libthapi-ctl: logging with THAPI_CTL_LOG_LEVEL

- Uses env var, default is 1=ERROR
- 0=disabled, 2=WARN, 3=INFO, 4=DEBUG
- Under the default log level, no message will be printed
  when THAPI_LTTNG_SESSION_ID is not set (application is linked with
  libthapi-ctl and calls start or stop tracing, but not run with
  iprof).

libthapictl/startstop.c

@@ -1,26 +1,87 @@
-#include <lttng/lttng-error.h>
+#include <assert.h>
+#include <stdarg.h>
 #include <stdlib.h>
 #include <stdio.h>
+#include <string.h>
 
 #include <lttng/lttng.h>
 
+
 #define THAPI_LTTNG_SESSION_ID_NAME "THAPI_LTTNG_SESSION_ID"
+#define THAPI_CTL_LOG_LEVEL_NAME "THAPI_CTL_LOG_LEVEL"
+
+#define THAPI_CTL_LOG_LEVEL_ERROR 1
+#define THAPI_CTL_LOG_LEVEL_INFO 2
+#define THAPI_CTL_LOG_LEVEL_WARN 3
+#define THAPI_CTL_LOG_LEVEL_DEBUG 4
+
+#define THAPI_CTL_DEFAULT_LOG_LEVEL THAPI_CTL_LOG_LEVEL_ERROR
+
+
+static const char* thapi_ctl_level_str[5] = {
+  "",
+  "ERROR",
+  "INFO",
+  "WARN",
+  "DEBUG"
+};
+
+
+int _thapi_ctl_log_level() {
+  static int level = -1;
+  if (level < 0) {
+    const char *log_level_str = getenv(THAPI_CTL_LOG_LEVEL_NAME);
+    if (log_level_str == NULL || strlen(log_level_str) == 0) {
+      level = THAPI_CTL_DEFAULT_LOG_LEVEL;
+    } else {
+      char *endptr;
+      level = strtol(log_level_str, &endptr, 10);
+      if (*endptr != '\0') {
+        level = 0;
+      }
+    }
+  }
+  return level;
+}
+
+
+void _thapi_ctl_log(int log_level, const char *fmt, ...) {
+  assert(log_level > 1 && log_level <= THAPI_CTL_LOG_LEVEL_DEBUG);
+  int config_level = _thapi_ctl_log_level();
+  if (log_level <= config_level) {
+    fprintf(stderr, "libthapi-ctl[%s]: ", thapi_ctl_level_str[log_level]);
+    va_list va;
+    va_start(va, fmt);
+    vfprintf(stderr, fmt, va);
+    va_end(va);
+    fprintf(stderr, "\n");
+  }
+}
 
 
 int thapi_start_tracing() {
   const char *session_id = getenv(THAPI_LTTNG_SESSION_ID_NAME);
   if (session_id == NULL) {
     // TODO: silently ignore this error? Apps should be able to be run with or
     // without iprof
-    fprintf(stderr, "Failed to start tracing on session, missing env var '%s'\n",
-            THAPI_LTTNG_SESSION_ID_NAME);
+    _thapi_ctl_log(THAPI_CTL_LOG_LEVEL_WARN,
+                   "Failed to start tracing on session, missing env var '%s'",
+                   THAPI_LTTNG_SESSION_ID_NAME);
     return -LTTNG_ERR_SESS_NOT_FOUND;
   }
   const int rval = lttng_start_tracing(session_id);
-  // TODO: do we really want to ignore double stop?
-  if (rval < 0 && rval != -LTTNG_ERR_TRACE_ALREADY_STARTED) {
-    fprintf(stderr, "Failed to start tracing on session '%s': %d\n", session_id,
-            rval);
+  if (rval < 0) {
+    if (rval == -LTTNG_ERR_TRACE_ALREADY_STARTED) {
+      _thapi_ctl_log(THAPI_CTL_LOG_LEVEL_INFO,
+                     "Session already started (id '%s')", session_id);
+    } else {
+      _thapi_ctl_log(THAPI_CTL_LOG_LEVEL_ERROR,
+                     "Failed to stop tracing on session '%s': %d",
+                     session_id, rval);
+    }
+  } else {
+    _thapi_ctl_log(THAPI_CTL_LOG_LEVEL_DEBUG,
+                   "Starting session '%s", session_id);
   }
   return rval;
 }
@@ -29,15 +90,25 @@ int thapi_start_tracing() {
 int thapi_stop_tracing() {
   const char *session_id = getenv(THAPI_LTTNG_SESSION_ID_NAME);
   if (session_id == NULL) {
-    fprintf(stderr, "Failed to stop tracing on session, missing env var '%s'\n",
-            THAPI_LTTNG_SESSION_ID_NAME);
+    _thapi_ctl_log(THAPI_CTL_LOG_LEVEL_WARN,
+                   "Failed to start tracing on session, missing env var '%s'",
+                   THAPI_LTTNG_SESSION_ID_NAME);
     return -LTTNG_ERR_SESS_NOT_FOUND;
   }
   const int rval = lttng_stop_tracing(session_id);
   // TODO: do we really want to ignore double stop?
-  if (rval < 0 && rval != -LTTNG_ERR_TRACE_ALREADY_STOPPED) {
-    fprintf(stderr, "Failed to stop tracing on session '%s': %d\n", session_id,
-            rval);
+  if (rval < 0) {
+    if (rval == -LTTNG_ERR_TRACE_ALREADY_STOPPED) {
+      _thapi_ctl_log(THAPI_CTL_LOG_LEVEL_INFO,
+                     "Session already stopped (id '%s')", session_id);
+    } else {
+      _thapi_ctl_log(THAPI_CTL_LOG_LEVEL_ERROR,
+                     "Failed to stop tracing on session '%s': %d",
+                     session_id, rval);
+    }
+  } else {
+    _thapi_ctl_log(THAPI_CTL_LOG_LEVEL_DEBUG,
+                   "Stopping session '%s", session_id);
   }
   return rval;
 }