Fix: only launch a new session daemon for the "create" command

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

diff --git a/src/bin/lttng/commands/create.c b/src/bin/lttng/commands/create.c
index ba62940c62fbb4dec65057d9942250d6c7d8fa7a..94c1c61836f5edd61dc5c4b8784d346875d0284b 100644 (file)
--- a/src/bin/lttng/commands/create.c
+++ b/src/bin/lttng/commands/create.c
@@ -27,6 +27,7 @@
 #include <sys/types.h>
 #include <time.h>
 #include <unistd.h>
+#include <signal.h>
 
 #include <common/mi-lttng.h>
 
@@ -550,6 +551,120 @@ error:
        return ret;
 }
 
+/*
+ *  spawn_sessiond
+ *
+ *  Spawn a session daemon by forking and execv.
+ */
+static int spawn_sessiond(char *pathname)
+{
+       int ret = 0;
+       pid_t pid;
+
+       MSG("Spawning a session daemon");
+       recv_child_signal = 0;
+       pid = fork();
+       if (pid == 0) {
+               /*
+                * Spawn session daemon and tell
+                * it to signal us when ready.
+                */
+               execlp(pathname, "lttng-sessiond", "--sig-parent", "--quiet", NULL);
+               /* execlp only returns if error happened */
+               if (errno == ENOENT) {
+                       ERR("No session daemon found. Use --sessiond-path.");
+               } else {
+                       PERROR("execlp");
+               }
+               kill(getppid(), SIGTERM);       /* wake parent */
+               exit(EXIT_FAILURE);
+       } else if (pid > 0) {
+               sessiond_pid = pid;
+               /*
+                * 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);
+               }
+               goto end;
+       } else {
+               PERROR("fork");
+               ret = -1;
+               goto end;
+       }
+
+end:
+       return ret;
+}
+
+/*
+ *  launch_sessiond
+ *
+ *  Check if the session daemon is available using
+ *  the liblttngctl API for the check. If not, try to
+ *  spawn a daemon.
+ */
+static int launch_sessiond(void)
+{
+       int ret;
+       char *pathname = NULL;
+
+       ret = lttng_session_daemon_alive();
+       if (ret) {
+               /* Sessiond is alive, not an error */
+               ret = 0;
+               goto end;
+       }
+
+       /* Try command line option path */
+       pathname = opt_sessiond_path;
+
+       /* Try LTTNG_SESSIOND_PATH env variable */
+       if (pathname == NULL) {
+               pathname = getenv(DEFAULT_SESSIOND_PATH_ENV);
+       }
+
+       /* Try with configured path */
+       if (pathname == NULL) {
+               if (CONFIG_SESSIOND_BIN[0] != '\0') {
+                       pathname = CONFIG_SESSIOND_BIN;
+               }
+       }
+
+       /* Try the default path */
+       if (pathname == NULL) {
+               pathname = INSTALL_BIN_PATH "/lttng-sessiond";
+       }
+
+       DBG("Session daemon binary path: %s", pathname);
+
+       /* Check existence and permissions */
+       ret = access(pathname, F_OK | X_OK);
+       if (ret < 0) {
+               ERR("No such file or access denied: %s", pathname);
+               goto end;
+       }
+
+       ret = spawn_sessiond(pathname);
+       if (ret < 0) {
+               ERR("Problem occurred when starting %s", pathname);
+       }
+end:
+       return ret;
+}
+
 /*
  *  The 'create <options>' first level command
  *
@@ -619,6 +734,15 @@ int cmd_create(int argc, const char **argv)
                goto end;
        }
 
+       /* Spawn a session daemon if needed */
+       if (!opt_no_sessiond) {
+               ret = launch_sessiond();
+               if (ret) {
+                       ret = CMD_ERROR;
+                       goto end;
+               }
+       }
+
        /* MI initialization */
        if (lttng_opt_mi) {
                writer = mi_lttng_writer_create(fileno(stdout), lttng_opt_mi);