yocto-sumo源码解析（十一）: recvfds

def recvfds(sock, size):
        ‘‘‘Receive an array of fds over an AF_UNIX socket.‘‘‘
        a = array.array(‘i‘)                                                           #声明一个整型数组，itemsize
        bytes_size = a.itemsize * size                                                 #数组容量设置
        msg, ancdata, flags, addr = sock.recvmsg(1, socket.CMSG_LEN(bytes_size))       #从套接字中读取数据到msg，ancdata,recvmsg函数是标准posix函数，可以参阅：http://pubs.opengroup.org/onlinepubs/009695399/functions/recvmsg.html
        if not msg and not ancdata:
            raise EOFError
        try:
            if len(ancdata) != 1:                                                      #对于接收到的附加数据，长度不为1个元组的情况下退出
                raise RuntimeError(‘received %d items of ancdata‘ %
                                   len(ancdata))
            cmsg_level, cmsg_type, cmsg_data = ancdata[0]                              #从附加数据中提取（cmsg_level, cmsg_type, cmsg_data）元组
            if (cmsg_level == socket.SOL_SOCKET and
                cmsg_type == socket.SCM_RIGHTS):
                if len(cmsg_data) % a.itemsize != 0:
                    raise ValueError
                a.frombytes(cmsg_data)                                                 #从cmsg_data中提取fd到数组a
                assert len(a) % 256 == msg[0]
                return list(a)
        except (ValueError, IndexError):
            pass
        raise RuntimeError(‘Invalid data received‘)