alistair23-linux/net/sunrpc/svc.c

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

#include <linux/linkage.h>
#include <linux/sched/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);