+/* void BEFOREPOLL_WANT_FDS(int want);
+ * Expects: int *nfds_io;
+ * Can perform non-local exit.
+ * Checks whether there is space for want fds. If so, sets *nfds_io.
+ * If not, sets *nfds_io and returns. */
+#define BEFOREPOLL_WANT_FDS(want) do{ \
+ if (*nfds_io<(want)) { *nfds_io=(want); return ERANGE; } \
+ *nfds_io=(want); \
+ }while(0)
+