X-Git-Url: https://git.lttng.org/?a=blobdiff_plain;f=src%2Fbin%2Flttng%2Flttng.c;h=36d4c913df48ab681cbfac27e428c3f7888d339c;hb=af87c45a6179026e263c3a9eb251ccf8ec9537e7;hp=57927d4f3d301f87ceb11a0ec85ea489b4e3f4bd;hpb=ba2926efa2f16966165993d654f99574c3624ef4;p=lttng-tools.git

diff --git a/src/bin/lttng/lttng.c b/src/bin/lttng/lttng.c
index 57927d4f3..36d4c913d 100644
--- a/src/bin/lttng/lttng.c
+++ b/src/bin/lttng/lttng.c
@@ -40,6 +40,7 @@ int opt_verbose;
 static int opt_no_sessiond;
 static char *opt_sessiond_path;
 static pid_t sessiond_pid;
+static volatile int recv_child_signal;
 
 enum {
 	OPT_SESSION_PATH,
@@ -81,23 +82,23 @@ static struct cmd_struct commands[] =  {
 static void usage(FILE *ofp)
 {
 	fprintf(ofp, "LTTng Trace Control " VERSION"\n\n");
-	fprintf(ofp, "usage: lttng [options] <command>\n");
+	fprintf(ofp, "usage: lttng [OPTIONS] <COMMAND>\n");
 	fprintf(ofp, "\n");
 	fprintf(ofp, "Options:\n");
 	fprintf(ofp, "  -h, --help             Show this help\n");
-	fprintf(ofp, "  -g, --group NAME       Unix tracing group name. (default: tracing)\n");
-	fprintf(ofp, "  -v, --verbose          Verbose mode\n");
+	fprintf(ofp, "      --list-options     Simple listing of lttng options\n");
+	fprintf(ofp, "      --list-commands    Simple listing of lttng commands\n");
+	fprintf(ofp, "  -v, --verbose          Increase verbosity\n");
 	fprintf(ofp, "  -q, --quiet            Quiet mode\n");
+	fprintf(ofp, "  -g, --group NAME       Unix tracing group name. (default: tracing)\n");
 	fprintf(ofp, "  -n, --no-sessiond      Don't spawn a session daemon\n");
 	fprintf(ofp, "      --sessiond-path    Session daemon full path\n");
-	fprintf(ofp, "      --list-options     Simple listing of lttng options\n");
-	fprintf(ofp, "      --list-commands    Simple listing of lttng commands\n");
 	fprintf(ofp, "\n");
 	fprintf(ofp, "Commands:\n");
-	fprintf(ofp, "    add-context     Add context to event or/and channel\n");
+	fprintf(ofp, "    add-context     Add context to event and/or channel\n");
 	fprintf(ofp, "    calibrate       Quantify LTTng overhead\n");
 	fprintf(ofp, "    create          Create tracing session\n");
-	fprintf(ofp, "    destroy         Teardown tracing session\n");
+	fprintf(ofp, "    destroy         Tear down tracing session\n");
 	fprintf(ofp, "    enable-channel  Enable tracing channel\n");
 	fprintf(ofp, "    enable-event    Enable tracing event\n");
 	fprintf(ofp, "    disable-channel Disable tracing channel\n");
@@ -181,12 +182,14 @@ static void sighandler(int sig)
 		case SIGCHLD:
 			DBG("SIGCHLD caugth");
 			waitpid(sessiond_pid, &status, 0);
+			recv_child_signal = 1;
 			/* Indicate that the session daemon died */
 			sessiond_pid = 0;
 			ERR("Session daemon died (exit status %d)", WEXITSTATUS(status));
 			break;
 		case SIGUSR1:
 			/* Notify is done */
+			recv_child_signal = 1;
 			DBG("SIGUSR1 caugth");
 			break;
 		default:
@@ -294,6 +297,7 @@ static int spawn_sessiond(char *pathname)
 	pid_t pid;
 
 	MSG("Spawning a session daemon");
+	recv_child_signal = 0;
 	pid = fork();
 	if (pid == 0) {
 		/*
@@ -307,12 +311,25 @@ static int spawn_sessiond(char *pathname)
 		} else {
 			perror("execlp");
 		}
-		kill(getppid(), SIGTERM);	/* unpause parent */
+		kill(getppid(), SIGTERM);	/* wake parent */
 		exit(EXIT_FAILURE);
 	} else if (pid > 0) {
 		sessiond_pid = pid;
-		/* Wait for lttng-sessiond to start */
-		pause();
+		/*
+		 * Wait for lttng-sessiond to start. We need to use a flag to check if
+		 * the signal has been sent to us, because the child can be scheduled
+		 * before the parent, and thus send the signal before this check. In
+		 * the signal handler, we set the recv_child_signal flag, so anytime we
+		 * check it after the fork is fine. Note that sleep() is interrupted
+		 * before the 1 second delay as soon as the signal is received, so it
+		 * will not cause visible delay for the user.
+		 */
+		while (!recv_child_signal) {
+			sleep(1);
+		}
+		/*
+		 * The signal handler will nullify sessiond_pid on SIGCHLD
+		 */
 		if (!sessiond_pid) {
 			exit(EXIT_FAILURE);
 		}