mdadm: Unify forks behaviour

If mdadm is run by udev or systemd, it gets a pipe as each stream.
Forks in the background may run after an event or service has been
processed when udev is detached from pipe. As a result process
fails quietly if any message is written.
To prevent from it, each fork has to close all parent streams. Leave
stderr and stdout opened only for debug purposes.
Unify it across all forks. Introduce other descriptors detection by
scanning /proc/self/fd directory. Add generic method for
managing systemd services.

Signed-off-by: Mariusz Tkaczyk <mariusz.tkaczyk@intel.com>

1 files changed, 80 insertions, 44 deletions

diff --git a/util.c b/util.c
index 579dd423..58796947 100644
--- a/util.c
+++ b/util.c
@@ -1915,7 +1915,7 @@ int mdmon_running(char *devnm)
 
 int start_mdmon(char *devnm)
 {
-	int i, skipped;
+	int i;
 	int len;
 	pid_t pid;
 	int status;
@@ -1929,7 +1929,10 @@ int start_mdmon(char *devnm)
 
 	if (check_env("MDADM_NO_MDMON"))
 		return 0;
+	if (continue_via_systemd(devnm, MDMON_SERVICE))
+		return 0;
 
+	/* That failed, try running mdmon directly */
 	len = readlink("/proc/self/exe", pathbuf, sizeof(pathbuf)-1);
 	if (len > 0) {
 		char *sl;
@@ -1943,51 +1946,9 @@ int start_mdmon(char *devnm)
 	} else
 		pathbuf[0] = '\0';
 
-	/* First try to run systemctl */
-	if (!check_env("MDADM_NO_SYSTEMCTL"))
-		switch(fork()) {
-		case 0:
-			/* FIXME yuk. CLOSE_EXEC?? */
-			skipped = 0;
-			for (i = 3; skipped < 20; i++)
-				if (close(i) < 0)
-					skipped++;
-				else
-					skipped = 0;
-
-			/* Don't want to see error messages from
-			 * systemctl.  If the service doesn't exist,
-			 * we start mdmon ourselves.
-			 */
-			close(2);
-			open("/dev/null", O_WRONLY);
-			snprintf(pathbuf, sizeof(pathbuf), "mdmon@%s.service",
-				 devnm);
-			status = execl("/usr/bin/systemctl", "systemctl",
-				       "start",
-				       pathbuf, NULL);
-			status = execl("/bin/systemctl", "systemctl", "start",
-				       pathbuf, NULL);
-			exit(1);
-		case -1: pr_err("cannot run mdmon. Array remains readonly\n");
-			return -1;
-		default: /* parent - good */
-			pid = wait(&status);
-			if (pid >= 0 && status == 0)
-				return 0;
-		}
-
-	/* That failed, try running mdmon directly */
 	switch(fork()) {
 	case 0:
-		/* FIXME yuk. CLOSE_EXEC?? */
-		skipped = 0;
-		for (i = 3; skipped < 20; i++)
-			if (close(i) < 0)
-				skipped++;
-			else
-				skipped = 0;
-
+		manage_fork_fds(1);
 		for (i = 0; paths[i]; i++)
 			if (paths[i][0]) {
 				execl(paths[i], paths[i],
@@ -2192,6 +2153,81 @@ void enable_fds(int devices)
 	setrlimit(RLIMIT_NOFILE, &lim);
 }
 
+/* Close all opened descriptors if needed and redirect
+ * streams to /dev/null.
+ * For debug purposed, leave STDOUT and STDERR untouched
+ * Returns:
+ *	1- if any error occurred
+ *	0- otherwise
+ */
+void manage_fork_fds(int close_all)
+{
+	DIR *dir;
+	struct dirent *dirent;
+
+	close(0);
+	open("/dev/null", O_RDWR);
+
+#ifndef DEBUG
+	dup2(0, 1);
+	dup2(0, 2);
+#endif
+
+	if (close_all == 0)
+		return;
+
+	dir = opendir("/proc/self/fd");
+	if (!dir) {
+		pr_err("Cannot open /proc/self/fd directory.\n");
+		return;
+	}
+	for (dirent = readdir(dir); dirent; dirent = readdir(dir)) {
+		int fd = -1;
+
+		if ((strcmp(dirent->d_name, ".") == 0) ||
+		    (strcmp(dirent->d_name, "..")) == 0)
+			continue;
+
+		fd = strtol(dirent->d_name, NULL, 10);
+		if (fd > 2)
+			close(fd);
+	}
+}
+
+/* In a systemd/udev world, it is best to get systemd to
+ * run daemon rather than running in the background.
+ * Returns:
+ *	1- if systemd service has been started
+ *	0- otherwise
+ */
+int continue_via_systemd(char *devnm, char *service_name)
+{
+	int pid, status;
+	char pathbuf[1024];
+
+	/* Simply return that service cannot be started */
+	if (check_env("MDADM_NO_SYSTEMCTL"))
+		return 0;
+	switch (fork()) {
+	case  0:
+		manage_fork_fds(1);
+		snprintf(pathbuf, sizeof(pathbuf),
+			 "%s@%s.service", service_name, devnm);
+		status = execl("/usr/bin/systemctl", "systemctl", "restart",
+			       pathbuf, NULL);
+		status = execl("/bin/systemctl", "systemctl", "restart",
+			       pathbuf, NULL);
+		exit(1);
+	case -1: /* Just do it ourselves. */
+		break;
+	default: /* parent - good */
+		pid = wait(&status);
+		if (pid >= 0 && status == 0)
+			return 1;
+	}
+	return 0;
+}
+
 int in_initrd(void)
 {
 	/* This is based on similar function in systemd. */