writeback: fix time ordering of the per superblock dirty inode lists 6

[linux-2.6/zen-sources.git] / net / sunrpc / svc.c

/*
 * linux/net/sunrpc/svc.c
 *
 * High-level RPC service routines
 *
 * Copyright (C) 1995, 1996 Olaf Kirch <okir@monad.swb.de>
 *
 * Multiple threads pools and NUMAisation
 * Copyright (c) 2006 Silicon Graphics, Inc.
 * by Greg Banks <gnb@melbourne.sgi.com>
 */

#include <linux/linkage.h>
#include <linux/sched.h>
#include <linux/errno.h>
#include <linux/net.h>
#include <linux/in.h>
#include <linux/mm.h>
#include <linux/interrupt.h>
#include <linux/module.h>

#include <linux/sunrpc/types.h>
#include <linux/sunrpc/xdr.h>
#include <linux/sunrpc/stats.h>
#include <linux/sunrpc/svcsock.h>
#include <linux/sunrpc/clnt.h>

#define RPCDBG_FACILITY RPCDBG_SVCDSP

#define svc_serv_is_pooled(serv)    ((serv)->sv_function)

/*
 * Mode for mapping cpus to pools.
 */
enum {
        SVC_POOL_AUTO = -1,     /* choose one of the others */
        SVC_POOL_GLOBAL,        /* no mapping, just a single global pool
                                 * (legacy & UP mode) */
        SVC_POOL_PERCPU,        /* one pool per cpu */
        SVC_POOL_PERNODE        /* one pool per numa node */
};
#define SVC_POOL_DEFAULT        SVC_POOL_GLOBAL

/*
 * Structure for mapping cpus to pools and vice versa.
 * Setup once during sunrpc initialisation.
 */
static struct svc_pool_map {
        int count;                      /* How many svc_servs use us */
        int mode;                       /* Note: int not enum to avoid
                                         * warnings about "enumeration value
                                         * not handled in switch" */
        unsigned int npools;
        unsigned int *pool_to;          /* maps pool id to cpu or node */
        unsigned int *to_pool;          /* maps cpu or node to pool id */
} svc_pool_map = {
        .count = 0,
        .mode = SVC_POOL_DEFAULT
};
static DEFINE_MUTEX(svc_pool_map_mutex);/* protects svc_pool_map.count only */

static int
param_set_pool_mode(const char *val, struct kernel_param *kp)
{
        int *ip = (int *)kp->arg;
        struct svc_pool_map *m = &svc_pool_map;
        int err;

        mutex_lock(&svc_pool_map_mutex);

        err = -EBUSY;
        if (m->count)
                goto out;

        err = 0;
        if (!strncmp(val, "auto", 4))
                *ip = SVC_POOL_AUTO;
        else if (!strncmp(val, "global", 6))
                *ip = SVC_POOL_GLOBAL;
        else if (!strncmp(val, "percpu", 6))
                *ip = SVC_POOL_PERCPU;
        else if (!strncmp(val, "pernode", 7))
                *ip = SVC_POOL_PERNODE;
        else
                err = -EINVAL;

out:
        mutex_unlock(&svc_pool_map_mutex);
        return err;
}

static int
param_get_pool_mode(char *buf, struct kernel_param *kp)
{
        int *ip = (int *)kp->arg;

        switch (*ip)
        {
        case SVC_POOL_AUTO:
                return strlcpy(buf, "auto", 20);
        case SVC_POOL_GLOBAL:
                return strlcpy(buf, "global", 20);
        case SVC_POOL_PERCPU:
                return strlcpy(buf, "percpu", 20);
        case SVC_POOL_PERNODE:
                return strlcpy(buf, "pernode", 20);
        default:
                return sprintf(buf, "%d", *ip);
        }
}

module_param_call(pool_mode, param_set_pool_mode, param_get_pool_mode,
                 &svc_pool_map.mode, 0644);

/*
 * Detect best pool mapping mode heuristically,
 * according to the machine's topology.
 */
static int
svc_pool_map_choose_mode(void)
{
        unsigned int node;

        if (num_online_nodes() > 1) {
                /*
                 * Actually have multiple NUMA nodes,
                 * so split pools on NUMA node boundaries
                 */
                return SVC_POOL_PERNODE;
        }

        node = any_online_node(node_online_map);
        if (nr_cpus_node(node) > 2) {
                /*
                 * Non-trivial SMP, or CONFIG_NUMA on
                 * non-NUMA hardware, e.g. with a generic
                 * x86_64 kernel on Xeons.  In this case we
                 * want to divide the pools on cpu boundaries.
                 */
                return SVC_POOL_PERCPU;
        }

        /* default: one global pool */
        return SVC_POOL_GLOBAL;
}

/*
 * Allocate the to_pool[] and pool_to[] arrays.
 * Returns 0 on success or an errno.
 */
static int
svc_pool_map_alloc_arrays(struct svc_pool_map *m, unsigned int maxpools)
{
        m->to_pool = kcalloc(maxpools, sizeof(unsigned int), GFP_KERNEL);
        if (!m->to_pool)
                goto fail;
        m->pool_to = kcalloc(maxpools, sizeof(unsigned int), GFP_KERNEL);
        if (!m->pool_to)
                goto fail_free;

        return 0;

fail_free:
        kfree(m->to_pool);
fail:
        return -ENOMEM;
}

/*
 * Initialise the pool map for SVC_POOL_PERCPU mode.
 * Returns number of pools or <0 on error.
 */
static int
svc_pool_map_init_percpu(struct svc_pool_map *m)
{
        unsigned int maxpools = nr_cpu_ids;
        unsigned int pidx = 0;
        unsigned int cpu;
        int err;

        err = svc_pool_map_alloc_arrays(m, maxpools);
        if (err)
                return err;

        for_each_online_cpu(cpu) {
                BUG_ON(pidx > maxpools);
                m->to_pool[cpu] = pidx;
                m->pool_to[pidx] = cpu;
                pidx++;
        }
        /* cpus brought online later all get mapped to pool0, sorry */

        return pidx;
};


/*
 * Initialise the pool map for SVC_POOL_PERNODE mode.
 * Returns number of pools or <0 on error.
 */
static int
svc_pool_map_init_pernode(struct svc_pool_map *m)
{
        unsigned int maxpools = nr_node_ids;
        unsigned int pidx = 0;
        unsigned int node;
        int err;

        err = svc_pool_map_alloc_arrays(m, maxpools);
        if (err)
                return err;

        for_each_node_with_cpus(node) {
                /* some architectures (e.g. SN2) have cpuless nodes */
                BUG_ON(pidx > maxpools);
                m->to_pool[node] = pidx;
                m->pool_to[pidx] = node;
                pidx++;
        }
        /* nodes brought online later all get mapped to pool0, sorry */

        return pidx;
}


/*
 * Add a reference to the global map of cpus to pools (and
 * vice versa).  Initialise the map if we're the first user.
 * Returns the number of pools.
 */
static unsigned int
svc_pool_map_get(void)
{
        struct svc_pool_map *m = &svc_pool_map;
        int npools = -1;

        mutex_lock(&svc_pool_map_mutex);

        if (m->count++) {
                mutex_unlock(&svc_pool_map_mutex);
                return m->npools;
        }

        if (m->mode == SVC_POOL_AUTO)
                m->mode = svc_pool_map_choose_mode();

        switch (m->mode) {
        case SVC_POOL_PERCPU:
                npools = svc_pool_map_init_percpu(m);
                break;
        case SVC_POOL_PERNODE:
                npools = svc_pool_map_init_pernode(m);
                break;
        }

        if (npools < 0) {
                /* default, or memory allocation failure */
                npools = 1;
                m->mode = SVC_POOL_GLOBAL;
        }
        m->npools = npools;

        mutex_unlock(&svc_pool_map_mutex);
        return m->npools;
}


/*
 * Drop a reference to the global map of cpus to pools.
 * When the last reference is dropped, the map data is
 * freed; this allows the sysadmin to change the pool
 * mode using the pool_mode module option without
 * rebooting or re-loading sunrpc.ko.
 */
static void
svc_pool_map_put(void)
{
        struct svc_pool_map *m = &svc_pool_map;

        mutex_lock(&svc_pool_map_mutex);

        if (!--m->count) {
                m->mode = SVC_POOL_DEFAULT;
                kfree(m->to_pool);
                kfree(m->pool_to);
                m->npools = 0;
        }

        mutex_unlock(&svc_pool_map_mutex);
}


/*
 * Set the current thread's cpus_allowed mask so that it
 * will only run on cpus in the given pool.
 *
 * Returns 1 and fills in oldmask iff a cpumask was applied.
 */
static inline int
svc_pool_map_set_cpumask(unsigned int pidx, cpumask_t *oldmask)
{
        struct svc_pool_map *m = &svc_pool_map;
        unsigned int node; /* or cpu */

        /*
         * The caller checks for sv_nrpools > 1, which
         * implies that we've been initialized.
         */
        BUG_ON(m->count == 0);

        switch (m->mode)
        {
        default:
                return 0;
        case SVC_POOL_PERCPU:
                node = m->pool_to[pidx];
                *oldmask = current->cpus_allowed;
                set_cpus_allowed(current, cpumask_of_cpu(node));
                return 1;
        case SVC_POOL_PERNODE:
                node = m->pool_to[pidx];
                *oldmask = current->cpus_allowed;
                set_cpus_allowed(current, node_to_cpumask(node));
                return 1;
        }
}

/*
 * Use the mapping mode to choose a pool for a given CPU.
 * Used when enqueueing an incoming RPC.  Always returns
 * a non-NULL pool pointer.
 */
struct svc_pool *
svc_pool_for_cpu(struct svc_serv *serv, int cpu)
{
        struct svc_pool_map *m = &svc_pool_map;
        unsigned int pidx = 0;

        /*
         * An uninitialised map happens in a pure client when
         * lockd is brought up, so silently treat it the
         * same as SVC_POOL_GLOBAL.
         */
        if (svc_serv_is_pooled(serv)) {
                switch (m->mode) {
                case SVC_POOL_PERCPU:
                        pidx = m->to_pool[cpu];
                        break;
                case SVC_POOL_PERNODE:
                        pidx = m->to_pool[cpu_to_node(cpu)];
                        break;
                }
        }
        return &serv->sv_pools[pidx % serv->sv_nrpools];
}


/*
 * Create an RPC service
 */
static struct svc_serv *
__svc_create(struct svc_program *prog, unsigned int bufsize, int npools,
           void (*shutdown)(struct svc_serv *serv))
{
        struct svc_serv *serv;
        int vers;
        unsigned int xdrsize;
        unsigned int i;

        if (!(serv = kzalloc(sizeof(*serv), GFP_KERNEL)))
                return NULL;
        serv->sv_name      = prog->pg_name;
        serv->sv_program   = prog;
        serv->sv_nrthreads = 1;
        serv->sv_stats     = prog->pg_stats;
        if (bufsize > RPCSVC_MAXPAYLOAD)
                bufsize = RPCSVC_MAXPAYLOAD;
        serv->sv_max_payload = bufsize? bufsize : 4096;
        serv->sv_max_mesg  = roundup(serv->sv_max_payload + PAGE_SIZE, PAGE_SIZE);
        serv->sv_shutdown  = shutdown;
        xdrsize = 0;
        while (prog) {
                prog->pg_lovers = prog->pg_nvers-1;
                for (vers=0; vers<prog->pg_nvers ; vers++)
                        if (prog->pg_vers[vers]) {
                                prog->pg_hivers = vers;
                                if (prog->pg_lovers > vers)
                                        prog->pg_lovers = vers;
                                if (prog->pg_vers[vers]->vs_xdrsize > xdrsize)
                                        xdrsize = prog->pg_vers[vers]->vs_xdrsize;
                        }
                prog = prog->pg_next;
        }
        serv->sv_xdrsize   = xdrsize;
        INIT_LIST_HEAD(&serv->sv_tempsocks);
        INIT_LIST_HEAD(&serv->sv_permsocks);
        init_timer(&serv->sv_temptimer);
        spin_lock_init(&serv->sv_lock);

        serv->sv_nrpools = npools;
        serv->sv_pools =
                kcalloc(serv->sv_nrpools, sizeof(struct svc_pool),
                        GFP_KERNEL);
        if (!serv->sv_pools) {
                kfree(serv);
                return NULL;
        }

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

                dprintk("svc: initialising pool %u for %s\n",
                                i, serv->sv_name);

                pool->sp_id = i;
                INIT_LIST_HEAD(&pool->sp_threads);
                INIT_LIST_HEAD(&pool->sp_sockets);
                INIT_LIST_HEAD(&pool->sp_all_threads);
                spin_lock_init(&pool->sp_lock);
        }


        /* Remove any stale portmap registrations */
        svc_register(serv, 0, 0);

        return serv;
}

struct svc_serv *
svc_create(struct svc_program *prog, unsigned int bufsize,
                void (*shutdown)(struct svc_serv *serv))
{
        return __svc_create(prog, bufsize, /*npools*/1, shutdown);
}

struct svc_serv *
svc_create_pooled(struct svc_program *prog, unsigned int bufsize,
                void (*shutdown)(struct svc_serv *serv),
                  svc_thread_fn func, int sig, struct module *mod)
{
        struct svc_serv *serv;
        unsigned int npools = svc_pool_map_get();

        serv = __svc_create(prog, bufsize, npools, shutdown);

        if (serv != NULL) {
                serv->sv_function = func;
                serv->sv_kill_signal = sig;
                serv->sv_module = mod;
        }

        return serv;
}

/*
 * Destroy an RPC service.  Should be called with the BKL held
 */
void
svc_destroy(struct svc_serv *serv)
{
        struct svc_sock *svsk;
        struct svc_sock *tmp;

        dprintk("svc: svc_destroy(%s, %d)\n",
                                serv->sv_program->pg_name,
                                serv->sv_nrthreads);

        if (serv->sv_nrthreads) {
                if (--(serv->sv_nrthreads) != 0) {
                        svc_sock_update_bufs(serv);
                        return;
                }
        } else
                printk("svc_destroy: no threads for serv=%p!\n", serv);

        del_timer_sync(&serv->sv_temptimer);

        list_for_each_entry_safe(svsk, tmp, &serv->sv_tempsocks, sk_list)
                svc_force_close_socket(svsk);

        if (serv->sv_shutdown)
                serv->sv_shutdown(serv);

        list_for_each_entry_safe(svsk, tmp, &serv->sv_permsocks, sk_list)
                svc_force_close_socket(svsk);

        BUG_ON(!list_empty(&serv->sv_permsocks));
        BUG_ON(!list_empty(&serv->sv_tempsocks));

        cache_clean_deferred(serv);

        if (svc_serv_is_pooled(serv))
                svc_pool_map_put();

        /* Unregister service with the portmapper */
        svc_register(serv, 0, 0);
        kfree(serv->sv_pools);
        kfree(serv);
}

/*
 * Allocate an RPC server's buffer space.
 * We allocate pages and place them in rq_argpages.
 */
static int
svc_init_buffer(struct svc_rqst *rqstp, unsigned int size)
{
        int pages;
        int arghi;

        pages = size / PAGE_SIZE + 1; /* extra page as we hold both request and reply.
                                       * We assume one is at most one page
                                       */
        arghi = 0;
        BUG_ON(pages > RPCSVC_MAXPAGES);
        while (pages) {
                struct page *p = alloc_page(GFP_KERNEL);
                if (!p)
                        break;
                rqstp->rq_pages[arghi++] = p;
                pages--;
        }
        return ! pages;
}

/*
 * Release an RPC server buffer
 */
static void
svc_release_buffer(struct svc_rqst *rqstp)
{
        int i;
        for (i=0; i<ARRAY_SIZE(rqstp->rq_pages); i++)
                if (rqstp->rq_pages[i])
                        put_page(rqstp->rq_pages[i]);
}

/*
 * Create a thread in the given pool.  Caller must hold BKL.
 * On a NUMA or SMP machine, with a multi-pool serv, the thread
 * will be restricted to run on the cpus belonging to the pool.
 */
static int
__svc_create_thread(svc_thread_fn func, struct svc_serv *serv,
                    struct svc_pool *pool)
{
        struct svc_rqst *rqstp;
        int             error = -ENOMEM;
        int             have_oldmask = 0;
        cpumask_t       oldmask;

        rqstp = kzalloc(sizeof(*rqstp), GFP_KERNEL);
        if (!rqstp)
                goto out;

        init_waitqueue_head(&rqstp->rq_wait);

        if (!(rqstp->rq_argp = kmalloc(serv->sv_xdrsize, GFP_KERNEL))
         || !(rqstp->rq_resp = kmalloc(serv->sv_xdrsize, GFP_KERNEL))
         || !svc_init_buffer(rqstp, serv->sv_max_mesg))
                goto out_thread;

        serv->sv_nrthreads++;
        spin_lock_bh(&pool->sp_lock);
        pool->sp_nrthreads++;
        list_add(&rqstp->rq_all, &pool->sp_all_threads);
        spin_unlock_bh(&pool->sp_lock);
        rqstp->rq_server = serv;
        rqstp->rq_pool = pool;

        if (serv->sv_nrpools > 1)
                have_oldmask = svc_pool_map_set_cpumask(pool->sp_id, &oldmask);

        error = kernel_thread((int (*)(void *)) func, rqstp, 0);

        if (have_oldmask)
                set_cpus_allowed(current, oldmask);

        if (error < 0)
                goto out_thread;
        svc_sock_update_bufs(serv);
        error = 0;
out:
        return error;

out_thread:
        svc_exit_thread(rqstp);
        goto out;
}

/*
 * Create a thread in the default pool.  Caller must hold BKL.
 */
int
svc_create_thread(svc_thread_fn func, struct svc_serv *serv)
{
        return __svc_create_thread(func, serv, &serv->sv_pools[0]);
}

/*
 * Choose a pool in which to create a new thread, for svc_set_num_threads
 */
static inline struct svc_pool *
choose_pool(struct svc_serv *serv, struct svc_pool *pool, unsigned int *state)
{
        if (pool != NULL)
                return pool;

        return &serv->sv_pools[(*state)++ % serv->sv_nrpools];
}

/*
 * Choose a thread to kill, for svc_set_num_threads
 */
static inline struct task_struct *
choose_victim(struct svc_serv *serv, struct svc_pool *pool, unsigned int *state)
{
        unsigned int i;
        struct task_struct *task = NULL;

        if (pool != NULL) {
                spin_lock_bh(&pool->sp_lock);
        } else {
                /* choose a pool in round-robin fashion */
                for (i = 0; i < serv->sv_nrpools; i++) {
                        pool = &serv->sv_pools[--(*state) % serv->sv_nrpools];
                        spin_lock_bh(&pool->sp_lock);
                        if (!list_empty(&pool->sp_all_threads))
                                goto found_pool;
                        spin_unlock_bh(&pool->sp_lock);
                }
                return NULL;
        }

found_pool:
        if (!list_empty(&pool->sp_all_threads)) {
                struct svc_rqst *rqstp;

                /*
                 * Remove from the pool->sp_all_threads list
                 * so we don't try to kill it again.
                 */
                rqstp = list_entry(pool->sp_all_threads.next, struct svc_rqst, rq_all);
                list_del_init(&rqstp->rq_all);
                task = rqstp->rq_task;
        }
        spin_unlock_bh(&pool->sp_lock);

        return task;
}

/*
 * Create or destroy enough new threads to make the number
 * of threads the given number.  If `pool' is non-NULL, applies
 * only to threads in that pool, otherwise round-robins between
 * all pools.  Must be called with a svc_get() reference and
 * the BKL held.
 *
 * Destroying threads relies on the service threads filling in
 * rqstp->rq_task, which only the nfs ones do.  Assumes the serv
 * has been created using svc_create_pooled().
 *
 * Based on code that used to be in nfsd_svc() but tweaked
 * to be pool-aware.
 */
int
svc_set_num_threads(struct svc_serv *serv, struct svc_pool *pool, int nrservs)
{
        struct task_struct *victim;
        int error = 0;
        unsigned int state = serv->sv_nrthreads-1;

        if (pool == NULL) {
                /* The -1 assumes caller has done a svc_get() */
                nrservs -= (serv->sv_nrthreads-1);
        } else {
                spin_lock_bh(&pool->sp_lock);
                nrservs -= pool->sp_nrthreads;
                spin_unlock_bh(&pool->sp_lock);
        }

        /* create new threads */
        while (nrservs > 0) {
                nrservs--;
                __module_get(serv->sv_module);
                error = __svc_create_thread(serv->sv_function, serv,
                                            choose_pool(serv, pool, &state));
                if (error < 0) {
                        module_put(serv->sv_module);
                        break;
                }
        }
        /* destroy old threads */
        while (nrservs < 0 &&
               (victim = choose_victim(serv, pool, &state)) != NULL) {
                send_sig(serv->sv_kill_signal, victim, 1);
                nrservs++;
        }

        return error;
}

/*
 * Called from a server thread as it's exiting.  Caller must hold BKL.
 */
void
svc_exit_thread(struct svc_rqst *rqstp)
{
        struct svc_serv *serv = rqstp->rq_server;
        struct svc_pool *pool = rqstp->rq_pool;

        svc_release_buffer(rqstp);
        kfree(rqstp->rq_resp);
        kfree(rqstp->rq_argp);
        kfree(rqstp->rq_auth_data);

        spin_lock_bh(&pool->sp_lock);
        pool->sp_nrthreads--;
        list_del(&rqstp->rq_all);
        spin_unlock_bh(&pool->sp_lock);

        kfree(rqstp);

        /* Release the server */
        if (serv)
                svc_destroy(serv);
}

/*
 * Register an RPC service with the local portmapper.
 * To unregister a service, call this routine with
 * proto and port == 0.
 */
int
svc_register(struct svc_serv *serv, int proto, unsigned short port)
{
        struct svc_program      *progp;
        unsigned long           flags;
        int                     i, error = 0, dummy;

        if (!port)
                clear_thread_flag(TIF_SIGPENDING);

        for (progp = serv->sv_program; progp; progp = progp->pg_next) {
                for (i = 0; i < progp->pg_nvers; i++) {
                        if (progp->pg_vers[i] == NULL)
                                continue;

                        dprintk("svc: svc_register(%s, %s, %d, %d)%s\n",
                                        progp->pg_name,
                                        proto == IPPROTO_UDP?  "udp" : "tcp",
                                        port,
                                        i,
                                        progp->pg_vers[i]->vs_hidden?
                                                " (but not telling portmap)" : "");

                        if (progp->pg_vers[i]->vs_hidden)
                                continue;

                        error = rpcb_register(progp->pg_prog, i, proto, port, &dummy);
                        if (error < 0)
                                break;
                        if (port && !dummy) {
                                error = -EACCES;
                                break;
                        }
                }
        }

        if (!port) {
                spin_lock_irqsave(&current->sighand->siglock, flags);
                recalc_sigpending();
                spin_unlock_irqrestore(&current->sighand->siglock, flags);
        }

        return error;
}

/*
 * Printk the given error with the address of the client that caused it.
 */
static int
__attribute__ ((format (printf, 2, 3)))
svc_printk(struct svc_rqst *rqstp, const char *fmt, ...)
{
        va_list args;
        int     r;
        char    buf[RPC_MAX_ADDRBUFLEN];

        if (!net_ratelimit())
                return 0;

        printk(KERN_WARNING "svc: %s: ",
                svc_print_addr(rqstp, buf, sizeof(buf)));

        va_start(args, fmt);
        r = vprintk(fmt, args);
        va_end(args);

        return r;
}

/*
 * Process the RPC request.
 */
int
svc_process(struct svc_rqst *rqstp)
{
        struct svc_program      *progp;
        struct svc_version      *versp = NULL;  /* compiler food */
        struct svc_procedure    *procp = NULL;
        struct kvec *           argv = &rqstp->rq_arg.head[0];
        struct kvec *           resv = &rqstp->rq_res.head[0];
        struct svc_serv         *serv = rqstp->rq_server;
        kxdrproc_t              xdr;
        __be32                  *statp;
        u32                     dir, prog, vers, proc;
        __be32                  auth_stat, rpc_stat;
        int                     auth_res;
        __be32                  *reply_statp;

        rpc_stat = rpc_success;

        if (argv->iov_len < 6*4)
                goto err_short_len;

        /* setup response xdr_buf.
         * Initially it has just one page
         */
        rqstp->rq_resused = 1;
        resv->iov_base = page_address(rqstp->rq_respages[0]);
        resv->iov_len = 0;
        rqstp->rq_res.pages = rqstp->rq_respages + 1;
        rqstp->rq_res.len = 0;
        rqstp->rq_res.page_base = 0;
        rqstp->rq_res.page_len = 0;
        rqstp->rq_res.buflen = PAGE_SIZE;
        rqstp->rq_res.tail[0].iov_base = NULL;
        rqstp->rq_res.tail[0].iov_len = 0;
        /* Will be turned off only in gss privacy case: */
        rqstp->rq_splice_ok = 1;
        /* tcp needs a space for the record length... */
        if (rqstp->rq_prot == IPPROTO_TCP)
                svc_putnl(resv, 0);

        rqstp->rq_xid = svc_getu32(argv);
        svc_putu32(resv, rqstp->rq_xid);

        dir  = svc_getnl(argv);
        vers = svc_getnl(argv);

        /* First words of reply: */
        svc_putnl(resv, 1);             /* REPLY */

        if (dir != 0)           /* direction != CALL */
                goto err_bad_dir;
        if (vers != 2)          /* RPC version number */
                goto err_bad_rpc;

        /* Save position in case we later decide to reject: */
        reply_statp = resv->iov_base + resv->iov_len;

        svc_putnl(resv, 0);             /* ACCEPT */

        rqstp->rq_prog = prog = svc_getnl(argv);        /* program number */
        rqstp->rq_vers = vers = svc_getnl(argv);        /* version number */
        rqstp->rq_proc = proc = svc_getnl(argv);        /* procedure number */

        progp = serv->sv_program;

        for (progp = serv->sv_program; progp; progp = progp->pg_next)
                if (prog == progp->pg_prog)
                        break;

        /*
         * Decode auth data, and add verifier to reply buffer.
         * We do this before anything else in order to get a decent
         * auth verifier.
         */
        auth_res = svc_authenticate(rqstp, &auth_stat);
        /* Also give the program a chance to reject this call: */
        if (auth_res == SVC_OK && progp) {
                auth_stat = rpc_autherr_badcred;
                auth_res = progp->pg_authenticate(rqstp);
        }
        switch (auth_res) {
        case SVC_OK:
                break;
        case SVC_GARBAGE:
                rpc_stat = rpc_garbage_args;
                goto err_bad;
        case SVC_SYSERR:
                rpc_stat = rpc_system_err;
                goto err_bad;
        case SVC_DENIED:
                goto err_bad_auth;
        case SVC_DROP:
                goto dropit;
        case SVC_COMPLETE:
                goto sendit;
        }

        if (progp == NULL)
                goto err_bad_prog;

        if (vers >= progp->pg_nvers ||
          !(versp = progp->pg_vers[vers]))
                goto err_bad_vers;

        procp = versp->vs_proc + proc;
        if (proc >= versp->vs_nproc || !procp->pc_func)
                goto err_bad_proc;
        rqstp->rq_server   = serv;
        rqstp->rq_procinfo = procp;

        /* Syntactic check complete */
        serv->sv_stats->rpccnt++;

        /* Build the reply header. */
        statp = resv->iov_base +resv->iov_len;
        svc_putnl(resv, RPC_SUCCESS);

        /* Bump per-procedure stats counter */
        procp->pc_count++;

        /* Initialize storage for argp and resp */
        memset(rqstp->rq_argp, 0, procp->pc_argsize);
        memset(rqstp->rq_resp, 0, procp->pc_ressize);

        /* un-reserve some of the out-queue now that we have a
         * better idea of reply size
         */
        if (procp->pc_xdrressize)
                svc_reserve_auth(rqstp, procp->pc_xdrressize<<2);

        /* Call the function that processes the request. */
        if (!versp->vs_dispatch) {
                /* Decode arguments */
                xdr = procp->pc_decode;
                if (xdr && !xdr(rqstp, argv->iov_base, rqstp->rq_argp))
                        goto err_garbage;

                *statp = procp->pc_func(rqstp, rqstp->rq_argp, rqstp->rq_resp);

                /* Encode reply */
                if (*statp == rpc_drop_reply) {
                        if (procp->pc_release)
                                procp->pc_release(rqstp, NULL, rqstp->rq_resp);
                        goto dropit;
                }
                if (*statp == rpc_success && (xdr = procp->pc_encode)
                 && !xdr(rqstp, resv->iov_base+resv->iov_len, rqstp->rq_resp)) {
                        dprintk("svc: failed to encode reply\n");
                        /* serv->sv_stats->rpcsystemerr++; */
                        *statp = rpc_system_err;
                }
        } else {
                dprintk("svc: calling dispatcher\n");
                if (!versp->vs_dispatch(rqstp, statp)) {
                        /* Release reply info */
                        if (procp->pc_release)
                                procp->pc_release(rqstp, NULL, rqstp->rq_resp);
                        goto dropit;
                }
        }

        /* Check RPC status result */
        if (*statp != rpc_success)
                resv->iov_len = ((void*)statp)  - resv->iov_base + 4;

        /* Release reply info */
        if (procp->pc_release)
                procp->pc_release(rqstp, NULL, rqstp->rq_resp);

        if (procp->pc_encode == NULL)
                goto dropit;

 sendit:
        if (svc_authorise(rqstp))
                goto dropit;
        return svc_send(rqstp);

 dropit:
        svc_authorise(rqstp);   /* doesn't hurt to call this twice */
        dprintk("svc: svc_process dropit\n");
        svc_drop(rqstp);
        return 0;

err_short_len:
        svc_printk(rqstp, "short len %Zd, dropping request\n",
                        argv->iov_len);

        goto dropit;                    /* drop request */

err_bad_dir:
        svc_printk(rqstp, "bad direction %d, dropping request\n", dir);

        serv->sv_stats->rpcbadfmt++;
        goto dropit;                    /* drop request */

err_bad_rpc:
        serv->sv_stats->rpcbadfmt++;
        svc_putnl(resv, 1);     /* REJECT */
        svc_putnl(resv, 0);     /* RPC_MISMATCH */
        svc_putnl(resv, 2);     /* Only RPCv2 supported */
        svc_putnl(resv, 2);
        goto sendit;

err_bad_auth:
        dprintk("svc: authentication failed (%d)\n", ntohl(auth_stat));
        serv->sv_stats->rpcbadauth++;
        /* Restore write pointer to location of accept status: */
        xdr_ressize_check(rqstp, reply_statp);
        svc_putnl(resv, 1);     /* REJECT */
        svc_putnl(resv, 1);     /* AUTH_ERROR */
        svc_putnl(resv, ntohl(auth_stat));      /* status */
        goto sendit;

err_bad_prog:
        dprintk("svc: unknown program %d\n", prog);
        serv->sv_stats->rpcbadfmt++;
        svc_putnl(resv, RPC_PROG_UNAVAIL);
        goto sendit;

err_bad_vers:
        svc_printk(rqstp, "unknown version (%d for prog %d, %s)\n",
                       vers, prog, progp->pg_name);

        serv->sv_stats->rpcbadfmt++;
        svc_putnl(resv, RPC_PROG_MISMATCH);
        svc_putnl(resv, progp->pg_lovers);
        svc_putnl(resv, progp->pg_hivers);
        goto sendit;

err_bad_proc:
        svc_printk(rqstp, "unknown procedure (%d)\n", proc);

        serv->sv_stats->rpcbadfmt++;
        svc_putnl(resv, RPC_PROC_UNAVAIL);
        goto sendit;

err_garbage:
        svc_printk(rqstp, "failed to decode args\n");

        rpc_stat = rpc_garbage_args;
err_bad:
        serv->sv_stats->rpcbadfmt++;
        svc_putnl(resv, ntohl(rpc_stat));
        goto sendit;
}

/*
 * Return (transport-specific) limit on the rpc payload.
 */
u32 svc_max_payload(const struct svc_rqst *rqstp)
{
        int max = RPCSVC_MAXPAYLOAD_TCP;

        if (rqstp->rq_sock->sk_sock->type == SOCK_DGRAM)
                max = RPCSVC_MAXPAYLOAD_UDP;
        if (rqstp->rq_server->sv_max_payload < max)
                max = rqstp->rq_server->sv_max_payload;
        return max;
}
EXPORT_SYMBOL_GPL(svc_max_payload);