svc_xprt.c

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/*
 * linux/net/sunrpc/svc_xprt.c
 *
 * Author: Tom Tucker <[email protected]>
 */

#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);
static void svc_delete_xprt(struct svc_xprt *xprt);

/* 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 net *net, 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(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 IS_ENABLED(CONFIG_IPV6)
    struct sockaddr_in6 sin6 = {
        .sin6_family        = AF_INET6,
        .sin6_addr      = IN6ADDR_ANY_INIT,
        .sin6_port      = htons(port),
    };
#endif
    struct sockaddr *sap;
    size_t len;

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

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

/*
 * 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.
 */
static 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);
}

void svc_add_new_perm_xprt(struct svc_serv *serv, struct svc_xprt *new)
{
    clear_bit(XPT_TEMP, &new->xpt_flags);
    spin_lock_bh(&serv->sv_lock);
    list_add(&new->xpt_list, &serv->sv_permsocks);
    spin_unlock_bh(&serv->sv_lock);
    svc_xprt_received(new);
}

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);
        }
        svc_add_new_perm_xprt(serv, newxprt);
        newport = svc_xprt_local_port(newxprt);
        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);

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_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);
        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;
}

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)) {
            /* Try to help the admin */
            net_notice_ratelimited("%s: too many open connections, consider increasing the %s\n",
                           serv->sv_name, serv->sv_maxconn ?
                           "max number of connections" :
                           "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);
        }
    }
}

int svc_alloc_arg(struct svc_rqst *rqstp)
{
    struct svc_serv *serv = rqstp->rq_server;
    struct xdr_buf *arg;
    int pages;
    int i;

    /* now allocate needed pages.  If we get a failure, sleep briefly */
    pages = (serv->sv_max_mesg + PAGE_SIZE) / PAGE_SIZE;
    BUG_ON(pages >= RPCSVC_MAXPAGES);
    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 */

    /* 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;
    return 0;
}

struct svc_xprt *svc_get_next_xprt(struct svc_rqst *rqstp, long timeout)
{
    struct svc_xprt *xprt;
    struct svc_pool     *pool = rqstp->rq_pool;
    DECLARE_WAITQUEUE(wait, current);
    long            time_left;

    /* 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);

        /* 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 ERR_PTR(-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 ERR_PTR(-EINTR);
            else
                return ERR_PTR(-EAGAIN);
        }
    }
    spin_unlock_bh(&pool->sp_lock);
    return xprt;
}

void svc_add_new_temp_xprt(struct svc_serv *serv, struct svc_xprt *newxpt)
{
    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);
}

static int svc_handle_xprt(struct svc_rqst *rqstp, struct svc_xprt *xprt)
{
    struct svc_serv *serv = rqstp->rq_server;
    int 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: */
        return 0;
    }
    if (test_bit(XPT_LISTENER, &xprt->xpt_flags)) {
        struct svc_xprt *newxpt;
        /*
         * We know this module_get will succeed because the
         * listener holds a reference too
         */
        __module_get(xprt->xpt_class->xcl_owner);
        svc_check_conn_limits(xprt->xpt_server);
        newxpt = xprt->xpt_ops->xpo_accept(xprt);
        if (newxpt)
            svc_add_new_temp_xprt(serv, newxpt);
    } else if (xprt->xpt_ops->xpo_has_wspace(xprt)) {
        /* XPT_DATA|XPT_DEFERRED case: */
        dprintk("svc: server %p, pool %u, transport %p, inuse=%d\n",
            rqstp, rqstp->rq_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);
        rqstp->rq_reserved = serv->sv_max_mesg;
        atomic_add(rqstp->rq_reserved, &xprt->xpt_reserved);
    }
    /* clear XPT_BUSY: */
    svc_xprt_received(xprt);
    return len;
}

/*
 * 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;
    int         len, err;

    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);

    err = svc_alloc_arg(rqstp);
    if (err)
        return err;

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

    xprt = svc_get_next_xprt(rqstp, timeout);
    if (IS_ERR(xprt))
        return PTR_ERR(xprt);

    len = svc_handle_xprt(rqstp, xprt);

    /* No data, incomplete (TCP) read, or accept() */
    if (len <= 0)
        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)
            || test_bit(XPT_CLOSE, &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
 */
static 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);
    BUG_ON(!list_empty(&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);

static void svc_close_list(struct svc_serv *serv, struct list_head *xprt_list, struct net *net)
{
    struct svc_xprt *xprt;

    spin_lock(&serv->sv_lock);
    list_for_each_entry(xprt, xprt_list, xpt_list) {
        if (xprt->xpt_net != net)
            continue;
        set_bit(XPT_CLOSE, &xprt->xpt_flags);
        set_bit(XPT_BUSY, &xprt->xpt_flags);
    }
    spin_unlock(&serv->sv_lock);
}

static void svc_clear_pools(struct svc_serv *serv, struct net *net)
{
    struct svc_pool *pool;
    struct svc_xprt *xprt;
    struct svc_xprt *tmp;
    int i;

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

        spin_lock_bh(&pool->sp_lock);
        list_for_each_entry_safe(xprt, tmp, &pool->sp_sockets, xpt_ready) {
            if (xprt->xpt_net != net)
                continue;
            list_del_init(&xprt->xpt_ready);
        }
        spin_unlock_bh(&pool->sp_lock);
    }
}

static void svc_clear_list(struct svc_serv *serv, struct list_head *xprt_list, struct net *net)
{
    struct svc_xprt *xprt;
    struct svc_xprt *tmp;
    LIST_HEAD(victims);

    spin_lock(&serv->sv_lock);
    list_for_each_entry_safe(xprt, tmp, xprt_list, xpt_list) {
        if (xprt->xpt_net != net)
            continue;
        list_move(&xprt->xpt_list, &victims);
    }
    spin_unlock(&serv->sv_lock);

    list_for_each_entry_safe(xprt, tmp, &victims, xpt_list)
        svc_delete_xprt(xprt);
}

void svc_close_net(struct svc_serv *serv, struct net *net)
{
    svc_close_list(serv, &serv->sv_tempsocks, net);
    svc_close_list(serv, &serv->sv_permsocks, net);

    svc_clear_pools(serv, net);
    /*
     * At this point the sp_sockets lists will stay empty, since
     * svc_xprt_enqueue will not add new entries without taking the
     * sp_lock and checking XPT_BUSY.
     */
    svc_clear_list(serv, &serv->sv_tempsocks, net);
    svc_clear_list(serv, &serv->sv_permsocks, net);
}

/*
 * 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;
}

struct svc_xprt *svc_find_xprt(struct svc_serv *serv, const char *xcl_name,
                   struct net *net, 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 (xprt->xpt_net != net)
            continue;
        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;
}

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);

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