- 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/urldata.h

@@ -559,6 +559,8 @@ struct ssh_conn {
   LIBSSH2_CHANNEL *ssh_channel; /* Secure Shell channel handle */
   LIBSSH2_SFTP *sftp_session;   /* SFTP handle */
   LIBSSH2_SFTP_HANDLE *sftp_handle;
+  int waitfor;                  /* current READ/WRITE bits to wait for */
+  int orig_waitfor;             /* default READ/WRITE bits wait for */
 #endif /* USE_LIBSSH2 */
 };
 
@@ -850,6 +852,13 @@ struct Curl_handler {
                        curl_socket_t *socks,
                        int numsocks);
 
+  /* Called from the multi interface during the DO_DONE, PERFORM and
+     WAITPERFORM phases, and it should then return a proper fd set. Not setting
+     this will make libcurl use the generic default one. */
+  int (*perform_getsock)(const struct connectdata *conn,
+                         curl_socket_t *socks,
+                         int numsocks);
+
   /* This function *MAY* be set to a protocol-dependent function that is run
    * by the curl_disconnect(), as a step in the disconnection.
    */