[libj6] Add log area and severity to j6::syslog()

User code can now set the log area and severity of log messages. This also updates the j6_log
syscall to take these parameters, but removes all calls to it except through j6::syslog().

src/kernel/logger.cpp

@@ -124,7 +124,8 @@ LOG_LEVEL_FUNCTION(info);
 LOG_LEVEL_FUNCTION(warn);
 LOG_LEVEL_FUNCTION(error);
 
-void fatal(logs area, const char *fmt, ...)
+void
+fatal(logs area, const char *fmt, ...)
 {
     logger *l = logger::s_log;
     if (!l) return;
@@ -137,4 +138,19 @@ void fatal(logs area, const char *fmt, ...)
     kassert(false, "log::fatal");
 }
 
+void
+log(logs area, level severity, const char *fmt, ...)
+{
+    logger *l = logger::s_log;
+    if (!l) return;
+
+    level limit = l->get_level(area);
+    if (severity > limit) return;
+
+    va_list args;
+    va_start(args, fmt);
+    l->output(severity, area, fmt, args);
+    va_end(args);
+}
+
 } // namespace log

src/kernel/logger.h

@@ -77,6 +77,7 @@ private:
     friend void warn   (logs area, const char *fmt, ...);
     friend void error  (logs area, const char *fmt, ...);
     friend void fatal  (logs area, const char *fmt, ...);
+    friend void log    (logs area, level severity, const char *fmt, ...);
 
     void output(level severity, logs area, const char *fmt, va_list args);
 
@@ -113,6 +114,8 @@ void warn   (logs area, const char *fmt, ...);
 void error  (logs area, const char *fmt, ...);
 void fatal  (logs area, const char *fmt, ...);
 
+void log    (logs area, level severity, const char *fmt, ...);
+
 } // namespace log
 
 extern log::logger &g_logger;

src/kernel/syscalls/system.cpp

@@ -21,10 +21,11 @@ namespace syscalls {
 using system = class ::system;
 
 j6_status_t
-log(const char *message)
+log(uint8_t area, uint8_t severity, const char *message)
 {
     thread &th = thread::current();
-    log::info(logs::syscall, "Message <%02lx:%02lx>: %s", th.parent().obj_id(), th.obj_id(), message);
+    log::log(static_cast<logs>(area), static_cast<log::level>(severity),
+        "<%02lx:%02lx>: %s", th.parent().obj_id(), th.obj_id(), message);
     return j6_status_ok;
 }