/*
 * 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>

#define RPCDBG_FACILITY RPCDBG_SVCDSP

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

#define svc_serv_is_pooled(serv)    ((serv)->sv_ops->svo_function)

#define SVC_POOL_DEFAULT        SVC_POOL_GLOBAL

/*
 * Structure for mapping cpus to pools and vice versa.
 * Setup once during sunrpc initialisation.
 */
struct svc_pool_map svc_pool_map = {
        .mode = SVC_POOL_DEFAULT
};
EXPORT_SYMBOL_GPL(svc_pool_map);

static DEFINE_MUTEX(svc_pool_map_mutex);/* protects svc_pool_map.count only */

static int
param_set_pool_mode(const char *val, const 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, const 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 (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).  Initialise the map if we're the first user.
 * Returns the number of pools.
 */
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;
}
EXPORT_SYMBOL_GPL(svc_pool_map_get);

/*
 * 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.
 */
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);
}
EXPORT_SYMBOL_GPL(svc_pool_map_put);

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_NO_NODE;
}
/*
 * 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;
        }
        }
}

/*
 * 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];
}

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;
}
EXPORT_SYMBOL_GPL(svc_rpcb_setup);

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

static int svc_uses_rpcbind(struct svc_serv *serv)
{
        struct svc_program      *progp;
        unsigned int            i;

        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;
                        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)
{
        INIT_LIST_HEAD(&serv->sv_cb_list);
        spin_lock_init(&serv->sv_cb_lock);
        init_waitqueue_head(&serv->sv_cb_waitq);
}
#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, unsigned int bufsize, int npools,
             const struct svc_serv_ops *ops)
{
        struct svc_serv *serv;
        unsigned 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_ops = ops;
        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);
        timer_setup(&serv->sv_temptimer, NULL, 0);
        spin_lock_init(&serv->sv_lock);

        __svc_init_bc(serv);

        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_sockets);
                INIT_LIST_HEAD(&pool->sp_all_threads);
                spin_lock_init(&pool->sp_lock);
        }

        return serv;
}

struct svc_serv *
svc_create(struct svc_program *prog, unsigned int bufsize,
           const struct svc_serv_ops *ops)
{
        return __svc_create(prog, bufsize, /*npools*/1, ops);
}
EXPORT_SYMBOL_GPL(svc_create);

struct svc_serv *
svc_create_pooled(struct svc_program *prog, unsigned int bufsize,
                  const struct svc_serv_ops *ops)
{
        struct svc_serv *serv;
        unsigned int npools = svc_pool_map_get();

        serv = __svc_create(prog, bufsize, npools, ops);
        if (!serv)
                goto out_err;
        return serv;
out_err:
        svc_pool_map_put();
        return NULL;
}
EXPORT_SYMBOL_GPL(svc_create_pooled);

void svc_shutdown_net(struct svc_serv *serv, struct net *net)
{
        svc_close_net(serv, net);

        if (serv->sv_ops->svo_shutdown)
                serv->sv_ops->svo_shutdown(serv, net);
}
EXPORT_SYMBOL_GPL(svc_shutdown_net);

/*
 * Destroy an RPC service. Should be called with appropriate locking to
 * protect the sv_nrthreads, sv_permsocks and sv_tempsocks.
 */
void
svc_destroy(struct svc_serv *serv)
{
        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);

        /*
         * The last user is gone and thus all sockets have to be destroyed to
         * the point. Check this.
         */
        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();

        kfree(serv->sv_pools);
        kfree(serv);
}
EXPORT_SYMBOL_GPL(svc_destroy);

/*
 * 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 node)
{
        unsigned int pages, arghi;

        /* bc_xprt uses fore channel allocated buffers */
        if (svc_is_backchannel(rqstp))
                return 1;

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

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

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

struct svc_rqst *
svc_rqst_alloc(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;

        __set_bit(RQ_BUSY, &rqstp->rq_flags);
        spin_lock_init(&rqstp->rq_lock);
        rqstp->rq_server = serv;
        rqstp->rq_pool = pool;

        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->sv_max_mesg, node))
                goto out_enomem;

        return rqstp;
out_enomem:
        svc_rqst_free(rqstp);
        return NULL;
}
EXPORT_SYMBOL_GPL(svc_rqst_alloc);

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

        rqstp = svc_rqst_alloc(serv, pool, node);
        if (!rqstp)
                return ERR_PTR(-ENOMEM);

        serv->sv_nrthreads++;
        spin_lock_bh(&pool->sp_lock);
        pool->sp_nrthreads++;
        list_add_rcu(&rqstp->rq_all, &pool->sp_all_threads);
        spin_unlock_bh(&pool->sp_lock);
        return rqstp;
}
EXPORT_SYMBOL_GPL(svc_prepare_thread);

/*
 * 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);
                set_bit(RQ_VICTIM, &rqstp->rq_flags);
                list_del_rcu(&rqstp->rq_all);
                task = rqstp->rq_task;
        }
        spin_unlock_bh(&pool->sp_lock);

        return task;
}

/* create new threads */
static int
svc_start_kthreads(struct svc_serv *serv, struct svc_pool *pool, int nrservs)
{
        struct svc_rqst *rqstp;
        struct task_struct *task;
        struct svc_pool *chosen_pool;
        unsigned int state = serv->sv_nrthreads-1;
        int node;

        do {
                nrservs--;
                chosen_pool = choose_pool(serv, pool, &state);

                node = svc_pool_map_get_node(chosen_pool->sp_id);
                rqstp = svc_prepare_thread(serv, chosen_pool, node);
                if (IS_ERR(rqstp))
                        return PTR_ERR(rqstp);

                __module_get(serv->sv_ops->svo_module);
                task = kthread_create_on_node(serv->sv_ops->svo_function, rqstp,
                                              node, "%s", serv->sv_name);
                if (IS_ERR(task)) {
                        module_put(serv->sv_ops->svo_module);
                        svc_exit_thread(rqstp);
                        return PTR_ERR(task);
                }

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

                svc_sock_update_bufs(serv);
                wake_up_process(task);
        } while (nrservs > 0);

        return 0;
}


/* destroy old threads */
static int
svc_signal_kthreads(struct svc_serv *serv, struct svc_pool *pool, int nrservs)
{
        struct task_struct *task;
        unsigned int state = serv->sv_nrthreads-1;

        /* destroy old threads */
        do {
                task = choose_victim(serv, pool, &state);
                if (task == NULL)
                        break;
                send_sig(SIGINT, task, 1);
                nrservs++;
        } while (nrservs < 0);

        return 0;
}

/*
 * 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.  Caller must ensure that mutual exclusion between this and
 * server startup or shutdown.
 *
 * 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)
{
        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);
        }

        if (nrservs > 0)
                return svc_start_kthreads(serv, pool, nrservs);
        if (nrservs < 0)
                return svc_signal_kthreads(serv, pool, nrservs);
        return 0;
}
EXPORT_SYMBOL_GPL(svc_set_num_threads);

/* destroy old threads */
static int
svc_stop_kthreads(struct svc_serv *serv, struct svc_pool *pool, int nrservs)
{
        struct task_struct *task;
        unsigned int state = serv->sv_nrthreads-1;

        /* destroy old threads */
        do {
                task = choose_victim(serv, pool, &state);
                if (task == NULL)
                        break;
                kthread_stop(task);
                nrservs++;
        } while (nrservs < 0);
        return 0;
}

int
svc_set_num_threads_sync(struct svc_serv *serv, struct svc_pool *pool, int nrservs)
{
        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);
        }

        if (nrservs > 0)
                return svc_start_kthreads(serv, pool, nrservs);
        if (nrservs < 0)
                return svc_stop_kthreads(serv, pool, nrservs);
        return 0;
}
EXPORT_SYMBOL_GPL(svc_set_num_threads_sync);

/*
 * Called from a server thread as it's exiting. Caller must hold the "service
 * mutex" for the service.
 */
void
svc_rqst_free(struct svc_rqst *rqstp)
{
        svc_release_buffer(rqstp);
        kfree(rqstp->rq_resp);
        kfree(rqstp->rq_argp);
        kfree(rqstp->rq_auth_data);
        kfree_rcu(rqstp, rq_rcu_head);
}
EXPORT_SYMBOL_GPL(svc_rqst_free);

void
svc_exit_thread(struct svc_rqst *rqstp)
{
        struct svc_serv *serv = rqstp->rq_server;
        struct svc_pool *pool = rqstp->rq_pool;

        spin_lock_bh(&pool->sp_lock);
        pool->sp_nrthreads--;
        if (!test_and_set_bit(RQ_VICTIM, &rqstp->rq_flags))
                list_del_rcu(&rqstp->rq_all);
        spin_unlock_bh(&pool->sp_lock);

        svc_rqst_free(rqstp);

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

        return error;
}

/**
 * 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)
{
        struct svc_program      *progp;
        const struct svc_version *vers;
        unsigned int            i;
        int                     error = 0;

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

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

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

                        if (vers->vs_hidden)
                                continue;

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

                        error = __svc_register(net, progp->pg_name, progp->pg_prog,
                                                i, family, proto, port);

                        if (vers->vs_rpcb_optnl) {
                                error = 0;
                                continue;
                        }

                        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);

        dprintk("svc: %s(%sv%u), error %d\n",
                        __func__, 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 svc_program *progp;
        unsigned long flags;
        unsigned int i;

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

                        dprintk("svc: attempting to unregister %sv%u\n",
                                progp->pg_name, i);
                        __svc_unregister(net, progp->pg_prog, i, progp->pg_name);
                }
        }

        spin_lock_irqsave(&current->sighand->siglock, flags);
        recalc_sigpending();
        spin_unlock_irqrestore(&current->sighand->siglock, flags);
}

/*
 * 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

/*
 * Common routine for processing the RPC request.
 */
static int
svc_process_common(struct svc_rqst *rqstp, struct kvec *argv, struct kvec *resv)
{
        struct svc_program      *progp;
        const struct svc_version *versp = NULL; /* compiler food */
        const struct svc_procedure *procp = NULL;
        struct svc_serv         *serv = rqstp->rq_server;
        __be32                  *statp;
        u32                     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;

        /* Will be turned off by GSS integrity and privacy services */
        set_bit(RQ_SPLICE_OK, &rqstp->rq_flags);
        /* Will be turned off only when NFSv4 Sessions are used */
        set_bit(RQ_USEDEFERRAL, &rqstp->rq_flags);
        clear_bit(RQ_DROPME, &rqstp->rq_flags);

        /* Setup reply header */
        rqstp->rq_xprt->xpt_ops->xpo_prep_reply_hdr(rqstp);

        svc_putu32(resv, rqstp->rq_xid);

        vers = svc_getnl(argv);

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

        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 */

        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:
                goto err_garbage;
        case SVC_SYSERR:
                rpc_stat = rpc_system_err;
                goto err_bad;
        case SVC_DENIED:
                goto err_bad_auth;
        case SVC_CLOSE:
                goto close;
        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;

        /*
         * 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 &&
            !test_bit(XPT_CONG_CTRL, &rqstp->rq_xprt->xpt_flags))
                goto err_bad_vers;

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

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

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

        /* Bump per-procedure stats counter */
        versp->vs_count[proc]++;

        /* 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
                 * XXX: why do we ignore the return value?
                 */
                if (procp->pc_decode &&
                    !procp->pc_decode(rqstp, argv->iov_base))
                        goto err_garbage;

                *statp = procp->pc_func(rqstp);

                /* Encode reply */
                if (*statp == rpc_drop_reply ||
                    test_bit(RQ_DROPME, &rqstp->rq_flags)) {
                        if (procp->pc_release)
                                procp->pc_release(rqstp);
                        goto dropit;
                }
                if (*statp == rpc_autherr_badcred) {
                        if (procp->pc_release)
                                procp->pc_release(rqstp);
                        goto err_bad_auth;
                }
                if (*statp == rpc_success && procp->pc_encode &&
                    !procp->pc_encode(rqstp, resv->iov_base + resv->iov_len)) {
                        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);
                        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);

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

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

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

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;
}

/*
 * Process the RPC request.
 */
int
svc_process(struct svc_rqst *rqstp)
{
        struct kvec             *argv = &rqstp->rq_arg.head[0];
        struct kvec             *resv = &rqstp->rq_res.head[0];
        struct svc_serv         *serv = rqstp->rq_server;
        u32                     dir;

        /*
         * 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_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;

        dir  = svc_getnl(argv);
        if (dir != 0) {
                /* direction != CALL */
                svc_printk(rqstp, "bad direction %d, dropping request\n", dir);
                serv->sv_stats->rpcbadfmt++;
                goto out_drop;
        }

        /* Returns 1 for send, 0 for drop */
        if (likely(svc_process_common(rqstp, argv, resv)))
                return svc_send(rqstp);

out_drop:
        svc_drop(rqstp);
        return 0;
}
EXPORT_SYMBOL_GPL(svc_process);

#if defined(CONFIG_SUNRPC_BACKCHANNEL)
/*
 * Process a backchannel RPC request that arrived over an existing
 * outbound connection
 */
int
bc_svc_process(struct svc_serv *serv, struct rpc_rqst *req,
               struct svc_rqst *rqstp)
{
        struct kvec     *argv = &rqstp->rq_arg.head[0];
        struct kvec     *resv = &rqstp->rq_res.head[0];
        struct rpc_task *task;
        int proc_error;
        int error;

        dprintk("svc: %s(%p)\n", __func__, req);

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

        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 result send buffer "put" position */
        resv->iov_len = 0;

        /*
         * Skip the next two words because they've already been
         * processed in the transport
         */
        svc_getu32(argv);       /* XID */
        svc_getnl(argv);        /* CALLDIR */

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

        atomic_inc(&req->rq_xprt->bc_free_slots);
        if (!proc_error) {
                /* Processing error: drop the request */
                xprt_free_bc_request(req);
                return 0;
        }

        /* Finally, send the reply synchronously */
        memcpy(&req->rq_snd_buf, &rqstp->rq_res, sizeof(req->rq_snd_buf));
        task = rpc_run_bc_task(req);
        if (IS_ERR(task)) {
                error = PTR_ERR(task);
                goto out;
        }

        WARN_ON_ONCE(atomic_read(&task->tk_count) != 1);
        error = task->tk_status;
        rpc_put_task(task);

out:
        dprintk("svc: %s(), error=%d\n", __func__, error);
        return error;
}
EXPORT_SYMBOL_GPL(bc_svc_process);
#endif /* CONFIG_SUNRPC_BACKCHANNEL */

/*
 * Return (transport-specific) limit on the rpc payload.
 */
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_fill_write_vector - Construct data argument for VFS write call
 * @rqstp: svc_rqst to operate on
 * @first: buffer containing first section of write payload
 * @total: total number of bytes of write payload
 *
 * Returns the number of elements populated in the data argument array.
 */
unsigned int svc_fill_write_vector(struct svc_rqst *rqstp, struct kvec *first,
                                   size_t total)
{
        struct kvec *vec = rqstp->rq_vec;
        struct page **pages;
        unsigned int i;

        /* Some types of transport can present the write payload
         * entirely in rq_arg.pages. In this case, @first is empty.
         */
        i = 0;
        if (first->iov_len) {
                vec[i].iov_base = first->iov_base;
                vec[i].iov_len = min_t(size_t, total, first->iov_len);
                total -= vec[i].iov_len;
                ++i;
        }

        WARN_ON_ONCE(rqstp->rq_arg.page_base != 0);
        pages = rqstp->rq_arg.pages;
        while (total) {
                vec[i].iov_base = page_address(*pages);
                vec[i].iov_len = min_t(size_t, total, PAGE_SIZE);
                total -= vec[i].iov_len;
                ++i;

                ++pages;
        }

        WARN_ON_ONCE(i > ARRAY_SIZE(rqstp->rq_vec));
        return i;
}
EXPORT_SYMBOL_GPL(svc_fill_write_vector);

/**
 * svc_fill_symlink_pathname - Construct pathname argument for VFS symlink call
 * @rqstp: svc_rqst to operate on
 * @first: buffer containing first section of pathname
 * @total: total length of the pathname argument
 *
 * Returns pointer to a NUL-terminated string, or an ERR_PTR. The buffer is
 * released automatically when @rqstp is recycled.
 */
char *svc_fill_symlink_pathname(struct svc_rqst *rqstp, struct kvec *first,
                                size_t total)
{
        struct xdr_buf *arg = &rqstp->rq_arg;
        struct page **pages;
        char *result;

        /* VFS API demands a NUL-terminated pathname. This function
         * uses a page from @rqstp as the pathname buffer, to enable
         * direct placement. Thus the total buffer size is PAGE_SIZE.
         * Space in this buffer for NUL-termination requires that we
         * cap the size of the returned symlink pathname just a
         * little early.
         */
        if (total > PAGE_SIZE - 1)
                return ERR_PTR(-ENAMETOOLONG);

        /* Some types of transport can present the pathname entirely
         * in rq_arg.pages. If not, then copy the pathname into one
         * page.
         */
        pages = arg->pages;
        WARN_ON_ONCE(arg->page_base != 0);
        if (first->iov_base == 0) {
                result = page_address(*pages);
                result[total] = '\0';
        } else {
                size_t len, remaining;
                char *dst;

                result = page_address(*(rqstp->rq_next_page++));
                dst = result;
                remaining = total;

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

                /* No more than one page left */
                if (remaining) {
                        len = min_t(size_t, remaining, PAGE_SIZE);
                        memcpy(dst, page_address(*pages), len);
                        dst += len;
                }

                *dst = '\0';
        }

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