os: Split Session_label from Session_policy

By splitting Session_policy into two classes, we make it more flexible.
Originally, the constructor accepted solely an args string, which made it
unusable for situations where we already have extracted the session
label (e.g., stored in the session meta data of a server). Now, the
extraction of the label from the args string is performed by the new
Session_label class instead, which, in turn, can be passed to the
constructor of Session_policy.

This change causes a minor API change. The following code

  Session_policy policy(session_args);

Must be turned into

  Session_label  label(session_args);
  Session_policy policy(label);

gems/src/server/tcp_terminal/main.cc

@@ -458,7 +458,8 @@ namespace Terminal {
 				Genode::size_t io_buffer_size = 4096;
 
 				try {
-					Genode::Session_policy policy(args);
+					Genode::Session_label  label(args);
+					Genode::Session_policy policy(label);
 
 					unsigned tcp_port = 0;
 					policy.attribute("port").value(&tcp_port);

libports/src/server/ffat_fs/main.cc

@@ -879,7 +879,8 @@ namespace File_system {
 				root[0] = 0;
 
 				try {
-					Session_policy policy(args);
+					Session_label  label(args);
+					Session_policy policy(label);
 
 					/*
 					 * Determine directory that is used as root directory of

libports/src/server/fs_log/main.cc

@@ -118,7 +118,8 @@ class Log_root : public Genode::Root_component<Log_component>
 			enum { FILENAME_MAX_LEN = 256 };
 			char filename[FILENAME_MAX_LEN];
 			try {
-				Session_policy policy(args);
+				Session_label  label(args);
+				Session_policy policy(label);
 				policy.attribute("file").value(filename, sizeof(filename));
 			} catch (...) {
 				PERR("Invalid session request, no matching policy");

os/include/os/session_policy.h

@@ -19,6 +19,34 @@
 
 namespace Genode {
 
+	class Session_label
+	{
+		public:
+
+			enum { MAX_LEN = 128 };
+
+		private:
+
+			char _buf[MAX_LEN];
+
+		public:
+
+			Session_label() { _buf[0] = 0; }
+
+			/**
+			 * Constructor
+			 *
+			 * \param args session-arguments as null-terminated string
+			 */
+			explicit Session_label(char const *args)
+			{
+				Arg_string::find_arg(args, "label").string(_buf, sizeof(_buf),
+				                                           "<undefined>");
+			}
+
+			char const *string() const { return _buf; }
+	};
+
 	/**
 	 * Query server-side policy for a session request
 	 */
@@ -37,19 +65,14 @@ namespace Genode {
 			 * Returns true if the start of the label matches the specified
 			 * match string
 			 */
-			static bool _label_matches(const char *label, const char *match) {
+			static bool _label_matches(Session_label const &label, char const *match) {
-				return strcmp(label, match, strlen(match)) == 0; }
+				return strcmp(label.string(), match, strlen(match)) == 0; }
 
 			/**
-			 * Query session policy from config
+			 * Query session policy from session label
 			 */
-			static Xml_node _query_policy(char const *args)
+			static Xml_node _query_policy(Session_label const &label)
 			{
-				enum { LABEL_LEN = 128 };
-				char session_label[LABEL_LEN];
-				Arg_string::find_arg(args, "label").
-					string(session_label, sizeof(session_label), "<unlabeled>");
-
 				/* find index of policy node that matches best */
 				int best_match = -1;
 				try {
@@ -62,11 +85,11 @@ namespace Genode {
 							continue;
 
 						/* label attribtute from policy node */
-						char policy_label[LABEL_LEN];
+						char policy_label[Session_label::MAX_LEN];
 						policy.attribute("label").value(policy_label,
 						                                sizeof(policy_label));
 
-						if (!_label_matches(session_label, policy_label)
+						if (!_label_matches(label, policy_label)
 						 || strlen(policy_label) < label_len)
 							continue;
 
@@ -92,18 +115,17 @@ namespace Genode {
 			 *                           policy defined for the session
 			 *                           request
 			 *
-			 * On construction, the 'Session_policy' looks up the 'policy'
+			 * On construction, the 'Session_policy' looks up the 'policy' XML
-			 * XML note that matches the label delivered as session argument.
+			 * note that matches the label provided as argument. The
-			 * The server-side policies are defined in one or more policy
+			 * server-side policies are defined in one or more policy subnodes
-			 * subnodes of the server's 'config' node. Each policy node has
+			 * of the server's 'config' node. Each policy node has a label
-			 * a label attribute. The if policy label matches the first
+			 * attribute. The if policy label matches the first part of the
-			 * part of the label delivered as session argument, the policy
+			 * label delivered as session argument, the policy matches. If
-			 * matches. If multiple policies match, the one with the largest
+			 * multiple policies match, the one with the largest label is
-			 * label is selected.
+			 * selected.
 			 */
-			Session_policy(char const *args)
+			explicit Session_policy(Session_label const &label)
-			: Xml_node(_query_policy(args))
+			: Xml_node(_query_policy(label)) { }
-			{ }
 	};
 }
 

os/src/drivers/uart/uart_component.h

@@ -221,7 +221,8 @@ namespace Uart {
 			Session_component *_create_session(const char *args)
 			{
 				try {
-					Session_policy policy(args);
+					Session_label  label(args);
+					Session_policy policy(label);
 
 					unsigned index = 0;
 					policy.attribute("uart").value(&index);

os/src/server/nic_bridge/component.h

@@ -171,7 +171,6 @@ namespace Net {
 
 			enum { MAX_IP_ADDR_LENGTH  = 16, };
 			char ip_addr[MAX_IP_ADDR_LENGTH];
-			char label[256];
 
 			Session_component *_create_session(const char *args)
 			{
@@ -180,11 +179,11 @@ namespace Net {
 				memset(ip_addr, 0, MAX_IP_ADDR_LENGTH);
 
 				 try {
-					Genode::Arg_string::find_arg(args, "label").string(label, sizeof(label), "");
+					Session_label  label(args);
-					Session_policy policy(args);
+					Session_policy policy(label);
 					policy.attribute("ip_addr").value(ip_addr, sizeof(ip_addr));
 
-					if (verbose) PDBG("policy: %s ip_addr = %s", label, ip_addr);
+					if (verbose) PDBG("policy: %s ip_addr = %s", label.string(), ip_addr);
 				} catch (Xml_node::Nonexistent_attribute) {
 					if (verbose) PDBG("Missing \"ip_addr\" attribute in policy definition");
 				} catch (Session_policy::No_policy_defined) {

os/src/server/nitpicker/main.cc

@@ -70,7 +70,8 @@ static Color session_color(char const *session_args)
 	Color color = WHITE;
 
 	try {
-		Session_policy policy(session_args);
+		Session_label  label(session_args);
+		Session_policy policy(label);
 
 		/* read color attribute */
 		policy.attribute("color").value(&color);

os/src/server/ram_fs/main.cc

@@ -437,7 +437,8 @@ namespace File_system {
 				root[0] = 0;
 
 				try {
-					Session_policy policy(args);
+					Session_label  label(args);
+					Session_policy policy(label);
 
 					/*
 					 * Determine directory that is used as root directory of

os/src/server/tar_fs/main.cc

@@ -450,7 +450,8 @@ namespace File_system {
 				root[0] = 0;
 
 				try {
-					Session_policy policy(args);
+					Session_label  label(args);
+					Session_policy policy(label);
 
 					/*
 					 * Determine directory that is used as root directory of