// SPDX-License-Identifier: GPL-2.0-only
/*
 * 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/signal.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/kthread.h>
#include <linux/slab.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>
#include <linux/sunrpc/bc_xprt.h>

#include <trace/events/sunrpc.h>

#include "fail.h"
#include "sunrpc.h"

#define RPCDBG_FACILITY RPCDBG_SVCDSP

static void svc_unregister(const struct svc_serv *serv, struct net *net);

#define SVC_POOL_DEFAULT        SVC_POOL_GLOBAL

/*
 * 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 */
};

/*
 * Structure for mapping cpus to pools and vice versa.
 * Setup once during sunrpc initialisation.
 */

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 */
};

static struct svc_pool_map svc_pool_map = {
        .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 svc_pool_map *m)
{
        int err, mode;

        mutex_lock(&svc_pool_map_mutex);

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

        if (err)
                goto out;

        if (m->count == 0)
                m->mode = mode;
        else if (mode != m->mode)
                err = -EBUSY;
out:
        mutex_unlock(&svc_pool_map_mutex);
        return err;
}

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

        return __param_set_pool_mode(val, m);
}

int sunrpc_set_pool_mode(const char *val)
{
        return __param_set_pool_mode(val, &svc_pool_map);
}
EXPORT_SYMBOL(sunrpc_set_pool_mode);

/**
 * sunrpc_get_pool_mode - get the current pool_mode for the host
 * @buf: where to write the current pool_mode
 * @size: size of @buf
 *
 * Grab the current pool_mode from the svc_pool_map and write
 * the resulting string to @buf. Returns the number of characters
 * written to @buf (a'la snprintf()).
 */
int
sunrpc_get_pool_mode(char *buf, size_t size)
{
        struct svc_pool_map *m = &svc_pool_map;

        switch (m->mode)
        {
        case SVC_POOL_AUTO:
                return snprintf(buf, size, "auto");
        case SVC_POOL_GLOBAL:
                return snprintf(buf, size, "global");
        case SVC_POOL_PERCPU:
                return snprintf(buf, size, "percpu");
        case SVC_POOL_PERNODE:
                return snprintf(buf, size, "pernode");
        default:
                return snprintf(buf, size, "%d", m->mode);
        }
}
EXPORT_SYMBOL(sunrpc_get_pool_mode);

static int
param_get_pool_mode(char *buf, const struct kernel_param *kp)
{
        char str[16];
        int len;

        len = sunrpc_get_pool_mode(str, ARRAY_SIZE(str));

        /* Ensure we have room for newline and NUL */
        len = min_t(int, len, ARRAY_SIZE(str) - 2);

        /* tack on the newline */
        str[len] = '\n';
        str[len + 1] = '\0';

        return sysfs_emit(buf, "%s", str);
}

module_param_call(pool_mode, param_set_pool_mode, param_get_pool_mode,
                  &svc_pool_map, 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 (nr_online_nodes > 1) {
                /*
                 * Actually have multiple NUMA nodes,
                 * so split pools on NUMA node boundaries
                 */
                return SVC_POOL_PERNODE;
        }

        node = first_online_node;
        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);
        m->to_pool = NULL;
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) if pools are in use.
 * Initialise the map if we're the first user.
 * Returns the number of pools. If this is '1', no reference
 * was taken.
 */
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 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.
 */
static void
svc_pool_map_put(void)
{
        struct svc_pool_map *m = &svc_pool_map;

        mutex_lock(&svc_pool_map_mutex);
        if (!--m->count) {
                kfree(m->to_pool);
                m->to_pool = NULL;
                kfree(m->pool_to);
                m->pool_to = NULL;
                m->npools = 0;
        }
        mutex_unlock(&svc_pool_map_mutex);
}

static int svc_pool_map_get_node(unsigned int pidx)
{
        const struct svc_pool_map *m = &svc_pool_map;

        if (m->count) {
                if (m->mode == SVC_POOL_PERCPU)
                        return cpu_to_node(m->pool_to[pidx]);
                if (m->mode == SVC_POOL_PERNODE)
                        return m->pool_to[pidx];
        }
        return numa_mem_id();
}
/*
 * Set the given thread's cpus_allowed mask so that it
 * will only run on cpus in the given pool.
 */
static inline void
svc_pool_map_set_cpumask(struct task_struct *task, unsigned int pidx)
{
        struct svc_pool_map *m = &svc_pool_map;
        unsigned int node = m->pool_to[pidx];

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

        switch (m->mode) {
        case SVC_POOL_PERCPU:
        {
                set_cpus_allowed_ptr(task, cpumask_of(node));
                break;
        }
        case SVC_POOL_PERNODE:
        {
                set_cpus_allowed_ptr(task, cpumask_of_node(node));
                break;
        }
        }
}

/**
 * svc_pool_for_cpu - Select pool to run a thread on this cpu
 * @serv: An RPC service
 *
 * Use the active CPU and the svc_pool_map's mode setting to
 * select the svc thread pool to use. Once initialized, the
 * svc_pool_map does not change.
 *
 * Return value:
 *   A pointer to an svc_pool
 */
struct svc_pool *svc_pool_for_cpu(struct svc_serv *serv)
{
        struct svc_pool_map *m = &svc_pool_map;
        int cpu = raw_smp_processor_id();
        unsigned int pidx = 0;

        if (serv->sv_nrpools <= 1)
                return serv->sv_pools;

        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];
}

static int svc_rpcb_setup(struct svc_serv *serv, struct net *net)
{
        int err;

        err = rpcb_create_local(net);
        if (err)
                return err;

        /* Remove any stale portmap registrations */
        svc_unregister(serv, net);
        return 0;
}

void svc_rpcb_cleanup(struct svc_serv *serv, struct net *net)
{
        svc_unregister(serv, net);
        rpcb_put_local(net);
}

static int svc_uses_rpcbind(struct svc_serv *serv)
{
        unsigned int            p, i;

        for (p = 0; p < serv->sv_nprogs; p++) {
                struct svc_program *progp = &serv->sv_programs[p];

                for (i = 0; i < progp->pg_nvers; i++) {
                        if (progp->pg_vers[i] == NULL)
                                continue;
                        if (!progp->pg_vers[i]->vs_hidden)
                                return 1;
                }
        }

        return 0;
}

int svc_bind(struct svc_serv *serv, struct net *net)
{
        if (!svc_uses_rpcbind(serv))
                return 0;
        return svc_rpcb_setup(serv, net);
}
EXPORT_SYMBOL_GPL(svc_bind);

#if defined(CONFIG_SUNRPC_BACKCHANNEL)
static void
__svc_init_bc(struct svc_serv *serv)
{
        lwq_init(&serv->sv_cb_list);
}
#else
static void
__svc_init_bc(struct svc_serv *serv)
{
}
#endif

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

        if (!(serv = kzalloc_obj(*serv)))
                return NULL;
        serv->sv_name      = prog->pg_name;
        serv->sv_programs  = prog;
        serv->sv_nprogs    = nprogs;
        serv->sv_stats     = 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_threadfn = threadfn;
        xdrsize = 0;
        for (i = 0; i < nprogs; i++) {
                struct svc_program *progp = &prog[i];

                progp->pg_lovers = progp->pg_nvers-1;
                for (vers = 0; vers < progp->pg_nvers ; vers++)
                        if (progp->pg_vers[vers]) {
                                progp->pg_hivers = vers;
                                if (progp->pg_lovers > vers)
                                        progp->pg_lovers = vers;
                                if (progp->pg_vers[vers]->vs_xdrsize > xdrsize)
                                        xdrsize = progp->pg_vers[vers]->vs_xdrsize;
                        }
        }
        serv->sv_xdrsize   = xdrsize;
        INIT_LIST_HEAD(&serv->sv_tempsocks);
        INIT_LIST_HEAD(&serv->sv_permsocks);
        timer_setup(&serv->sv_temptimer, NULL, 0);
        spin_lock_init(&serv->sv_lock);

        __svc_init_bc(serv);

        serv->sv_nrpools = npools;
        serv->sv_pools =
                kzalloc_objs(struct svc_pool, serv->sv_nrpools);
        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;
                lwq_init(&pool->sp_xprts);
                INIT_LIST_HEAD(&pool->sp_all_threads);
                init_llist_head(&pool->sp_idle_threads);

                percpu_counter_init(&pool->sp_messages_arrived, 0, GFP_KERNEL);
                percpu_counter_init(&pool->sp_sockets_queued, 0, GFP_KERNEL);
                percpu_counter_init(&pool->sp_threads_woken, 0, GFP_KERNEL);
        }

        return serv;
}

/**
 * svc_create - Create an RPC service
 * @prog: the RPC program the new service will handle
 * @bufsize: maximum message size for @prog
 * @threadfn: a function to service RPC requests for @prog
 *
 * Returns an instantiated struct svc_serv object or NULL.
 */
struct svc_serv *svc_create(struct svc_program *prog, unsigned int bufsize,
                            int (*threadfn)(void *data))
{
        return __svc_create(prog, 1, NULL, bufsize, 1, threadfn);
}
EXPORT_SYMBOL_GPL(svc_create);

/**
 * svc_create_pooled - Create an RPC service with pooled threads
 * @prog:  Array of RPC programs the new service will handle
 * @nprogs: Number of programs in the array
 * @stats: the stats struct if desired
 * @bufsize: maximum message size for @prog
 * @threadfn: a function to service RPC requests for @prog
 *
 * Returns an instantiated struct svc_serv object or NULL.
 */
struct svc_serv *svc_create_pooled(struct svc_program *prog,
                                   unsigned int nprogs,
                                   struct svc_stat *stats,
                                   unsigned int bufsize,
                                   int (*threadfn)(void *data))
{
        struct svc_serv *serv;
        unsigned int npools = svc_pool_map_get();

        serv = __svc_create(prog, nprogs, stats, bufsize, npools, threadfn);
        if (!serv)
                goto out_err;
        serv->sv_is_pooled = true;
        return serv;
out_err:
        svc_pool_map_put();
        return NULL;
}
EXPORT_SYMBOL_GPL(svc_create_pooled);

/*
 * Destroy an RPC service. Should be called with appropriate locking to
 * protect sv_permsocks and sv_tempsocks.
 */
void
svc_destroy(struct svc_serv **servp)
{
        struct svc_serv *serv = *servp;
        unsigned int i;

        *servp = NULL;

        dprintk("svc: svc_destroy(%s)\n", serv->sv_programs->pg_name);
        timer_shutdown_sync(&serv->sv_temptimer);

        /*
         * Remaining transports at this point are not expected.
         */
        WARN_ONCE(!list_empty(&serv->sv_permsocks),
                  "SVC: permsocks remain for %s\n", serv->sv_programs->pg_name);
        WARN_ONCE(!list_empty(&serv->sv_tempsocks),
                  "SVC: tempsocks remain for %s\n", serv->sv_programs->pg_name);

        cache_clean_deferred(serv);

        if (serv->sv_is_pooled)
                svc_pool_map_put();

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

                percpu_counter_destroy(&pool->sp_messages_arrived);
                percpu_counter_destroy(&pool->sp_sockets_queued);
                percpu_counter_destroy(&pool->sp_threads_woken);
        }
        kfree(serv->sv_pools);
        kfree(serv);
}
EXPORT_SYMBOL_GPL(svc_destroy);

static bool
svc_init_buffer(struct svc_rqst *rqstp, const struct svc_serv *serv, int node)
{
        rqstp->rq_maxpages = svc_serv_maxpages(serv);

        /* rq_pages' last entry is NULL for historical reasons. */
        rqstp->rq_pages = kcalloc_node(rqstp->rq_maxpages + 1,
                                       sizeof(struct page *),
                                       GFP_KERNEL, node);
        if (!rqstp->rq_pages)
                return false;

        return true;
}

/*
 * Release an RPC server buffer
 */
static void
svc_release_buffer(struct svc_rqst *rqstp)
{
        unsigned long i;

        for (i = 0; i < rqstp->rq_maxpages; i++)
                if (rqstp->rq_pages[i])
                        put_page(rqstp->rq_pages[i]);
        kfree(rqstp->rq_pages);
}

static void
svc_rqst_free(struct svc_rqst *rqstp)
{
        folio_batch_release(&rqstp->rq_fbatch);
        kfree(rqstp->rq_bvec);
        svc_release_buffer(rqstp);
        if (rqstp->rq_scratch_folio)
                folio_put(rqstp->rq_scratch_folio);
        kfree(rqstp->rq_resp);
        kfree(rqstp->rq_argp);
        kfree(rqstp->rq_auth_data);
        kfree_rcu(rqstp, rq_rcu_head);
}

static struct svc_rqst *
svc_prepare_thread(struct svc_serv *serv, struct svc_pool *pool, int node)
{
        struct svc_rqst *rqstp;

        rqstp = kzalloc_node(sizeof(*rqstp), GFP_KERNEL, node);
        if (!rqstp)
                return rqstp;

        folio_batch_init(&rqstp->rq_fbatch);

        rqstp->rq_server = serv;
        rqstp->rq_pool = pool;

        rqstp->rq_scratch_folio = __folio_alloc_node(GFP_KERNEL, 0, node);
        if (!rqstp->rq_scratch_folio)
                goto out_enomem;

        rqstp->rq_argp = kmalloc_node(serv->sv_xdrsize, GFP_KERNEL, node);
        if (!rqstp->rq_argp)
                goto out_enomem;

        rqstp->rq_resp = kmalloc_node(serv->sv_xdrsize, GFP_KERNEL, node);
        if (!rqstp->rq_resp)
                goto out_enomem;

        if (!svc_init_buffer(rqstp, serv, node))
                goto out_enomem;

        rqstp->rq_bvec = kcalloc_node(rqstp->rq_maxpages,
                                      sizeof(struct bio_vec),
                                      GFP_KERNEL, node);
        if (!rqstp->rq_bvec)
                goto out_enomem;

        rqstp->rq_err = -EAGAIN; /* No error yet */

        serv->sv_nrthreads += 1;
        pool->sp_nrthreads += 1;

        /* Protected by whatever lock the service uses when calling
         * svc_set_num_threads()
         */
        list_add_rcu(&rqstp->rq_all, &pool->sp_all_threads);

        return rqstp;

out_enomem:
        svc_rqst_free(rqstp);
        return NULL;
}

/**
 * svc_pool_wake_idle_thread - Awaken an idle thread in @pool
 * @pool: service thread pool
 *
 * Can be called from soft IRQ or process context. Finding an idle
 * service thread and marking it BUSY is atomic with respect to
 * other calls to svc_pool_wake_idle_thread().
 *
 */
void svc_pool_wake_idle_thread(struct svc_pool *pool)
{
        struct svc_rqst *rqstp;
        struct llist_node *ln;

        rcu_read_lock();
        ln = READ_ONCE(pool->sp_idle_threads.first);
        if (ln) {
                rqstp = llist_entry(ln, struct svc_rqst, rq_idle);
                WRITE_ONCE(rqstp->rq_qtime, ktime_get());
                if (!task_is_running(rqstp->rq_task)) {
                        wake_up_process(rqstp->rq_task);
                        trace_svc_pool_thread_wake(pool, rqstp->rq_task->pid);
                        percpu_counter_inc(&pool->sp_threads_woken);
                } else {
                        trace_svc_pool_thread_running(pool, rqstp->rq_task->pid);
                }
                rcu_read_unlock();
                return;
        }
        rcu_read_unlock();
        trace_svc_pool_thread_noidle(pool, 0);
}
EXPORT_SYMBOL_GPL(svc_pool_wake_idle_thread);

/**
 * svc_new_thread - spawn a new thread in the given pool
 * @serv: the serv to which the pool belongs
 * @pool: pool in which thread should be spawned
 *
 * Create a new thread inside @pool, which is a part of @serv.
 * Caller must hold the service mutex.
 *
 * Returns 0 on success, or -errno on failure.
 */
int svc_new_thread(struct svc_serv *serv, struct svc_pool *pool)
{
        struct svc_rqst *rqstp;
        struct task_struct *task;
        int node;
        int err = 0;

        node = svc_pool_map_get_node(pool->sp_id);

        rqstp = svc_prepare_thread(serv, pool, node);
        if (!rqstp)
                return -ENOMEM;
        task = kthread_create_on_node(serv->sv_threadfn, rqstp,
                                      node, "%s", serv->sv_name);
        if (IS_ERR(task)) {
                err = PTR_ERR(task);
                goto out;
        }

        rqstp->rq_task = task;
        if (serv->sv_nrpools > 1)
                svc_pool_map_set_cpumask(task, pool->sp_id);

        svc_sock_update_bufs(serv);
        wake_up_process(task);

        /* Wait for the thread to signal initialization status */
        wait_var_event(&rqstp->rq_err, rqstp->rq_err != -EAGAIN);
        err = rqstp->rq_err;
out:
        if (err)
                svc_exit_thread(rqstp);
        return err;
}
EXPORT_SYMBOL_GPL(svc_new_thread);

static int
svc_start_kthreads(struct svc_serv *serv, struct svc_pool *pool, int nrservs)
{
        int err = 0;

        while (!err && nrservs--)
                err = svc_new_thread(serv, pool);

        return err;
}

static int
svc_stop_kthreads(struct svc_serv *serv, struct svc_pool *pool, int nrservs)
{
        do {
                set_bit(SP_VICTIM_REMAINS, &pool->sp_flags);
                set_bit(SP_NEED_VICTIM, &pool->sp_flags);
                svc_pool_wake_idle_thread(pool);
                wait_on_bit(&pool->sp_flags, SP_VICTIM_REMAINS, TASK_IDLE);
                nrservs++;
        } while (nrservs < 0);
        return 0;
}

/**
 * svc_set_pool_threads - adjust number of threads per pool
 * @serv: RPC service to adjust
 * @pool: Specific pool from which to choose threads
 * @min_threads: min number of threads to run in @pool
 * @max_threads: max number of threads in @pool (0 means kill all threads)
 *
 * Create or destroy threads in @pool to bring it into an acceptable range
 * between @min_threads and @max_threads.
 *
 * If @min_threads is 0 or larger than @max_threads, then it is ignored and
 * the pool will be set to run a static @max_threads number of threads.
 *
 * Caller must ensure mutual exclusion between this and server startup or
 * shutdown.
 *
 * Returns zero on success or a negative errno if an error occurred while
 * starting a thread.
 */
int
svc_set_pool_threads(struct svc_serv *serv, struct svc_pool *pool,
                     unsigned int min_threads, unsigned int max_threads)
{
        int delta;

        if (!pool)
                return -EINVAL;

        /* clamp min threads to the max */
        if (min_threads > max_threads)
                min_threads = max_threads;

        pool->sp_nrthrmin = min_threads;
        pool->sp_nrthrmax = max_threads;

        /*
         * When min_threads is set, then only change the number of
         * threads to bring it within an acceptable range.
         */
        if (min_threads) {
                if (pool->sp_nrthreads > max_threads)
                        delta = max_threads;
                else if (pool->sp_nrthreads < min_threads)
                        delta = min_threads;
                else
                        return 0;
        } else {
                delta = max_threads;
        }

        delta -= pool->sp_nrthreads;
        if (delta > 0)
                return svc_start_kthreads(serv, pool, delta);
        if (delta < 0)
                return svc_stop_kthreads(serv, pool, delta);
        return 0;
}
EXPORT_SYMBOL_GPL(svc_set_pool_threads);

/**
 * svc_set_num_threads - adjust number of threads in serv
 * @serv: RPC service to adjust
 * @min_threads: min number of threads to run per pool
 * @nrservs: New number of threads for @serv (0 means kill all threads)
 *
 * Create or destroy threads in @serv to bring it to @nrservs. If there
 * are multiple pools then the new threads or victims will be distributed
 * evenly among them.
 *
 * Caller must ensure mutual exclusion between this and server startup or
 * shutdown.
 *
 * Returns zero on success or a negative errno if an error occurred while
 * starting a thread. On failure, some pools may have already been
 * adjusted; the caller is responsible for recovery.
 */
int
svc_set_num_threads(struct svc_serv *serv, unsigned int min_threads,
                    unsigned int nrservs)
{
        unsigned int base = nrservs / serv->sv_nrpools;
        unsigned int remain = nrservs % serv->sv_nrpools;
        int i, err = 0;

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

                if (remain) {
                        ++threads;
                        --remain;
                }

                err = svc_set_pool_threads(serv, pool, min_threads, threads);
                if (err)
                        break;
        }
        return err;
}
EXPORT_SYMBOL_GPL(svc_set_num_threads);

/**
 * svc_rqst_replace_page - Replace one page in rq_pages[]
 * @rqstp: svc_rqst with pages to replace
 * @page: replacement page
 *
 * When replacing a page in rq_pages, batch the release of the
 * replaced pages to avoid hammering the page allocator.
 *
 * Return values:
 *   %true: page replaced
 *   %false: array bounds checking failed
 */
bool svc_rqst_replace_page(struct svc_rqst *rqstp, struct page *page)
{
        struct page **begin = rqstp->rq_pages;
        struct page **end = &rqstp->rq_pages[rqstp->rq_maxpages];

        if (unlikely(rqstp->rq_next_page < begin || rqstp->rq_next_page > end)) {
                trace_svc_replace_page_err(rqstp);
                return false;
        }

        if (*rqstp->rq_next_page) {
                if (!folio_batch_add(&rqstp->rq_fbatch,
                                page_folio(*rqstp->rq_next_page)))
                        __folio_batch_release(&rqstp->rq_fbatch);
        }

        get_page(page);
        *(rqstp->rq_next_page++) = page;
        return true;
}
EXPORT_SYMBOL_GPL(svc_rqst_replace_page);

/**
 * svc_rqst_release_pages - Release Reply buffer pages
 * @rqstp: RPC transaction context
 *
 * Release response pages that might still be in flight after
 * svc_send, and any spliced filesystem-owned pages.
 */
void svc_rqst_release_pages(struct svc_rqst *rqstp)
{
        int i, count = rqstp->rq_next_page - rqstp->rq_respages;

        if (count) {
                release_pages(rqstp->rq_respages, count);
                for (i = 0; i < count; i++)
                        rqstp->rq_respages[i] = NULL;
        }
}

/**
 * svc_exit_thread - finalise the termination of a sunrpc server thread
 * @rqstp: the svc_rqst which represents the thread.
 *
 * When a thread started with svc_new_thread() exits it must call
 * svc_exit_thread() as its last act.  This must be done with the
 * service mutex held.  Normally this is held by a DIFFERENT thread, the
 * one that is calling svc_set_num_threads() and which will wait for
 * SP_VICTIM_REMAINS to be cleared before dropping the mutex.  If the
 * thread exits for any reason other than svc_thread_should_stop()
 * returning %true (which indicated that svc_set_num_threads() is
 * waiting for it to exit), then it must take the service mutex itself,
 * which can only safely be done using mutex_try_lock().
 */
void
svc_exit_thread(struct svc_rqst *rqstp)
{
        struct svc_serv *serv = rqstp->rq_server;
        struct svc_pool *pool = rqstp->rq_pool;

        list_del_rcu(&rqstp->rq_all);

        pool->sp_nrthreads -= 1;
        serv->sv_nrthreads -= 1;
        svc_sock_update_bufs(serv);

        svc_rqst_free(rqstp);

        clear_and_wake_up_bit(SP_VICTIM_REMAINS, &pool->sp_flags);
}
EXPORT_SYMBOL_GPL(svc_exit_thread);

/*
 * Register an "inet" protocol family netid with the local
 * rpcbind daemon via an rpcbind v4 SET request.
 *
 * No netconfig infrastructure is available in the kernel, so
 * we map IP_ protocol numbers to netids by hand.
 *
 * Returns zero on success; a negative errno value is returned
 * if any error occurs.
 */
static int __svc_rpcb_register4(struct net *net, const u32 program,
                                const u32 version,
                                const unsigned short protocol,
                                const unsigned short port)
{
        const struct sockaddr_in sin = {
                .sin_family             = AF_INET,
                .sin_addr.s_addr        = htonl(INADDR_ANY),
                .sin_port               = htons(port),
        };
        const char *netid;
        int error;

        switch (protocol) {
        case IPPROTO_UDP:
                netid = RPCBIND_NETID_UDP;
                break;
        case IPPROTO_TCP:
                netid = RPCBIND_NETID_TCP;
                break;
        default:
                return -ENOPROTOOPT;
        }

        error = rpcb_v4_register(net, program, version,
                                        (const struct sockaddr *)&sin, netid);

        /*
         * User space didn't support rpcbind v4, so retry this
         * registration request with the legacy rpcbind v2 protocol.
         */
        if (error == -EPROTONOSUPPORT)
                error = rpcb_register(net, program, version, protocol, port);

        return error;
}

#if IS_ENABLED(CONFIG_IPV6)
/*
 * Register an "inet6" protocol family netid with the local
 * rpcbind daemon via an rpcbind v4 SET request.
 *
 * No netconfig infrastructure is available in the kernel, so
 * we map IP_ protocol numbers to netids by hand.
 *
 * Returns zero on success; a negative errno value is returned
 * if any error occurs.
 */
static int __svc_rpcb_register6(struct net *net, const u32 program,
                                const u32 version,
                                const unsigned short protocol,
                                const unsigned short port)
{
        const struct sockaddr_in6 sin6 = {
                .sin6_family            = AF_INET6,
                .sin6_addr              = IN6ADDR_ANY_INIT,
                .sin6_port              = htons(port),
        };
        const char *netid;
        int error;

        switch (protocol) {
        case IPPROTO_UDP:
                netid = RPCBIND_NETID_UDP6;
                break;
        case IPPROTO_TCP:
                netid = RPCBIND_NETID_TCP6;
                break;
        default:
                return -ENOPROTOOPT;
        }

        error = rpcb_v4_register(net, program, version,
                                        (const struct sockaddr *)&sin6, netid);

        /*
         * User space didn't support rpcbind version 4, so we won't
         * use a PF_INET6 listener.
         */
        if (error == -EPROTONOSUPPORT)
                error = -EAFNOSUPPORT;

        return error;
}
#endif  /* IS_ENABLED(CONFIG_IPV6) */

/*
 * Register a kernel RPC service via rpcbind version 4.
 *
 * Returns zero on success; a negative errno value is returned
 * if any error occurs.
 */
static int __svc_register(struct net *net, const char *progname,
                          const u32 program, const u32 version,
                          const int family,
                          const unsigned short protocol,
                          const unsigned short port)
{
        int error = -EAFNOSUPPORT;

        switch (family) {
        case PF_INET:
                error = __svc_rpcb_register4(net, program, version,
                                                protocol, port);
                break;
#if IS_ENABLED(CONFIG_IPV6)
        case PF_INET6:
                error = __svc_rpcb_register6(net, program, version,
                                                protocol, port);
#endif
        }

        trace_svc_register(progname, version, family, protocol, port, error);
        return error;
}

static
int svc_rpcbind_set_version(struct net *net,
                            const struct svc_program *progp,
                            u32 version, int family,
                            unsigned short proto,
                            unsigned short port)
{
        return __svc_register(net, progp->pg_name, progp->pg_prog,
                                version, family, proto, port);

}

int svc_generic_rpcbind_set(struct net *net,
                            const struct svc_program *progp,
                            u32 version, int family,
                            unsigned short proto,
                            unsigned short port)
{
        const struct svc_version *vers = progp->pg_vers[version];
        int error;

        if (vers == NULL)
                return 0;

        if (vers->vs_hidden) {
                trace_svc_noregister(progp->pg_name, version, proto,
                                     port, family, 0);
                return 0;
        }

        /*
         * Don't register a UDP port if we need congestion
         * control.
         */
        if (vers->vs_need_cong_ctrl && proto == IPPROTO_UDP)
                return 0;

        error = svc_rpcbind_set_version(net, progp, version,
                                        family, proto, port);

        return (vers->vs_rpcb_optnl) ? 0 : error;
}
EXPORT_SYMBOL_GPL(svc_generic_rpcbind_set);

/**
 * svc_register - register an RPC service with the local portmapper
 * @serv: svc_serv struct for the service to register
 * @net: net namespace for the service to register
 * @family: protocol family of service's listener socket
 * @proto: transport protocol number to advertise
 * @port: port to advertise
 *
 * Service is registered for any address in the passed-in protocol family
 */
int svc_register(const struct svc_serv *serv, struct net *net,
                 const int family, const unsigned short proto,
                 const unsigned short port)
{
        unsigned int            p, i;
        int                     error = 0;

        WARN_ON_ONCE(proto == 0 && port == 0);
        if (proto == 0 && port == 0)
                return -EINVAL;

        for (p = 0; p < serv->sv_nprogs; p++) {
                struct svc_program *progp = &serv->sv_programs[p];

                for (i = 0; i < progp->pg_nvers; i++) {

                        error = progp->pg_rpcbind_set(net, progp, i,
                                        family, proto, port);
                        if (error < 0) {
                                printk(KERN_WARNING "svc: failed to register "
                                        "%sv%u RPC service (errno %d).\n",
                                        progp->pg_name, i, -error);
                                break;
                        }
                }
        }

        return error;
}

/*
 * If user space is running rpcbind, it should take the v4 UNSET
 * and clear everything for this [program, version].  If user space
 * is running portmap, it will reject the v4 UNSET, but won't have
 * any "inet6" entries anyway.  So a PMAP_UNSET should be sufficient
 * in this case to clear all existing entries for [program, version].
 */
static void __svc_unregister(struct net *net, const u32 program, const u32 version,
                             const char *progname)
{
        int error;

        error = rpcb_v4_register(net, program, version, NULL, "");

        /*
         * User space didn't support rpcbind v4, so retry this
         * request with the legacy rpcbind v2 protocol.
         */
        if (error == -EPROTONOSUPPORT)
                error = rpcb_register(net, program, version, 0, 0);

        trace_svc_unregister(progname, version, error);
}

/*
 * All netids, bind addresses and ports registered for [program, version]
 * are removed from the local rpcbind database (if the service is not
 * hidden) to make way for a new instance of the service.
 *
 * The result of unregistration is reported via dprintk for those who want
 * verification of the result, but is otherwise not important.
 */
static void svc_unregister(const struct svc_serv *serv, struct net *net)
{
        struct sighand_struct *sighand;
        unsigned long flags;
        unsigned int p, i;

        clear_thread_flag(TIF_SIGPENDING);

        for (p = 0; p < serv->sv_nprogs; p++) {
                struct svc_program *progp = &serv->sv_programs[p];

                for (i = 0; i < progp->pg_nvers; i++) {
                        if (progp->pg_vers[i] == NULL)
                                continue;
                        if (progp->pg_vers[i]->vs_hidden)
                                continue;
                        __svc_unregister(net, progp->pg_prog, i, progp->pg_name);
                }
        }

        rcu_read_lock();
        sighand = rcu_dereference(current->sighand);
        spin_lock_irqsave(&sighand->siglock, flags);
        recalc_sigpending();
        spin_unlock_irqrestore(&sighand->siglock, flags);
        rcu_read_unlock();
}

/*
 * dprintk the given error with the address of the client that caused it.
 */
#if IS_ENABLED(CONFIG_SUNRPC_DEBUG)
static __printf(2, 3)
void svc_printk(struct svc_rqst *rqstp, const char *fmt, ...)
{
        struct va_format vaf;
        va_list args;
        char    buf[RPC_MAX_ADDRBUFLEN];

        va_start(args, fmt);

        vaf.fmt = fmt;
        vaf.va = &args;

        dprintk("svc: %s: %pV", svc_print_addr(rqstp, buf, sizeof(buf)), &vaf);

        va_end(args);
}
#else
static __printf(2,3) void svc_printk(struct svc_rqst *rqstp, const char *fmt, ...) {}
#endif

__be32
svc_generic_init_request(struct svc_rqst *rqstp,
                const struct svc_program *progp,
                struct svc_process_info *ret)
{
        const struct svc_version *versp = NULL; /* compiler food */
        const struct svc_procedure *procp = NULL;

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

        /*
         * Some protocol versions (namely NFSv4) require some form of
         * congestion control.  (See RFC 7530 section 3.1 paragraph 2)
         * In other words, UDP is not allowed. We mark those when setting
         * up the svc_xprt, and verify that here.
         *
         * The spec is not very clear about what error should be returned
         * when someone tries to access a server that is listening on UDP
         * for lower versions. RPC_PROG_MISMATCH seems to be the closest
         * fit.
         */
        if (versp->vs_need_cong_ctrl && rqstp->rq_xprt &&
            !test_bit(XPT_CONG_CTRL, &rqstp->rq_xprt->xpt_flags))
                goto err_bad_vers;

        if (rqstp->rq_proc >= versp->vs_nproc)
                goto err_bad_proc;
        rqstp->rq_procinfo = procp = &versp->vs_proc[rqstp->rq_proc];

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

        /* Bump per-procedure stats counter */
        this_cpu_inc(versp->vs_count[rqstp->rq_proc]);

        ret->dispatch = versp->vs_dispatch;
        return rpc_success;
err_bad_vers:
        ret->mismatch.lovers = progp->pg_lovers;
        ret->mismatch.hivers = progp->pg_hivers;
        return rpc_prog_mismatch;
err_bad_proc:
        return rpc_proc_unavail;
}
EXPORT_SYMBOL_GPL(svc_generic_init_request);

/*
 * Common routine for processing the RPC request.
 */
static int
svc_process_common(struct svc_rqst *rqstp)
{
        struct xdr_stream       *xdr = &rqstp->rq_res_stream;
        struct svc_program      *progp = NULL;
        const struct svc_procedure *procp = NULL;
        struct svc_serv         *serv = rqstp->rq_server;
        struct svc_process_info process;
        enum svc_auth_status    auth_res;
        unsigned int            aoffset;
        int                     pr, rc;
        __be32                  *p;

        /* Reset the accept_stat for the RPC */
        rqstp->rq_accept_statp = NULL;

        /* Will be turned off only when NFSv4 Sessions are used */
        set_bit(RQ_USEDEFERRAL, &rqstp->rq_flags);
        clear_bit(RQ_DROPME, &rqstp->rq_flags);

        /* Construct the first words of the reply: */
        svcxdr_init_encode(rqstp);
        xdr_stream_encode_be32(xdr, rqstp->rq_xid);
        xdr_stream_encode_be32(xdr, rpc_reply);

        p = xdr_inline_decode(&rqstp->rq_arg_stream, XDR_UNIT * 4);
        if (unlikely(!p))
                goto err_short_len;
        if (*p++ != cpu_to_be32(RPC_VERSION))
                goto err_bad_rpc;

        xdr_stream_encode_be32(xdr, rpc_msg_accepted);

        rqstp->rq_prog = be32_to_cpup(p++);
        rqstp->rq_vers = be32_to_cpup(p++);
        rqstp->rq_proc = be32_to_cpup(p);

        for (pr = 0; pr < serv->sv_nprogs; pr++)
                if (rqstp->rq_prog == serv->sv_programs[pr].pg_prog)
                        progp = &serv->sv_programs[pr];

        /*
         * 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);
        /* Also give the program a chance to reject this call: */
        if (auth_res == SVC_OK && progp)
                auth_res = progp->pg_authenticate(rqstp);
        trace_svc_authenticate(rqstp, auth_res);
        switch (auth_res) {
        case SVC_OK:
                break;
        case SVC_GARBAGE:
                rqstp->rq_auth_stat = rpc_autherr_badcred;
                goto err_bad_auth;
        case SVC_DENIED:
                goto err_bad_auth;
        case SVC_CLOSE:
                goto close;
        case SVC_DROP:
                goto dropit;
        case SVC_COMPLETE:
                goto sendit;
        default:
                pr_warn_once("Unexpected svc_auth_status (%d)\n", auth_res);
                rqstp->rq_auth_stat = rpc_autherr_failed;
                goto err_bad_auth;
        }

        if (progp == NULL)
                goto err_bad_prog;

        switch (progp->pg_init_request(rqstp, progp, &process)) {
        case rpc_success:
                break;
        case rpc_prog_unavail:
                goto err_bad_prog;
        case rpc_prog_mismatch:
                goto err_bad_vers;
        case rpc_proc_unavail:
                goto err_bad_proc;
        }

        procp = rqstp->rq_procinfo;
        /* Should this check go into the dispatcher? */
        if (!procp || !procp->pc_func)
                goto err_bad_proc;

        /* Syntactic check complete */
        if (serv->sv_stats)
                serv->sv_stats->rpccnt++;
        trace_svc_process(rqstp, progp->pg_name);

        aoffset = xdr_stream_pos(xdr);

        /* 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. */
        rc = process.dispatch(rqstp);
        xdr_finish_decode(xdr);

        if (!rc)
                goto dropit;
        if (rqstp->rq_auth_stat != rpc_auth_ok)
                goto err_bad_auth;

        if (*rqstp->rq_accept_statp != rpc_success)
                xdr_truncate_encode(xdr, aoffset);

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

 sendit:
        if (svc_authorise(rqstp))
                goto close_xprt;
        return 1;               /* Caller can now send it */

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

 close:
        svc_authorise(rqstp);
close_xprt:
        if (rqstp->rq_xprt && test_bit(XPT_TEMP, &rqstp->rq_xprt->xpt_flags))
                svc_xprt_close(rqstp->rq_xprt);
        dprintk("svc: svc_process close\n");
        return 0;

err_short_len:
        svc_printk(rqstp, "short len %u, dropping request\n",
                   rqstp->rq_arg.len);
        goto close_xprt;

err_bad_rpc:
        if (serv->sv_stats)
                serv->sv_stats->rpcbadfmt++;
        xdr_stream_encode_u32(xdr, RPC_MSG_DENIED);
        xdr_stream_encode_u32(xdr, RPC_MISMATCH);
        /* Only RPCv2 supported */
        xdr_stream_encode_u32(xdr, RPC_VERSION);
        xdr_stream_encode_u32(xdr, RPC_VERSION);
        return 1;       /* don't wrap */

err_bad_auth:
        dprintk("svc: authentication failed (%d)\n",
                be32_to_cpu(rqstp->rq_auth_stat));
        if (serv->sv_stats)
                serv->sv_stats->rpcbadauth++;
        /* Restore write pointer to location of reply status: */
        xdr_truncate_encode(xdr, XDR_UNIT * 2);
        xdr_stream_encode_u32(xdr, RPC_MSG_DENIED);
        xdr_stream_encode_u32(xdr, RPC_AUTH_ERROR);
        xdr_stream_encode_be32(xdr, rqstp->rq_auth_stat);
        goto sendit;

err_bad_prog:
        dprintk("svc: unknown program %d\n", rqstp->rq_prog);
        if (serv->sv_stats)
                serv->sv_stats->rpcbadfmt++;
        *rqstp->rq_accept_statp = rpc_prog_unavail;
        goto sendit;

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

        if (serv->sv_stats)
                serv->sv_stats->rpcbadfmt++;
        *rqstp->rq_accept_statp = rpc_prog_mismatch;

        /*
         * svc_authenticate() has already added the verifier and
         * advanced the stream just past rq_accept_statp.
         */
        xdr_stream_encode_u32(xdr, process.mismatch.lovers);
        xdr_stream_encode_u32(xdr, process.mismatch.hivers);
        goto sendit;

err_bad_proc:
        svc_printk(rqstp, "unknown procedure (%d)\n", rqstp->rq_proc);

        if (serv->sv_stats)
                serv->sv_stats->rpcbadfmt++;
        *rqstp->rq_accept_statp = rpc_proc_unavail;
        goto sendit;
}

/*
 * Drop request
 */
static void svc_drop(struct svc_rqst *rqstp)
{
        trace_svc_drop(rqstp);
}

static void svc_release_rqst(struct svc_rqst *rqstp)
{
        const struct svc_procedure *procp = rqstp->rq_procinfo;

        if (procp && procp->pc_release)
                procp->pc_release(rqstp);
}

/**
 * svc_process - Execute one RPC transaction
 * @rqstp: RPC transaction context
 *
 */
void svc_process(struct svc_rqst *rqstp)
{
        struct kvec             *resv = &rqstp->rq_res.head[0];
        __be32 *p;

#if IS_ENABLED(CONFIG_FAIL_SUNRPC)
        if (!fail_sunrpc.ignore_server_disconnect &&
            should_fail(&fail_sunrpc.attr, 1))
                svc_xprt_deferred_close(rqstp->rq_xprt);
#endif

        /*
         * Setup response xdr_buf.
         * Initially it has just one page
         */
        rqstp->rq_next_page = &rqstp->rq_respages[1];
        resv->iov_base = page_address(rqstp->rq_respages[0]);
        resv->iov_len = 0;
        rqstp->rq_res.pages = rqstp->rq_next_page;
        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;

        svcxdr_init_decode(rqstp);
        p = xdr_inline_decode(&rqstp->rq_arg_stream, XDR_UNIT * 2);
        if (unlikely(!p))
                goto out_drop;
        rqstp->rq_xid = *p++;
        if (unlikely(*p != rpc_call))
                goto out_baddir;

        if (!svc_process_common(rqstp)) {
                svc_release_rqst(rqstp);
                goto out_drop;
        }
        svc_send(rqstp);
        svc_release_rqst(rqstp);
        return;

out_baddir:
        svc_printk(rqstp, "bad direction 0x%08x, dropping request\n",
                   be32_to_cpu(*p));
        if (rqstp->rq_server->sv_stats)
                rqstp->rq_server->sv_stats->rpcbadfmt++;
out_drop:
        svc_drop(rqstp);
}

#if defined(CONFIG_SUNRPC_BACKCHANNEL)
/**
 * svc_process_bc - process a reverse-direction RPC request
 * @req: RPC request to be used for client-side processing
 * @rqstp: server-side execution context
 *
 */
void svc_process_bc(struct rpc_rqst *req, struct svc_rqst *rqstp)
{
        struct rpc_timeout timeout = {
                .to_increment           = 0,
        };
        struct rpc_task *task;
        int proc_error;

        /* Build the svc_rqst used by the common processing routine */
        rqstp->rq_xid = req->rq_xid;
        rqstp->rq_prot = req->rq_xprt->prot;
        rqstp->rq_bc_net = req->rq_xprt->xprt_net;

        rqstp->rq_addrlen = sizeof(req->rq_xprt->addr);
        memcpy(&rqstp->rq_addr, &req->rq_xprt->addr, rqstp->rq_addrlen);
        memcpy(&rqstp->rq_arg, &req->rq_rcv_buf, sizeof(rqstp->rq_arg));
        memcpy(&rqstp->rq_res, &req->rq_snd_buf, sizeof(rqstp->rq_res));

        /* Adjust the argument buffer length */
        rqstp->rq_arg.len = req->rq_private_buf.len;
        if (rqstp->rq_arg.len <= rqstp->rq_arg.head[0].iov_len) {
                rqstp->rq_arg.head[0].iov_len = rqstp->rq_arg.len;
                rqstp->rq_arg.page_len = 0;
        } else if (rqstp->rq_arg.len <= rqstp->rq_arg.head[0].iov_len +
                        rqstp->rq_arg.page_len)
                rqstp->rq_arg.page_len = rqstp->rq_arg.len -
                        rqstp->rq_arg.head[0].iov_len;
        else
                rqstp->rq_arg.len = rqstp->rq_arg.head[0].iov_len +
                        rqstp->rq_arg.page_len;

        /* Reset the response buffer */
        rqstp->rq_res.head[0].iov_len = 0;

        /*
         * Skip the XID and calldir fields because they've already
         * been processed by the caller.
         */
        svcxdr_init_decode(rqstp);
        if (!xdr_inline_decode(&rqstp->rq_arg_stream, XDR_UNIT * 2))
                return;

        /* Parse and execute the bc call */
        proc_error = svc_process_common(rqstp);

        atomic_dec(&req->rq_xprt->bc_slot_count);
        if (!proc_error) {
                /* Processing error: drop the request */
                xprt_free_bc_request(req);
                svc_release_rqst(rqstp);
                return;
        }
        /* Finally, send the reply synchronously */
        if (rqstp->bc_to_initval > 0) {
                timeout.to_initval = rqstp->bc_to_initval;
                timeout.to_retries = rqstp->bc_to_retries;
        } else {
                timeout.to_initval = req->rq_xprt->timeout->to_initval;
                timeout.to_retries = req->rq_xprt->timeout->to_retries;
        }
        timeout.to_maxval = timeout.to_initval;
        memcpy(&req->rq_snd_buf, &rqstp->rq_res, sizeof(req->rq_snd_buf));
        task = rpc_run_bc_task(req, &timeout);
        svc_release_rqst(rqstp);

        if (IS_ERR(task))
                return;

        WARN_ON_ONCE(atomic_read(&task->tk_count) != 1);
        rpc_put_task(task);
}
#endif /* CONFIG_SUNRPC_BACKCHANNEL */

/**
 * svc_max_payload - Return transport-specific limit on the RPC payload
 * @rqstp: RPC transaction context
 *
 * Returns the maximum number of payload bytes the current transport
 * allows.
 */
u32 svc_max_payload(const struct svc_rqst *rqstp)
{
        u32 max = rqstp->rq_xprt->xpt_class->xcl_max_payload;

        if (rqstp->rq_server->sv_max_payload < max)
                max = rqstp->rq_server->sv_max_payload;
        return max;
}
EXPORT_SYMBOL_GPL(svc_max_payload);

/**
 * svc_proc_name - Return RPC procedure name in string form
 * @rqstp: svc_rqst to operate on
 *
 * Return value:
 *   Pointer to a NUL-terminated string
 */
const char *svc_proc_name(const struct svc_rqst *rqstp)
{
        if (rqstp && rqstp->rq_procinfo)
                return rqstp->rq_procinfo->pc_name;
        return "unknown";
}


/**
 * svc_encode_result_payload - mark a range of bytes as a result payload
 * @rqstp: svc_rqst to operate on
 * @offset: payload's byte offset in rqstp->rq_res
 * @length: size of payload, in bytes
 *
 * Returns zero on success, or a negative errno if a permanent
 * error occurred.
 */
int svc_encode_result_payload(struct svc_rqst *rqstp, unsigned int offset,
                              unsigned int length)
{
        return rqstp->rq_xprt->xpt_ops->xpo_result_payload(rqstp, offset,
                                                           length);
}
EXPORT_SYMBOL_GPL(svc_encode_result_payload);

/**
 * svc_fill_symlink_pathname - Construct pathname argument for VFS symlink call
 * @rqstp: svc_rqst to operate on
 * @first: buffer containing first section of pathname
 * @p: buffer containing remaining section of pathname
 * @total: total length of the pathname argument
 *
 * The VFS symlink API demands a NUL-terminated pathname in mapped memory.
 * Returns pointer to a NUL-terminated string, or an ERR_PTR. Caller must free
 * the returned string.
 */
char *svc_fill_symlink_pathname(struct svc_rqst *rqstp, struct kvec *first,
                                void *p, size_t total)
{
        size_t len, remaining;
        char *result, *dst;

        result = kmalloc(total + 1, GFP_KERNEL);
        if (!result)
                return ERR_PTR(-ESERVERFAULT);

        dst = result;
        remaining = total;

        len = min_t(size_t, total, first->iov_len);
        if (len) {
                memcpy(dst, first->iov_base, len);
                dst += len;
                remaining -= len;
        }

        if (remaining) {
                len = min_t(size_t, remaining, PAGE_SIZE);
                memcpy(dst, p, len);
                dst += len;
        }

        *dst = '\0';

        /* Sanity check: Linux doesn't allow the pathname argument to
         * contain a NUL byte.
         */
        if (strlen(result) != total) {
                kfree(result);
                return ERR_PTR(-EINVAL);
        }
        return result;
}
EXPORT_SYMBOL_GPL(svc_fill_symlink_pathname);