[sheepdog] [sheepdog/sheepdog] c0f2aa: initial accelio support

[Hitoshi Mitake]

  Branch: refs/heads/accelio-v1.4
  Home:   https://github.com/sheepdog/sheepdog
  Commit: c0f2aa078ea532bedab840b8bb4852994760cd7c
      https://github.com/sheepdog/sheepdog/commit/c0f2aa078ea532bedab840b8bb4852994760cd7c
  Author: Hitoshi Mitake <mitake.hitoshi at lab.ntt.co.jp>
  Date:   2015-10-10 (Sat, 10 Oct 2015)

  Changed paths:
    M configure.ac
    M include/internal_proto.h
    M include/net.h
    A include/xio.h
    M lib/Makefile.am
    M lib/sockfd_cache.c
    A lib/xio.c
    M sheep/Makefile.am
    M sheep/gateway.c
    M sheep/request.c
    M sheep/sheep.c
    M sheep/sheep_priv.h
    A sheep/xio.c
    M shepherd/Makefile.am

  Log Message:
  -----------
  initial accelio support

This patch adds a support of accelio, an library of RPC which wraps
TCP and RDMA in clean way, to sheepdog. With this change, sheepdog
will be able to utilize high speed interconnect like infiniband.

The code is very early stage and have bunch of ToDos. However, I'd
like to share it and want the community to help the implementation.

How to build:
 1. install accelio
 2. ./configure --enable-accelio
 3. make

How to use:
 $ sheep -i transport=rdma,host=xxx,port=yyy ...

Minor ToDos:
 - clean up code (e.g. comment out)
 - remove known segfault bugs
 - sane error handling
 - remove memory leaks

Major ToDos:
 - enhance code for utilizing RDMA
 - rx/tx in worker threads (I'm not sure it is effective because RDMA
   helps to reduce CPU consumption)

Signed-off-by: Hitoshi Mitake <mitake.hitoshi at lab.ntt.co.jp>