openstack queens安装

pip install networking-generic-switch==1.0.1

c/_cffi_backend.c:15:17: fatal error: ffi.h: No such file or directory
       #include <ffi.h>
                       ^
      compilation terminated.
      error: command 'gcc' failed with exit status 1

  centos
sudo yum install libffi-devel
Ubuntu

$ sudo apt-get install libffi-dev