xref: /openbmc/linux/fs/nfsd/nfssvc.c (revision 3b23dc52)

// SPDX-License-Identifier: GPL-2.0
/*
 * Central processing for nfsd.
 *
 * Authors:	Olaf Kirch (okir@monad.swb.de)
 *
 * Copyright (C) 1995, 1996, 1997 Olaf Kirch <okir@monad.swb.de>
 */

#include <linux/sched/signal.h>
#include <linux/freezer.h>
#include <linux/module.h>
#include <linux/fs_struct.h>
#include <linux/swap.h>

#include <linux/sunrpc/stats.h>
#include <linux/sunrpc/svcsock.h>
#include <linux/sunrpc/svc_xprt.h>
#include <linux/lockd/bind.h>
#include <linux/nfsacl.h>
#include <linux/seq_file.h>
#include <linux/inetdevice.h>
#include <net/addrconf.h>
#include <net/ipv6.h>
#include <net/net_namespace.h>
#include "nfsd.h"
#include "cache.h"
#include "vfs.h"
#include "netns.h"

#define NFSDDBG_FACILITY	NFSDDBG_SVC

extern struct svc_program	nfsd_program;
static int			nfsd(void *vrqstp);

/*
 * nfsd_mutex protects nn->nfsd_serv -- both the pointer itself and the members
 * of the svc_serv struct. In particular, ->sv_nrthreads but also to some
 * extent ->sv_temp_socks and ->sv_permsocks. It also protects nfsdstats.th_cnt
 *
 * If (out side the lock) nn->nfsd_serv is non-NULL, then it must point to a
 * properly initialised 'struct svc_serv' with ->sv_nrthreads > 0. That number
 * of nfsd threads must exist and each must listed in ->sp_all_threads in each
 * entry of ->sv_pools[].
 *
 * Transitions of the thread count between zero and non-zero are of particular
 * interest since the svc_serv needs to be created and initialized at that
 * point, or freed.
 *
 * Finally, the nfsd_mutex also protects some of the global variables that are
 * accessed when nfsd starts and that are settable via the write_* routines in
 * nfsctl.c. In particular:
 *
 *	user_recovery_dirname
 *	user_lease_time
 *	nfsd_versions
 */
DEFINE_MUTEX(nfsd_mutex);

/*
 * nfsd_drc_lock protects nfsd_drc_max_pages and nfsd_drc_pages_used.
 * nfsd_drc_max_pages limits the total amount of memory available for
 * version 4.1 DRC caches.
 * nfsd_drc_pages_used tracks the current version 4.1 DRC memory usage.
 */
spinlock_t	nfsd_drc_lock;
unsigned long	nfsd_drc_max_mem;
unsigned long	nfsd_drc_mem_used;

#if defined(CONFIG_NFSD_V2_ACL) || defined(CONFIG_NFSD_V3_ACL)
static struct svc_stat	nfsd_acl_svcstats;
static const struct svc_version *nfsd_acl_version[] = {
	[2] = &nfsd_acl_version2,
	[3] = &nfsd_acl_version3,
};

#define NFSD_ACL_MINVERS            2
#define NFSD_ACL_NRVERS		ARRAY_SIZE(nfsd_acl_version)
static const struct svc_version *nfsd_acl_versions[NFSD_ACL_NRVERS];

static struct svc_program	nfsd_acl_program = {
	.pg_prog		= NFS_ACL_PROGRAM,
	.pg_nvers		= NFSD_ACL_NRVERS,
	.pg_vers		= nfsd_acl_versions,
	.pg_name		= "nfsacl",
	.pg_class		= "nfsd",
	.pg_stats		= &nfsd_acl_svcstats,
	.pg_authenticate	= &svc_set_client,
};

static struct svc_stat	nfsd_acl_svcstats = {
	.program	= &nfsd_acl_program,
};
#endif /* defined(CONFIG_NFSD_V2_ACL) || defined(CONFIG_NFSD_V3_ACL) */

static const struct svc_version *nfsd_version[] = {
	[2] = &nfsd_version2,
#if defined(CONFIG_NFSD_V3)
	[3] = &nfsd_version3,
#endif
#if defined(CONFIG_NFSD_V4)
	[4] = &nfsd_version4,
#endif
};

#define NFSD_MINVERS    	2
#define NFSD_NRVERS		ARRAY_SIZE(nfsd_version)
static const struct svc_version *nfsd_versions[NFSD_NRVERS];

struct svc_program		nfsd_program = {
#if defined(CONFIG_NFSD_V2_ACL) || defined(CONFIG_NFSD_V3_ACL)
	.pg_next		= &nfsd_acl_program,
#endif
	.pg_prog		= NFS_PROGRAM,		/* program number */
	.pg_nvers		= NFSD_NRVERS,		/* nr of entries in nfsd_version */
	.pg_vers		= nfsd_versions,	/* version table */
	.pg_name		= "nfsd",		/* program name */
	.pg_class		= "nfsd",		/* authentication class */
	.pg_stats		= &nfsd_svcstats,	/* version table */
	.pg_authenticate	= &svc_set_client,	/* export authentication */

};

static bool nfsd_supported_minorversions[NFSD_SUPPORTED_MINOR_VERSION + 1] = {
	[0] = 1,
	[1] = 1,
	[2] = 1,
};

int nfsd_vers(int vers, enum vers_op change)
{
	if (vers < NFSD_MINVERS || vers >= NFSD_NRVERS)
		return 0;
	switch(change) {
	case NFSD_SET:
		nfsd_versions[vers] = nfsd_version[vers];
#if defined(CONFIG_NFSD_V2_ACL) || defined(CONFIG_NFSD_V3_ACL)
		if (vers < NFSD_ACL_NRVERS)
			nfsd_acl_versions[vers] = nfsd_acl_version[vers];
#endif
		break;
	case NFSD_CLEAR:
		nfsd_versions[vers] = NULL;
#if defined(CONFIG_NFSD_V2_ACL) || defined(CONFIG_NFSD_V3_ACL)
		if (vers < NFSD_ACL_NRVERS)
			nfsd_acl_versions[vers] = NULL;
#endif
		break;
	case NFSD_TEST:
		return nfsd_versions[vers] != NULL;
	case NFSD_AVAIL:
		return nfsd_version[vers] != NULL;
	}
	return 0;
}

static void
nfsd_adjust_nfsd_versions4(void)
{
	unsigned i;

	for (i = 0; i <= NFSD_SUPPORTED_MINOR_VERSION; i++) {
		if (nfsd_supported_minorversions[i])
			return;
	}
	nfsd_vers(4, NFSD_CLEAR);
}

int nfsd_minorversion(u32 minorversion, enum vers_op change)
{
	if (minorversion > NFSD_SUPPORTED_MINOR_VERSION &&
	    change != NFSD_AVAIL)
		return -1;
	switch(change) {
	case NFSD_SET:
		nfsd_supported_minorversions[minorversion] = true;
		nfsd_vers(4, NFSD_SET);
		break;
	case NFSD_CLEAR:
		nfsd_supported_minorversions[minorversion] = false;
		nfsd_adjust_nfsd_versions4();
		break;
	case NFSD_TEST:
		return nfsd_supported_minorversions[minorversion];
	case NFSD_AVAIL:
		return minorversion <= NFSD_SUPPORTED_MINOR_VERSION;
	}
	return 0;
}

/*
 * Maximum number of nfsd processes
 */
#define	NFSD_MAXSERVS		8192

int nfsd_nrthreads(struct net *net)
{
	int rv = 0;
	struct nfsd_net *nn = net_generic(net, nfsd_net_id);

	mutex_lock(&nfsd_mutex);
	if (nn->nfsd_serv)
		rv = nn->nfsd_serv->sv_nrthreads;
	mutex_unlock(&nfsd_mutex);
	return rv;
}

static int nfsd_init_socks(struct net *net)
{
	int error;
	struct nfsd_net *nn = net_generic(net, nfsd_net_id);

	if (!list_empty(&nn->nfsd_serv->sv_permsocks))
		return 0;

	error = svc_create_xprt(nn->nfsd_serv, "udp", net, PF_INET, NFS_PORT,
					SVC_SOCK_DEFAULTS);
	if (error < 0)
		return error;

	error = svc_create_xprt(nn->nfsd_serv, "tcp", net, PF_INET, NFS_PORT,
					SVC_SOCK_DEFAULTS);
	if (error < 0)
		return error;

	return 0;
}

static int nfsd_users = 0;

static int nfsd_startup_generic(int nrservs)
{
	int ret;

	if (nfsd_users++)
		return 0;

	/*
	 * Readahead param cache - will no-op if it already exists.
	 * (Note therefore results will be suboptimal if number of
	 * threads is modified after nfsd start.)
	 */
	ret = nfsd_racache_init(2*nrservs);
	if (ret)
		goto dec_users;

	ret = nfs4_state_start();
	if (ret)
		goto out_racache;
	return 0;

out_racache:
	nfsd_racache_shutdown();
dec_users:
	nfsd_users--;
	return ret;
}

static void nfsd_shutdown_generic(void)
{
	if (--nfsd_users)
		return;

	nfs4_state_shutdown();
	nfsd_racache_shutdown();
}

static bool nfsd_needs_lockd(void)
{
#if defined(CONFIG_NFSD_V3)
	return (nfsd_versions[2] != NULL) || (nfsd_versions[3] != NULL);
#else
	return (nfsd_versions[2] != NULL);
#endif
}

static int nfsd_startup_net(int nrservs, struct net *net)
{
	struct nfsd_net *nn = net_generic(net, nfsd_net_id);
	int ret;

	if (nn->nfsd_net_up)
		return 0;

	ret = nfsd_startup_generic(nrservs);
	if (ret)
		return ret;
	ret = nfsd_init_socks(net);
	if (ret)
		goto out_socks;

	if (nfsd_needs_lockd() && !nn->lockd_up) {
		ret = lockd_up(net);
		if (ret)
			goto out_socks;
		nn->lockd_up = 1;
	}

	ret = nfs4_state_start_net(net);
	if (ret)
		goto out_lockd;

	nn->nfsd_net_up = true;
	return 0;

out_lockd:
	if (nn->lockd_up) {
		lockd_down(net);
		nn->lockd_up = 0;
	}
out_socks:
	nfsd_shutdown_generic();
	return ret;
}

static void nfsd_shutdown_net(struct net *net)
{
	struct nfsd_net *nn = net_generic(net, nfsd_net_id);

	nfs4_state_shutdown_net(net);
	if (nn->lockd_up) {
		lockd_down(net);
		nn->lockd_up = 0;
	}
	nn->nfsd_net_up = false;
	nfsd_shutdown_generic();
}

static int nfsd_inetaddr_event(struct notifier_block *this, unsigned long event,
	void *ptr)
{
	struct in_ifaddr *ifa = (struct in_ifaddr *)ptr;
	struct net_device *dev = ifa->ifa_dev->dev;
	struct net *net = dev_net(dev);
	struct nfsd_net *nn = net_generic(net, nfsd_net_id);
	struct sockaddr_in sin;

	if ((event != NETDEV_DOWN) ||
	    !atomic_inc_not_zero(&nn->ntf_refcnt))
		goto out;

	if (nn->nfsd_serv) {
		dprintk("nfsd_inetaddr_event: removed %pI4\n", &ifa->ifa_local);
		sin.sin_family = AF_INET;
		sin.sin_addr.s_addr = ifa->ifa_local;
		svc_age_temp_xprts_now(nn->nfsd_serv, (struct sockaddr *)&sin);
	}
	atomic_dec(&nn->ntf_refcnt);
	wake_up(&nn->ntf_wq);

out:
	return NOTIFY_DONE;
}

static struct notifier_block nfsd_inetaddr_notifier = {
	.notifier_call = nfsd_inetaddr_event,
};

#if IS_ENABLED(CONFIG_IPV6)
static int nfsd_inet6addr_event(struct notifier_block *this,
	unsigned long event, void *ptr)
{
	struct inet6_ifaddr *ifa = (struct inet6_ifaddr *)ptr;
	struct net_device *dev = ifa->idev->dev;
	struct net *net = dev_net(dev);
	struct nfsd_net *nn = net_generic(net, nfsd_net_id);
	struct sockaddr_in6 sin6;

	if ((event != NETDEV_DOWN) ||
	    !atomic_inc_not_zero(&nn->ntf_refcnt))
		goto out;

	if (nn->nfsd_serv) {
		dprintk("nfsd_inet6addr_event: removed %pI6\n", &ifa->addr);
		sin6.sin6_family = AF_INET6;
		sin6.sin6_addr = ifa->addr;
		if (ipv6_addr_type(&sin6.sin6_addr) & IPV6_ADDR_LINKLOCAL)
			sin6.sin6_scope_id = ifa->idev->dev->ifindex;
		svc_age_temp_xprts_now(nn->nfsd_serv, (struct sockaddr *)&sin6);
	}
	atomic_dec(&nn->ntf_refcnt);
	wake_up(&nn->ntf_wq);
out:
	return NOTIFY_DONE;
}

static struct notifier_block nfsd_inet6addr_notifier = {
	.notifier_call = nfsd_inet6addr_event,
};
#endif

/* Only used under nfsd_mutex, so this atomic may be overkill: */
static atomic_t nfsd_notifier_refcount = ATOMIC_INIT(0);

static void nfsd_last_thread(struct svc_serv *serv, struct net *net)
{
	struct nfsd_net *nn = net_generic(net, nfsd_net_id);

	atomic_dec(&nn->ntf_refcnt);
	/* check if the notifier still has clients */
	if (atomic_dec_return(&nfsd_notifier_refcount) == 0) {
		unregister_inetaddr_notifier(&nfsd_inetaddr_notifier);
#if IS_ENABLED(CONFIG_IPV6)
		unregister_inet6addr_notifier(&nfsd_inet6addr_notifier);
#endif
	}
	wait_event(nn->ntf_wq, atomic_read(&nn->ntf_refcnt) == 0);

	/*
	 * write_ports can create the server without actually starting
	 * any threads--if we get shut down before any threads are
	 * started, then nfsd_last_thread will be run before any of this
	 * other initialization has been done except the rpcb information.
	 */
	svc_rpcb_cleanup(serv, net);
	if (!nn->nfsd_net_up)
		return;

	nfsd_shutdown_net(net);
	printk(KERN_WARNING "nfsd: last server has exited, flushing export "
			    "cache\n");
	nfsd_export_flush(net);
}

void nfsd_reset_versions(void)
{
	int i;

	for (i = 0; i < NFSD_NRVERS; i++)
		if (nfsd_vers(i, NFSD_TEST))
			return;

	for (i = 0; i < NFSD_NRVERS; i++)
		if (i != 4)
			nfsd_vers(i, NFSD_SET);
		else {
			int minor = 0;
			while (nfsd_minorversion(minor, NFSD_SET) >= 0)
				minor++;
		}
}

/*
 * Each session guarantees a negotiated per slot memory cache for replies
 * which in turn consumes memory beyond the v2/v3/v4.0 server. A dedicated
 * NFSv4.1 server might want to use more memory for a DRC than a machine
 * with mutiple services.
 *
 * Impose a hard limit on the number of pages for the DRC which varies
 * according to the machines free pages. This is of course only a default.
 *
 * For now this is a #defined shift which could be under admin control
 * in the future.
 */
static void set_max_drc(void)
{
	#define NFSD_DRC_SIZE_SHIFT	7
	nfsd_drc_max_mem = (nr_free_buffer_pages()
					>> NFSD_DRC_SIZE_SHIFT) * PAGE_SIZE;
	nfsd_drc_mem_used = 0;
	spin_lock_init(&nfsd_drc_lock);
	dprintk("%s nfsd_drc_max_mem %lu \n", __func__, nfsd_drc_max_mem);
}

static int nfsd_get_default_max_blksize(void)
{
	struct sysinfo i;
	unsigned long long target;
	unsigned long ret;

	si_meminfo(&i);
	target = (i.totalram - i.totalhigh) << PAGE_SHIFT;
	/*
	 * Aim for 1/4096 of memory per thread This gives 1MB on 4Gig
	 * machines, but only uses 32K on 128M machines.  Bottom out at
	 * 8K on 32M and smaller.  Of course, this is only a default.
	 */
	target >>= 12;

	ret = NFSSVC_MAXBLKSIZE;
	while (ret > target && ret >= 8*1024*2)
		ret /= 2;
	return ret;
}

static const struct svc_serv_ops nfsd_thread_sv_ops = {
	.svo_shutdown		= nfsd_last_thread,
	.svo_function		= nfsd,
	.svo_enqueue_xprt	= svc_xprt_do_enqueue,
	.svo_setup		= svc_set_num_threads,
	.svo_module		= THIS_MODULE,
};

int nfsd_create_serv(struct net *net)
{
	int error;
	struct nfsd_net *nn = net_generic(net, nfsd_net_id);

	WARN_ON(!mutex_is_locked(&nfsd_mutex));
	if (nn->nfsd_serv) {
		svc_get(nn->nfsd_serv);
		return 0;
	}
	if (nfsd_max_blksize == 0)
		nfsd_max_blksize = nfsd_get_default_max_blksize();
	nfsd_reset_versions();
	nn->nfsd_serv = svc_create_pooled(&nfsd_program, nfsd_max_blksize,
						&nfsd_thread_sv_ops);
	if (nn->nfsd_serv == NULL)
		return -ENOMEM;

	nn->nfsd_serv->sv_maxconn = nn->max_connections;
	error = svc_bind(nn->nfsd_serv, net);
	if (error < 0) {
		svc_destroy(nn->nfsd_serv);
		return error;
	}

	set_max_drc();
	/* check if the notifier is already set */
	if (atomic_inc_return(&nfsd_notifier_refcount) == 1) {
		register_inetaddr_notifier(&nfsd_inetaddr_notifier);
#if IS_ENABLED(CONFIG_IPV6)
		register_inet6addr_notifier(&nfsd_inet6addr_notifier);
#endif
	}
	atomic_inc(&nn->ntf_refcnt);
	ktime_get_real_ts64(&nn->nfssvc_boot); /* record boot time */
	return 0;
}

int nfsd_nrpools(struct net *net)
{
	struct nfsd_net *nn = net_generic(net, nfsd_net_id);

	if (nn->nfsd_serv == NULL)
		return 0;
	else
		return nn->nfsd_serv->sv_nrpools;
}

int nfsd_get_nrthreads(int n, int *nthreads, struct net *net)
{
	int i = 0;
	struct nfsd_net *nn = net_generic(net, nfsd_net_id);

	if (nn->nfsd_serv != NULL) {
		for (i = 0; i < nn->nfsd_serv->sv_nrpools && i < n; i++)
			nthreads[i] = nn->nfsd_serv->sv_pools[i].sp_nrthreads;
	}

	return 0;
}

void nfsd_destroy(struct net *net)
{
	struct nfsd_net *nn = net_generic(net, nfsd_net_id);
	int destroy = (nn->nfsd_serv->sv_nrthreads == 1);

	if (destroy)
		svc_shutdown_net(nn->nfsd_serv, net);
	svc_destroy(nn->nfsd_serv);
	if (destroy)
		nn->nfsd_serv = NULL;
}

int nfsd_set_nrthreads(int n, int *nthreads, struct net *net)
{
	int i = 0;
	int tot = 0;
	int err = 0;
	struct nfsd_net *nn = net_generic(net, nfsd_net_id);

	WARN_ON(!mutex_is_locked(&nfsd_mutex));

	if (nn->nfsd_serv == NULL || n <= 0)
		return 0;

	if (n > nn->nfsd_serv->sv_nrpools)
		n = nn->nfsd_serv->sv_nrpools;

	/* enforce a global maximum number of threads */
	tot = 0;
	for (i = 0; i < n; i++) {
		nthreads[i] = min(nthreads[i], NFSD_MAXSERVS);
		tot += nthreads[i];
	}
	if (tot > NFSD_MAXSERVS) {
		/* total too large: scale down requested numbers */
		for (i = 0; i < n && tot > 0; i++) {
		    	int new = nthreads[i] * NFSD_MAXSERVS / tot;
			tot -= (nthreads[i] - new);
			nthreads[i] = new;
		}
		for (i = 0; i < n && tot > 0; i++) {
			nthreads[i]--;
			tot--;
		}
	}

	/*
	 * There must always be a thread in pool 0; the admin
	 * can't shut down NFS completely using pool_threads.
	 */
	if (nthreads[0] == 0)
		nthreads[0] = 1;

	/* apply the new numbers */
	svc_get(nn->nfsd_serv);
	for (i = 0; i < n; i++) {
		err = nn->nfsd_serv->sv_ops->svo_setup(nn->nfsd_serv,
				&nn->nfsd_serv->sv_pools[i], nthreads[i]);
		if (err)
			break;
	}
	nfsd_destroy(net);
	return err;
}

/*
 * Adjust the number of threads and return the new number of threads.
 * This is also the function that starts the server if necessary, if
 * this is the first time nrservs is nonzero.
 */
int
nfsd_svc(int nrservs, struct net *net)
{
	int	error;
	bool	nfsd_up_before;
	struct nfsd_net *nn = net_generic(net, nfsd_net_id);

	mutex_lock(&nfsd_mutex);
	dprintk("nfsd: creating service\n");

	nrservs = max(nrservs, 0);
	nrservs = min(nrservs, NFSD_MAXSERVS);
	error = 0;

	if (nrservs == 0 && nn->nfsd_serv == NULL)
		goto out;

	error = nfsd_create_serv(net);
	if (error)
		goto out;

	nfsd_up_before = nn->nfsd_net_up;

	error = nfsd_startup_net(nrservs, net);
	if (error)
		goto out_destroy;
	error = nn->nfsd_serv->sv_ops->svo_setup(nn->nfsd_serv,
			NULL, nrservs);
	if (error)
		goto out_shutdown;
	/* We are holding a reference to nn->nfsd_serv which
	 * we don't want to count in the return value,
	 * so subtract 1
	 */
	error = nn->nfsd_serv->sv_nrthreads - 1;
out_shutdown:
	if (error < 0 && !nfsd_up_before)
		nfsd_shutdown_net(net);
out_destroy:
	nfsd_destroy(net);		/* Release server */
out:
	mutex_unlock(&nfsd_mutex);
	return error;
}


/*
 * This is the NFS server kernel thread
 */
static int
nfsd(void *vrqstp)
{
	struct svc_rqst *rqstp = (struct svc_rqst *) vrqstp;
	struct svc_xprt *perm_sock = list_entry(rqstp->rq_server->sv_permsocks.next, typeof(struct svc_xprt), xpt_list);
	struct net *net = perm_sock->xpt_net;
	struct nfsd_net *nn = net_generic(net, nfsd_net_id);
	int err;

	/* Lock module and set up kernel thread */
	mutex_lock(&nfsd_mutex);

	/* At this point, the thread shares current->fs
	 * with the init process. We need to create files with the
	 * umask as defined by the client instead of init's umask. */
	if (unshare_fs_struct() < 0) {
		printk("Unable to start nfsd thread: out of memory\n");
		goto out;
	}

	current->fs->umask = 0;

	/*
	 * thread is spawned with all signals set to SIG_IGN, re-enable
	 * the ones that will bring down the thread
	 */
	allow_signal(SIGKILL);
	allow_signal(SIGHUP);
	allow_signal(SIGINT);
	allow_signal(SIGQUIT);

	nfsdstats.th_cnt++;
	mutex_unlock(&nfsd_mutex);

	set_freezable();

	/*
	 * The main request loop
	 */
	for (;;) {
		/* Update sv_maxconn if it has changed */
		rqstp->rq_server->sv_maxconn = nn->max_connections;

		/*
		 * Find a socket with data available and call its
		 * recvfrom routine.
		 */
		while ((err = svc_recv(rqstp, 60*60*HZ)) == -EAGAIN)
			;
		if (err == -EINTR)
			break;
		validate_process_creds();
		svc_process(rqstp);
		validate_process_creds();
	}

	/* Clear signals before calling svc_exit_thread() */
	flush_signals(current);

	mutex_lock(&nfsd_mutex);
	nfsdstats.th_cnt --;

out:
	rqstp->rq_server = NULL;

	/* Release the thread */
	svc_exit_thread(rqstp);

	nfsd_destroy(net);

	/* Release module */
	mutex_unlock(&nfsd_mutex);
	module_put_and_exit(0);
	return 0;
}

static __be32 map_new_errors(u32 vers, __be32 nfserr)
{
	if (nfserr == nfserr_jukebox && vers == 2)
		return nfserr_dropit;
	if (nfserr == nfserr_wrongsec && vers < 4)
		return nfserr_acces;
	return nfserr;
}

/*
 * A write procedure can have a large argument, and a read procedure can
 * have a large reply, but no NFSv2 or NFSv3 procedure has argument and
 * reply that can both be larger than a page.  The xdr code has taken
 * advantage of this assumption to be a sloppy about bounds checking in
 * some cases.  Pending a rewrite of the NFSv2/v3 xdr code to fix that
 * problem, we enforce these assumptions here:
 */
static bool nfs_request_too_big(struct svc_rqst *rqstp,
				const struct svc_procedure *proc)
{
	/*
	 * The ACL code has more careful bounds-checking and is not
	 * susceptible to this problem:
	 */
	if (rqstp->rq_prog != NFS_PROGRAM)
		return false;
	/*
	 * Ditto NFSv4 (which can in theory have argument and reply both
	 * more than a page):
	 */
	if (rqstp->rq_vers >= 4)
		return false;
	/* The reply will be small, we're OK: */
	if (proc->pc_xdrressize > 0 &&
	    proc->pc_xdrressize < XDR_QUADLEN(PAGE_SIZE))
		return false;

	return rqstp->rq_arg.len > PAGE_SIZE;
}

int
nfsd_dispatch(struct svc_rqst *rqstp, __be32 *statp)
{
	const struct svc_procedure *proc;
	__be32			nfserr;
	__be32			*nfserrp;

	dprintk("nfsd_dispatch: vers %d proc %d\n",
				rqstp->rq_vers, rqstp->rq_proc);
	proc = rqstp->rq_procinfo;

	if (nfs_request_too_big(rqstp, proc)) {
		dprintk("nfsd: NFSv%d argument too large\n", rqstp->rq_vers);
		*statp = rpc_garbage_args;
		return 1;
	}
	/*
	 * Give the xdr decoder a chance to change this if it wants
	 * (necessary in the NFSv4.0 compound case)
	 */
	rqstp->rq_cachetype = proc->pc_cachetype;
	/* Decode arguments */
	if (proc->pc_decode &&
	    !proc->pc_decode(rqstp, (__be32*)rqstp->rq_arg.head[0].iov_base)) {
		dprintk("nfsd: failed to decode arguments!\n");
		*statp = rpc_garbage_args;
		return 1;
	}

	/* Check whether we have this call in the cache. */
	switch (nfsd_cache_lookup(rqstp)) {
	case RC_DROPIT:
		return 0;
	case RC_REPLY:
		return 1;
	case RC_DOIT:;
		/* do it */
	}

	/* need to grab the location to store the status, as
	 * nfsv4 does some encoding while processing
	 */
	nfserrp = rqstp->rq_res.head[0].iov_base
		+ rqstp->rq_res.head[0].iov_len;
	rqstp->rq_res.head[0].iov_len += sizeof(__be32);

	/* Now call the procedure handler, and encode NFS status. */
	nfserr = proc->pc_func(rqstp);
	nfserr = map_new_errors(rqstp->rq_vers, nfserr);
	if (nfserr == nfserr_dropit || test_bit(RQ_DROPME, &rqstp->rq_flags)) {
		dprintk("nfsd: Dropping request; may be revisited later\n");
		nfsd_cache_update(rqstp, RC_NOCACHE, NULL);
		return 0;
	}

	if (rqstp->rq_proc != 0)
		*nfserrp++ = nfserr;

	/* Encode result.
	 * For NFSv2, additional info is never returned in case of an error.
	 */
	if (!(nfserr && rqstp->rq_vers == 2)) {
		if (proc->pc_encode && !proc->pc_encode(rqstp, nfserrp)) {
			/* Failed to encode result. Release cache entry */
			dprintk("nfsd: failed to encode result!\n");
			nfsd_cache_update(rqstp, RC_NOCACHE, NULL);
			*statp = rpc_system_err;
			return 1;
		}
	}

	/* Store reply in cache. */
	nfsd_cache_update(rqstp, rqstp->rq_cachetype, statp + 1);
	return 1;
}

int nfsd_pool_stats_open(struct inode *inode, struct file *file)
{
	int ret;
	struct nfsd_net *nn = net_generic(inode->i_sb->s_fs_info, nfsd_net_id);

	mutex_lock(&nfsd_mutex);
	if (nn->nfsd_serv == NULL) {
		mutex_unlock(&nfsd_mutex);
		return -ENODEV;
	}
	/* bump up the psudo refcount while traversing */
	svc_get(nn->nfsd_serv);
	ret = svc_pool_stats_open(nn->nfsd_serv, file);
	mutex_unlock(&nfsd_mutex);
	return ret;
}

int nfsd_pool_stats_release(struct inode *inode, struct file *file)
{
	int ret = seq_release(inode, file);
	struct net *net = inode->i_sb->s_fs_info;

	mutex_lock(&nfsd_mutex);
	/* this function really, really should have been called svc_put() */
	nfsd_destroy(net);
	mutex_unlock(&nfsd_mutex);
	return ret;
}