lvmnotify.c: Check to see if dbus daemon is running

The lvm dbus daemon will auto activate on dbus API calls.  To
prevent the dbus daemon starting when lvm command line tools are
being used we will check to see if the daemon is running first.
If the daemon is not running, we will not notify the daemon.

For this check to work it requires the changes done previously
with commit: 3fdf449348

Reviewed-by: David Teigland <teigland@redhat.com>

lib/notify/lvmnotify.c

@@ -15,17 +15,79 @@
 #define LVM_DBUS_DESTINATION "com.redhat.lvmdbus1"
 #define LVM_DBUS_PATH        "/com/redhat/lvmdbus1/Manager"
 #define LVM_DBUS_INTERFACE   "com.redhat.lvmdbus1.Manager"
+#define LVM_DBUS_LOCK_FILE   "/var/lock/lvm/lvmdbusd"
+#define LVM_DBUS_LOCK_FILE_ENV_KEY        "LVM_DBUSD_LOCKFILE"
 #define SD_BUS_SYSTEMD_NO_SUCH_UNIT_ERROR "org.freedesktop.systemd1.NoSuchUnit"
 #define SD_BUS_DBUS_SERVICE_UNKNOWN_ERROR "org.freedesktop.DBus.Error.ServiceUnknown"
 
 #ifdef NOTIFYDBUS_SUPPORT
 #include <systemd/sd-bus.h>
+#include <fcntl.h>
+#include <stdlib.h>
+#include <unistd.h>
+#include <errno.h>
 
 int lvmnotify_is_supported(void)
 {
 	return 1;
 }
 
+static int lvmdbusd_running(void)
+{
+	int fd = 0;
+	int rc = 0;
+	int errno_cpy = 0;
+	int running = 0;
+	const char *lockfile = NULL;
+
+	/*
+	 * lvm dbusd uses a lock file with a lock on it, thus to determine if the daemon is running
+	 * requires that you attempt to lock the file as well.  Thus the existence of the file does
+	 * not mean it's running, but the absence of the file does indicate it's not running.
+	 *
+	 * See lvmdbusd for more details.
+	 */
+
+	lockfile = getenv(LVM_DBUS_LOCK_FILE_ENV_KEY);
+	if (!lockfile) {
+		lockfile = LVM_DBUS_LOCK_FILE;
+	}
+
+	errno = 0;
+	fd = open(lockfile, O_RDWR);
+	if (-1 == fd) {
+		errno_cpy = errno;
+		if (errno_cpy == ENOENT) {
+			return 0;
+		} else {
+			/* Safest option is to return running when we encounter unexpected errors */
+			log_debug_dbus("Unexpected errno: %d on lockfile open, returning running", errno_cpy);
+			return 1;
+		}
+	}
+
+	/* Need to ensure we close lock FD now */
+	errno = 0;
+	rc = lockf(fd, F_TLOCK|F_TEST, 0);
+	if (-1 != rc) {
+		/* Not locked, thus not running */
+		running = 0;
+	} else {
+		errno_cpy = errno;
+		if (errno_cpy == EACCES || errno_cpy == EAGAIN) {
+			/* Locked, so daemon is running */
+			running = 1;
+		} else {
+			log_debug_dbus("Unexpected errno: %d on lockf, returning running", errno_cpy);
+			running = 1 ;
+		}
+	}
+
+	close(fd);
+	return running;
+}
+
+
 void lvmnotify_send(struct cmd_context *cmd)
 {
 	static const char _dbus_notification_failed_msg[] = "D-Bus notification failed";
@@ -43,6 +105,12 @@ void lvmnotify_send(struct cmd_context *cmd)
 	cmd->lv_notify = 0;
 	cmd->pv_notify = 0;
 
+	/* If lvmdbusd isn't running, don't notify as you will start it as it will auto activate */
+	if (!lvmdbusd_running()) {
+		log_debug_dbus("dbus damon not running, not notifying");
+		return;
+	}
+
 	cmd_name = get_cmd_name();
 
 	ret = sd_bus_open_system(&bus);