file '/noux_process.log'.

libports/src/server/fs_log/main.cc

@@ -0,0 +1,170 @@
+/*
+ * \brief  LOG service that writes to a file
+ * \author Alexander Tarasikov <tarasikov@ksyslabs.org>
+ * \author Norman Feske <norman.feske@genode-labs.com>
+ * \date   2013-05-07
+ */
+
+/*
+ * Copyright (C) 2013 Ksys Labs LLC
+ * Copyright (C) 2012-2013 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.
+ */
+
+/* Genode includes */
+#include <base/env.h>
+#include <base/rpc_server.h>
+#include <base/sleep.h>
+#include <root/component.h>
+#include <util/string.h>
+#include <os/session_policy.h>
+#include <cap_session/connection.h>
+#include <log_session/log_session.h>
+
+/* libc includes */
+#include <fcntl.h>
+#include <unistd.h>
+
+
+class Log_component : public Genode::Rpc_object<Genode::Log_session>
+{
+	public:
+
+		enum { LABEL_LEN = 64 };
+
+	private:
+
+		typedef Genode::size_t size_t;
+
+		char   _label[LABEL_LEN];
+		size_t _label_len;
+		int    _fd;
+
+	public:
+
+		/**
+		 * Constructor
+		 */
+		Log_component(const char *label, char const *filename)
+		:
+			_fd(::open(filename, O_CREAT | O_WRONLY | O_APPEND))
+		{
+			using namespace Genode;
+
+			if (_fd < 0) {
+				PERR("unable to open \"%s\"", filename);
+				throw Root::Unavailable();
+			}
+
+			snprintf(_label, LABEL_LEN, "[%s] ", label);
+			_label_len = strlen(_label);
+
+			PINF("log client \"%s\" to file \"%s\")", label, filename);
+		}
+
+		/**
+		 * Destructor
+		 */
+		~Log_component() { ::close(_fd); }
+
+
+		/*****************
+		 ** Log session **
+		 *****************/
+
+		/**
+		 * Write a log-message to the file.
+		 */
+		size_t write(String const &string_buf)
+		{
+			if (!(string_buf.is_valid_string())) {
+				PERR("corrupted string");
+				return 0;
+			}
+
+			char const *string       = string_buf.string();
+			Genode::size_t const len = Genode::strlen(string);
+
+			::write(_fd, _label, _label_len);
+			::write(_fd, string, len);
+
+			return len;
+		}
+};
+
+
+class Log_root : public Genode::Root_component<Log_component>
+{
+	private:
+
+		int _fd;
+
+	protected:
+
+		/**
+		 * Root component interface
+		 */
+		Log_component *_create_session(const char *args)
+		{
+			using namespace Genode;
+
+			char label_buf[Log_component::LABEL_LEN];
+			Arg label_arg = Arg_string::find_arg(args, "label");
+			label_arg.string(label_buf, sizeof(label_buf), "");
+
+			/* obtain file name from configured policy */
+			enum { FILENAME_MAX_LEN = 256 };
+			char filename[FILENAME_MAX_LEN];
+			try {
+				Session_policy policy(args);
+				policy.attribute("file").value(filename, sizeof(filename));
+			} catch (...) {
+				PERR("Invalid session request, no matching policy");
+				throw Root::Unavailable();
+			}
+
+			return new (md_alloc()) Log_component(label_buf, filename);
+		}
+
+	public:
+
+		/**
+		 * Constructor
+		 *
+		 * \param session_ep  entry point for managing cpu session objects
+		 * \param md_alloc    meta-data allocator to be used by root component
+		 */
+		Log_root(Genode::Rpc_entrypoint *session_ep, Genode::Allocator *md_alloc)
+		: Genode::Root_component<Log_component>(session_ep, md_alloc) { }
+};
+
+
+int main(int argc, char **argv)
+{
+	using namespace Genode;
+
+	/*
+	 * Initialize server entry point
+	 *
+	 * Use a large stack because we are calling libc functions from the
+	 * context of the entrypoint.
+	 */
+	enum { STACK_SIZE = sizeof(addr_t)*16*1024 };
+	static Cap_connection cap;
+	static Rpc_entrypoint ep(&cap, STACK_SIZE, "fs_log_ep");
+
+	static Log_root log_root(&ep, env()->heap());
+
+	/*
+	 * Announce services
+	 */
+	env()->parent()->announce(ep.manage(&log_root));
+
+	/**
+	 * Got to sleep forever
+	 */
+	sleep_forever();
+	return 0;
+}

libports/src/server/fs_log/target.mk

@@ -0,0 +1,3 @@
+TARGET = fs_log
+SRC_CC = main.cc
+LIBS   = base libc_fs libc