Merge /spare/repo/linux-2.6/

[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_call().
 *  -   xprt_call transmits the message and installs the caller on the
 *      socket'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 socket. 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>
 *
 *  TCP callback races fixes (C) 1998 Red Hat Software <alan@redhat.com>
 *  TCP send fixes (C) 1998 Red Hat Software <alan@redhat.com>
 *  TCP NFS related read + write fixes
 *   (C) 1999 Dave Airlie, University of Limerick, Ireland <airlied@linux.ie>
 *
 *  Rewrite of larges part of the code in order to stabilize TCP stuff.
 *  Fix behaviour when socket buffer is full.
 *   (C) 1999 Trond Myklebust <trond.myklebust@fys.uio.no>
 */

#include <linux/types.h>
#include <linux/slab.h>
#include <linux/capability.h>
#include <linux/sched.h>
#include <linux/errno.h>
#include <linux/socket.h>
#include <linux/in.h>
#include <linux/net.h>
#include <linux/mm.h>
#include <linux/udp.h>
#include <linux/tcp.h>
#include <linux/sunrpc/clnt.h>
#include <linux/file.h>
#include <linux/workqueue.h>
#include <linux/random.h>

#include <net/sock.h>
#include <net/checksum.h>
#include <net/udp.h>
#include <net/tcp.h>

/*
 * Local variables
 */

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

#define XPRT_MAX_BACKOFF        (8)
#define XPRT_IDLE_TIMEOUT       (5*60*HZ)
#define XPRT_MAX_RESVPORT       (800)

/*
 * 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_disconnect(struct rpc_xprt *);
static void     xprt_connect_status(struct rpc_task *task);
static struct rpc_xprt * xprt_setup(int proto, struct sockaddr_in *ap,
                                                struct rpc_timeout *to);
static struct socket *xprt_create_socket(struct rpc_xprt *, int, int);
static void     xprt_bind_socket(struct rpc_xprt *, struct socket *);
static int      __xprt_get_cong(struct rpc_xprt *, struct rpc_task *);

static int      xprt_clear_backlog(struct rpc_xprt *xprt);

#ifdef RPC_DEBUG_DATA
/*
 * Print the buffer contents (first 128 bytes only--just enough for
 * diropres return).
 */
static void
xprt_pktdump(char *msg, u32 *packet, unsigned int count)
{
        u8      *buf = (u8 *) packet;
        int     j;

        dprintk("RPC:      %s\n", msg);
        for (j = 0; j < count && j < 128; j += 4) {
                if (!(j & 31)) {
                        if (j)
                                dprintk("\n");
                        dprintk("0x%04x ", j);
                }
                dprintk("%02x%02x%02x%02x ",
                        buf[j], buf[j+1], buf[j+2], buf[j+3]);
        }
        dprintk("\n");
}
#else
static inline void
xprt_pktdump(char *msg, u32 *packet, unsigned int count)
{
        /* NOP */
}
#endif

/*
 * Look up RPC transport given an INET socket
 */
static inline struct rpc_xprt *
xprt_from_sock(struct sock *sk)
{
        return (struct rpc_xprt *) sk->sk_user_data;
}

/*
 * Serialize write access to sockets, in order to prevent different
 * requests from interfering with each other.
 * Also prevents TCP socket 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->sockstate)) {
                if (task == xprt->snd_task)
                        return 1;
                if (task == NULL)
                        return 0;
                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->sockstate);
        smp_mb__after_clear_bit();
out_sleep:
        dprintk("RPC: %4d failed to lock socket %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->sock_lock);
        retval = __xprt_lock_write(xprt, task);
        spin_unlock_bh(&xprt->sock_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->sockstate))
                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->sockstate);
        smp_mb__after_clear_bit();
}

/*
 * Releases the socket 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->sockstate);
                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->sock_lock);
        __xprt_release_write(xprt, task);
        spin_unlock_bh(&xprt->sock_lock);
}

/*
 * Write data to socket.
 */
static inline int
xprt_sendmsg(struct rpc_xprt *xprt, struct rpc_rqst *req)
{
        struct socket   *sock = xprt->sock;
        struct xdr_buf  *xdr = &req->rq_snd_buf;
        struct sockaddr *addr = NULL;
        int addrlen = 0;
        unsigned int    skip;
        int             result;

        if (!sock)
                return -ENOTCONN;

        xprt_pktdump("packet data:",
                                req->rq_svec->iov_base,
                                req->rq_svec->iov_len);

        /* For UDP, we need to provide an address */
        if (!xprt->stream) {
                addr = (struct sockaddr *) &xprt->addr;
                addrlen = sizeof(xprt->addr);
        }
        /* Dont repeat bytes */
        skip = req->rq_bytes_sent;

        clear_bit(SOCK_ASYNC_NOSPACE, &sock->flags);
        result = xdr_sendpages(sock, addr, addrlen, xdr, skip, MSG_DONTWAIT);

        dprintk("RPC:      xprt_sendmsg(%d) = %d\n", xdr->len - skip, result);

        if (result >= 0)
                return result;

        switch (result) {
        case -ECONNREFUSED:
                /* When the server has died, an ICMP port unreachable message
                 * prompts ECONNREFUSED.
                 */
        case -EAGAIN:
                break;
        case -ECONNRESET:
        case -ENOTCONN:
        case -EPIPE:
                /* connection broken */
                if (xprt->stream)
                        result = -ENOTCONN;
                break;
        default:
                printk(KERN_NOTICE "RPC: sendmsg returned error %d\n", -result);
        }
        return result;
}

/*
 * 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;
}

/*
 * Reset the major timeout value
 */
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;
}

/*
 * Adjust timeout values etc for next retransmit
 */
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->sock_lock);
                rpc_init_rtt(req->rq_task->tk_client->cl_rtt, to->to_initval);
                spin_unlock_bh(&xprt->sock_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;
}

/*
 * Close down a transport socket
 */
static void
xprt_close(struct rpc_xprt *xprt)
{
        struct socket   *sock = xprt->sock;
        struct sock     *sk = xprt->inet;

        if (!sk)
                return;

        write_lock_bh(&sk->sk_callback_lock);
        xprt->inet = NULL;
        xprt->sock = NULL;

        sk->sk_user_data    = NULL;
        sk->sk_data_ready   = xprt->old_data_ready;
        sk->sk_state_change = xprt->old_state_change;
        sk->sk_write_space  = xprt->old_write_space;
        write_unlock_bh(&sk->sk_callback_lock);

        sk->sk_no_check  = 0;

        sock_release(sock);
}

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

        xprt_disconnect(xprt);
        xprt_close(xprt);
        xprt_release_write(xprt, NULL);
}

/*
 * Mark a transport as disconnected
 */
static void
xprt_disconnect(struct rpc_xprt *xprt)
{
        dprintk("RPC:      disconnected transport %p\n", xprt);
        spin_lock_bh(&xprt->sock_lock);
        xprt_clear_connected(xprt);
        rpc_wake_up_status(&xprt->pending, -ENOTCONN);
        spin_unlock_bh(&xprt->sock_lock);
}

/*
 * Used to allow disconnection when we've been idle
 */
static void
xprt_init_autodisconnect(unsigned long data)
{
        struct rpc_xprt *xprt = (struct rpc_xprt *)data;

        spin_lock(&xprt->sock_lock);
        if (!list_empty(&xprt->recv) || xprt->shutdown)
                goto out_abort;
        if (test_and_set_bit(XPRT_LOCKED, &xprt->sockstate))
                goto out_abort;
        spin_unlock(&xprt->sock_lock);
        /* Let keventd close the socket */
        if (test_bit(XPRT_CONNECTING, &xprt->sockstate) != 0)
                xprt_release_write(xprt, NULL);
        else
                schedule_work(&xprt->task_cleanup);
        return;
out_abort:
        spin_unlock(&xprt->sock_lock);
}

static void xprt_socket_connect(void *args)
{
        struct rpc_xprt *xprt = (struct rpc_xprt *)args;
        struct socket *sock = xprt->sock;
        int status = -EIO;

        if (xprt->shutdown || xprt->addr.sin_port == 0)
                goto out;

        /*
         * Start by resetting any existing state
         */
        xprt_close(xprt);
        sock = xprt_create_socket(xprt, xprt->prot, xprt->resvport);
        if (sock == NULL) {
                /* couldn't create socket or bind to reserved port;
                 * this is likely a permanent error, so cause an abort */
                goto out;
        }
        xprt_bind_socket(xprt, sock);
        xprt_sock_setbufsize(xprt);

        status = 0;
        if (!xprt->stream)
                goto out;

        /*
         * Tell the socket layer to start connecting...
         */
        status = sock->ops->connect(sock, (struct sockaddr *) &xprt->addr,
                        sizeof(xprt->addr), O_NONBLOCK);
        dprintk("RPC: %p  connect status %d connected %d sock state %d\n",
                        xprt, -status, xprt_connected(xprt), sock->sk->sk_state);
        if (status < 0) {
                switch (status) {
                        case -EINPROGRESS:
                        case -EALREADY:
                                goto out_clear;
                }
        }
out:
        if (status < 0)
                rpc_wake_up_status(&xprt->pending, status);
        else
                rpc_wake_up(&xprt->pending);
out_clear:
        smp_mb__before_clear_bit();
        clear_bit(XPRT_CONNECTING, &xprt->sockstate);
        smp_mb__after_clear_bit();
}

/*
 * Attempt to connect a TCP socket.
 *
 */
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))
                goto out_write;

        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);
        if (!test_and_set_bit(XPRT_CONNECTING, &xprt->sockstate)) {
                /* Note: if we are here due to a dropped connection
                 *       we delay reconnecting by RPC_REESTABLISH_TIMEOUT/HZ
                 *       seconds
                 */
                if (xprt->sock != NULL)
                        schedule_delayed_work(&xprt->sock_connect,
                                        RPC_REESTABLISH_TIMEOUT);
                else {
                        schedule_work(&xprt->sock_connect);
                        if (!RPC_IS_ASYNC(task))
                                flush_scheduled_work();
                }
        }
        return;
 out_write:
        xprt_release_write(xprt, task);
}

/*
 * We arrive here when awoken from waiting on connection establishment.
 */
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;
        }

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

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

/*
 * Look up the RPC request corresponding to a reply, and then lock it.
 */
static inline 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;
}

/*
 * Complete reply received.
 * The TCP code relies on us to remove the request from xprt->pending.
 */
static 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;
}

static size_t
skb_read_bits(skb_reader_t *desc, void *to, size_t len)
{
        if (len > desc->count)
                len = desc->count;
        if (skb_copy_bits(desc->skb, desc->offset, to, len))
                return 0;
        desc->count -= len;
        desc->offset += len;
        return len;
}

static size_t
skb_read_and_csum_bits(skb_reader_t *desc, void *to, size_t len)
{
        unsigned int csum2, pos;

        if (len > desc->count)
                len = desc->count;
        pos = desc->offset;
        csum2 = skb_copy_and_csum_bits(desc->skb, pos, to, len, 0);
        desc->csum = csum_block_add(desc->csum, csum2, pos);
        desc->count -= len;
        desc->offset += len;
        return len;
}

/*
 * We have set things up such that we perform the checksum of the UDP
 * packet in parallel with the copies into the RPC client iovec.  -DaveM
 */
int
csum_partial_copy_to_xdr(struct xdr_buf *xdr, struct sk_buff *skb)
{
        skb_reader_t desc;

        desc.skb = skb;
        desc.offset = sizeof(struct udphdr);
        desc.count = skb->len - desc.offset;

        if (skb->ip_summed == CHECKSUM_UNNECESSARY)
                goto no_checksum;

        desc.csum = csum_partial(skb->data, desc.offset, skb->csum);
        if (xdr_partial_copy_from_skb(xdr, 0, &desc, skb_read_and_csum_bits) < 0)
                return -1;
        if (desc.offset != skb->len) {
                unsigned int csum2;
                csum2 = skb_checksum(skb, desc.offset, skb->len - desc.offset, 0);
                desc.csum = csum_block_add(desc.csum, csum2, desc.offset);
        }
        if (desc.count)
                return -1;
        if ((unsigned short)csum_fold(desc.csum))
                return -1;
        return 0;
no_checksum:
        if (xdr_partial_copy_from_skb(xdr, 0, &desc, skb_read_bits) < 0)
                return -1;
        if (desc.count)
                return -1;
        return 0;
}

/*
 * Input handler for RPC replies. Called from a bottom half and hence
 * atomic.
 */
static void
udp_data_ready(struct sock *sk, int len)
{
        struct rpc_task *task;
        struct rpc_xprt *xprt;
        struct rpc_rqst *rovr;
        struct sk_buff  *skb;
        int err, repsize, copied;
        u32 _xid, *xp;

        read_lock(&sk->sk_callback_lock);
        dprintk("RPC:      udp_data_ready...\n");
        if (!(xprt = xprt_from_sock(sk))) {
                printk("RPC:      udp_data_ready request not found!\n");
                goto out;
        }

        dprintk("RPC:      udp_data_ready client %p\n", xprt);

        if ((skb = skb_recv_datagram(sk, 0, 1, &err)) == NULL)
                goto out;

        if (xprt->shutdown)
                goto dropit;

        repsize = skb->len - sizeof(struct udphdr);
        if (repsize < 4) {
                printk("RPC: impossible RPC reply size %d!\n", repsize);
                goto dropit;
        }

        /* Copy the XID from the skb... */
        xp = skb_header_pointer(skb, sizeof(struct udphdr),
                                sizeof(_xid), &_xid);
        if (xp == NULL)
                goto dropit;

        /* Look up and lock the request corresponding to the given XID */
        spin_lock(&xprt->sock_lock);
        rovr = xprt_lookup_rqst(xprt, *xp);
        if (!rovr)
                goto out_unlock;
        task = rovr->rq_task;

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

        if ((copied = rovr->rq_private_buf.buflen) > repsize)
                copied = repsize;

        /* Suck it into the iovec, verify checksum if not done by hw. */
        if (csum_partial_copy_to_xdr(&rovr->rq_private_buf, skb))
                goto out_unlock;

        /* Something worked... */
        dst_confirm(skb->dst);

        xprt_complete_rqst(xprt, rovr, copied);

 out_unlock:
        spin_unlock(&xprt->sock_lock);
 dropit:
        skb_free_datagram(sk, skb);
 out:
        read_unlock(&sk->sk_callback_lock);
}

/*
 * Copy from an skb into memory and shrink the skb.
 */
static inline size_t
tcp_copy_data(skb_reader_t *desc, void *p, size_t len)
{
        if (len > desc->count)
                len = desc->count;
        if (skb_copy_bits(desc->skb, desc->offset, p, len)) {
                dprintk("RPC:      failed to copy %zu bytes from skb. %zu bytes remain\n",
                                len, desc->count);
                return 0;
        }
        desc->offset += len;
        desc->count -= len;
        dprintk("RPC:      copied %zu bytes from skb. %zu bytes remain\n",
                        len, desc->count);
        return len;
}

/*
 * TCP read fragment marker
 */
static inline void
tcp_read_fraghdr(struct rpc_xprt *xprt, skb_reader_t *desc)
{
        size_t len, used;
        char *p;

        p = ((char *) &xprt->tcp_recm) + xprt->tcp_offset;
        len = sizeof(xprt->tcp_recm) - xprt->tcp_offset;
        used = tcp_copy_data(desc, p, len);
        xprt->tcp_offset += used;
        if (used != len)
                return;
        xprt->tcp_reclen = ntohl(xprt->tcp_recm);
        if (xprt->tcp_reclen & 0x80000000)
                xprt->tcp_flags |= XPRT_LAST_FRAG;
        else
                xprt->tcp_flags &= ~XPRT_LAST_FRAG;
        xprt->tcp_reclen &= 0x7fffffff;
        xprt->tcp_flags &= ~XPRT_COPY_RECM;
        xprt->tcp_offset = 0;
        /* Sanity check of the record length */
        if (xprt->tcp_reclen < 4) {
                printk(KERN_ERR "RPC: Invalid TCP record fragment length\n");
                xprt_disconnect(xprt);
        }
        dprintk("RPC:      reading TCP record fragment of length %d\n",
                        xprt->tcp_reclen);
}

static void
tcp_check_recm(struct rpc_xprt *xprt)
{
        dprintk("RPC:      xprt = %p, tcp_copied = %lu, tcp_offset = %u, tcp_reclen = %u, tcp_flags = %lx\n",
                        xprt, xprt->tcp_copied, xprt->tcp_offset, xprt->tcp_reclen, xprt->tcp_flags);
        if (xprt->tcp_offset == xprt->tcp_reclen) {
                xprt->tcp_flags |= XPRT_COPY_RECM;
                xprt->tcp_offset = 0;
                if (xprt->tcp_flags & XPRT_LAST_FRAG) {
                        xprt->tcp_flags &= ~XPRT_COPY_DATA;
                        xprt->tcp_flags |= XPRT_COPY_XID;
                        xprt->tcp_copied = 0;
                }
        }
}

/*
 * TCP read xid
 */
static inline void
tcp_read_xid(struct rpc_xprt *xprt, skb_reader_t *desc)
{
        size_t len, used;
        char *p;

        len = sizeof(xprt->tcp_xid) - xprt->tcp_offset;
        dprintk("RPC:      reading XID (%Zu bytes)\n", len);
        p = ((char *) &xprt->tcp_xid) + xprt->tcp_offset;
        used = tcp_copy_data(desc, p, len);
        xprt->tcp_offset += used;
        if (used != len)
                return;
        xprt->tcp_flags &= ~XPRT_COPY_XID;
        xprt->tcp_flags |= XPRT_COPY_DATA;
        xprt->tcp_copied = 4;
        dprintk("RPC:      reading reply for XID %08x\n",
                                                ntohl(xprt->tcp_xid));
        tcp_check_recm(xprt);
}

/*
 * TCP read and complete request
 */
static inline void
tcp_read_request(struct rpc_xprt *xprt, skb_reader_t *desc)
{
        struct rpc_rqst *req;
        struct xdr_buf *rcvbuf;
        size_t len;
        ssize_t r;

        /* Find and lock the request corresponding to this xid */
        spin_lock(&xprt->sock_lock);
        req = xprt_lookup_rqst(xprt, xprt->tcp_xid);
        if (!req) {
                xprt->tcp_flags &= ~XPRT_COPY_DATA;
                dprintk("RPC:      XID %08x request not found!\n",
                                ntohl(xprt->tcp_xid));
                spin_unlock(&xprt->sock_lock);
                return;
        }

        rcvbuf = &req->rq_private_buf;
        len = desc->count;
        if (len > xprt->tcp_reclen - xprt->tcp_offset) {
                skb_reader_t my_desc;

                len = xprt->tcp_reclen - xprt->tcp_offset;
                memcpy(&my_desc, desc, sizeof(my_desc));
                my_desc.count = len;
                r = xdr_partial_copy_from_skb(rcvbuf, xprt->tcp_copied,
                                          &my_desc, tcp_copy_data);
                desc->count -= r;
                desc->offset += r;
        } else
                r = xdr_partial_copy_from_skb(rcvbuf, xprt->tcp_copied,
                                          desc, tcp_copy_data);

        if (r > 0) {
                xprt->tcp_copied += r;
                xprt->tcp_offset += r;
        }
        if (r != len) {
                /* Error when copying to the receive buffer,
                 * usually because we weren't able to allocate
                 * additional buffer pages. All we can do now
                 * is turn off XPRT_COPY_DATA, so the request
                 * will not receive any additional updates,
                 * and time out.
                 * Any remaining data from this record will
                 * be discarded.
                 */
                xprt->tcp_flags &= ~XPRT_COPY_DATA;
                dprintk("RPC:      XID %08x truncated request\n",
                                ntohl(xprt->tcp_xid));
                dprintk("RPC:      xprt = %p, tcp_copied = %lu, tcp_offset = %u, tcp_reclen = %u\n",
                                xprt, xprt->tcp_copied, xprt->tcp_offset, xprt->tcp_reclen);
                goto out;
        }

        dprintk("RPC:      XID %08x read %Zd bytes\n",
                        ntohl(xprt->tcp_xid), r);
        dprintk("RPC:      xprt = %p, tcp_copied = %lu, tcp_offset = %u, tcp_reclen = %u\n",
                        xprt, xprt->tcp_copied, xprt->tcp_offset, xprt->tcp_reclen);

        if (xprt->tcp_copied == req->rq_private_buf.buflen)
                xprt->tcp_flags &= ~XPRT_COPY_DATA;
        else if (xprt->tcp_offset == xprt->tcp_reclen) {
                if (xprt->tcp_flags & XPRT_LAST_FRAG)
                        xprt->tcp_flags &= ~XPRT_COPY_DATA;
        }

out:
        if (!(xprt->tcp_flags & XPRT_COPY_DATA)) {
                dprintk("RPC: %4d received reply complete\n",
                                req->rq_task->tk_pid);
                xprt_complete_rqst(xprt, req, xprt->tcp_copied);
        }
        spin_unlock(&xprt->sock_lock);
        tcp_check_recm(xprt);
}

/*
 * TCP discard extra bytes from a short read
 */
static inline void
tcp_read_discard(struct rpc_xprt *xprt, skb_reader_t *desc)
{
        size_t len;

        len = xprt->tcp_reclen - xprt->tcp_offset;
        if (len > desc->count)
                len = desc->count;
        desc->count -= len;
        desc->offset += len;
        xprt->tcp_offset += len;
        dprintk("RPC:      discarded %Zu bytes\n", len);
        tcp_check_recm(xprt);
}

/*
 * TCP record receive routine
 * We first have to grab the record marker, then the XID, then the data.
 */
static int
tcp_data_recv(read_descriptor_t *rd_desc, struct sk_buff *skb,
                unsigned int offset, size_t len)
{
        struct rpc_xprt *xprt = rd_desc->arg.data;
        skb_reader_t desc = {
                .skb    = skb,
                .offset = offset,
                .count  = len,
                .csum   = 0
        };

        dprintk("RPC:      tcp_data_recv\n");
        do {
                /* Read in a new fragment marker if necessary */
                /* Can we ever really expect to get completely empty fragments? */
                if (xprt->tcp_flags & XPRT_COPY_RECM) {
                        tcp_read_fraghdr(xprt, &desc);
                        continue;
                }
                /* Read in the xid if necessary */
                if (xprt->tcp_flags & XPRT_COPY_XID) {
                        tcp_read_xid(xprt, &desc);
                        continue;
                }
                /* Read in the request data */
                if (xprt->tcp_flags & XPRT_COPY_DATA) {
                        tcp_read_request(xprt, &desc);
                        continue;
                }
                /* Skip over any trailing bytes on short reads */
                tcp_read_discard(xprt, &desc);
        } while (desc.count);
        dprintk("RPC:      tcp_data_recv done\n");
        return len - desc.count;
}

static void tcp_data_ready(struct sock *sk, int bytes)
{
        struct rpc_xprt *xprt;
        read_descriptor_t rd_desc;

        read_lock(&sk->sk_callback_lock);
        dprintk("RPC:      tcp_data_ready...\n");
        if (!(xprt = xprt_from_sock(sk))) {
                printk("RPC:      tcp_data_ready socket info not found!\n");
                goto out;
        }
        if (xprt->shutdown)
                goto out;

        /* We use rd_desc to pass struct xprt to tcp_data_recv */
        rd_desc.arg.data = xprt;
        rd_desc.count = 65536;
        tcp_read_sock(sk, &rd_desc, tcp_data_recv);
out:
        read_unlock(&sk->sk_callback_lock);
}

static void
tcp_state_change(struct sock *sk)
{
        struct rpc_xprt *xprt;

        read_lock(&sk->sk_callback_lock);
        if (!(xprt = xprt_from_sock(sk)))
                goto out;
        dprintk("RPC:      tcp_state_change client %p...\n", xprt);
        dprintk("RPC:      state %x conn %d dead %d zapped %d\n",
                                sk->sk_state, xprt_connected(xprt),
                                sock_flag(sk, SOCK_DEAD),
                                sock_flag(sk, SOCK_ZAPPED));

        switch (sk->sk_state) {
        case TCP_ESTABLISHED:
                spin_lock_bh(&xprt->sock_lock);
                if (!xprt_test_and_set_connected(xprt)) {
                        /* Reset TCP record info */
                        xprt->tcp_offset = 0;
                        xprt->tcp_reclen = 0;
                        xprt->tcp_copied = 0;
                        xprt->tcp_flags = XPRT_COPY_RECM | XPRT_COPY_XID;
                        rpc_wake_up(&xprt->pending);
                }
                spin_unlock_bh(&xprt->sock_lock);
                break;
        case TCP_SYN_SENT:
        case TCP_SYN_RECV:
                break;
        default:
                xprt_disconnect(xprt);
                break;
        }
 out:
        read_unlock(&sk->sk_callback_lock);
}

/*
 * Called when more output buffer space is available for this socket.
 * We try not to wake our writers until they can make "significant"
 * progress, otherwise we'll waste resources thrashing sock_sendmsg
 * with a bunch of small requests.
 */
static void
xprt_write_space(struct sock *sk)
{
        struct rpc_xprt *xprt;
        struct socket   *sock;

        read_lock(&sk->sk_callback_lock);
        if (!(xprt = xprt_from_sock(sk)) || !(sock = sk->sk_socket))
                goto out;
        if (xprt->shutdown)
                goto out;

        /* Wait until we have enough socket memory */
        if (xprt->stream) {
                /* from net/core/stream.c:sk_stream_write_space */
                if (sk_stream_wspace(sk) < sk_stream_min_wspace(sk))
                        goto out;
        } else {
                /* from net/core/sock.c:sock_def_write_space */
                if (!sock_writeable(sk))
                        goto out;
        }

        if (!test_and_clear_bit(SOCK_NOSPACE, &sock->flags))
                goto out;

        spin_lock_bh(&xprt->sock_lock);
        if (xprt->snd_task)
                rpc_wake_up_task(xprt->snd_task);
        spin_unlock_bh(&xprt->sock_lock);
out:
        read_unlock(&sk->sk_callback_lock);
}

/*
 * 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->sock_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->sock_lock);
}

/*
 * Place the actual RPC call.
 * We have to copy the iovec because sendmsg fiddles with its contents.
 */
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->sock_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->sock_lock);
        return err;
}

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, retry = 0;


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

        /* set up everything as needed. */
        /* Write the record marker */
        if (xprt->stream) {
                u32     *marker = req->rq_svec[0].iov_base;

                *marker = htonl(0x80000000|(req->rq_slen-sizeof(*marker)));
        }

        smp_rmb();
        if (!req->rq_received) {
                if (list_empty(&req->rq_list)) {
                        spin_lock_bh(&xprt->sock_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->sock_lock);
                        xprt_reset_majortimeo(req);
                        /* Turn off autodisconnect */
                        del_singleshot_timer_sync(&xprt->timer);
                }
        } else if (!req->rq_bytes_sent)
                return;

        /* Continue transmitting the packet/record. We must be careful
         * to cope with writespace callbacks arriving _after_ we have
         * called xprt_sendmsg().
         */
        while (1) {
                req->rq_xtime = jiffies;
                status = xprt_sendmsg(xprt, req);

                if (status < 0)
                        break;

                if (xprt->stream) {
                        req->rq_bytes_sent += status;

                        /* If we've sent the entire packet, immediately
                         * reset the count of bytes sent. */
                        if (req->rq_bytes_sent >= req->rq_slen) {
                                req->rq_bytes_sent = 0;
                                goto out_receive;
                        }
                } else {
                        if (status >= req->rq_slen)
                                goto out_receive;
                        status = -EAGAIN;
                        break;
                }

                dprintk("RPC: %4d xmit incomplete (%d left of %d)\n",
                                task->tk_pid, req->rq_slen - req->rq_bytes_sent,
                                req->rq_slen);

                status = -EAGAIN;
                if (retry++ > 50)
                        break;
        }

        /* 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 -EAGAIN:
                if (test_bit(SOCK_ASYNC_NOSPACE, &xprt->sock->flags)) {
                        /* Protect against races with xprt_write_space */
                        spin_lock_bh(&xprt->sock_lock);
                        /* Don't race with disconnect */
                        if (!xprt_connected(xprt))
                                task->tk_status = -ENOTCONN;
                        else if (test_bit(SOCK_NOSPACE, &xprt->sock->flags)) {
                                task->tk_timeout = req->rq_timeout;
                                rpc_sleep_on(&xprt->pending, task, NULL, NULL);
                        }
                        spin_unlock_bh(&xprt->sock_lock);
                        return;
                }
                /* Keep holding the socket if it is blocked */
                rpc_delay(task, HZ>>4);
                return;
        case -ECONNREFUSED:
                task->tk_timeout = RPC_REESTABLISH_TIMEOUT;
                rpc_sleep_on(&xprt->sending, task, NULL, NULL);
        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->sock_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->sock_lock);
}

/*
 * Reserve an RPC call slot.
 */
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);
}

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

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

/*
 * Allocate a 'unique' XID
 */
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));
}

/*
 * Initialize RPC request
 */
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));
}

/*
 * Release an RPC call 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->sock_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 + XPRT_IDLE_TIMEOUT);
        spin_unlock_bh(&xprt->sock_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->xprt_lock);
        list_add(&req->rq_list, &xprt->free);
        xprt_clear_backlog(xprt);
        spin_unlock(&xprt->xprt_lock);
}

/*
 * Set default timeout parameters
 */
static void
xprt_default_timeout(struct rpc_timeout *to, int proto)
{
        if (proto == IPPROTO_UDP)
                xprt_set_timeout(to, 5,  5 * HZ);
        else
                xprt_set_timeout(to, 5, 60 * HZ);
}

/*
 * Set constant timeout
 */
void
xprt_set_timeout(struct rpc_timeout *to, unsigned int retr, unsigned long incr)
{
        to->to_initval   = 
        to->to_increment = incr;
        to->to_maxval    = incr * retr;
        to->to_retries   = retr;
        to->to_exponential = 0;
}

unsigned int xprt_udp_slot_table_entries = RPC_DEF_SLOT_TABLE;
unsigned int xprt_tcp_slot_table_entries = RPC_DEF_SLOT_TABLE;

/*
 * Initialize an RPC client
 */
static struct rpc_xprt *
xprt_setup(int proto, struct sockaddr_in *ap, struct rpc_timeout *to)
{
        struct rpc_xprt *xprt;
        unsigned int entries;
        size_t slot_table_size;
        struct rpc_rqst *req;

        dprintk("RPC:      setting up %s transport...\n",
                                proto == IPPROTO_UDP? "UDP" : "TCP");

        entries = (proto == IPPROTO_TCP)?
                xprt_tcp_slot_table_entries : xprt_udp_slot_table_entries;

        if ((xprt = kmalloc(sizeof(struct rpc_xprt), GFP_KERNEL)) == NULL)
                return ERR_PTR(-ENOMEM);
        memset(xprt, 0, sizeof(*xprt)); /* Nnnngh! */
        xprt->max_reqs = entries;
        slot_table_size = entries * sizeof(xprt->slot[0]);
        xprt->slot = kmalloc(slot_table_size, GFP_KERNEL);
        if (xprt->slot == NULL) {
                kfree(xprt);
                return ERR_PTR(-ENOMEM);
        }
        memset(xprt->slot, 0, slot_table_size);

        xprt->addr = *ap;
        xprt->prot = proto;
        xprt->stream = (proto == IPPROTO_TCP)? 1 : 0;
        if (xprt->stream) {
                xprt->cwnd = RPC_MAXCWND(xprt);
                xprt->nocong = 1;
                xprt->max_payload = (1U << 31) - 1;
        } else {
                xprt->cwnd = RPC_INITCWND;
                xprt->max_payload = (1U << 16) - (MAX_HEADER << 3);
        }
        spin_lock_init(&xprt->sock_lock);
        spin_lock_init(&xprt->xprt_lock);
        init_waitqueue_head(&xprt->cong_wait);

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

        /* Set timeout parameters */
        if (to) {
                xprt->timeout = *to;
        } else
                xprt_default_timeout(&xprt->timeout, xprt->prot);

        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[entries-1]; req >= &xprt->slot[0]; req--)
                list_add(&req->rq_list, &xprt->free);

        xprt_init_xid(xprt);

        /* Check whether we want to use a reserved port */
        xprt->resvport = capable(CAP_NET_BIND_SERVICE) ? 1 : 0;

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

/*
 * Bind to a reserved port
 */
static inline int xprt_bindresvport(struct rpc_xprt *xprt, struct socket *sock)
{
        struct sockaddr_in myaddr = {
                .sin_family = AF_INET,
        };
        int             err, port;

        /* Were we already bound to a given port? Try to reuse it */
        port = xprt->port;
        do {
                myaddr.sin_port = htons(port);
                err = sock->ops->bind(sock, (struct sockaddr *) &myaddr,
                                                sizeof(myaddr));
                if (err == 0) {
                        xprt->port = port;
                        return 0;
                }
                if (--port == 0)
                        port = XPRT_MAX_RESVPORT;
        } while (err == -EADDRINUSE && port != xprt->port);

        printk("RPC: Can't bind to reserved port (%d).\n", -err);
        return err;
}

static void
xprt_bind_socket(struct rpc_xprt *xprt, struct socket *sock)
{
        struct sock     *sk = sock->sk;

        if (xprt->inet)
                return;

        write_lock_bh(&sk->sk_callback_lock);
        sk->sk_user_data = xprt;
        xprt->old_data_ready = sk->sk_data_ready;
        xprt->old_state_change = sk->sk_state_change;
        xprt->old_write_space = sk->sk_write_space;
        if (xprt->prot == IPPROTO_UDP) {
                sk->sk_data_ready = udp_data_ready;
                sk->sk_no_check = UDP_CSUM_NORCV;
                xprt_set_connected(xprt);
        } else {
                tcp_sk(sk)->nonagle = 1;        /* disable Nagle's algorithm */
                sk->sk_data_ready = tcp_data_ready;
                sk->sk_state_change = tcp_state_change;
                xprt_clear_connected(xprt);
        }
        sk->sk_write_space = xprt_write_space;

        /* Reset to new socket */
        xprt->sock = sock;
        xprt->inet = sk;
        write_unlock_bh(&sk->sk_callback_lock);

        return;
}

/*
 * Set socket buffer length
 */
void
xprt_sock_setbufsize(struct rpc_xprt *xprt)
{
        struct sock *sk = xprt->inet;

        if (xprt->stream)
                return;
        if (xprt->rcvsize) {
                sk->sk_userlocks |= SOCK_RCVBUF_LOCK;
                sk->sk_rcvbuf = xprt->rcvsize * xprt->max_reqs *  2;
        }
        if (xprt->sndsize) {
                sk->sk_userlocks |= SOCK_SNDBUF_LOCK;
                sk->sk_sndbuf = xprt->sndsize * xprt->max_reqs * 2;
                sk->sk_write_space(sk);
        }
}

/*
 * Datastream sockets are created here, but xprt_connect will create
 * and connect stream sockets.
 */
static struct socket * xprt_create_socket(struct rpc_xprt *xprt, int proto, int resvport)
{
        struct socket   *sock;
        int             type, err;

        dprintk("RPC:      xprt_create_socket(%s %d)\n",
                           (proto == IPPROTO_UDP)? "udp" : "tcp", proto);

        type = (proto == IPPROTO_UDP)? SOCK_DGRAM : SOCK_STREAM;

        if ((err = sock_create_kern(PF_INET, type, proto, &sock)) < 0) {
                printk("RPC: can't create socket (%d).\n", -err);
                return NULL;
        }

        /* If the caller has the capability, bind to a reserved port */
        if (resvport && xprt_bindresvport(xprt, sock) < 0) {
                printk("RPC: can't bind to reserved port.\n");
                goto failed;
        }

        return sock;

failed:
        sock_release(sock);
        return NULL;
}

/*
 * Create an RPC client transport given the protocol and peer address.
 */
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;
}

/*
 * Prepare for transport shutdown.
 */
static void
xprt_shutdown(struct rpc_xprt *xprt)
{
        xprt->shutdown = 1;
        rpc_wake_up(&xprt->sending);
        rpc_wake_up(&xprt->resend);
        rpc_wake_up(&xprt->pending);
        rpc_wake_up(&xprt->backlog);
        wake_up(&xprt->cong_wait);
        del_timer_sync(&xprt->timer);

        /* synchronously wait for connect worker to finish */
        cancel_delayed_work(&xprt->sock_connect);
        flush_scheduled_work();
}

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

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

        return 0;
}