[PATCH] RPC: separate TCP and UDP write space callbacks

[mirror_ubuntu-bionic-kernel.git] / net / sunrpc / xprt.c

/*
 *  linux/net/sunrpc/xprt.c
 *
 *  This is a generic RPC call interface supporting congestion avoidance,
 *  and asynchronous calls.
 *
 *  The interface works like this:
 *
 *  -   When a process places a call, it allocates a request slot if
 *      one is available. Otherwise, it sleeps on the backlog queue
 *      (xprt_reserve).
 *  -   Next, the caller puts together the RPC message, stuffs it into
 *      the request struct, and calls xprt_transmit().
 *  -   xprt_transmit sends the message and installs the caller on the
 *      transport's wait list. At the same time, it installs a timer that
 *      is run after the packet's timeout has expired.
 *  -   When a packet arrives, the data_ready handler walks the list of
 *      pending requests for that transport. If a matching XID is found, the
 *      caller is woken up, and the timer removed.
 *  -   When no reply arrives within the timeout interval, the timer is
 *      fired by the kernel and runs xprt_timer(). It either adjusts the
 *      timeout values (minor timeout) or wakes up the caller with a status
 *      of -ETIMEDOUT.
 *  -   When the caller receives a notification from RPC that a reply arrived,
 *      it should release the RPC slot, and process the reply.
 *      If the call timed out, it may choose to retry the operation by
 *      adjusting the initial timeout value, and simply calling rpc_call
 *      again.
 *
 *  Support for async RPC is done through a set of RPC-specific scheduling
 *  primitives that `transparently' work for processes as well as async
 *  tasks that rely on callbacks.
 *
 *  Copyright (C) 1995-1997, Olaf Kirch <okir@monad.swb.de>
 *
 *  Transport switch API copyright (C) 2005, Chuck Lever <cel@netapp.com>
 */

#include <linux/module.h>

#include <linux/types.h>
#include <linux/interrupt.h>
#include <linux/workqueue.h>
#include <linux/random.h>

#include <linux/sunrpc/clnt.h>

/*
 * Local variables
 */

#ifdef RPC_DEBUG
# undef  RPC_DEBUG_DATA
# define RPCDBG_FACILITY        RPCDBG_XPRT
#endif

/*
 * Local functions
 */
static void     xprt_request_init(struct rpc_task *, struct rpc_xprt *);
static inline void      do_xprt_reserve(struct rpc_task *);
static void     xprt_connect_status(struct rpc_task *task);
static int      __xprt_get_cong(struct rpc_xprt *, struct rpc_task *);

static int      xprt_clear_backlog(struct rpc_xprt *xprt);

/*
 * Serialize write access to transports, in order to prevent different
 * requests from interfering with each other.
 * Also prevents transport connects from colliding with writes.
 */
static int
__xprt_lock_write(struct rpc_xprt *xprt, struct rpc_task *task)
{
        struct rpc_rqst *req = task->tk_rqstp;

        if (test_and_set_bit(XPRT_LOCKED, &xprt->state)) {
                if (task == xprt->snd_task)
                        return 1;
                goto out_sleep;
        }
        if (xprt->nocong || __xprt_get_cong(xprt, task)) {
                xprt->snd_task = task;
                if (req) {
                        req->rq_bytes_sent = 0;
                        req->rq_ntrans++;
                }
                return 1;
        }
        smp_mb__before_clear_bit();
        clear_bit(XPRT_LOCKED, &xprt->state);
        smp_mb__after_clear_bit();
out_sleep:
        dprintk("RPC: %4d failed to lock transport %p\n", task->tk_pid, xprt);
        task->tk_timeout = 0;
        task->tk_status = -EAGAIN;
        if (req && req->rq_ntrans)
                rpc_sleep_on(&xprt->resend, task, NULL, NULL);
        else
                rpc_sleep_on(&xprt->sending, task, NULL, NULL);
        return 0;
}

static inline int
xprt_lock_write(struct rpc_xprt *xprt, struct rpc_task *task)
{
        int retval;

        spin_lock_bh(&xprt->transport_lock);
        retval = __xprt_lock_write(xprt, task);
        spin_unlock_bh(&xprt->transport_lock);
        return retval;
}


static void
__xprt_lock_write_next(struct rpc_xprt *xprt)
{
        struct rpc_task *task;

        if (test_and_set_bit(XPRT_LOCKED, &xprt->state))
                return;
        if (!xprt->nocong && RPCXPRT_CONGESTED(xprt))
                goto out_unlock;
        task = rpc_wake_up_next(&xprt->resend);
        if (!task) {
                task = rpc_wake_up_next(&xprt->sending);
                if (!task)
                        goto out_unlock;
        }
        if (xprt->nocong || __xprt_get_cong(xprt, task)) {
                struct rpc_rqst *req = task->tk_rqstp;
                xprt->snd_task = task;
                if (req) {
                        req->rq_bytes_sent = 0;
                        req->rq_ntrans++;
                }
                return;
        }
out_unlock:
        smp_mb__before_clear_bit();
        clear_bit(XPRT_LOCKED, &xprt->state);
        smp_mb__after_clear_bit();
}

/*
 * Releases the transport for use by other requests.
 */
static void
__xprt_release_write(struct rpc_xprt *xprt, struct rpc_task *task)
{
        if (xprt->snd_task == task) {
                xprt->snd_task = NULL;
                smp_mb__before_clear_bit();
                clear_bit(XPRT_LOCKED, &xprt->state);
                smp_mb__after_clear_bit();
                __xprt_lock_write_next(xprt);
        }
}

static inline void
xprt_release_write(struct rpc_xprt *xprt, struct rpc_task *task)
{
        spin_lock_bh(&xprt->transport_lock);
        __xprt_release_write(xprt, task);
        spin_unlock_bh(&xprt->transport_lock);
}

/*
 * Van Jacobson congestion avoidance. Check if the congestion window
 * overflowed. Put the task to sleep if this is the case.
 */
static int
__xprt_get_cong(struct rpc_xprt *xprt, struct rpc_task *task)
{
        struct rpc_rqst *req = task->tk_rqstp;

        if (req->rq_cong)
                return 1;
        dprintk("RPC: %4d xprt_cwnd_limited cong = %ld cwnd = %ld\n",
                        task->tk_pid, xprt->cong, xprt->cwnd);
        if (RPCXPRT_CONGESTED(xprt))
                return 0;
        req->rq_cong = 1;
        xprt->cong += RPC_CWNDSCALE;
        return 1;
}

/*
 * Adjust the congestion window, and wake up the next task
 * that has been sleeping due to congestion
 */
static void
__xprt_put_cong(struct rpc_xprt *xprt, struct rpc_rqst *req)
{
        if (!req->rq_cong)
                return;
        req->rq_cong = 0;
        xprt->cong -= RPC_CWNDSCALE;
        __xprt_lock_write_next(xprt);
}

/*
 * Adjust RPC congestion window
 * We use a time-smoothed congestion estimator to avoid heavy oscillation.
 */
static void
xprt_adjust_cwnd(struct rpc_xprt *xprt, int result)
{
        unsigned long   cwnd;

        cwnd = xprt->cwnd;
        if (result >= 0 && cwnd <= xprt->cong) {
                /* The (cwnd >> 1) term makes sure
                 * the result gets rounded properly. */
                cwnd += (RPC_CWNDSCALE * RPC_CWNDSCALE + (cwnd >> 1)) / cwnd;
                if (cwnd > RPC_MAXCWND(xprt))
                        cwnd = RPC_MAXCWND(xprt);
                __xprt_lock_write_next(xprt);
        } else if (result == -ETIMEDOUT) {
                cwnd >>= 1;
                if (cwnd < RPC_CWNDSCALE)
                        cwnd = RPC_CWNDSCALE;
        }
        dprintk("RPC:      cong %ld, cwnd was %ld, now %ld\n",
                        xprt->cong, xprt->cwnd, cwnd);
        xprt->cwnd = cwnd;
}

/**
 * xprt_wake_pending_tasks - wake all tasks on a transport's pending queue
 * @xprt: transport with waiting tasks
 * @status: result code to plant in each task before waking it
 *
 */
void xprt_wake_pending_tasks(struct rpc_xprt *xprt, int status)
{
        if (status < 0)
                rpc_wake_up_status(&xprt->pending, status);
        else
                rpc_wake_up(&xprt->pending);
}

/**
 * xprt_wait_for_buffer_space - wait for transport output buffer to clear
 * @task: task to be put to sleep
 *
 */
void xprt_wait_for_buffer_space(struct rpc_task *task)
{
        struct rpc_rqst *req = task->tk_rqstp;
        struct rpc_xprt *xprt = req->rq_xprt;

        task->tk_timeout = req->rq_timeout;
        rpc_sleep_on(&xprt->pending, task, NULL, NULL);
}

/**
 * xprt_write_space - wake the task waiting for transport output buffer space
 * @xprt: transport with waiting tasks
 *
 * Can be called in a soft IRQ context, so xprt_write_space never sleeps.
 */
void xprt_write_space(struct rpc_xprt *xprt)
{
        if (unlikely(xprt->shutdown))
                return;

        spin_lock_bh(&xprt->transport_lock);
        if (xprt->snd_task) {
                dprintk("RPC:      write space: waking waiting task on xprt %p\n",
                                xprt);
                rpc_wake_up_task(xprt->snd_task);
        }
        spin_unlock_bh(&xprt->transport_lock);
}

static void xprt_reset_majortimeo(struct rpc_rqst *req)
{
        struct rpc_timeout *to = &req->rq_xprt->timeout;

        req->rq_majortimeo = req->rq_timeout;
        if (to->to_exponential)
                req->rq_majortimeo <<= to->to_retries;
        else
                req->rq_majortimeo += to->to_increment * to->to_retries;
        if (req->rq_majortimeo > to->to_maxval || req->rq_majortimeo == 0)
                req->rq_majortimeo = to->to_maxval;
        req->rq_majortimeo += jiffies;
}

/**
 * xprt_adjust_timeout - adjust timeout values for next retransmit
 * @req: RPC request containing parameters to use for the adjustment
 *
 */
int xprt_adjust_timeout(struct rpc_rqst *req)
{
        struct rpc_xprt *xprt = req->rq_xprt;
        struct rpc_timeout *to = &xprt->timeout;
        int status = 0;

        if (time_before(jiffies, req->rq_majortimeo)) {
                if (to->to_exponential)
                        req->rq_timeout <<= 1;
                else
                        req->rq_timeout += to->to_increment;
                if (to->to_maxval && req->rq_timeout >= to->to_maxval)
                        req->rq_timeout = to->to_maxval;
                req->rq_retries++;
                pprintk("RPC: %lu retrans\n", jiffies);
        } else {
                req->rq_timeout = to->to_initval;
                req->rq_retries = 0;
                xprt_reset_majortimeo(req);
                /* Reset the RTT counters == "slow start" */
                spin_lock_bh(&xprt->transport_lock);
                rpc_init_rtt(req->rq_task->tk_client->cl_rtt, to->to_initval);
                spin_unlock_bh(&xprt->transport_lock);
                pprintk("RPC: %lu timeout\n", jiffies);
                status = -ETIMEDOUT;
        }

        if (req->rq_timeout == 0) {
                printk(KERN_WARNING "xprt_adjust_timeout: rq_timeout = 0!\n");
                req->rq_timeout = 5 * HZ;
        }
        return status;
}

static void xprt_autoclose(void *args)
{
        struct rpc_xprt *xprt = (struct rpc_xprt *)args;

        xprt_disconnect(xprt);
        xprt->ops->close(xprt);
        xprt_release_write(xprt, NULL);
}

/**
 * xprt_disconnect - mark a transport as disconnected
 * @xprt: transport to flag for disconnect
 *
 */
void xprt_disconnect(struct rpc_xprt *xprt)
{
        dprintk("RPC:      disconnected transport %p\n", xprt);
        spin_lock_bh(&xprt->transport_lock);
        xprt_clear_connected(xprt);
        xprt_wake_pending_tasks(xprt, -ENOTCONN);
        spin_unlock_bh(&xprt->transport_lock);
}

static void
xprt_init_autodisconnect(unsigned long data)
{
        struct rpc_xprt *xprt = (struct rpc_xprt *)data;

        spin_lock(&xprt->transport_lock);
        if (!list_empty(&xprt->recv) || xprt->shutdown)
                goto out_abort;
        if (test_and_set_bit(XPRT_LOCKED, &xprt->state))
                goto out_abort;
        spin_unlock(&xprt->transport_lock);
        if (xprt_connecting(xprt))
                xprt_release_write(xprt, NULL);
        else
                schedule_work(&xprt->task_cleanup);
        return;
out_abort:
        spin_unlock(&xprt->transport_lock);
}

/**
 * xprt_connect - schedule a transport connect operation
 * @task: RPC task that is requesting the connect
 *
 */
void xprt_connect(struct rpc_task *task)
{
        struct rpc_xprt *xprt = task->tk_xprt;

        dprintk("RPC: %4d xprt_connect xprt %p %s connected\n", task->tk_pid,
                        xprt, (xprt_connected(xprt) ? "is" : "is not"));

        if (xprt->shutdown) {
                task->tk_status = -EIO;
                return;
        }
        if (!xprt->addr.sin_port) {
                task->tk_status = -EIO;
                return;
        }
        if (!xprt_lock_write(xprt, task))
                return;
        if (xprt_connected(xprt))
                xprt_release_write(xprt, task);
        else {
                if (task->tk_rqstp)
                        task->tk_rqstp->rq_bytes_sent = 0;

                task->tk_timeout = RPC_CONNECT_TIMEOUT;
                rpc_sleep_on(&xprt->pending, task, xprt_connect_status, NULL);
                xprt->ops->connect(task);
        }
        return;
}

static void xprt_connect_status(struct rpc_task *task)
{
        struct rpc_xprt *xprt = task->tk_xprt;

        if (task->tk_status >= 0) {
                dprintk("RPC: %4d xprt_connect_status: connection established\n",
                                task->tk_pid);
                return;
        }

        switch (task->tk_status) {
        case -ECONNREFUSED:
        case -ECONNRESET:
                dprintk("RPC: %4d xprt_connect_status: server %s refused connection\n",
                                task->tk_pid, task->tk_client->cl_server);
                break;
        case -ENOTCONN:
                dprintk("RPC: %4d xprt_connect_status: connection broken\n",
                                task->tk_pid);
                break;
        case -ETIMEDOUT:
                dprintk("RPC: %4d xprt_connect_status: connect attempt timed out\n",
                                task->tk_pid);
                break;
        default:
                dprintk("RPC: %4d xprt_connect_status: error %d connecting to server %s\n",
                                task->tk_pid, -task->tk_status, task->tk_client->cl_server);
                xprt_release_write(xprt, task);
                task->tk_status = -EIO;
                return;
        }

        /* if soft mounted, just cause this RPC to fail */
        if (RPC_IS_SOFT(task)) {
                xprt_release_write(xprt, task);
                task->tk_status = -EIO;
        }
}

/**
 * xprt_lookup_rqst - find an RPC request corresponding to an XID
 * @xprt: transport on which the original request was transmitted
 * @xid: RPC XID of incoming reply
 *
 */
struct rpc_rqst *xprt_lookup_rqst(struct rpc_xprt *xprt, u32 xid)
{
        struct list_head *pos;
        struct rpc_rqst *req = NULL;

        list_for_each(pos, &xprt->recv) {
                struct rpc_rqst *entry = list_entry(pos, struct rpc_rqst, rq_list);
                if (entry->rq_xid == xid) {
                        req = entry;
                        break;
                }
        }
        return req;
}

/**
 * xprt_complete_rqst - called when reply processing is complete
 * @xprt: controlling transport
 * @req: RPC request that just completed
 * @copied: actual number of bytes received from the transport
 *
 */
void xprt_complete_rqst(struct rpc_xprt *xprt, struct rpc_rqst *req, int copied)
{
        struct rpc_task *task = req->rq_task;
        struct rpc_clnt *clnt = task->tk_client;

        /* Adjust congestion window */
        if (!xprt->nocong) {
                unsigned timer = task->tk_msg.rpc_proc->p_timer;
                xprt_adjust_cwnd(xprt, copied);
                __xprt_put_cong(xprt, req);
                if (timer) {
                        if (req->rq_ntrans == 1)
                                rpc_update_rtt(clnt->cl_rtt, timer,
                                                (long)jiffies - req->rq_xtime);
                        rpc_set_timeo(clnt->cl_rtt, timer, req->rq_ntrans - 1);
                }
        }

#ifdef RPC_PROFILE
        /* Profile only reads for now */
        if (copied > 1024) {
                static unsigned long    nextstat;
                static unsigned long    pkt_rtt, pkt_len, pkt_cnt;

                pkt_cnt++;
                pkt_len += req->rq_slen + copied;
                pkt_rtt += jiffies - req->rq_xtime;
                if (time_before(nextstat, jiffies)) {
                        printk("RPC: %lu %ld cwnd\n", jiffies, xprt->cwnd);
                        printk("RPC: %ld %ld %ld %ld stat\n",
                                        jiffies, pkt_cnt, pkt_len, pkt_rtt);
                        pkt_rtt = pkt_len = pkt_cnt = 0;
                        nextstat = jiffies + 5 * HZ;
                }
        }
#endif

        dprintk("RPC: %4d has input (%d bytes)\n", task->tk_pid, copied);
        list_del_init(&req->rq_list);
        req->rq_received = req->rq_private_buf.len = copied;

        /* ... and wake up the process. */
        rpc_wake_up_task(task);
        return;
}

/*
 * RPC receive timeout handler.
 */
static void
xprt_timer(struct rpc_task *task)
{
        struct rpc_rqst *req = task->tk_rqstp;
        struct rpc_xprt *xprt = req->rq_xprt;

        spin_lock(&xprt->transport_lock);
        if (req->rq_received)
                goto out;

        xprt_adjust_cwnd(req->rq_xprt, -ETIMEDOUT);
        __xprt_put_cong(xprt, req);

        dprintk("RPC: %4d xprt_timer (%s request)\n",
                task->tk_pid, req ? "pending" : "backlogged");

        task->tk_status  = -ETIMEDOUT;
out:
        task->tk_timeout = 0;
        rpc_wake_up_task(task);
        spin_unlock(&xprt->transport_lock);
}

/**
 * xprt_prepare_transmit - reserve the transport before sending a request
 * @task: RPC task about to send a request
 *
 */
int xprt_prepare_transmit(struct rpc_task *task)
{
        struct rpc_rqst *req = task->tk_rqstp;
        struct rpc_xprt *xprt = req->rq_xprt;
        int err = 0;

        dprintk("RPC: %4d xprt_prepare_transmit\n", task->tk_pid);

        if (xprt->shutdown)
                return -EIO;

        spin_lock_bh(&xprt->transport_lock);
        if (req->rq_received && !req->rq_bytes_sent) {
                err = req->rq_received;
                goto out_unlock;
        }
        if (!__xprt_lock_write(xprt, task)) {
                err = -EAGAIN;
                goto out_unlock;
        }

        if (!xprt_connected(xprt)) {
                err = -ENOTCONN;
                goto out_unlock;
        }
out_unlock:
        spin_unlock_bh(&xprt->transport_lock);
        return err;
}

/**
 * xprt_transmit - send an RPC request on a transport
 * @task: controlling RPC task
 *
 * We have to copy the iovec because sendmsg fiddles with its contents.
 */
void xprt_transmit(struct rpc_task *task)
{
        struct rpc_clnt *clnt = task->tk_client;
        struct rpc_rqst *req = task->tk_rqstp;
        struct rpc_xprt *xprt = req->rq_xprt;
        int status;

        dprintk("RPC: %4d xprt_transmit(%u)\n", task->tk_pid, req->rq_slen);

        smp_rmb();
        if (!req->rq_received) {
                if (list_empty(&req->rq_list)) {
                        spin_lock_bh(&xprt->transport_lock);
                        /* Update the softirq receive buffer */
                        memcpy(&req->rq_private_buf, &req->rq_rcv_buf,
                                        sizeof(req->rq_private_buf));
                        /* Add request to the receive list */
                        list_add_tail(&req->rq_list, &xprt->recv);
                        spin_unlock_bh(&xprt->transport_lock);
                        xprt_reset_majortimeo(req);
                        /* Turn off autodisconnect */
                        del_singleshot_timer_sync(&xprt->timer);
                }
        } else if (!req->rq_bytes_sent)
                return;

        status = xprt->ops->send_request(task);
        if (!status)
                goto out_receive;

        /* Note: at this point, task->tk_sleeping has not yet been set,
         *       hence there is no danger of the waking up task being put on
         *       schedq, and being picked up by a parallel run of rpciod().
         */
        task->tk_status = status;

        switch (status) {
        case -ECONNREFUSED:
                task->tk_timeout = RPC_REESTABLISH_TIMEOUT;
                rpc_sleep_on(&xprt->sending, task, NULL, NULL);
        case -EAGAIN:
        case -ENOTCONN:
                return;
        default:
                if (xprt->stream)
                        xprt_disconnect(xprt);
        }
        xprt_release_write(xprt, task);
        return;
 out_receive:
        dprintk("RPC: %4d xmit complete\n", task->tk_pid);
        /* Set the task's receive timeout value */
        spin_lock_bh(&xprt->transport_lock);
        if (!xprt->nocong) {
                int timer = task->tk_msg.rpc_proc->p_timer;
                task->tk_timeout = rpc_calc_rto(clnt->cl_rtt, timer);
                task->tk_timeout <<= rpc_ntimeo(clnt->cl_rtt, timer) + req->rq_retries;
                if (task->tk_timeout > xprt->timeout.to_maxval || task->tk_timeout == 0)
                        task->tk_timeout = xprt->timeout.to_maxval;
        } else
                task->tk_timeout = req->rq_timeout;
        /* Don't race with disconnect */
        if (!xprt_connected(xprt))
                task->tk_status = -ENOTCONN;
        else if (!req->rq_received)
                rpc_sleep_on(&xprt->pending, task, NULL, xprt_timer);
        __xprt_release_write(xprt, task);
        spin_unlock_bh(&xprt->transport_lock);
}

static inline void do_xprt_reserve(struct rpc_task *task)
{
        struct rpc_xprt *xprt = task->tk_xprt;

        task->tk_status = 0;
        if (task->tk_rqstp)
                return;
        if (!list_empty(&xprt->free)) {
                struct rpc_rqst *req = list_entry(xprt->free.next, struct rpc_rqst, rq_list);
                list_del_init(&req->rq_list);
                task->tk_rqstp = req;
                xprt_request_init(task, xprt);
                return;
        }
        dprintk("RPC:      waiting for request slot\n");
        task->tk_status = -EAGAIN;
        task->tk_timeout = 0;
        rpc_sleep_on(&xprt->backlog, task, NULL, NULL);
}

/**
 * xprt_reserve - allocate an RPC request slot
 * @task: RPC task requesting a slot allocation
 *
 * If no more slots are available, place the task on the transport's
 * backlog queue.
 */
void xprt_reserve(struct rpc_task *task)
{
        struct rpc_xprt *xprt = task->tk_xprt;

        task->tk_status = -EIO;
        if (!xprt->shutdown) {
                spin_lock(&xprt->reserve_lock);
                do_xprt_reserve(task);
                spin_unlock(&xprt->reserve_lock);
        }
}

static inline u32 xprt_alloc_xid(struct rpc_xprt *xprt)
{
        return xprt->xid++;
}

static inline void xprt_init_xid(struct rpc_xprt *xprt)
{
        get_random_bytes(&xprt->xid, sizeof(xprt->xid));
}

static void xprt_request_init(struct rpc_task *task, struct rpc_xprt *xprt)
{
        struct rpc_rqst *req = task->tk_rqstp;

        req->rq_timeout = xprt->timeout.to_initval;
        req->rq_task    = task;
        req->rq_xprt    = xprt;
        req->rq_xid     = xprt_alloc_xid(xprt);
        dprintk("RPC: %4d reserved req %p xid %08x\n", task->tk_pid,
                        req, ntohl(req->rq_xid));
}

/**
 * xprt_release - release an RPC request slot
 * @task: task which is finished with the slot
 *
 */
void xprt_release(struct rpc_task *task)
{
        struct rpc_xprt *xprt = task->tk_xprt;
        struct rpc_rqst *req;

        if (!(req = task->tk_rqstp))
                return;
        spin_lock_bh(&xprt->transport_lock);
        __xprt_release_write(xprt, task);
        __xprt_put_cong(xprt, req);
        if (!list_empty(&req->rq_list))
                list_del(&req->rq_list);
        xprt->last_used = jiffies;
        if (list_empty(&xprt->recv) && !xprt->shutdown)
                mod_timer(&xprt->timer,
                                xprt->last_used + RPC_IDLE_DISCONNECT_TIMEOUT);
        spin_unlock_bh(&xprt->transport_lock);
        task->tk_rqstp = NULL;
        memset(req, 0, sizeof(*req));   /* mark unused */

        dprintk("RPC: %4d release request %p\n", task->tk_pid, req);

        spin_lock(&xprt->reserve_lock);
        list_add(&req->rq_list, &xprt->free);
        xprt_clear_backlog(xprt);
        spin_unlock(&xprt->reserve_lock);
}

/**
 * xprt_set_timeout - set constant RPC timeout
 * @to: RPC timeout parameters to set up
 * @retr: number of retries
 * @incr: amount of increase after each retry
 *
 */
void xprt_set_timeout(struct rpc_timeout *to, unsigned int retr, unsigned long incr)
{
        to->to_initval   = 
        to->to_increment = incr;
        to->to_maxval    = to->to_initval + (incr * retr);
        to->to_retries   = retr;
        to->to_exponential = 0;
}

static struct rpc_xprt *xprt_setup(int proto, struct sockaddr_in *ap, struct rpc_timeout *to)
{
        int result;
        struct rpc_xprt *xprt;
        struct rpc_rqst *req;

        if ((xprt = kmalloc(sizeof(struct rpc_xprt), GFP_KERNEL)) == NULL)
                return ERR_PTR(-ENOMEM);
        memset(xprt, 0, sizeof(*xprt)); /* Nnnngh! */

        xprt->addr = *ap;

        switch (proto) {
        case IPPROTO_UDP:
                result = xs_setup_udp(xprt, to);
                break;
        case IPPROTO_TCP:
                result = xs_setup_tcp(xprt, to);
                break;
        default:
                printk(KERN_ERR "RPC: unrecognized transport protocol: %d\n",
                                proto);
                result = -EIO;
                break;
        }
        if (result) {
                kfree(xprt);
                return ERR_PTR(result);
        }

        spin_lock_init(&xprt->transport_lock);
        spin_lock_init(&xprt->reserve_lock);
        init_waitqueue_head(&xprt->cong_wait);

        INIT_LIST_HEAD(&xprt->free);
        INIT_LIST_HEAD(&xprt->recv);
        INIT_WORK(&xprt->task_cleanup, xprt_autoclose, xprt);
        init_timer(&xprt->timer);
        xprt->timer.function = xprt_init_autodisconnect;
        xprt->timer.data = (unsigned long) xprt;
        xprt->last_used = jiffies;

        rpc_init_wait_queue(&xprt->pending, "xprt_pending");
        rpc_init_wait_queue(&xprt->sending, "xprt_sending");
        rpc_init_wait_queue(&xprt->resend, "xprt_resend");
        rpc_init_priority_wait_queue(&xprt->backlog, "xprt_backlog");

        /* initialize free list */
        for (req = &xprt->slot[xprt->max_reqs-1]; req >= &xprt->slot[0]; req--)
                list_add(&req->rq_list, &xprt->free);

        xprt_init_xid(xprt);

        dprintk("RPC:      created transport %p with %u slots\n", xprt,
                        xprt->max_reqs);
        
        return xprt;
}

/**
 * xprt_create_proto - create an RPC client transport
 * @proto: requested transport protocol
 * @sap: remote peer's address
 * @to: timeout parameters for new transport
 *
 */
struct rpc_xprt *xprt_create_proto(int proto, struct sockaddr_in *sap, struct rpc_timeout *to)
{
        struct rpc_xprt *xprt;

        xprt = xprt_setup(proto, sap, to);
        if (IS_ERR(xprt))
                dprintk("RPC:      xprt_create_proto failed\n");
        else
                dprintk("RPC:      xprt_create_proto created xprt %p\n", xprt);
        return xprt;
}

static void xprt_shutdown(struct rpc_xprt *xprt)
{
        xprt->shutdown = 1;
        rpc_wake_up(&xprt->sending);
        rpc_wake_up(&xprt->resend);
        xprt_wake_pending_tasks(xprt, -EIO);
        rpc_wake_up(&xprt->backlog);
        wake_up(&xprt->cong_wait);
        del_timer_sync(&xprt->timer);
}

static int xprt_clear_backlog(struct rpc_xprt *xprt) {
        rpc_wake_up_next(&xprt->backlog);
        wake_up(&xprt->cong_wait);
        return 1;
}

/**
 * xprt_destroy - destroy an RPC transport, killing off all requests.
 * @xprt: transport to destroy
 *
 */
int xprt_destroy(struct rpc_xprt *xprt)
{
        dprintk("RPC:      destroying transport %p\n", xprt);
        xprt_shutdown(xprt);
        xprt->ops->destroy(xprt);
        kfree(xprt);

        return 0;
}