umask-util: add helper that resets umask until end of current code block

src/nspawn/nspawn.c

@@ -2216,13 +2216,12 @@ static int copy_devnodes(const char *dest) {
                 "tty\0"
                 "net/tun\0";
 
-        _unused_ _cleanup_umask_ mode_t u;
         const char *d;
         int r = 0;
 
         assert(dest);
 
-        u = umask(0000);
+        BLOCK_WITH_UMASK(0000);
 
         /* Create /dev/net, so that we can create /dev/net/tun in it */
         if (userns_mkdir(dest, "/dev/net", 0755, 0, 0) < 0)
@@ -2299,11 +2298,10 @@ static int copy_devnodes(const char *dest) {
 }
 
 static int make_extra_nodes(const char *dest) {
-        _unused_ _cleanup_umask_ mode_t u;
         size_t i;
         int r;
 
-        u = umask(0000);
+        BLOCK_WITH_UMASK(0000);
 
         for (i = 0; i < arg_n_extra_nodes; i++) {
                 _cleanup_free_ char *path = NULL;
@@ -2500,12 +2498,11 @@ static int setup_kmsg(int kmsg_socket) {
         _cleanup_(unlink_and_freep) char *from = NULL;
         _cleanup_free_ char *fifo = NULL;
         _cleanup_close_ int fd = -1;
-        _unused_ _cleanup_umask_ mode_t u;
         int r;
 
         assert(kmsg_socket >= 0);
 
-        u = umask(0000);
+        BLOCK_WITH_UMASK(0000);
 
         /* We create the kmsg FIFO as as temporary file in /run, but immediately delete it after bind mounting it to
          * /proc/kmsg. While FIFOs on the reading side behave very similar to /proc/kmsg, their writing side behaves