fdset: add new fdset_consume() helper

src/shared/fdset.c

@@ -80,6 +80,19 @@ int fdset_put(FDSet *s, int fd) {
         return set_put(MAKE_SET(s), FD_TO_PTR(fd));
 }
 
+int fdset_consume(FDSet *s, int fd) {
+        int r;
+
+        assert(s);
+        assert(fd >= 0);
+
+        r = fdset_put(s, fd);
+        if (r < 0)
+                safe_close(fd);
+
+        return r;
+}
+
 int fdset_put_dup(FDSet *s, int fd) {
         _cleanup_close_ int copy = -EBADF;
         int r;