summaryrefslogtreecommitdiffstats
path: root/fs/lockd/host.c
blob: c8ab7d70390dcc48da2858c441d59998a7fbc5ce (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
/*
 * linux/fs/lockd/host.c
 *
 * Management for NLM peer hosts. The nlm_host struct is shared
 * between client and server implementation. The only reason to
 * do so is to reduce code bloat.
 *
 * Copyright (C) 1996, Olaf Kirch <okir@monad.swb.de>
 */

#include <linux/types.h>
#include <linux/slab.h>
#include <linux/in.h>
#include <linux/in6.h>
#include <linux/sunrpc/clnt.h>
#include <linux/sunrpc/svc.h>
#include <linux/lockd/lockd.h>
#include <linux/lockd/sm_inter.h>
#include <linux/mutex.h>

#include <net/ipv6.h>

#define NLMDBG_FACILITY		NLMDBG_HOSTCACHE
#define NLM_HOST_NRHASH		32
#define NLM_HOST_REBIND		(60 * HZ)
#define NLM_HOST_EXPIRE		(300 * HZ)
#define NLM_HOST_COLLECT	(120 * HZ)

static struct hlist_head	nlm_hosts[NLM_HOST_NRHASH];
static unsigned long		next_gc;
static int			nrhosts;
static DEFINE_MUTEX(nlm_host_mutex);

static void			nlm_gc_hosts(void);
static struct nsm_handle	*nsm_find(const struct sockaddr *sap,
						const size_t salen,
						const char *hostname,
						const size_t hostname_len,
						const int create);

struct nlm_lookup_host_info {
	const int		server;		/* search for server|client */
	const struct sockaddr	*sap;		/* address to search for */
	const size_t		salen;		/* it's length */
	const unsigned short	protocol;	/* transport to search for*/
	const u32		version;	/* NLM version to search for */
	const char		*hostname;	/* remote's hostname */
	const size_t		hostname_len;	/* it's length */
	const struct sockaddr	*src_sap;	/* our address (optional) */
	const size_t		src_len;	/* it's length */
};

/*
 * Hash function must work well on big- and little-endian platforms
 */
static unsigned int __nlm_hash32(const __be32 n)
{
	unsigned int hash = (__force u32)n ^ ((__force u32)n >> 16);
	return hash ^ (hash >> 8);
}

static unsigned int __nlm_hash_addr4(const struct sockaddr *sap)
{
	const struct sockaddr_in *sin = (struct sockaddr_in *)sap;
	return __nlm_hash32(sin->sin_addr.s_addr);
}

static unsigned int __nlm_hash_addr6(const struct sockaddr *sap)
{
	const struct sockaddr_in6 *sin6 = (struct sockaddr_in6 *)sap;
	const struct in6_addr addr = sin6->sin6_addr;
	return __nlm_hash32(addr.s6_addr32[0]) ^
	       __nlm_hash32(addr.s6_addr32[1]) ^
	       __nlm_hash32(addr.s6_addr32[2]) ^
	       __nlm_hash32(addr.s6_addr32[3]);
}

static unsigned int nlm_hash_address(const struct sockaddr *sap)
{
	unsigned int hash;

	switch (sap->sa_family) {
	case AF_INET:
		hash = __nlm_hash_addr4(sap);
		break;
	case AF_INET6:
		hash = __nlm_hash_addr6(sap);
		break;
	default:
		hash = 0;
	}
	return hash & (NLM_HOST_NRHASH - 1);
}

static void nlm_clear_port(struct sockaddr *sap)
{
	switch (sap->sa_family) {
	case AF_INET:
		((struct sockaddr_in *)sap)->sin_port = 0;
		break;
	case AF_INET6:
		((struct sockaddr_in6 *)sap)->sin6_port = 0;
		break;
	}
}

static void nlm_display_address(const struct sockaddr *sap,
				char *buf, const size_t len)
{
	const struct sockaddr_in *sin = (struct sockaddr_in *)sap;
	const struct sockaddr_in6 *sin6 = (struct sockaddr_in6 *)sap;

	switch (sap->sa_family) {
	case AF_UNSPEC:
		snprintf(buf, len, "unspecified");
		break;
	case AF_INET:
		snprintf(buf, len, NIPQUAD_FMT, NIPQUAD(sin->sin_addr.s_addr));
		break;
	case AF_INET6:
		if (ipv6_addr_v4mapped(&sin6->sin6_addr))
			snprintf(buf, len, NIPQUAD_FMT,
				 NIPQUAD(sin6->sin6_addr.s6_addr32[3]));
		else
			snprintf(buf, len, "%pI6", &sin6->sin6_addr);
		break;
	default:
		snprintf(buf, len, "unsupported address family");
		break;
	}
}

/*
 * Common host lookup routine for server & client
 */
static struct nlm_host *nlm_lookup_host(struct nlm_lookup_host_info *ni)
{
	struct hlist_head *chain;
	struct hlist_node *pos;
	struct nlm_host	*host;
	struct nsm_handle *nsm = NULL;

	mutex_lock(&nlm_host_mutex);

	if (time_after_eq(jiffies, next_gc))
		nlm_gc_hosts();

	/* We may keep several nlm_host objects for a peer, because each
	 * nlm_host is identified by
	 * (address, protocol, version, server/client)
	 * We could probably simplify this a little by putting all those
	 * different NLM rpc_clients into one single nlm_host object.
	 * This would allow us to have one nlm_host per address.
	 */
	chain = &nlm_hosts[nlm_hash_address(ni->sap)];
	hlist_for_each_entry(host, pos, chain, h_hash) {
		if (!nlm_cmp_addr(nlm_addr(host), ni->sap))
			continue;

		/* See if we have an NSM handle for this client */
		if (!nsm)
			nsm = host->h_nsmhandle;

		if (host->h_proto != ni->protocol)
			continue;
		if (host->h_version != ni->version)
			continue;
		if (host->h_server != ni->server)
			continue;
		if (!nlm_cmp_addr(nlm_srcaddr(host), ni->src_sap))
			continue;

		/* Move to head of hash chain. */
		hlist_del(&host->h_hash);
		hlist_add_head(&host->h_hash, chain);

		nlm_get_host(host);
		dprintk("lockd: nlm_lookup_host found host %s (%s)\n",
				host->h_name, host->h_addrbuf);
		goto out;
	}

	/*
	 * The host wasn't in our hash table.  If we don't
	 * have an NSM handle for it yet, create one.
	 */
	if (nsm)
		atomic_inc(&nsm->sm_count);
	else {
		host = NULL;
		nsm = nsm_find(ni->sap, ni->salen,
				ni->hostname, ni->hostname_len, 1);
		if (!nsm) {
			dprintk("lockd: nlm_lookup_host failed; "
				"no nsm handle\n");
			goto out;
		}
	}

	host = kzalloc(sizeof(*host), GFP_KERNEL);
	if (!host) {
		nsm_release(nsm);
		dprintk("lockd: nlm_lookup_host failed; no memory\n");
		goto out;
	}
	host->h_name	   = nsm->sm_name;
	memcpy(nlm_addr(host), ni->sap, ni->salen);
	host->h_addrlen = ni->salen;
	nlm_clear_port(nlm_addr(host));
	memcpy(nlm_srcaddr(host), ni->src_sap, ni->src_len);
	host->h_version    = ni->version;
	host->h_proto      = ni->protocol;
	host->h_rpcclnt    = NULL;
	mutex_init(&host->h_mutex);
	host->h_nextrebind = jiffies + NLM_HOST_REBIND;
	host->h_expires    = jiffies + NLM_HOST_EXPIRE;
	atomic_set(&host->h_count, 1);
	init_waitqueue_head(&host->h_gracewait);
	init_rwsem(&host->h_rwsem);
	host->h_state      = 0;			/* pseudo NSM state */
	host->h_nsmstate   = 0;			/* real NSM state */
	host->h_nsmhandle  = nsm;
	host->h_server	   = ni->server;
	hlist_add_head(&host->h_hash, chain);
	INIT_LIST_HEAD(&host->h_lockowners);
	spin_lock_init(&host->h_lock);
	INIT_LIST_HEAD(&host->h_granted);
	INIT_LIST_HEAD(&host->h_reclaim);

	nrhosts++;

	nlm_display_address((struct sockaddr *)&host->h_addr,
				host->h_addrbuf, sizeof(host->h_addrbuf));
	nlm_display_address((struct sockaddr *)&host->h_srcaddr,
				host->h_srcaddrbuf, sizeof(host->h_srcaddrbuf));

	dprintk("lockd: nlm_lookup_host created host %s\n",
			host->h_name);

out:
	mutex_unlock(&nlm_host_mutex);
	return host;
}

/*
 * Destroy a host
 */
static void
nlm_destroy_host(struct nlm_host *host)
{
	struct rpc_clnt	*clnt;

	BUG_ON(!list_empty(&host->h_lockowners));
	BUG_ON(atomic_read(&host->h_count));

	/*
	 * Release NSM handle and unmonitor host.
	 */
	nsm_unmonitor(host);

	clnt = host->h_rpcclnt;
	if (clnt != NULL)
		rpc_shutdown_client(clnt);
	kfree(host);
}

/**
 * nlmclnt_lookup_host - Find an NLM host handle matching a remote server
 * @sap: network address of server
 * @salen: length of server address
 * @protocol: transport protocol to use
 * @version: NLM protocol version
 * @hostname: '\0'-terminated hostname of server
 *
 * Returns an nlm_host structure that matches the passed-in
 * [server address, transport protocol, NLM version, server hostname].
 * If one doesn't already exist in the host cache, a new handle is
 * created and returned.
 */
struct nlm_host *nlmclnt_lookup_host(const struct sockaddr *sap,
				     const size_t salen,
				     const unsigned short protocol,
				     const u32 version, const char *hostname)
{
	const struct sockaddr source = {
		.sa_family	= AF_UNSPEC,
	};
	struct nlm_lookup_host_info ni = {
		.server		= 0,
		.sap		= sap,
		.salen		= salen,
		.protocol	= protocol,
		.version	= version,
		.hostname	= hostname,
		.hostname_len	= strlen(hostname),
		.src_sap	= &source,
		.src_len	= sizeof(source),
	};

	dprintk("lockd: %s(host='%s', vers=%u, proto=%s)\n", __func__,
			(hostname ? hostname : "<none>"), version,
			(protocol == IPPROTO_UDP ? "udp" : "tcp"));

	return nlm_lookup_host(&ni);
}

/**
 * nlmsvc_lookup_host - Find an NLM host handle matching a remote client
 * @rqstp: incoming NLM request
 * @hostname: name of client host
 * @hostname_len: length of client hostname
 *
 * Returns an nlm_host structure that matches the [client address,
 * transport protocol, NLM version, client hostname] of the passed-in
 * NLM request.  If one doesn't already exist in the host cache, a
 * new handle is created and returned.
 *
 * Before possibly creating a new nlm_host, construct a sockaddr
 * for a specific source address in case the local system has
 * multiple network addresses.  The family of the address in
 * rq_daddr is guaranteed to be the same as the family of the
 * address in rq_addr, so it's safe to use the same family for
 * the source address.
 */
struct nlm_host *nlmsvc_lookup_host(const struct svc_rqst *rqstp,
				    const char *hostname,
				    const size_t hostname_len)
{
	struct sockaddr_in sin = {
		.sin_family	= AF_INET,
	};
	struct sockaddr_in6 sin6 = {
		.sin6_family	= AF_INET6,
	};
	struct nlm_lookup_host_info ni = {
		.server		= 1,
		.sap		= svc_addr(rqstp),
		.salen		= rqstp->rq_addrlen,
		.protocol	= rqstp->rq_prot,
		.version	= rqstp->rq_vers,
		.hostname	= hostname,
		.hostname_len	= hostname_len,
		.src_len	= rqstp->rq_addrlen,
	};

	dprintk("lockd: %s(host='%*s', vers=%u, proto=%s)\n", __func__,
			(int)hostname_len, hostname, rqstp->rq_vers,
			(rqstp->rq_prot == IPPROTO_UDP ? "udp" : "tcp"));

	switch (ni.sap->sa_family) {
	case AF_INET:
		sin.sin_addr.s_addr = rqstp->rq_daddr.addr.s_addr;
		ni.src_sap = (struct sockaddr *)&sin;
		break;
	case AF_INET6:
		ipv6_addr_copy(&sin6.sin6_addr, &rqstp->rq_daddr.addr6);
		ni.src_sap = (struct sockaddr *)&sin6;
		break;
	default:
		return NULL;
	}

	return nlm_lookup_host(&ni);
}

/*
 * Create the NLM RPC client for an NLM peer
 */
struct rpc_clnt *
nlm_bind_host(struct nlm_host *host)
{
	struct rpc_clnt	*clnt;

	dprintk("lockd: nlm_bind_host %s (%s), my addr=%s\n",
			host->h_name, host->h_addrbuf, host->h_srcaddrbuf);

	/* Lock host handle */
	mutex_lock(&host->h_mutex);

	/* If we've already created an RPC client, check whether
	 * RPC rebind is required
	 */
	if ((clnt = host->h_rpcclnt) != NULL) {
		if (time_after_eq(jiffies, host->h_nextrebind)) {
			rpc_force_rebind(clnt);
			host->h_nextrebind = jiffies + NLM_HOST_REBIND;
			dprintk("lockd: next rebind in %lu jiffies\n",
					host->h_nextrebind - jiffies);
		}
	} else {
		unsigned long increment = nlmsvc_timeout;
		struct rpc_timeout timeparms = {
			.to_initval	= increment,
			.to_increment	= increment,
			.to_maxval	= increment * 6UL,
			.to_retries	= 5U,
		};
		struct rpc_create_args args = {
			.protocol	= host->h_proto,
			.address	= nlm_addr(host),
			.addrsize	= host->h_addrlen,
			.saddress	= nlm_srcaddr(host),
			.timeout	= &timeparms,
			.servername	= host->h_name,
			.program	= &nlm_program,
			.version	= host->h_version,
			.authflavor	= RPC_AUTH_UNIX,
			.flags		= (RPC_CLNT_CREATE_NOPING |
					   RPC_CLNT_CREATE_AUTOBIND),
		};

		/*
		 * lockd retries server side blocks automatically so we want
		 * those to be soft RPC calls. Client side calls need to be
		 * hard RPC tasks.
		 */
		if (!host->h_server)
			args.flags |= RPC_CLNT_CREATE_HARDRTRY;

		clnt = rpc_create(&args);
		if (!IS_ERR(clnt))
			host->h_rpcclnt = clnt;
		else {
			printk("lockd: couldn't create RPC handle for %s\n", host->h_name);
			clnt = NULL;
		}
	}

	mutex_unlock(&host->h_mutex);
	return clnt;
}

/*
 * Force a portmap lookup of the remote lockd port
 */
void
nlm_rebind_host(struct nlm_host *host)
{
	dprintk("lockd: rebind host %s\n", host->h_name);
	if (host->h_rpcclnt && time_after_eq(jiffies, host->h_nextrebind)) {
		rpc_force_rebind(host->h_rpcclnt);
		host->h_nextrebind = jiffies + NLM_HOST_REBIND;
	}
}

/*
 * Increment NLM host count
 */
struct nlm_host * nlm_get_host(struct nlm_host *host)
{
	if (host) {
		dprintk("lockd: get host %s\n", host->h_name);
		atomic_inc(&host->h_count);
		host->h_expires = jiffies + NLM_HOST_EXPIRE;
	}
	return host;
}

/*
 * Release NLM host after use
 */
void nlm_release_host(struct nlm_host *host)
{
	if (host != NULL) {
		dprintk("lockd: release host %s\n", host->h_name);
		BUG_ON(atomic_read(&host->h_count) < 0);
		if (atomic_dec_and_test(&host->h_count)) {
			BUG_ON(!list_empty(&host->h_lockowners));
			BUG_ON(!list_empty(&host->h_granted));
			BUG_ON(!list_empty(&host->h_reclaim));
		}
	}
}

/*
 * We were notified that the host indicated by address &sin
 * has rebooted.
 * Release all resources held by that peer.
 */
void nlm_host_rebooted(const struct sockaddr_in *sin,
				const char *hostname,
				unsigned int hostname_len,
				u32 new_state)
{
	struct hlist_head *chain;
	struct hlist_node *pos;
	struct nsm_handle *nsm;
	struct nlm_host	*host;

	nsm = nsm_find((struct sockaddr *)sin, sizeof(*sin),
			hostname, hostname_len, 0);
	if (nsm == NULL) {
		dprintk("lockd: never saw rebooted peer '%.*s' before\n",
				hostname_len, hostname);
		return;
	}

	dprintk("lockd: nlm_host_rebooted(%.*s, %s)\n",
			hostname_len, hostname, nsm->sm_addrbuf);

	/* When reclaiming locks on this peer, make sure that
	 * we set up a new notification */
	nsm->sm_monitored = 0;

	/* Mark all hosts tied to this NSM state as having rebooted.
	 * We run the loop repeatedly, because we drop the host table
	 * lock for this.
	 * To avoid processing a host several times, we match the nsmstate.
	 */
again:	mutex_lock(&nlm_host_mutex);
	for (chain = nlm_hosts; chain < nlm_hosts + NLM_HOST_NRHASH; ++chain) {
		hlist_for_each_entry(host, pos, chain, h_hash) {
			if (host->h_nsmhandle == nsm
			 && host->h_nsmstate != new_state) {
				host->h_nsmstate = new_state;
				host->h_state++;

				nlm_get_host(host);
				mutex_unlock(&nlm_host_mutex);

				if (host->h_server) {
					/* We're server for this guy, just ditch
					 * all the locks he held. */
					nlmsvc_free_host_resources(host);
				} else {
					/* He's the server, initiate lock recovery. */
					nlmclnt_recovery(host);
				}

				nlm_release_host(host);
				goto again;
			}
		}
	}

	mutex_unlock(&nlm_host_mutex);
}

/*
 * Shut down the hosts module.
 * Note that this routine is called only at server shutdown time.
 */
void
nlm_shutdown_hosts(void)
{
	struct hlist_head *chain;
	struct hlist_node *pos;
	struct nlm_host	*host;

	dprintk("lockd: shutting down host module\n");
	mutex_lock(&nlm_host_mutex);

	/* First, make all hosts eligible for gc */
	dprintk("lockd: nuking all hosts...\n");
	for (chain = nlm_hosts; chain < nlm_hosts + NLM_HOST_NRHASH; ++chain) {
		hlist_for_each_entry(host, pos, chain, h_hash) {
			host->h_expires = jiffies - 1;
			if (host->h_rpcclnt) {
				rpc_shutdown_client(host->h_rpcclnt);
				host->h_rpcclnt = NULL;
			}
		}
	}

	/* Then, perform a garbage collection pass */
	nlm_gc_hosts();
	mutex_unlock(&nlm_host_mutex);

	/* complain if any hosts are left */
	if (nrhosts) {
		printk(KERN_WARNING "lockd: couldn't shutdown host module!\n");
		dprintk("lockd: %d hosts left:\n", nrhosts);
		for (chain = nlm_hosts; chain < nlm_hosts + NLM_HOST_NRHASH; ++chain) {
			hlist_for_each_entry(host, pos, chain, h_hash) {
				dprintk("       %s (cnt %d use %d exp %ld)\n",
					host->h_name, atomic_read(&host->h_count),
					host->h_inuse, host->h_expires);
			}
		}
	}
}

/*
 * Garbage collect any unused NLM hosts.
 * This GC combines reference counting for async operations with
 * mark & sweep for resources held by remote clients.
 */
static void
nlm_gc_hosts(void)
{
	struct hlist_head *chain;
	struct hlist_node *pos, *next;
	struct nlm_host	*host;

	dprintk("lockd: host garbage collection\n");
	for (chain = nlm_hosts; chain < nlm_hosts + NLM_HOST_NRHASH; ++chain) {
		hlist_for_each_entry(host, pos, chain, h_hash)
			host->h_inuse = 0;
	}

	/* Mark all hosts that hold locks, blocks or shares */
	nlmsvc_mark_resources();

	for (chain = nlm_hosts; chain < nlm_hosts + NLM_HOST_NRHASH; ++chain) {
		hlist_for_each_entry_safe(host, pos, next, chain, h_hash) {
			if (atomic_read(&host->h_count) || host->h_inuse
			 || time_before(jiffies, host->h_expires)) {
				dprintk("nlm_gc_hosts skipping %s (cnt %d use %d exp %ld)\n",
					host->h_name, atomic_read(&host->h_count),
					host->h_inuse, host->h_expires);
				continue;
			}
			dprintk("lockd: delete host %s\n", host->h_name);
			hlist_del_init(&host->h_hash);

			nlm_destroy_host(host);
			nrhosts--;
		}
	}

	next_gc = jiffies + NLM_HOST_COLLECT;
}


/*
 * Manage NSM handles
 */
static LIST_HEAD(nsm_handles);
static DEFINE_SPINLOCK(nsm_lock);

static struct nsm_handle *nsm_find(const struct sockaddr *sap,
				   const size_t salen,
				   const char *hostname,
				   const size_t hostname_len,
				   const int create)
{
	struct nsm_handle *nsm = NULL;
	struct nsm_handle *pos;

	if (!sap)
		return NULL;

	if (hostname && memchr(hostname, '/', hostname_len) != NULL) {
		if (printk_ratelimit()) {
			printk(KERN_WARNING "Invalid hostname \"%.*s\" "
					    "in NFS lock request\n",
				(int)hostname_len, hostname);
		}
		return NULL;
	}

retry:
	spin_lock(&nsm_lock);
	list_for_each_entry(pos, &nsm_handles, sm_link) {

		if (hostname && nsm_use_hostnames) {
			if (strlen(pos->sm_name) != hostname_len
			 || memcmp(pos->sm_name, hostname, hostname_len))
				continue;
		} else if (!nlm_cmp_addr(nsm_addr(pos), sap))
			continue;
		atomic_inc(&pos->sm_count);
		kfree(nsm);
		nsm = pos;
		goto found;
	}
	if (nsm) {
		list_add(&nsm->sm_link, &nsm_handles);
		goto found;
	}
	spin_unlock(&nsm_lock);

	if (!create)
		return NULL;

	nsm = kzalloc(sizeof(*nsm) + hostname_len + 1, GFP_KERNEL);
	if (nsm == NULL)
		return NULL;

	memcpy(nsm_addr(nsm), sap, salen);
	nsm->sm_addrlen = salen;
	nsm->sm_name = (char *) (nsm + 1);
	memcpy(nsm->sm_name, hostname, hostname_len);
	nsm->sm_name[hostname_len] = '\0';
	nlm_display_address((struct sockaddr *)&nsm->sm_addr,
				nsm->sm_addrbuf, sizeof(nsm->sm_addrbuf));
	atomic_set(&nsm->sm_count, 1);
	goto retry;

found:
	spin_unlock(&nsm_lock);
	return nsm;
}

/*
 * Release an NSM handle
 */
void
nsm_release(struct nsm_handle *nsm)
{
	if (!nsm)
		return;
	if (atomic_dec_and_lock(&nsm->sm_count, &nsm_lock)) {
		list_del(&nsm->sm_link);
		spin_unlock(&nsm_lock);
		kfree(nsm);
	}
}