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[linux-2.6/linux-acpi-2.6/ibm-acpi-2.6.git] / net / sunrpc / svc_xprt.c

/*
 * linux/net/sunrpc/svc_xprt.c
 *
 * Author: Tom Tucker <tom@opengridcomputing.com>
 */

#include <linux/sched.h>
#include <linux/errno.h>
#include <linux/freezer.h>
#include <linux/kthread.h>
#include <linux/slab.h>
#include <net/sock.h>
#include <linux/sunrpc/stats.h>
#include <linux/sunrpc/svc_xprt.h>
#include <linux/sunrpc/svcsock.h>
#include <linux/sunrpc/xprt.h>
#include <linux/module.h>

#define RPCDBG_FACILITY RPCDBG_SVCXPRT

static struct svc_deferred_req *svc_deferred_dequeue(struct svc_xprt *xprt);
static int svc_deferred_recv(struct svc_rqst *rqstp);
static struct cache_deferred_req *svc_defer(struct cache_req *req);
static void svc_age_temp_xprts(unsigned long closure);

/* apparently the "standard" is that clients close
 * idle connections after 5 minutes, servers after
 * 6 minutes
 *   http://www.connectathon.org/talks96/nfstcp.pdf
 */
static int svc_conn_age_period = 6*60;

/* List of registered transport classes */
static DEFINE_SPINLOCK(svc_xprt_class_lock);
static LIST_HEAD(svc_xprt_class_list);

/* SMP locking strategy:
 *
 *      svc_pool->sp_lock protects most of the fields of that pool.
 *      svc_serv->sv_lock protects sv_tempsocks, sv_permsocks, sv_tmpcnt.
 *      when both need to be taken (rare), svc_serv->sv_lock is first.
 *      BKL protects svc_serv->sv_nrthread.
 *      svc_sock->sk_lock protects the svc_sock->sk_deferred list
 *             and the ->sk_info_authunix cache.
 *
 *      The XPT_BUSY bit in xprt->xpt_flags prevents a transport being
 *      enqueued multiply. During normal transport processing this bit
 *      is set by svc_xprt_enqueue and cleared by svc_xprt_received.
 *      Providers should not manipulate this bit directly.
 *
 *      Some flags can be set to certain values at any time
 *      providing that certain rules are followed:
 *
 *      XPT_CONN, XPT_DATA:
 *              - Can be set or cleared at any time.
 *              - After a set, svc_xprt_enqueue must be called to enqueue
 *                the transport for processing.
 *              - After a clear, the transport must be read/accepted.
 *                If this succeeds, it must be set again.
 *      XPT_CLOSE:
 *              - Can set at any time. It is never cleared.
 *      XPT_DEAD:
 *              - Can only be set while XPT_BUSY is held which ensures
 *                that no other thread will be using the transport or will
 *                try to set XPT_DEAD.
 */

int svc_reg_xprt_class(struct svc_xprt_class *xcl)
{
        struct svc_xprt_class *cl;
        int res = -EEXIST;

        dprintk("svc: Adding svc transport class '%s'\n", xcl->xcl_name);

        INIT_LIST_HEAD(&xcl->xcl_list);
        spin_lock(&svc_xprt_class_lock);
        /* Make sure there isn't already a class with the same name */
        list_for_each_entry(cl, &svc_xprt_class_list, xcl_list) {
                if (strcmp(xcl->xcl_name, cl->xcl_name) == 0)
                        goto out;
        }
        list_add_tail(&xcl->xcl_list, &svc_xprt_class_list);
        res = 0;
out:
        spin_unlock(&svc_xprt_class_lock);
        return res;
}
EXPORT_SYMBOL_GPL(svc_reg_xprt_class);

void svc_unreg_xprt_class(struct svc_xprt_class *xcl)
{
        dprintk("svc: Removing svc transport class '%s'\n", xcl->xcl_name);
        spin_lock(&svc_xprt_class_lock);
        list_del_init(&xcl->xcl_list);
        spin_unlock(&svc_xprt_class_lock);
}
EXPORT_SYMBOL_GPL(svc_unreg_xprt_class);

/*
 * Format the transport list for printing
 */
int svc_print_xprts(char *buf, int maxlen)
{
        struct svc_xprt_class *xcl;
        char tmpstr[80];
        int len = 0;
        buf[0] = '\0';

        spin_lock(&svc_xprt_class_lock);
        list_for_each_entry(xcl, &svc_xprt_class_list, xcl_list) {
                int slen;

                sprintf(tmpstr, "%s %d\n", xcl->xcl_name, xcl->xcl_max_payload);
                slen = strlen(tmpstr);
                if (len + slen > maxlen)
                        break;
                len += slen;
                strcat(buf, tmpstr);
        }
        spin_unlock(&svc_xprt_class_lock);

        return len;
}

static void svc_xprt_free(struct kref *kref)
{
        struct svc_xprt *xprt =
                container_of(kref, struct svc_xprt, xpt_ref);
        struct module *owner = xprt->xpt_class->xcl_owner;
        if (test_bit(XPT_CACHE_AUTH, &xprt->xpt_flags))
                svcauth_unix_info_release(xprt);
        put_net(xprt->xpt_net);
        /* See comment on corresponding get in xs_setup_bc_tcp(): */
        if (xprt->xpt_bc_xprt)
                xprt_put(xprt->xpt_bc_xprt);
        xprt->xpt_ops->xpo_free(xprt);
        module_put(owner);
}

void svc_xprt_put(struct svc_xprt *xprt)
{
        kref_put(&xprt->xpt_ref, svc_xprt_free);
}
EXPORT_SYMBOL_GPL(svc_xprt_put);

/*
 * Called by transport drivers to initialize the transport independent
 * portion of the transport instance.
 */
void svc_xprt_init(struct svc_xprt_class *xcl, struct svc_xprt *xprt,
                   struct svc_serv *serv)
{
        memset(xprt, 0, sizeof(*xprt));
        xprt->xpt_class = xcl;
        xprt->xpt_ops = xcl->xcl_ops;
        kref_init(&xprt->xpt_ref);
        xprt->xpt_server = serv;
        INIT_LIST_HEAD(&xprt->xpt_list);
        INIT_LIST_HEAD(&xprt->xpt_ready);
        INIT_LIST_HEAD(&xprt->xpt_deferred);
        INIT_LIST_HEAD(&xprt->xpt_users);
        mutex_init(&xprt->xpt_mutex);
        spin_lock_init(&xprt->xpt_lock);
        set_bit(XPT_BUSY, &xprt->xpt_flags);
        rpc_init_wait_queue(&xprt->xpt_bc_pending, "xpt_bc_pending");
        xprt->xpt_net = get_net(&init_net);
}
EXPORT_SYMBOL_GPL(svc_xprt_init);

static struct svc_xprt *__svc_xpo_create(struct svc_xprt_class *xcl,
                                         struct svc_serv *serv,
                                         struct net *net,
                                         const int family,
                                         const unsigned short port,
                                         int flags)
{
        struct sockaddr_in sin = {
                .sin_family             = AF_INET,
                .sin_addr.s_addr        = htonl(INADDR_ANY),
                .sin_port               = htons(port),
        };
#if defined(CONFIG_IPV6) || defined(CONFIG_IPV6_MODULE)
        struct sockaddr_in6 sin6 = {
                .sin6_family            = AF_INET6,
                .sin6_addr              = IN6ADDR_ANY_INIT,
                .sin6_port              = htons(port),
        };
#endif  /* defined(CONFIG_IPV6) || defined(CONFIG_IPV6_MODULE) */
        struct sockaddr *sap;
        size_t len;

        switch (family) {
        case PF_INET:
                sap = (struct sockaddr *)&sin;
                len = sizeof(sin);
                break;
#if defined(CONFIG_IPV6) || defined(CONFIG_IPV6_MODULE)
        case PF_INET6:
                sap = (struct sockaddr *)&sin6;
                len = sizeof(sin6);
                break;
#endif  /* defined(CONFIG_IPV6) || defined(CONFIG_IPV6_MODULE) */
        default:
                return ERR_PTR(-EAFNOSUPPORT);
        }

        return xcl->xcl_ops->xpo_create(serv, net, sap, len, flags);
}

int svc_create_xprt(struct svc_serv *serv, const char *xprt_name,
                    struct net *net, const int family,
                    const unsigned short port, int flags)
{
        struct svc_xprt_class *xcl;

        dprintk("svc: creating transport %s[%d]\n", xprt_name, port);
        spin_lock(&svc_xprt_class_lock);
        list_for_each_entry(xcl, &svc_xprt_class_list, xcl_list) {
                struct svc_xprt *newxprt;
                unsigned short newport;

                if (strcmp(xprt_name, xcl->xcl_name))
                        continue;

                if (!try_module_get(xcl->xcl_owner))
                        goto err;

                spin_unlock(&svc_xprt_class_lock);
                newxprt = __svc_xpo_create(xcl, serv, net, family, port, flags);
                if (IS_ERR(newxprt)) {
                        module_put(xcl->xcl_owner);
                        return PTR_ERR(newxprt);
                }

                clear_bit(XPT_TEMP, &newxprt->xpt_flags);
                spin_lock_bh(&serv->sv_lock);
                list_add(&newxprt->xpt_list, &serv->sv_permsocks);
                spin_unlock_bh(&serv->sv_lock);
                newport = svc_xprt_local_port(newxprt);
                clear_bit(XPT_BUSY, &newxprt->xpt_flags);
                return newport;
        }
 err:
        spin_unlock(&svc_xprt_class_lock);
        dprintk("svc: transport %s not found\n", xprt_name);

        /* This errno is exposed to user space.  Provide a reasonable
         * perror msg for a bad transport. */
        return -EPROTONOSUPPORT;
}
EXPORT_SYMBOL_GPL(svc_create_xprt);

/*
 * Copy the local and remote xprt addresses to the rqstp structure
 */
void svc_xprt_copy_addrs(struct svc_rqst *rqstp, struct svc_xprt *xprt)
{
        memcpy(&rqstp->rq_addr, &xprt->xpt_remote, xprt->xpt_remotelen);
        rqstp->rq_addrlen = xprt->xpt_remotelen;

        /*
         * Destination address in request is needed for binding the
         * source address in RPC replies/callbacks later.
         */
        memcpy(&rqstp->rq_daddr, &xprt->xpt_local, xprt->xpt_locallen);
        rqstp->rq_daddrlen = xprt->xpt_locallen;
}
EXPORT_SYMBOL_GPL(svc_xprt_copy_addrs);

/**
 * svc_print_addr - Format rq_addr field for printing
 * @rqstp: svc_rqst struct containing address to print
 * @buf: target buffer for formatted address
 * @len: length of target buffer
 *
 */
char *svc_print_addr(struct svc_rqst *rqstp, char *buf, size_t len)
{
        return __svc_print_addr(svc_addr(rqstp), buf, len);
}
EXPORT_SYMBOL_GPL(svc_print_addr);

/*
 * Queue up an idle server thread.  Must have pool->sp_lock held.
 * Note: this is really a stack rather than a queue, so that we only
 * use as many different threads as we need, and the rest don't pollute
 * the cache.
 */
static void svc_thread_enqueue(struct svc_pool *pool, struct svc_rqst *rqstp)
{
        list_add(&rqstp->rq_list, &pool->sp_threads);
}

/*
 * Dequeue an nfsd thread.  Must have pool->sp_lock held.
 */
static void svc_thread_dequeue(struct svc_pool *pool, struct svc_rqst *rqstp)
{
        list_del(&rqstp->rq_list);
}

static bool svc_xprt_has_something_to_do(struct svc_xprt *xprt)
{
        if (xprt->xpt_flags & ((1<<XPT_CONN)|(1<<XPT_CLOSE)))
                return true;
        if (xprt->xpt_flags & ((1<<XPT_DATA)|(1<<XPT_DEFERRED)))
                return xprt->xpt_ops->xpo_has_wspace(xprt);
        return false;
}

/*
 * Queue up a transport with data pending. If there are idle nfsd
 * processes, wake 'em up.
 *
 */
void svc_xprt_enqueue(struct svc_xprt *xprt)
{
        struct svc_serv *serv = xprt->xpt_server;
        struct svc_pool *pool;
        struct svc_rqst *rqstp;
        int cpu;

        if (!svc_xprt_has_something_to_do(xprt))
                return;

        cpu = get_cpu();
        pool = svc_pool_for_cpu(xprt->xpt_server, cpu);
        put_cpu();

        spin_lock_bh(&pool->sp_lock);

        if (!list_empty(&pool->sp_threads) &&
            !list_empty(&pool->sp_sockets))
                printk(KERN_ERR
                       "svc_xprt_enqueue: "
                       "threads and transports both waiting??\n");

        pool->sp_stats.packets++;

        /* Mark transport as busy. It will remain in this state until
         * the provider calls svc_xprt_received. We update XPT_BUSY
         * atomically because it also guards against trying to enqueue
         * the transport twice.
         */
        if (test_and_set_bit(XPT_BUSY, &xprt->xpt_flags)) {
                /* Don't enqueue transport while already enqueued */
                dprintk("svc: transport %p busy, not enqueued\n", xprt);
                goto out_unlock;
        }

        if (!list_empty(&pool->sp_threads)) {
                rqstp = list_entry(pool->sp_threads.next,
                                   struct svc_rqst,
                                   rq_list);
                dprintk("svc: transport %p served by daemon %p\n",
                        xprt, rqstp);
                svc_thread_dequeue(pool, rqstp);
                if (rqstp->rq_xprt)
                        printk(KERN_ERR
                                "svc_xprt_enqueue: server %p, rq_xprt=%p!\n",
                                rqstp, rqstp->rq_xprt);
                rqstp->rq_xprt = xprt;
                svc_xprt_get(xprt);
                rqstp->rq_reserved = serv->sv_max_mesg;
                atomic_add(rqstp->rq_reserved, &xprt->xpt_reserved);
                pool->sp_stats.threads_woken++;
                wake_up(&rqstp->rq_wait);
        } else {
                dprintk("svc: transport %p put into queue\n", xprt);
                list_add_tail(&xprt->xpt_ready, &pool->sp_sockets);
                pool->sp_stats.sockets_queued++;
        }

out_unlock:
        spin_unlock_bh(&pool->sp_lock);
}
EXPORT_SYMBOL_GPL(svc_xprt_enqueue);

/*
 * Dequeue the first transport.  Must be called with the pool->sp_lock held.
 */
static struct svc_xprt *svc_xprt_dequeue(struct svc_pool *pool)
{
        struct svc_xprt *xprt;

        if (list_empty(&pool->sp_sockets))
                return NULL;

        xprt = list_entry(pool->sp_sockets.next,
                          struct svc_xprt, xpt_ready);
        list_del_init(&xprt->xpt_ready);

        dprintk("svc: transport %p dequeued, inuse=%d\n",
                xprt, atomic_read(&xprt->xpt_ref.refcount));

        return xprt;
}

/*
 * svc_xprt_received conditionally queues the transport for processing
 * by another thread. The caller must hold the XPT_BUSY bit and must
 * not thereafter touch transport data.
 *
 * Note: XPT_DATA only gets cleared when a read-attempt finds no (or
 * insufficient) data.
 */
void svc_xprt_received(struct svc_xprt *xprt)
{
        BUG_ON(!test_bit(XPT_BUSY, &xprt->xpt_flags));
        /* As soon as we clear busy, the xprt could be closed and
         * 'put', so we need a reference to call svc_xprt_enqueue with:
         */
        svc_xprt_get(xprt);
        clear_bit(XPT_BUSY, &xprt->xpt_flags);
        svc_xprt_enqueue(xprt);
        svc_xprt_put(xprt);
}
EXPORT_SYMBOL_GPL(svc_xprt_received);

/**
 * svc_reserve - change the space reserved for the reply to a request.
 * @rqstp:  The request in question
 * @space: new max space to reserve
 *
 * Each request reserves some space on the output queue of the transport
 * to make sure the reply fits.  This function reduces that reserved
 * space to be the amount of space used already, plus @space.
 *
 */
void svc_reserve(struct svc_rqst *rqstp, int space)
{
        space += rqstp->rq_res.head[0].iov_len;

        if (space < rqstp->rq_reserved) {
                struct svc_xprt *xprt = rqstp->rq_xprt;
                atomic_sub((rqstp->rq_reserved - space), &xprt->xpt_reserved);
                rqstp->rq_reserved = space;

                svc_xprt_enqueue(xprt);
        }
}
EXPORT_SYMBOL_GPL(svc_reserve);

static void svc_xprt_release(struct svc_rqst *rqstp)
{
        struct svc_xprt *xprt = rqstp->rq_xprt;

        rqstp->rq_xprt->xpt_ops->xpo_release_rqst(rqstp);

        kfree(rqstp->rq_deferred);
        rqstp->rq_deferred = NULL;

        svc_free_res_pages(rqstp);
        rqstp->rq_res.page_len = 0;
        rqstp->rq_res.page_base = 0;

        /* Reset response buffer and release
         * the reservation.
         * But first, check that enough space was reserved
         * for the reply, otherwise we have a bug!
         */
        if ((rqstp->rq_res.len) >  rqstp->rq_reserved)
                printk(KERN_ERR "RPC request reserved %d but used %d\n",
                       rqstp->rq_reserved,
                       rqstp->rq_res.len);

        rqstp->rq_res.head[0].iov_len = 0;
        svc_reserve(rqstp, 0);
        rqstp->rq_xprt = NULL;

        svc_xprt_put(xprt);
}

/*
 * External function to wake up a server waiting for data
 * This really only makes sense for services like lockd
 * which have exactly one thread anyway.
 */
void svc_wake_up(struct svc_serv *serv)
{
        struct svc_rqst *rqstp;
        unsigned int i;
        struct svc_pool *pool;

        for (i = 0; i < serv->sv_nrpools; i++) {
                pool = &serv->sv_pools[i];

                spin_lock_bh(&pool->sp_lock);
                if (!list_empty(&pool->sp_threads)) {
                        rqstp = list_entry(pool->sp_threads.next,
                                           struct svc_rqst,
                                           rq_list);
                        dprintk("svc: daemon %p woken up.\n", rqstp);
                        /*
                        svc_thread_dequeue(pool, rqstp);
                        rqstp->rq_xprt = NULL;
                         */
                        wake_up(&rqstp->rq_wait);
                }
                spin_unlock_bh(&pool->sp_lock);
        }
}
EXPORT_SYMBOL_GPL(svc_wake_up);

int svc_port_is_privileged(struct sockaddr *sin)
{
        switch (sin->sa_family) {
        case AF_INET:
                return ntohs(((struct sockaddr_in *)sin)->sin_port)
                        < PROT_SOCK;
        case AF_INET6:
                return ntohs(((struct sockaddr_in6 *)sin)->sin6_port)
                        < PROT_SOCK;
        default:
                return 0;
        }
}

/*
 * Make sure that we don't have too many active connections. If we have,
 * something must be dropped. It's not clear what will happen if we allow
 * "too many" connections, but when dealing with network-facing software,
 * we have to code defensively. Here we do that by imposing hard limits.
 *
 * There's no point in trying to do random drop here for DoS
 * prevention. The NFS clients does 1 reconnect in 15 seconds. An
 * attacker can easily beat that.
 *
 * The only somewhat efficient mechanism would be if drop old
 * connections from the same IP first. But right now we don't even
 * record the client IP in svc_sock.
 *
 * single-threaded services that expect a lot of clients will probably
 * need to set sv_maxconn to override the default value which is based
 * on the number of threads
 */
static void svc_check_conn_limits(struct svc_serv *serv)
{
        unsigned int limit = serv->sv_maxconn ? serv->sv_maxconn :
                                (serv->sv_nrthreads+3) * 20;

        if (serv->sv_tmpcnt > limit) {
                struct svc_xprt *xprt = NULL;
                spin_lock_bh(&serv->sv_lock);
                if (!list_empty(&serv->sv_tempsocks)) {
                        if (net_ratelimit()) {
                                /* Try to help the admin */
                                printk(KERN_NOTICE "%s: too many open  "
                                       "connections, consider increasing %s\n",
                                       serv->sv_name, serv->sv_maxconn ?
                                       "the max number of connections." :
                                       "the number of threads.");
                        }
                        /*
                         * Always select the oldest connection. It's not fair,
                         * but so is life
                         */
                        xprt = list_entry(serv->sv_tempsocks.prev,
                                          struct svc_xprt,
                                          xpt_list);
                        set_bit(XPT_CLOSE, &xprt->xpt_flags);
                        svc_xprt_get(xprt);
                }
                spin_unlock_bh(&serv->sv_lock);

                if (xprt) {
                        svc_xprt_enqueue(xprt);
                        svc_xprt_put(xprt);
                }
        }
}

/*
 * Receive the next request on any transport.  This code is carefully
 * organised not to touch any cachelines in the shared svc_serv
 * structure, only cachelines in the local svc_pool.
 */
int svc_recv(struct svc_rqst *rqstp, long timeout)
{
        struct svc_xprt         *xprt = NULL;
        struct svc_serv         *serv = rqstp->rq_server;
        struct svc_pool         *pool = rqstp->rq_pool;
        int                     len, i;
        int                     pages;
        struct xdr_buf          *arg;
        DECLARE_WAITQUEUE(wait, current);
        long                    time_left;

        dprintk("svc: server %p waiting for data (to = %ld)\n",
                rqstp, timeout);

        if (rqstp->rq_xprt)
                printk(KERN_ERR
                        "svc_recv: service %p, transport not NULL!\n",
                         rqstp);
        if (waitqueue_active(&rqstp->rq_wait))
                printk(KERN_ERR
                        "svc_recv: service %p, wait queue active!\n",
                         rqstp);

        /* now allocate needed pages.  If we get a failure, sleep briefly */
        pages = (serv->sv_max_mesg + PAGE_SIZE) / PAGE_SIZE;
        for (i = 0; i < pages ; i++)
                while (rqstp->rq_pages[i] == NULL) {
                        struct page *p = alloc_page(GFP_KERNEL);
                        if (!p) {
                                set_current_state(TASK_INTERRUPTIBLE);
                                if (signalled() || kthread_should_stop()) {
                                        set_current_state(TASK_RUNNING);
                                        return -EINTR;
                                }
                                schedule_timeout(msecs_to_jiffies(500));
                        }
                        rqstp->rq_pages[i] = p;
                }
        rqstp->rq_pages[i++] = NULL; /* this might be seen in nfs_read_actor */
        BUG_ON(pages >= RPCSVC_MAXPAGES);

        /* Make arg->head point to first page and arg->pages point to rest */
        arg = &rqstp->rq_arg;
        arg->head[0].iov_base = page_address(rqstp->rq_pages[0]);
        arg->head[0].iov_len = PAGE_SIZE;
        arg->pages = rqstp->rq_pages + 1;
        arg->page_base = 0;
        /* save at least one page for response */
        arg->page_len = (pages-2)*PAGE_SIZE;
        arg->len = (pages-1)*PAGE_SIZE;
        arg->tail[0].iov_len = 0;

        try_to_freeze();
        cond_resched();
        if (signalled() || kthread_should_stop())
                return -EINTR;

        /* Normally we will wait up to 5 seconds for any required
         * cache information to be provided.
         */
        rqstp->rq_chandle.thread_wait = 5*HZ;

        spin_lock_bh(&pool->sp_lock);
        xprt = svc_xprt_dequeue(pool);
        if (xprt) {
                rqstp->rq_xprt = xprt;
                svc_xprt_get(xprt);
                rqstp->rq_reserved = serv->sv_max_mesg;
                atomic_add(rqstp->rq_reserved, &xprt->xpt_reserved);

                /* As there is a shortage of threads and this request
                 * had to be queued, don't allow the thread to wait so
                 * long for cache updates.
                 */
                rqstp->rq_chandle.thread_wait = 1*HZ;
        } else {
                /* No data pending. Go to sleep */
                svc_thread_enqueue(pool, rqstp);

                /*
                 * We have to be able to interrupt this wait
                 * to bring down the daemons ...
                 */
                set_current_state(TASK_INTERRUPTIBLE);

                /*
                 * checking kthread_should_stop() here allows us to avoid
                 * locking and signalling when stopping kthreads that call
                 * svc_recv. If the thread has already been woken up, then
                 * we can exit here without sleeping. If not, then it
                 * it'll be woken up quickly during the schedule_timeout
                 */
                if (kthread_should_stop()) {
                        set_current_state(TASK_RUNNING);
                        spin_unlock_bh(&pool->sp_lock);
                        return -EINTR;
                }

                add_wait_queue(&rqstp->rq_wait, &wait);
                spin_unlock_bh(&pool->sp_lock);

                time_left = schedule_timeout(timeout);

                try_to_freeze();

                spin_lock_bh(&pool->sp_lock);
                remove_wait_queue(&rqstp->rq_wait, &wait);
                if (!time_left)
                        pool->sp_stats.threads_timedout++;

                xprt = rqstp->rq_xprt;
                if (!xprt) {
                        svc_thread_dequeue(pool, rqstp);
                        spin_unlock_bh(&pool->sp_lock);
                        dprintk("svc: server %p, no data yet\n", rqstp);
                        if (signalled() || kthread_should_stop())
                                return -EINTR;
                        else
                                return -EAGAIN;
                }
        }
        spin_unlock_bh(&pool->sp_lock);

        len = 0;
        if (test_bit(XPT_CLOSE, &xprt->xpt_flags)) {
                dprintk("svc_recv: found XPT_CLOSE\n");
                svc_delete_xprt(xprt);
                /* Leave XPT_BUSY set on the dead xprt: */
                goto out;
        }
        if (test_bit(XPT_LISTENER, &xprt->xpt_flags)) {
                struct svc_xprt *newxpt;
                newxpt = xprt->xpt_ops->xpo_accept(xprt);
                if (newxpt) {
                        /*
                         * We know this module_get will succeed because the
                         * listener holds a reference too
                         */
                        __module_get(newxpt->xpt_class->xcl_owner);
                        svc_check_conn_limits(xprt->xpt_server);
                        spin_lock_bh(&serv->sv_lock);
                        set_bit(XPT_TEMP, &newxpt->xpt_flags);
                        list_add(&newxpt->xpt_list, &serv->sv_tempsocks);
                        serv->sv_tmpcnt++;
                        if (serv->sv_temptimer.function == NULL) {
                                /* setup timer to age temp transports */
                                setup_timer(&serv->sv_temptimer,
                                            svc_age_temp_xprts,
                                            (unsigned long)serv);
                                mod_timer(&serv->sv_temptimer,
                                          jiffies + svc_conn_age_period * HZ);
                        }
                        spin_unlock_bh(&serv->sv_lock);
                        svc_xprt_received(newxpt);
                }
        } else if (xprt->xpt_ops->xpo_has_wspace(xprt)) {
                dprintk("svc: server %p, pool %u, transport %p, inuse=%d\n",
                        rqstp, pool->sp_id, xprt,
                        atomic_read(&xprt->xpt_ref.refcount));
                rqstp->rq_deferred = svc_deferred_dequeue(xprt);
                if (rqstp->rq_deferred)
                        len = svc_deferred_recv(rqstp);
                else
                        len = xprt->xpt_ops->xpo_recvfrom(rqstp);
                dprintk("svc: got len=%d\n", len);
        }
        svc_xprt_received(xprt);

        /* No data, incomplete (TCP) read, or accept() */
        if (len == 0 || len == -EAGAIN)
                goto out;

        clear_bit(XPT_OLD, &xprt->xpt_flags);

        rqstp->rq_secure = svc_port_is_privileged(svc_addr(rqstp));
        rqstp->rq_chandle.defer = svc_defer;

        if (serv->sv_stats)
                serv->sv_stats->netcnt++;
        return len;
out:
        rqstp->rq_res.len = 0;
        svc_xprt_release(rqstp);
        return -EAGAIN;
}
EXPORT_SYMBOL_GPL(svc_recv);

/*
 * Drop request
 */
void svc_drop(struct svc_rqst *rqstp)
{
        dprintk("svc: xprt %p dropped request\n", rqstp->rq_xprt);
        svc_xprt_release(rqstp);
}
EXPORT_SYMBOL_GPL(svc_drop);

/*
 * Return reply to client.
 */
int svc_send(struct svc_rqst *rqstp)
{
        struct svc_xprt *xprt;
        int             len;
        struct xdr_buf  *xb;

        xprt = rqstp->rq_xprt;
        if (!xprt)
                return -EFAULT;

        /* release the receive skb before sending the reply */
        rqstp->rq_xprt->xpt_ops->xpo_release_rqst(rqstp);

        /* calculate over-all length */
        xb = &rqstp->rq_res;
        xb->len = xb->head[0].iov_len +
                xb->page_len +
                xb->tail[0].iov_len;

        /* Grab mutex to serialize outgoing data. */
        mutex_lock(&xprt->xpt_mutex);
        if (test_bit(XPT_DEAD, &xprt->xpt_flags))
                len = -ENOTCONN;
        else
                len = xprt->xpt_ops->xpo_sendto(rqstp);
        mutex_unlock(&xprt->xpt_mutex);
        rpc_wake_up(&xprt->xpt_bc_pending);
        svc_xprt_release(rqstp);

        if (len == -ECONNREFUSED || len == -ENOTCONN || len == -EAGAIN)
                return 0;
        return len;
}

/*
 * Timer function to close old temporary transports, using
 * a mark-and-sweep algorithm.
 */
static void svc_age_temp_xprts(unsigned long closure)
{
        struct svc_serv *serv = (struct svc_serv *)closure;
        struct svc_xprt *xprt;
        struct list_head *le, *next;
        LIST_HEAD(to_be_aged);

        dprintk("svc_age_temp_xprts\n");

        if (!spin_trylock_bh(&serv->sv_lock)) {
                /* busy, try again 1 sec later */
                dprintk("svc_age_temp_xprts: busy\n");
                mod_timer(&serv->sv_temptimer, jiffies + HZ);
                return;
        }

        list_for_each_safe(le, next, &serv->sv_tempsocks) {
                xprt = list_entry(le, struct svc_xprt, xpt_list);

                /* First time through, just mark it OLD. Second time
                 * through, close it. */
                if (!test_and_set_bit(XPT_OLD, &xprt->xpt_flags))
                        continue;
                if (atomic_read(&xprt->xpt_ref.refcount) > 1 ||
                    test_bit(XPT_BUSY, &xprt->xpt_flags))
                        continue;
                svc_xprt_get(xprt);
                list_move(le, &to_be_aged);
                set_bit(XPT_CLOSE, &xprt->xpt_flags);
                set_bit(XPT_DETACHED, &xprt->xpt_flags);
        }
        spin_unlock_bh(&serv->sv_lock);

        while (!list_empty(&to_be_aged)) {
                le = to_be_aged.next;
                /* fiddling the xpt_list node is safe 'cos we're XPT_DETACHED */
                list_del_init(le);
                xprt = list_entry(le, struct svc_xprt, xpt_list);

                dprintk("queuing xprt %p for closing\n", xprt);

                /* a thread will dequeue and close it soon */
                svc_xprt_enqueue(xprt);
                svc_xprt_put(xprt);
        }

        mod_timer(&serv->sv_temptimer, jiffies + svc_conn_age_period * HZ);
}

static void call_xpt_users(struct svc_xprt *xprt)
{
        struct svc_xpt_user *u;

        spin_lock(&xprt->xpt_lock);
        while (!list_empty(&xprt->xpt_users)) {
                u = list_first_entry(&xprt->xpt_users, struct svc_xpt_user, list);
                list_del(&u->list);
                u->callback(u);
        }
        spin_unlock(&xprt->xpt_lock);
}

/*
 * Remove a dead transport
 */
void svc_delete_xprt(struct svc_xprt *xprt)
{
        struct svc_serv *serv = xprt->xpt_server;
        struct svc_deferred_req *dr;

        /* Only do this once */
        if (test_and_set_bit(XPT_DEAD, &xprt->xpt_flags))
                BUG();

        dprintk("svc: svc_delete_xprt(%p)\n", xprt);
        xprt->xpt_ops->xpo_detach(xprt);

        spin_lock_bh(&serv->sv_lock);
        if (!test_and_set_bit(XPT_DETACHED, &xprt->xpt_flags))
                list_del_init(&xprt->xpt_list);
        /*
         * The only time we're called while xpt_ready is still on a list
         * is while the list itself is about to be destroyed (in
         * svc_destroy).  BUT svc_xprt_enqueue could still be attempting
         * to add new entries to the sp_sockets list, so we can't leave
         * a freed xprt on it.
         */
        list_del_init(&xprt->xpt_ready);
        if (test_bit(XPT_TEMP, &xprt->xpt_flags))
                serv->sv_tmpcnt--;
        spin_unlock_bh(&serv->sv_lock);

        while ((dr = svc_deferred_dequeue(xprt)) != NULL)
                kfree(dr);

        call_xpt_users(xprt);
        svc_xprt_put(xprt);
}

void svc_close_xprt(struct svc_xprt *xprt)
{
        set_bit(XPT_CLOSE, &xprt->xpt_flags);
        if (test_and_set_bit(XPT_BUSY, &xprt->xpt_flags))
                /* someone else will have to effect the close */
                return;
        /*
         * We expect svc_close_xprt() to work even when no threads are
         * running (e.g., while configuring the server before starting
         * any threads), so if the transport isn't busy, we delete
         * it ourself:
         */
        svc_delete_xprt(xprt);
}
EXPORT_SYMBOL_GPL(svc_close_xprt);

void svc_close_all(struct list_head *xprt_list)
{
        struct svc_xprt *xprt;
        struct svc_xprt *tmp;

        /*
         * The server is shutting down, and no more threads are running.
         * svc_xprt_enqueue() might still be running, but at worst it
         * will re-add the xprt to sp_sockets, which will soon get
         * freed.  So we don't bother with any more locking, and don't
         * leave the close to the (nonexistent) server threads:
         */
        list_for_each_entry_safe(xprt, tmp, xprt_list, xpt_list) {
                set_bit(XPT_CLOSE, &xprt->xpt_flags);
                svc_delete_xprt(xprt);
        }
}

/*
 * Handle defer and revisit of requests
 */

static void svc_revisit(struct cache_deferred_req *dreq, int too_many)
{
        struct svc_deferred_req *dr =
                container_of(dreq, struct svc_deferred_req, handle);
        struct svc_xprt *xprt = dr->xprt;

        spin_lock(&xprt->xpt_lock);
        set_bit(XPT_DEFERRED, &xprt->xpt_flags);
        if (too_many || test_bit(XPT_DEAD, &xprt->xpt_flags)) {
                spin_unlock(&xprt->xpt_lock);
                dprintk("revisit canceled\n");
                svc_xprt_put(xprt);
                kfree(dr);
                return;
        }
        dprintk("revisit queued\n");
        dr->xprt = NULL;
        list_add(&dr->handle.recent, &xprt->xpt_deferred);
        spin_unlock(&xprt->xpt_lock);
        svc_xprt_enqueue(xprt);
        svc_xprt_put(xprt);
}

/*
 * Save the request off for later processing. The request buffer looks
 * like this:
 *
 * <xprt-header><rpc-header><rpc-pagelist><rpc-tail>
 *
 * This code can only handle requests that consist of an xprt-header
 * and rpc-header.
 */
static struct cache_deferred_req *svc_defer(struct cache_req *req)
{
        struct svc_rqst *rqstp = container_of(req, struct svc_rqst, rq_chandle);
        struct svc_deferred_req *dr;

        if (rqstp->rq_arg.page_len || !rqstp->rq_usedeferral)
                return NULL; /* if more than a page, give up FIXME */
        if (rqstp->rq_deferred) {
                dr = rqstp->rq_deferred;
                rqstp->rq_deferred = NULL;
        } else {
                size_t skip;
                size_t size;
                /* FIXME maybe discard if size too large */
                size = sizeof(struct svc_deferred_req) + rqstp->rq_arg.len;
                dr = kmalloc(size, GFP_KERNEL);
                if (dr == NULL)
                        return NULL;

                dr->handle.owner = rqstp->rq_server;
                dr->prot = rqstp->rq_prot;
                memcpy(&dr->addr, &rqstp->rq_addr, rqstp->rq_addrlen);
                dr->addrlen = rqstp->rq_addrlen;
                dr->daddr = rqstp->rq_daddr;
                dr->argslen = rqstp->rq_arg.len >> 2;
                dr->xprt_hlen = rqstp->rq_xprt_hlen;

                /* back up head to the start of the buffer and copy */
                skip = rqstp->rq_arg.len - rqstp->rq_arg.head[0].iov_len;
                memcpy(dr->args, rqstp->rq_arg.head[0].iov_base - skip,
                       dr->argslen << 2);
        }
        svc_xprt_get(rqstp->rq_xprt);
        dr->xprt = rqstp->rq_xprt;
        rqstp->rq_dropme = true;

        dr->handle.revisit = svc_revisit;
        return &dr->handle;
}

/*
 * recv data from a deferred request into an active one
 */
static int svc_deferred_recv(struct svc_rqst *rqstp)
{
        struct svc_deferred_req *dr = rqstp->rq_deferred;

        /* setup iov_base past transport header */
        rqstp->rq_arg.head[0].iov_base = dr->args + (dr->xprt_hlen>>2);
        /* The iov_len does not include the transport header bytes */
        rqstp->rq_arg.head[0].iov_len = (dr->argslen<<2) - dr->xprt_hlen;
        rqstp->rq_arg.page_len = 0;
        /* The rq_arg.len includes the transport header bytes */
        rqstp->rq_arg.len     = dr->argslen<<2;
        rqstp->rq_prot        = dr->prot;
        memcpy(&rqstp->rq_addr, &dr->addr, dr->addrlen);
        rqstp->rq_addrlen     = dr->addrlen;
        /* Save off transport header len in case we get deferred again */
        rqstp->rq_xprt_hlen   = dr->xprt_hlen;
        rqstp->rq_daddr       = dr->daddr;
        rqstp->rq_respages    = rqstp->rq_pages;
        return (dr->argslen<<2) - dr->xprt_hlen;
}


static struct svc_deferred_req *svc_deferred_dequeue(struct svc_xprt *xprt)
{
        struct svc_deferred_req *dr = NULL;

        if (!test_bit(XPT_DEFERRED, &xprt->xpt_flags))
                return NULL;
        spin_lock(&xprt->xpt_lock);
        if (!list_empty(&xprt->xpt_deferred)) {
                dr = list_entry(xprt->xpt_deferred.next,
                                struct svc_deferred_req,
                                handle.recent);
                list_del_init(&dr->handle.recent);
        } else
                clear_bit(XPT_DEFERRED, &xprt->xpt_flags);
        spin_unlock(&xprt->xpt_lock);
        return dr;
}

/**
 * svc_find_xprt - find an RPC transport instance
 * @serv: pointer to svc_serv to search
 * @xcl_name: C string containing transport's class name
 * @af: Address family of transport's local address
 * @port: transport's IP port number
 *
 * Return the transport instance pointer for the endpoint accepting
 * connections/peer traffic from the specified transport class,
 * address family and port.
 *
 * Specifying 0 for the address family or port is effectively a
 * wild-card, and will result in matching the first transport in the
 * service's list that has a matching class name.
 */
struct svc_xprt *svc_find_xprt(struct svc_serv *serv, const char *xcl_name,
                               const sa_family_t af, const unsigned short port)
{
        struct svc_xprt *xprt;
        struct svc_xprt *found = NULL;

        /* Sanity check the args */
        if (serv == NULL || xcl_name == NULL)
                return found;

        spin_lock_bh(&serv->sv_lock);
        list_for_each_entry(xprt, &serv->sv_permsocks, xpt_list) {
                if (strcmp(xprt->xpt_class->xcl_name, xcl_name))
                        continue;
                if (af != AF_UNSPEC && af != xprt->xpt_local.ss_family)
                        continue;
                if (port != 0 && port != svc_xprt_local_port(xprt))
                        continue;
                found = xprt;
                svc_xprt_get(xprt);
                break;
        }
        spin_unlock_bh(&serv->sv_lock);
        return found;
}
EXPORT_SYMBOL_GPL(svc_find_xprt);

static int svc_one_xprt_name(const struct svc_xprt *xprt,
                             char *pos, int remaining)
{
        int len;

        len = snprintf(pos, remaining, "%s %u\n",
                        xprt->xpt_class->xcl_name,
                        svc_xprt_local_port(xprt));
        if (len >= remaining)
                return -ENAMETOOLONG;
        return len;
}

/**
 * svc_xprt_names - format a buffer with a list of transport names
 * @serv: pointer to an RPC service
 * @buf: pointer to a buffer to be filled in
 * @buflen: length of buffer to be filled in
 *
 * Fills in @buf with a string containing a list of transport names,
 * each name terminated with '\n'.
 *
 * Returns positive length of the filled-in string on success; otherwise
 * a negative errno value is returned if an error occurs.
 */
int svc_xprt_names(struct svc_serv *serv, char *buf, const int buflen)
{
        struct svc_xprt *xprt;
        int len, totlen;
        char *pos;

        /* Sanity check args */
        if (!serv)
                return 0;

        spin_lock_bh(&serv->sv_lock);

        pos = buf;
        totlen = 0;
        list_for_each_entry(xprt, &serv->sv_permsocks, xpt_list) {
                len = svc_one_xprt_name(xprt, pos, buflen - totlen);
                if (len < 0) {
                        *buf = '\0';
                        totlen = len;
                }
                if (len <= 0)
                        break;

                pos += len;
                totlen += len;
        }

        spin_unlock_bh(&serv->sv_lock);
        return totlen;
}
EXPORT_SYMBOL_GPL(svc_xprt_names);


/*----------------------------------------------------------------------------*/

static void *svc_pool_stats_start(struct seq_file *m, loff_t *pos)
{
        unsigned int pidx = (unsigned int)*pos;
        struct svc_serv *serv = m->private;

        dprintk("svc_pool_stats_start, *pidx=%u\n", pidx);

        if (!pidx)
                return SEQ_START_TOKEN;
        return (pidx > serv->sv_nrpools ? NULL : &serv->sv_pools[pidx-1]);
}

static void *svc_pool_stats_next(struct seq_file *m, void *p, loff_t *pos)
{
        struct svc_pool *pool = p;
        struct svc_serv *serv = m->private;

        dprintk("svc_pool_stats_next, *pos=%llu\n", *pos);

        if (p == SEQ_START_TOKEN) {
                pool = &serv->sv_pools[0];
        } else {
                unsigned int pidx = (pool - &serv->sv_pools[0]);
                if (pidx < serv->sv_nrpools-1)
                        pool = &serv->sv_pools[pidx+1];
                else
                        pool = NULL;
        }
        ++*pos;
        return pool;
}

static void svc_pool_stats_stop(struct seq_file *m, void *p)
{
}

static int svc_pool_stats_show(struct seq_file *m, void *p)
{
        struct svc_pool *pool = p;

        if (p == SEQ_START_TOKEN) {
                seq_puts(m, "# pool packets-arrived sockets-enqueued threads-woken threads-timedout\n");
                return 0;
        }

        seq_printf(m, "%u %lu %lu %lu %lu\n",
                pool->sp_id,
                pool->sp_stats.packets,
                pool->sp_stats.sockets_queued,
                pool->sp_stats.threads_woken,
                pool->sp_stats.threads_timedout);

        return 0;
}

static const struct seq_operations svc_pool_stats_seq_ops = {
        .start  = svc_pool_stats_start,
        .next   = svc_pool_stats_next,
        .stop   = svc_pool_stats_stop,
        .show   = svc_pool_stats_show,
};

int svc_pool_stats_open(struct svc_serv *serv, struct file *file)
{
        int err;

        err = seq_open(file, &svc_pool_stats_seq_ops);
        if (!err)
                ((struct seq_file *) file->private_data)->private = serv;
        return err;
}
EXPORT_SYMBOL(svc_pool_stats_open);

/*----------------------------------------------------------------------------*/