Fix comments and enforce expected return values

[lttng-tools.git] / src / bin / lttng / lttng.c

diff --git a/src/bin/lttng/lttng.c b/src/bin/lttng/lttng.c
index 57927d4f3d301f87ceb11a0ec85ea489b4e3f4bd..36d4c913df48ab681cbfac27e428c3f7888d339c 100644 (file)
--- 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);
                }