#define BIO_FLAGS_IO_SPECIAL 0x04
#define BIO_FLAGS_RWS (BIO_FLAGS_READ|BIO_FLAGS_WRITE|BIO_FLAGS_IO_SPECIAL)
#define BIO_FLAGS_SHOULD_RETRY 0x08
+#ifndef BIO_FLAGS_UPLINK
+/* "UPLINK" flag denotes file descriptors provided by application.
+ It defaults to 0, as most platforms don't require UPLINK interface. */
+#define BIO_FLAGS_UPLINK 0
+#endif
/* Used in BIO_gethostbyname() */
#define BIO_GHBN_CTRL_HITS 1