- Using the libssh2 0.19 function libssh2_session_block_directions(), libcurl

now has an improved ability to do right when the multi interface (both
  "regular" and multi_socket) is used for SCP and SFTP transfers. This should
  result in (much) less busy-loop situations and thus less CPU usage with no
  speed loss.

lib/file.c

@@ -119,6 +119,7 @@ const struct Curl_handler Curl_handler_file = {
   ZERO_NULL,                            /* doing */
   ZERO_NULL,                            /* proto_getsock */
   ZERO_NULL,                            /* doing_getsock */
+  ZERO_NULL,                            /* perform_getsock */
   ZERO_NULL,                            /* disconnect */
   0,                                    /* defport */
   PROT_FILE                             /* protocol */