From: Philippe Proulx <eeppeliteloop@gmail.com>
Date: Thu, 27 Aug 2015 15:52:33 +0000 (-0400)
Subject: Daemonize sessiond on `lttng create`
X-Git-Url: http://git.efficios.com/?p=lttng-tools.git;a=commitdiff_plain;h=bbd44cae042d871887fb7207c5144f68d47cb3a8

Daemonize sessiond on `lttng create`

Since the session daemon forked by `lttng create` shares its
standard output/error FDs when not using `--daemonize`, redirecting
the standard output/error of this command to another program "hangs"
because the session daemon never terminates.

Example that's not working (when sessiond is not running):

    lttng create | wc

or:

    lttng 2>&1 | wc

Using sessiond's `--daemonize` option makes it close its FDs. This
option also ensures that when the sessiond process exits, it has forked
itself as a daemon and is ready to accept commands. Therefore we don't
need to catch SIGCHLD and SIGUSR1; just waitpid() on sessiond's PID and
make sure it exited normally and with an exit status of 0 to continue.

Signed-off-by: Philippe Proulx <eeppeliteloop@gmail.com>
Signed-off-by: Jérémie Galarneau <jeremie.galarneau@efficios.com>
---

diff --git a/src/bin/lttng/commands/create.c b/src/bin/lttng/commands/create.c
index 94c1c6183..3b679ca71 100644
--- a/src/bin/lttng/commands/create.c
+++ b/src/bin/lttng/commands/create.c
@@ -28,6 +28,7 @@
 #include <time.h>
 #include <unistd.h>
 #include <signal.h>
+#include <sys/wait.h>
 
 #include <common/mi-lttng.h>
 
@@ -562,14 +563,13 @@ static int spawn_sessiond(char *pathname)
 	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.
+		 * Spawn session daemon in daemon mode.
 		 */
-		execlp(pathname, "lttng-sessiond", "--sig-parent", "--quiet", NULL);
+		execlp(pathname, "lttng-sessiond",
+				"--daemonize", NULL);
 		/* execlp only returns if error happened */
 		if (errno == ENOENT) {
 			ERR("No session daemon found. Use --sessiond-path.");
@@ -579,25 +579,34 @@ static int spawn_sessiond(char *pathname)
 		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);
-		}
+		int status;
+
 		/*
-		 * The signal handler will nullify sessiond_pid on SIGCHLD
+		 * In daemon mode (--daemonize), sessiond only exits when
+		 * it's ready to accept commands.
 		 */
-		if (!sessiond_pid) {
-			exit(EXIT_FAILURE);
+		for (;;) {
+			waitpid(pid, &status, 0);
+
+			if (WIFSIGNALED(status)) {
+				ERR("Session daemon was killed by signal %d",
+						WTERMSIG(status));
+				ret = -1;
+			        goto end;
+			} else if (WIFEXITED(status)) {
+				DBG("Session daemon terminated normally (exit status: %d)",
+						WEXITSTATUS(status));
+
+				if (WEXITSTATUS(status) != 0) {
+					ERR("Session daemon terminated with an error (exit status: %d)",
+							WEXITSTATUS(status));
+					ret = -1;
+				        goto end;
+				}
+				break;
+			}
 		}
+
 		goto end;
 	} else {
 		PERROR("fork");
diff --git a/src/bin/lttng/lttng.c b/src/bin/lttng/lttng.c
index 4d2df2deb..bf07c83b7 100644
--- a/src/bin/lttng/lttng.c
+++ b/src/bin/lttng/lttng.c
@@ -38,8 +38,6 @@
 static char *progname;
 int opt_no_sessiond;
 char *opt_sessiond_path;
-pid_t sessiond_pid;
-volatile int recv_child_signal;
 
 char *opt_relayd_path;
 
@@ -203,26 +201,11 @@ static void clean_exit(int code)
  */
 static void sighandler(int sig)
 {
-	int status;
-
 	switch (sig) {
 		case SIGTERM:
 			DBG("SIGTERM caught");
 			clean_exit(EXIT_FAILURE);
 			break;
-		case SIGCHLD:
-			DBG("SIGCHLD caught");
-			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 caught");
-			break;
 		default:
 			DBG("Unknown signal %d caught", sig);
 			break;
@@ -250,21 +233,12 @@ static int set_signal_handler(void)
 	sa.sa_handler = sighandler;
 	sa.sa_mask = sigset;
 	sa.sa_flags = 0;
-	if ((ret = sigaction(SIGUSR1, &sa, NULL)) < 0) {
-		PERROR("sigaction");
-		goto end;
-	}
 
 	if ((ret = sigaction(SIGTERM, &sa, NULL)) < 0) {
 		PERROR("sigaction");
 		goto end;
 	}
 
-	if ((ret = sigaction(SIGCHLD, &sa, NULL)) < 0) {
-		PERROR("sigaction");
-		goto end;
-	}
-
 end:
 	return ret;
 }
diff --git a/src/bin/lttng/utils.h b/src/bin/lttng/utils.h
index 075573193..b0e44f66e 100644
--- a/src/bin/lttng/utils.h
+++ b/src/bin/lttng/utils.h
@@ -26,7 +26,6 @@
 extern char *opt_relayd_path;
 extern int opt_no_sessiond;
 extern char * opt_sessiond_path;
-extern volatile int recv_child_signal;
 extern pid_t sessiond_pid;
 
 struct cmd_struct;