fs/nfs/dns_resolve.c - linux - Git at Google

 // SPDX-License-Identifier: GPL-2.0
 /*
  * linux/fs/nfs/dns_resolve.c
  *
  * Copyright (c) 2009 Trond Myklebust <Trond.Myklebust@netapp.com>
  *
  * Resolves DNS hostnames into valid ip addresses
  */

 #ifdef CONFIG_NFS_USE_KERNEL_DNS

 #include <linux/module.h>
 #include <linux/sunrpc/clnt.h>
 #include <linux/sunrpc/addr.h>
 #include <linux/dns_resolver.h>
 #include "dns_resolve.h"

 ssize_t nfs_dns_resolve_name(struct net *net, char *name, size_t namelen,
 		struct sockaddr *sa, size_t salen)
 {
 	ssize_t ret;
 	char *ip_addr = NULL;
 	int ip_len;

 	ip_len = dns_query(net, NULL, name, namelen, NULL, &ip_addr, NULL,
 			   false);
 	if (ip_len > 0)
 		ret = rpc_pton(net, ip_addr, ip_len, sa, salen);
 	else
 		ret = -ESRCH;
 	kfree(ip_addr);
 	return ret;
 }

 #else

 #include <linux/module.h>
 #include <linux/hash.h>
 #include <linux/string.h>
 #include <linux/kmod.h>
 #include <linux/slab.h>
 #include <linux/module.h>
 #include <linux/socket.h>
 #include <linux/seq_file.h>
 #include <linux/inet.h>
 #include <linux/sunrpc/clnt.h>
 #include <linux/sunrpc/addr.h>
 #include <linux/sunrpc/cache.h>
 #include <linux/sunrpc/svcauth.h>
 #include <linux/sunrpc/rpc_pipe_fs.h>
 #include <linux/nfs_fs.h>

 #include "nfs4_fs.h"
 #include "dns_resolve.h"
 #include "cache_lib.h"
 #include "netns.h"

 #define NFS_DNS_HASHBITS 4
 #define NFS_DNS_HASHTBL_SIZE (1 << NFS_DNS_HASHBITS)

 struct nfs_dns_ent {
 	struct cache_head h;

 	char *hostname;
 	size_t namelen;

 	struct sockaddr_storage addr;
 	size_t addrlen;
 	struct rcu_head rcu_head;
 };


 static void nfs_dns_ent_update(struct cache_head *cnew,
 		struct cache_head *ckey)
 {
 	struct nfs_dns_ent *new;
 	struct nfs_dns_ent *key;

 	new = container_of(cnew, struct nfs_dns_ent, h);
 	key = container_of(ckey, struct nfs_dns_ent, h);

 	memcpy(&new->addr, &key->addr, key->addrlen);
 	new->addrlen = key->addrlen;
 }

 static void nfs_dns_ent_init(struct cache_head *cnew,
 		struct cache_head *ckey)
 {
 	struct nfs_dns_ent *new;
 	struct nfs_dns_ent *key;

 	new = container_of(cnew, struct nfs_dns_ent, h);
 	key = container_of(ckey, struct nfs_dns_ent, h);

 	kfree(new->hostname);
 	new->hostname = kstrndup(key->hostname, key->namelen, GFP_KERNEL);
 	if (new->hostname) {
 		new->namelen = key->namelen;
 		nfs_dns_ent_update(cnew, ckey);
 	} else {
 		new->namelen = 0;
 		new->addrlen = 0;
 	}
 }

 static void nfs_dns_ent_free_rcu(struct rcu_head *head)
 {
 	struct nfs_dns_ent *item;

 	item = container_of(head, struct nfs_dns_ent, rcu_head);
 	kfree(item->hostname);
 	kfree(item);
 }

 static void nfs_dns_ent_put(struct kref *ref)
 {
 	struct nfs_dns_ent *item;

 	item = container_of(ref, struct nfs_dns_ent, h.ref);
 	call_rcu(&item->rcu_head, nfs_dns_ent_free_rcu);
 }

 static struct cache_head *nfs_dns_ent_alloc(void)
 {
 	struct nfs_dns_ent *item = kmalloc(sizeof(*item), GFP_KERNEL);

 	if (item != NULL) {
 		item->hostname = NULL;
 		item->namelen = 0;
 		item->addrlen = 0;
 		return &item->h;
 	}
 	return NULL;
 };

 static unsigned int nfs_dns_hash(const struct nfs_dns_ent *key)
 {
 	return hash_str(key->hostname, NFS_DNS_HASHBITS);
 }

 static void nfs_dns_request(struct cache_detail *cd,
 		struct cache_head *ch,
 		char **bpp, int *blen)
 {
 	struct nfs_dns_ent *key = container_of(ch, struct nfs_dns_ent, h);

 	qword_add(bpp, blen, key->hostname);
 	(*bpp)[-1] = '\n';
 }

 static int nfs_dns_upcall(struct cache_detail *cd,
 		struct cache_head *ch)
 {
 	struct nfs_dns_ent *key = container_of(ch, struct nfs_dns_ent, h);
 	int ret;

 	ret = nfs_cache_upcall(cd, key->hostname);
 	if (ret)
 		ret = sunrpc_cache_pipe_upcall(cd, ch);
 	return ret;
 }

 static int nfs_dns_match(struct cache_head *ca,
 		struct cache_head *cb)
 {
 	struct nfs_dns_ent *a;
 	struct nfs_dns_ent *b;

 	a = container_of(ca, struct nfs_dns_ent, h);
 	b = container_of(cb, struct nfs_dns_ent, h);

 	if (a->namelen == 0 || a->namelen != b->namelen)
 		return 0;
 	return memcmp(a->hostname, b->hostname, a->namelen) == 0;
 }

 static int nfs_dns_show(struct seq_file *m, struct cache_detail *cd,
 		struct cache_head *h)
 {
 	struct nfs_dns_ent *item;
 	long ttl;

 	if (h == NULL) {
 		seq_puts(m, "# ip address      hostname        ttl\n");
 		return 0;
 	}
 	item = container_of(h, struct nfs_dns_ent, h);
 	ttl = item->h.expiry_time - seconds_since_boot();
 	if (ttl < 0)
 		ttl = 0;

 	if (!test_bit(CACHE_NEGATIVE, &h->flags)) {
 		char buf[INET6_ADDRSTRLEN+IPV6_SCOPE_ID_LEN+1];

 		rpc_ntop((struct sockaddr *)&item->addr, buf, sizeof(buf));
 		seq_printf(m, "%15s ", buf);
 	} else
 		seq_puts(m, "<none>          ");
 	seq_printf(m, "%15s %ld\n", item->hostname, ttl);
 	return 0;
 }

 static struct nfs_dns_ent *nfs_dns_lookup(struct cache_detail *cd,
 		struct nfs_dns_ent *key)
 {
 	struct cache_head *ch;

 	ch = sunrpc_cache_lookup_rcu(cd,
 			&key->h,
 			nfs_dns_hash(key));
 	if (!ch)
 		return NULL;
 	return container_of(ch, struct nfs_dns_ent, h);
 }

 static struct nfs_dns_ent *nfs_dns_update(struct cache_detail *cd,
 		struct nfs_dns_ent *new,
 		struct nfs_dns_ent *key)
 {
 	struct cache_head *ch;

 	ch = sunrpc_cache_update(cd,
 			&new->h, &key->h,
 			nfs_dns_hash(key));
 	if (!ch)
 		return NULL;
 	return container_of(ch, struct nfs_dns_ent, h);
 }

 static int nfs_dns_parse(struct cache_detail *cd, char *buf, int buflen)
 {
 	char buf1[NFS_DNS_HOSTNAME_MAXLEN+1];
 	struct nfs_dns_ent key, *item;
 	unsigned int ttl;
 	ssize_t len;
 	int ret = -EINVAL;

 	if (buf[buflen-1] != '\n')
 		goto out;
 	buf[buflen-1] = '\0';

 	len = qword_get(&buf, buf1, sizeof(buf1));
 	if (len <= 0)
 		goto out;
 	key.addrlen = rpc_pton(cd->net, buf1, len,
 			(struct sockaddr *)&key.addr,
 			sizeof(key.addr));

 	len = qword_get(&buf, buf1, sizeof(buf1));
 	if (len <= 0)
 		goto out;

 	key.hostname = buf1;
 	key.namelen = len;
 	memset(&key.h, 0, sizeof(key.h));

 	if (get_uint(&buf, &ttl) < 0)
 		goto out;
 	if (ttl == 0)
 		goto out;
 	key.h.expiry_time = ttl + seconds_since_boot();

 	ret = -ENOMEM;
 	item = nfs_dns_lookup(cd, &key);
 	if (item == NULL)
 		goto out;

 	if (key.addrlen == 0)
 		set_bit(CACHE_NEGATIVE, &key.h.flags);

 	item = nfs_dns_update(cd, &key, item);
 	if (item == NULL)
 		goto out;

 	ret = 0;
 	cache_put(&item->h, cd);
 out:
 	return ret;
 }

 static int do_cache_lookup(struct cache_detail *cd,
 		struct nfs_dns_ent *key,
 		struct nfs_dns_ent **item,
 		struct nfs_cache_defer_req *dreq)
 {
 	int ret = -ENOMEM;

 	*item = nfs_dns_lookup(cd, key);
 	if (*item) {
 		ret = cache_check(cd, &(*item)->h, &dreq->req);
 		if (ret)
 			*item = NULL;
 	}
 	return ret;
 }

 static int do_cache_lookup_nowait(struct cache_detail *cd,
 		struct nfs_dns_ent *key,
 		struct nfs_dns_ent **item)
 {
 	int ret = -ENOMEM;

 	*item = nfs_dns_lookup(cd, key);
 	if (!*item)
 		goto out_err;
 	ret = -ETIMEDOUT;
 	if (!test_bit(CACHE_VALID, &(*item)->h.flags)
 			|| (*item)->h.expiry_time < seconds_since_boot()
 			|| cd->flush_time > (*item)->h.last_refresh)
 		goto out_put;
 	ret = -ENOENT;
 	if (test_bit(CACHE_NEGATIVE, &(*item)->h.flags))
 		goto out_put;
 	return 0;
 out_put:
 	cache_put(&(*item)->h, cd);
 out_err:
 	*item = NULL;
 	return ret;
 }

 static int do_cache_lookup_wait(struct cache_detail *cd,
 		struct nfs_dns_ent *key,
 		struct nfs_dns_ent **item)
 {
 	struct nfs_cache_defer_req *dreq;
 	int ret = -ENOMEM;

 	dreq = nfs_cache_defer_req_alloc();
 	if (!dreq)
 		goto out;
 	ret = do_cache_lookup(cd, key, item, dreq);
 	if (ret == -EAGAIN) {
 		ret = nfs_cache_wait_for_upcall(dreq);
 		if (!ret)
 			ret = do_cache_lookup_nowait(cd, key, item);
 	}
 	nfs_cache_defer_req_put(dreq);
 out:
 	return ret;
 }

 ssize_t nfs_dns_resolve_name(struct net *net, char *name,
 		size_t namelen, struct sockaddr *sa, size_t salen)
 {
 	struct nfs_dns_ent key = {
 		.hostname = name,
 		.namelen = namelen,
 	};
 	struct nfs_dns_ent *item = NULL;
 	ssize_t ret;
 	struct nfs_net *nn = net_generic(net, nfs_net_id);

 	ret = do_cache_lookup_wait(nn->nfs_dns_resolve, &key, &item);
 	if (ret == 0) {
 		if (salen >= item->addrlen) {
 			memcpy(sa, &item->addr, item->addrlen);
 			ret = item->addrlen;
 		} else
 			ret = -EOVERFLOW;
 		cache_put(&item->h, nn->nfs_dns_resolve);
 	} else if (ret == -ENOENT)
 		ret = -ESRCH;
 	return ret;
 }

 static struct cache_detail nfs_dns_resolve_template = {
 	.owner		= THIS_MODULE,
 	.hash_size	= NFS_DNS_HASHTBL_SIZE,
 	.name		= "dns_resolve",
 	.cache_put	= nfs_dns_ent_put,
 	.cache_upcall	= nfs_dns_upcall,
 	.cache_request	= nfs_dns_request,
 	.cache_parse	= nfs_dns_parse,
 	.cache_show	= nfs_dns_show,
 	.match		= nfs_dns_match,
 	.init		= nfs_dns_ent_init,
 	.update		= nfs_dns_ent_update,
 	.alloc		= nfs_dns_ent_alloc,
 };


 int nfs_dns_resolver_cache_init(struct net *net)
 {
 	int err;
 	struct nfs_net *nn = net_generic(net, nfs_net_id);

 	nn->nfs_dns_resolve = cache_create_net(&nfs_dns_resolve_template, net);
 	if (IS_ERR(nn->nfs_dns_resolve))
 		return PTR_ERR(nn->nfs_dns_resolve);

 	err = nfs_cache_register_net(net, nn->nfs_dns_resolve);
 	if (err)
 		goto err_reg;
 	return 0;

 err_reg:
 	cache_destroy_net(nn->nfs_dns_resolve, net);
 	return err;
 }

 void nfs_dns_resolver_cache_destroy(struct net *net)
 {
 	struct nfs_net *nn = net_generic(net, nfs_net_id);

 	nfs_cache_unregister_net(net, nn->nfs_dns_resolve);
 	cache_destroy_net(nn->nfs_dns_resolve, net);
 }

 static int nfs4_dns_net_init(struct net *net)
 {
 	return nfs_dns_resolver_cache_init(net);
 }

 static void nfs4_dns_net_exit(struct net *net)
 {
 	nfs_dns_resolver_cache_destroy(net);
 }

 static struct pernet_operations nfs4_dns_resolver_ops = {
 	.init = nfs4_dns_net_init,
 	.exit = nfs4_dns_net_exit,
 };

 static int rpc_pipefs_event(struct notifier_block *nb, unsigned long event,
 			   void *ptr)
 {
 	struct super_block *sb = ptr;
 	struct net *net = sb->s_fs_info;
 	struct nfs_net *nn = net_generic(net, nfs_net_id);
 	struct cache_detail *cd = nn->nfs_dns_resolve;
 	int ret = 0;

 	if (cd == NULL)
 		return 0;

 	if (!try_module_get(THIS_MODULE))
 		return 0;

 	switch (event) {
 	case RPC_PIPEFS_MOUNT:
 		ret = nfs_cache_register_sb(sb, cd);
 		break;
 	case RPC_PIPEFS_UMOUNT:
 		nfs_cache_unregister_sb(sb, cd);
 		break;
 	default:
 		ret = -ENOTSUPP;
 		break;
 	}
 	module_put(THIS_MODULE);
 	return ret;
 }

 static struct notifier_block nfs_dns_resolver_block = {
 	.notifier_call	= rpc_pipefs_event,
 };

 int nfs_dns_resolver_init(void)
 {
 	int err;

 	err = register_pernet_subsys(&nfs4_dns_resolver_ops);
 	if (err < 0)
 		goto out;
 	err = rpc_pipefs_notifier_register(&nfs_dns_resolver_block);
 	if (err < 0)
 		goto out1;
 	return 0;
 out1:
 	unregister_pernet_subsys(&nfs4_dns_resolver_ops);
 out:
 	return err;
 }

 void nfs_dns_resolver_destroy(void)
 {
 	rpc_pipefs_notifier_unregister(&nfs_dns_resolver_block);
 	unregister_pernet_subsys(&nfs4_dns_resolver_ops);
 }
 #endif
	// SPDX-License-Identifier: GPL-2.0
	/*
	* linux/fs/nfs/dns_resolve.c
	*
	* Copyright (c) 2009 Trond Myklebust <Trond.Myklebust@netapp.com>
	*
	* Resolves DNS hostnames into valid ip addresses
	*/

	#ifdef CONFIG_NFS_USE_KERNEL_DNS

	#include <linux/module.h>
	#include <linux/sunrpc/clnt.h>
	#include <linux/sunrpc/addr.h>
	#include <linux/dns_resolver.h>
	#include "dns_resolve.h"

	ssize_t nfs_dns_resolve_name(struct net net, char name, size_t namelen,
	struct sockaddr *sa, size_t salen)
	{
	ssize_t ret;
	char *ip_addr = NULL;
	int ip_len;

	ip_len = dns_query(net, NULL, name, namelen, NULL, &ip_addr, NULL,
	false);
	if (ip_len > 0)
	ret = rpc_pton(net, ip_addr, ip_len, sa, salen);
	else
	ret = -ESRCH;
	kfree(ip_addr);
	return ret;
	}

	#else

	#include <linux/module.h>
	#include <linux/hash.h>
	#include <linux/string.h>
	#include <linux/kmod.h>
	#include <linux/slab.h>
	#include <linux/module.h>
	#include <linux/socket.h>
	#include <linux/seq_file.h>
	#include <linux/inet.h>
	#include <linux/sunrpc/clnt.h>
	#include <linux/sunrpc/addr.h>
	#include <linux/sunrpc/cache.h>
	#include <linux/sunrpc/svcauth.h>
	#include <linux/sunrpc/rpc_pipe_fs.h>
	#include <linux/nfs_fs.h>

	#include "nfs4_fs.h"
	#include "dns_resolve.h"
	#include "cache_lib.h"
	#include "netns.h"

	#define NFS_DNS_HASHBITS 4
	#define NFS_DNS_HASHTBL_SIZE (1 << NFS_DNS_HASHBITS)

	struct nfs_dns_ent {
	struct cache_head h;

	char *hostname;
	size_t namelen;

	struct sockaddr_storage addr;
	size_t addrlen;
	struct rcu_head rcu_head;
	};


	static void nfs_dns_ent_update(struct cache_head *cnew,
	struct cache_head *ckey)
	{
	struct nfs_dns_ent *new;
	struct nfs_dns_ent *key;

	new = container_of(cnew, struct nfs_dns_ent, h);
	key = container_of(ckey, struct nfs_dns_ent, h);

	memcpy(&new->addr, &key->addr, key->addrlen);
	new->addrlen = key->addrlen;
	}

	static void nfs_dns_ent_init(struct cache_head *cnew,
	struct cache_head *ckey)
	{
	struct nfs_dns_ent *new;
	struct nfs_dns_ent *key;

	new = container_of(cnew, struct nfs_dns_ent, h);
	key = container_of(ckey, struct nfs_dns_ent, h);

	kfree(new->hostname);
	new->hostname = kstrndup(key->hostname, key->namelen, GFP_KERNEL);
	if (new->hostname) {
	new->namelen = key->namelen;
	nfs_dns_ent_update(cnew, ckey);
	} else {
	new->namelen = 0;
	new->addrlen = 0;
	}
	}

	static void nfs_dns_ent_free_rcu(struct rcu_head *head)
	{
	struct nfs_dns_ent *item;

	item = container_of(head, struct nfs_dns_ent, rcu_head);
	kfree(item->hostname);
	kfree(item);
	}

	static void nfs_dns_ent_put(struct kref *ref)
	{
	struct nfs_dns_ent *item;

	item = container_of(ref, struct nfs_dns_ent, h.ref);
	call_rcu(&item->rcu_head, nfs_dns_ent_free_rcu);
	}

	static struct cache_head *nfs_dns_ent_alloc(void)
	{
	struct nfs_dns_ent item = kmalloc(sizeof(item), GFP_KERNEL);

	if (item != NULL) {
	item->hostname = NULL;
	item->namelen = 0;
	item->addrlen = 0;
	return &item->h;
	}
	return NULL;
	};

	static unsigned int nfs_dns_hash(const struct nfs_dns_ent *key)
	{
	return hash_str(key->hostname, NFS_DNS_HASHBITS);
	}

	static void nfs_dns_request(struct cache_detail *cd,
	struct cache_head *ch,
	char *bpp, int blen)
	{
	struct nfs_dns_ent *key = container_of(ch, struct nfs_dns_ent, h);

	qword_add(bpp, blen, key->hostname);
	(*bpp)[-1] = '\n';
	}

	static int nfs_dns_upcall(struct cache_detail *cd,
	struct cache_head *ch)
	{
	struct nfs_dns_ent *key = container_of(ch, struct nfs_dns_ent, h);
	int ret;

	ret = nfs_cache_upcall(cd, key->hostname);
	if (ret)
	ret = sunrpc_cache_pipe_upcall(cd, ch);
	return ret;
	}

	static int nfs_dns_match(struct cache_head *ca,
	struct cache_head *cb)
	{
	struct nfs_dns_ent *a;
	struct nfs_dns_ent *b;

	a = container_of(ca, struct nfs_dns_ent, h);
	b = container_of(cb, struct nfs_dns_ent, h);

	if (a->namelen == 0 \|\| a->namelen != b->namelen)
	return 0;
	return memcmp(a->hostname, b->hostname, a->namelen) == 0;
	}

	static int nfs_dns_show(struct seq_file m, struct cache_detail cd,
	struct cache_head *h)
	{
	struct nfs_dns_ent *item;
	long ttl;

	if (h == NULL) {
	seq_puts(m, "# ip address hostname ttl\n");
	return 0;
	}
	item = container_of(h, struct nfs_dns_ent, h);
	ttl = item->h.expiry_time - seconds_since_boot();
	if (ttl < 0)
	ttl = 0;

	if (!test_bit(CACHE_NEGATIVE, &h->flags)) {
	char buf[INET6_ADDRSTRLEN+IPV6_SCOPE_ID_LEN+1];

	rpc_ntop((struct sockaddr *)&item->addr, buf, sizeof(buf));
	seq_printf(m, "%15s ", buf);
	} else
	seq_puts(m, "<none> ");
	seq_printf(m, "%15s %ld\n", item->hostname, ttl);
	return 0;
	}

	static struct nfs_dns_ent nfs_dns_lookup(struct cache_detail cd,
	struct nfs_dns_ent *key)
	{
	struct cache_head *ch;

	ch = sunrpc_cache_lookup_rcu(cd,
	&key->h,
	nfs_dns_hash(key));
	if (!ch)
	return NULL;
	return container_of(ch, struct nfs_dns_ent, h);
	}

	static struct nfs_dns_ent nfs_dns_update(struct cache_detail cd,
	struct nfs_dns_ent *new,
	struct nfs_dns_ent *key)
	{
	struct cache_head *ch;

	ch = sunrpc_cache_update(cd,
	&new->h, &key->h,
	nfs_dns_hash(key));
	if (!ch)
	return NULL;
	return container_of(ch, struct nfs_dns_ent, h);
	}

	static int nfs_dns_parse(struct cache_detail cd, char buf, int buflen)
	{
	char buf1[NFS_DNS_HOSTNAME_MAXLEN+1];
	struct nfs_dns_ent key, *item;
	unsigned int ttl;
	ssize_t len;
	int ret = -EINVAL;

	if (buf[buflen-1] != '\n')
	goto out;
	buf[buflen-1] = '\0';

	len = qword_get(&buf, buf1, sizeof(buf1));
	if (len <= 0)
	goto out;
	key.addrlen = rpc_pton(cd->net, buf1, len,
	(struct sockaddr *)&key.addr,
	sizeof(key.addr));

	len = qword_get(&buf, buf1, sizeof(buf1));
	if (len <= 0)
	goto out;

	key.hostname = buf1;
	key.namelen = len;
	memset(&key.h, 0, sizeof(key.h));

	if (get_uint(&buf, &ttl) < 0)
	goto out;
	if (ttl == 0)
	goto out;
	key.h.expiry_time = ttl + seconds_since_boot();

	ret = -ENOMEM;
	item = nfs_dns_lookup(cd, &key);
	if (item == NULL)
	goto out;

	if (key.addrlen == 0)
	set_bit(CACHE_NEGATIVE, &key.h.flags);

	item = nfs_dns_update(cd, &key, item);
	if (item == NULL)
	goto out;

	ret = 0;
	cache_put(&item->h, cd);
	out:
	return ret;
	}

	static int do_cache_lookup(struct cache_detail *cd,
	struct nfs_dns_ent *key,
	struct nfs_dns_ent **item,
	struct nfs_cache_defer_req *dreq)
	{
	int ret = -ENOMEM;

	*item = nfs_dns_lookup(cd, key);
	if (*item) {
	ret = cache_check(cd, &(*item)->h, &dreq->req);
	if (ret)
	*item = NULL;
	}
	return ret;
	}

	static int do_cache_lookup_nowait(struct cache_detail *cd,
	struct nfs_dns_ent *key,
	struct nfs_dns_ent **item)
	{
	int ret = -ENOMEM;

	*item = nfs_dns_lookup(cd, key);
	if (!*item)
	goto out_err;
	ret = -ETIMEDOUT;
	if (!test_bit(CACHE_VALID, &(*item)->h.flags)
	\|\| (*item)->h.expiry_time < seconds_since_boot()
	\|\| cd->flush_time > (*item)->h.last_refresh)
	goto out_put;
	ret = -ENOENT;
	if (test_bit(CACHE_NEGATIVE, &(*item)->h.flags))
	goto out_put;
	return 0;
	out_put:
	cache_put(&(*item)->h, cd);
	out_err:
	*item = NULL;
	return ret;
	}

	static int do_cache_lookup_wait(struct cache_detail *cd,
	struct nfs_dns_ent *key,
	struct nfs_dns_ent **item)
	{
	struct nfs_cache_defer_req *dreq;
	int ret = -ENOMEM;

	dreq = nfs_cache_defer_req_alloc();
	if (!dreq)
	goto out;
	ret = do_cache_lookup(cd, key, item, dreq);
	if (ret == -EAGAIN) {
	ret = nfs_cache_wait_for_upcall(dreq);
	if (!ret)
	ret = do_cache_lookup_nowait(cd, key, item);
	}
	nfs_cache_defer_req_put(dreq);
	out:
	return ret;
	}

	ssize_t nfs_dns_resolve_name(struct net net, char name,
	size_t namelen, struct sockaddr *sa, size_t salen)
	{
	struct nfs_dns_ent key = {
	.hostname = name,
	.namelen = namelen,
	};
	struct nfs_dns_ent *item = NULL;
	ssize_t ret;
	struct nfs_net *nn = net_generic(net, nfs_net_id);

	ret = do_cache_lookup_wait(nn->nfs_dns_resolve, &key, &item);
	if (ret == 0) {
	if (salen >= item->addrlen) {
	memcpy(sa, &item->addr, item->addrlen);
	ret = item->addrlen;
	} else
	ret = -EOVERFLOW;
	cache_put(&item->h, nn->nfs_dns_resolve);
	} else if (ret == -ENOENT)
	ret = -ESRCH;
	return ret;
	}

	static struct cache_detail nfs_dns_resolve_template = {
	.owner = THIS_MODULE,
	.hash_size = NFS_DNS_HASHTBL_SIZE,
	.name = "dns_resolve",
	.cache_put = nfs_dns_ent_put,
	.cache_upcall = nfs_dns_upcall,
	.cache_request = nfs_dns_request,
	.cache_parse = nfs_dns_parse,
	.cache_show = nfs_dns_show,
	.match = nfs_dns_match,
	.init = nfs_dns_ent_init,
	.update = nfs_dns_ent_update,
	.alloc = nfs_dns_ent_alloc,
	};


	int nfs_dns_resolver_cache_init(struct net *net)
	{
	int err;
	struct nfs_net *nn = net_generic(net, nfs_net_id);

	nn->nfs_dns_resolve = cache_create_net(&nfs_dns_resolve_template, net);
	if (IS_ERR(nn->nfs_dns_resolve))
	return PTR_ERR(nn->nfs_dns_resolve);

	err = nfs_cache_register_net(net, nn->nfs_dns_resolve);
	if (err)
	goto err_reg;
	return 0;

	err_reg:
	cache_destroy_net(nn->nfs_dns_resolve, net);
	return err;
	}

	void nfs_dns_resolver_cache_destroy(struct net *net)
	{
	struct nfs_net *nn = net_generic(net, nfs_net_id);

	nfs_cache_unregister_net(net, nn->nfs_dns_resolve);
	cache_destroy_net(nn->nfs_dns_resolve, net);
	}

	static int nfs4_dns_net_init(struct net *net)
	{
	return nfs_dns_resolver_cache_init(net);
	}

	static void nfs4_dns_net_exit(struct net *net)
	{
	nfs_dns_resolver_cache_destroy(net);
	}

	static struct pernet_operations nfs4_dns_resolver_ops = {
	.init = nfs4_dns_net_init,
	.exit = nfs4_dns_net_exit,
	};

	static int rpc_pipefs_event(struct notifier_block *nb, unsigned long event,
	void *ptr)
	{
	struct super_block *sb = ptr;
	struct net *net = sb->s_fs_info;
	struct nfs_net *nn = net_generic(net, nfs_net_id);
	struct cache_detail *cd = nn->nfs_dns_resolve;
	int ret = 0;

	if (cd == NULL)
	return 0;

	if (!try_module_get(THIS_MODULE))
	return 0;

	switch (event) {
	case RPC_PIPEFS_MOUNT:
	ret = nfs_cache_register_sb(sb, cd);
	break;
	case RPC_PIPEFS_UMOUNT:
	nfs_cache_unregister_sb(sb, cd);
	break;
	default:
	ret = -ENOTSUPP;
	break;
	}
	module_put(THIS_MODULE);
	return ret;
	}

	static struct notifier_block nfs_dns_resolver_block = {
	.notifier_call = rpc_pipefs_event,
	};

	int nfs_dns_resolver_init(void)
	{
	int err;

	err = register_pernet_subsys(&nfs4_dns_resolver_ops);
	if (err < 0)
	goto out;
	err = rpc_pipefs_notifier_register(&nfs_dns_resolver_block);
	if (err < 0)
	goto out1;
	return 0;
	out1:
	unregister_pernet_subsys(&nfs4_dns_resolver_ops);
	out:
	return err;
	}

	void nfs_dns_resolver_destroy(void)
	{
	rpc_pipefs_notifier_unregister(&nfs_dns_resolver_block);
	unregister_pernet_subsys(&nfs4_dns_resolver_ops);
	}
	#endif