lvmetad: check pid for warning case

When command is not using lvmetad because
use_lvmetad=0 in the config, but the lvmetad
pidfile exists, print a warning (previously
this checked for the socket existing instead
of the pidfile existing.)

lib/cache/lvmetad.c

@@ -165,6 +165,13 @@ void lvmetad_make_unused(struct cmd_context *cmd)
 		stack;
 }
 
+int lvmetad_pidfile_present(void)
+{
+	const char *pidfile = getenv("LVM_LVMETAD_PIDFILE") ?: LVMETAD_PIDFILE;
+
+	return !access(pidfile, F_OK);
+}
+
 int lvmetad_socket_present(void)
 {
 	const char *socket = _lvmetad_socket ?: LVMETAD_SOCKET;

lib/cache/lvmetad.h

@@ -52,6 +52,12 @@ void lvmetad_set_socket(const char *);
  */
 int lvmetad_socket_present(void);
 
+/*
+ * Check if lvmetad pidfile is present, indicating that the lvmetad
+ * process is running or not.
+ */
+int lvmetad_pidfile_present(void);
+
 /*
  * Set the "lvmetad validity token" (currently only consists of the lvmetad
  * filter. See lvm.conf.

lib/commands/toolcontext.c

@@ -1720,7 +1720,7 @@ static int _init_lvmetad(struct cmd_context *cmd)
 	}
 
 	if (!find_config_tree_bool(cmd, global_use_lvmetad_CFG, NULL)) {
-		if (lvmetad_socket_present())
+		if (lvmetad_pidfile_present())
 			log_warn("WARNING: Not using lvmetad because config setting use_lvmetad=0.");
 		return 1;
 	}