RPC中缓冲器的开辟

static void
call_allocate(struct rpc_task *task)
{
    unsigned int slack = task->tk_msg.rpc_cred->cr_auth->au_cslack;
    struct rpc_rqst *req = task->tk_rqstp;
    struct rpc_xprt *xprt = task->tk_xprt;
    struct rpc_procinfo *proc = task->tk_msg.rpc_proc;

    dprint_status(task);

    task->tk_status = 0;
    task->tk_action = call_bind;

    if (req->rq_buffer)
        return;

    if (proc->p_proc != 0) {
        BUG_ON(proc->p_arglen == 0);
        if (proc->p_decode != NULL)
            BUG_ON(proc->p_replen == 0);
    }

    /*
     * Calculate the size (in quads) of the RPC call
     * and reply headers, and convert both values
     * to byte sizes.
     */
    req->rq_callsize = RPC_CALLHDRSIZE + (slack << 1) + proc->p_arglen;
    req->rq_callsize <<= 2;
    req->rq_rcvsize = RPC_REPHDRSIZE + slack + proc-> p_replen;             //这就是在nfs4xdr.c中，所设定的编码大小
    req->rq_rcvsize <<= 2;

    req->rq_buffer = xprt->ops->buf_alloc(task,                                      //会注册不同的函数，开辟不同大小的缓冲器
                    req->rq_callsize + req->rq_rcvsize);
    if (req->rq_buffer != NULL)
        return;

    dprintk("RPC: %5u rpc_buffer allocation failed\n", task->tk_pid);

    if (RPC_IS_ASYNC(task) || !signalled()) {
        task->tk_action = call_allocate;
        rpc_delay(task, HZ>>4);
        return;
    }

    rpc_exit(task, -ERESTARTSYS);