autofs: best effort to maintain mounttab and mountdtab

When an automounted filesystem is successfully unmounted, call
rpc.umntall(8) with the -k flag.

rpc.umntall(8) is used to clean up /var/db/mounttab on the client and
/var/db/mountdtab on the server. This is only useful for NFSv3.

PR:     251906
Reviewed by: trasz
Differential Revision:  https://reviews.freebsd.org/D27801

usr.sbin/autofs/automount.c

@@ -80,6 +80,8 @@ unmount_by_statfs(const struct statfs *sb, bool force)
 	free(fsid_str);
 	if (error != 0)
 		log_warn("cannot unmount %s", sb->f_mntonname);
+	else
+		rpc_umntall();
 
 	return (error);
 }

usr.sbin/autofs/autounmountd.c

@@ -170,7 +170,8 @@ unmount_by_fsid(const fsid_t fsid, const char *mountpoint)
 			log_warn("cannot unmount %s (%s)",
 			    mountpoint, fsid_str);
 		}
-	}
+	} else
+		rpc_umntall();
 
 	free(fsid_str);
 

usr.sbin/autofs/common.c

@@ -1204,6 +1204,19 @@ lesser_daemon(void)
 	}
 }
 
+/*
+ * Applicable to NFSv3 only, see rpc.umntall(8).
+ */
+void
+rpc_umntall(void)
+{
+	FILE *f;
+
+	f = auto_popen("rpc.umntall", "-k", NULL);
+	assert(f != NULL);
+	auto_pclose(f);
+}
+
 int
 main(int argc, char **argv)
 {

usr.sbin/autofs/common.h

@@ -96,6 +96,7 @@ char	*defined_expand(const char *string);
 void	defined_init(void);
 void	defined_parse_and_add(char *def);
 void	lesser_daemon(void);
+void	rpc_umntall(void);
 
 int	main_automount(int argc, char **argv);
 int	main_automountd(int argc, char **argv);