on master branch:

API call memif_create request configures new memif interface as intended. 

memif_create_reply should return sw_if_idx of the created interface, but it is always zero-valued with no error (retval == 0). The sw_if_index is correct in the VPP. 

Tested using VAT cli, the zero index can be also seen in the output message. 

Please also verify that the memif type interfaces can be dumped using sw_interface_dump (it also didn't work for me).

Here is the commit which possibly broked it:

commit 30349b075cf939549980f2a32e030b32f6d07e9a

Author: Jon Loeliger <jdl@netgate.com>

Date:   Tue Jan 16 16:37:16 2018 -0600

    memif: Add new API calls to manage memif socket names.