+#define CHAN_EOF_SENT 0x04
+#define CHAN_EOF_RCVD 0x08
+
+#define CHAN_RBUF 16*1024
+
+/* check whether 'efd' is still in use */
+#define CHANNEL_EFD_INPUT_ACTIVE(c) \
+ (compat20 && c->extended_usage == CHAN_EXTENDED_READ && \
+ (c->efd != -1 || \
+ buffer_len(&c->extended) > 0))
+#define CHANNEL_EFD_OUTPUT_ACTIVE(c) \
+ (compat20 && c->extended_usage == CHAN_EXTENDED_WRITE && \
+ c->efd != -1 && (!(c->flags & (CHAN_EOF_RCVD|CHAN_CLOSE_RCVD)) || \
+ buffer_len(&c->extended) > 0))