root/fs/nfsd/nfscache.c

DEFINITIONS

1. nfsd_cache_size_limit
2. nfsd_hashsize
3. nfsd_cache_hash
4. nfsd_reply_cache_alloc
5. nfsd_reply_cache_free_locked
6. nfsd_reply_cache_free
7. nfsd_reply_cache_init
8. nfsd_reply_cache_shutdown
9. lru_put_end
10. prune_bucket
11. prune_cache_entries
12. nfsd_reply_cache_count
13. nfsd_reply_cache_scan
14. nfsd_cache_csum
15. nfsd_cache_key_cmp
16. nfsd_cache_insert
17. nfsd_cache_lookup
18. nfsd_cache_update
19. nfsd_cache_append
20. nfsd_reply_cache_stats_show
21. nfsd_reply_cache_stats_open

   1 // SPDX-License-Identifier: GPL-2.0
   2 /*
   3  * Request reply cache. This is currently a global cache, but this may
   4  * change in the future and be a per-client cache.
   5  *
   6  * This code is heavily inspired by the 44BSD implementation, although
   7  * it does things a bit differently.
   8  *
   9  * Copyright (C) 1995, 1996 Olaf Kirch <okir@monad.swb.de>
  10  */
  11 
  12 #include <linux/sunrpc/svc_xprt.h>
  13 #include <linux/slab.h>
  14 #include <linux/vmalloc.h>
  15 #include <linux/sunrpc/addr.h>
  16 #include <linux/highmem.h>
  17 #include <linux/log2.h>
  18 #include <linux/hash.h>
  19 #include <net/checksum.h>
  20 
  21 #include "nfsd.h"
  22 #include "cache.h"
  23 
  24 #define NFSDDBG_FACILITY        NFSDDBG_REPCACHE
  25 
  26 /*
  27  * We use this value to determine the number of hash buckets from the max
  28  * cache size, the idea being that when the cache is at its maximum number
  29  * of entries, then this should be the average number of entries per bucket.
  30  */
  31 #define TARGET_BUCKET_SIZE      64
  32 
  33 struct nfsd_drc_bucket {
  34         struct rb_root rb_head;
  35         struct list_head lru_head;
  36         spinlock_t cache_lock;
  37 };
  38 
  39 static int      nfsd_cache_append(struct svc_rqst *rqstp, struct kvec *vec);
  40 static unsigned long nfsd_reply_cache_count(struct shrinker *shrink,
  41                                             struct shrink_control *sc);
  42 static unsigned long nfsd_reply_cache_scan(struct shrinker *shrink,
  43                                            struct shrink_control *sc);
  44 
  45 /*
  46  * Put a cap on the size of the DRC based on the amount of available
  47  * low memory in the machine.
  48  *
  49  *  64MB:    8192
  50  * 128MB:   11585
  51  * 256MB:   16384
  52  * 512MB:   23170
  53  *   1GB:   32768
  54  *   2GB:   46340
  55  *   4GB:   65536
  56  *   8GB:   92681
  57  *  16GB:  131072
  58  *
  59  * ...with a hard cap of 256k entries. In the worst case, each entry will be
  60  * ~1k, so the above numbers should give a rough max of the amount of memory
  61  * used in k.
  62  *
  63  * XXX: these limits are per-container, so memory used will increase
  64  * linearly with number of containers.  Maybe that's OK.
  65  */
  66 static unsigned int
  67 nfsd_cache_size_limit(void)
  68 {
  69         unsigned int limit;
  70         unsigned long low_pages = totalram_pages() - totalhigh_pages();
  71 
  72         limit = (16 * int_sqrt(low_pages)) << (PAGE_SHIFT-10);
  73         return min_t(unsigned int, limit, 256*1024);
  74 }
  75 
  76 /*
  77  * Compute the number of hash buckets we need. Divide the max cachesize by
  78  * the "target" max bucket size, and round up to next power of two.
  79  */
  80 static unsigned int
  81 nfsd_hashsize(unsigned int limit)
  82 {
  83         return roundup_pow_of_two(limit / TARGET_BUCKET_SIZE);
  84 }
  85 
  86 static u32
  87 nfsd_cache_hash(__be32 xid, struct nfsd_net *nn)
  88 {
  89         return hash_32(be32_to_cpu(xid), nn->maskbits);
  90 }
  91 
  92 static struct svc_cacherep *
  93 nfsd_reply_cache_alloc(struct svc_rqst *rqstp, __wsum csum,
  94                         struct nfsd_net *nn)
  95 {
  96         struct svc_cacherep     *rp;
  97 
  98         rp = kmem_cache_alloc(nn->drc_slab, GFP_KERNEL);
  99         if (rp) {
 100                 rp->c_state = RC_UNUSED;
 101                 rp->c_type = RC_NOCACHE;
 102                 RB_CLEAR_NODE(&rp->c_node);
 103                 INIT_LIST_HEAD(&rp->c_lru);
 104 
 105                 memset(&rp->c_key, 0, sizeof(rp->c_key));
 106                 rp->c_key.k_xid = rqstp->rq_xid;
 107                 rp->c_key.k_proc = rqstp->rq_proc;
 108                 rpc_copy_addr((struct sockaddr *)&rp->c_key.k_addr, svc_addr(rqstp));
 109                 rpc_set_port((struct sockaddr *)&rp->c_key.k_addr, rpc_get_port(svc_addr(rqstp)));
 110                 rp->c_key.k_prot = rqstp->rq_prot;
 111                 rp->c_key.k_vers = rqstp->rq_vers;
 112                 rp->c_key.k_len = rqstp->rq_arg.len;
 113                 rp->c_key.k_csum = csum;
 114         }
 115         return rp;
 116 }
 117 
 118 static void
 119 nfsd_reply_cache_free_locked(struct nfsd_drc_bucket *b, struct svc_cacherep *rp,
 120                                 struct nfsd_net *nn)
 121 {
 122         if (rp->c_type == RC_REPLBUFF && rp->c_replvec.iov_base) {
 123                 nn->drc_mem_usage -= rp->c_replvec.iov_len;
 124                 kfree(rp->c_replvec.iov_base);
 125         }
 126         if (rp->c_state != RC_UNUSED) {
 127                 rb_erase(&rp->c_node, &b->rb_head);
 128                 list_del(&rp->c_lru);
 129                 atomic_dec(&nn->num_drc_entries);
 130                 nn->drc_mem_usage -= sizeof(*rp);
 131         }
 132         kmem_cache_free(nn->drc_slab, rp);
 133 }
 134 
 135 static void
 136 nfsd_reply_cache_free(struct nfsd_drc_bucket *b, struct svc_cacherep *rp,
 137                         struct nfsd_net *nn)
 138 {
 139         spin_lock(&b->cache_lock);
 140         nfsd_reply_cache_free_locked(b, rp, nn);
 141         spin_unlock(&b->cache_lock);
 142 }
 143 
 144 int nfsd_reply_cache_init(struct nfsd_net *nn)
 145 {
 146         unsigned int hashsize;
 147         unsigned int i;
 148         int status = 0;
 149 
 150         nn->max_drc_entries = nfsd_cache_size_limit();
 151         atomic_set(&nn->num_drc_entries, 0);
 152         hashsize = nfsd_hashsize(nn->max_drc_entries);
 153         nn->maskbits = ilog2(hashsize);
 154 
 155         nn->nfsd_reply_cache_shrinker.scan_objects = nfsd_reply_cache_scan;
 156         nn->nfsd_reply_cache_shrinker.count_objects = nfsd_reply_cache_count;
 157         nn->nfsd_reply_cache_shrinker.seeks = 1;
 158         status = register_shrinker(&nn->nfsd_reply_cache_shrinker);
 159         if (status)
 160                 goto out_nomem;
 161 
 162         nn->drc_slab = kmem_cache_create("nfsd_drc",
 163                                 sizeof(struct svc_cacherep), 0, 0, NULL);
 164         if (!nn->drc_slab)
 165                 goto out_shrinker;
 166 
 167         nn->drc_hashtbl = kcalloc(hashsize,
 168                                 sizeof(*nn->drc_hashtbl), GFP_KERNEL);
 169         if (!nn->drc_hashtbl) {
 170                 nn->drc_hashtbl = vzalloc(array_size(hashsize,
 171                                                  sizeof(*nn->drc_hashtbl)));
 172                 if (!nn->drc_hashtbl)
 173                         goto out_slab;
 174         }
 175 
 176         for (i = 0; i < hashsize; i++) {
 177                 INIT_LIST_HEAD(&nn->drc_hashtbl[i].lru_head);
 178                 spin_lock_init(&nn->drc_hashtbl[i].cache_lock);
 179         }
 180         nn->drc_hashsize = hashsize;
 181 
 182         return 0;
 183 out_slab:
 184         kmem_cache_destroy(nn->drc_slab);
 185 out_shrinker:
 186         unregister_shrinker(&nn->nfsd_reply_cache_shrinker);
 187 out_nomem:
 188         printk(KERN_ERR "nfsd: failed to allocate reply cache\n");
 189         return -ENOMEM;
 190 }
 191 
 192 void nfsd_reply_cache_shutdown(struct nfsd_net *nn)
 193 {
 194         struct svc_cacherep     *rp;
 195         unsigned int i;
 196 
 197         unregister_shrinker(&nn->nfsd_reply_cache_shrinker);
 198 
 199         for (i = 0; i < nn->drc_hashsize; i++) {
 200                 struct list_head *head = &nn->drc_hashtbl[i].lru_head;
 201                 while (!list_empty(head)) {
 202                         rp = list_first_entry(head, struct svc_cacherep, c_lru);
 203                         nfsd_reply_cache_free_locked(&nn->drc_hashtbl[i],
 204                                                                         rp, nn);
 205                 }
 206         }
 207 
 208         kvfree(nn->drc_hashtbl);
 209         nn->drc_hashtbl = NULL;
 210         nn->drc_hashsize = 0;
 211 
 212         kmem_cache_destroy(nn->drc_slab);
 213         nn->drc_slab = NULL;
 214 }
 215 
 216 /*
 217  * Move cache entry to end of LRU list, and queue the cleaner to run if it's
 218  * not already scheduled.
 219  */
 220 static void
 221 lru_put_end(struct nfsd_drc_bucket *b, struct svc_cacherep *rp)
 222 {
 223         rp->c_timestamp = jiffies;
 224         list_move_tail(&rp->c_lru, &b->lru_head);
 225 }
 226 
 227 static long
 228 prune_bucket(struct nfsd_drc_bucket *b, struct nfsd_net *nn)
 229 {
 230         struct svc_cacherep *rp, *tmp;
 231         long freed = 0;
 232 
 233         list_for_each_entry_safe(rp, tmp, &b->lru_head, c_lru) {
 234                 /*
 235                  * Don't free entries attached to calls that are still
 236                  * in-progress, but do keep scanning the list.
 237                  */
 238                 if (rp->c_state == RC_INPROG)
 239                         continue;
 240                 if (atomic_read(&nn->num_drc_entries) <= nn->max_drc_entries &&
 241                     time_before(jiffies, rp->c_timestamp + RC_EXPIRE))
 242                         break;
 243                 nfsd_reply_cache_free_locked(b, rp, nn);
 244                 freed++;
 245         }
 246         return freed;
 247 }
 248 
 249 /*
 250  * Walk the LRU list and prune off entries that are older than RC_EXPIRE.
 251  * Also prune the oldest ones when the total exceeds the max number of entries.
 252  */
 253 static long
 254 prune_cache_entries(struct nfsd_net *nn)
 255 {
 256         unsigned int i;
 257         long freed = 0;
 258 
 259         for (i = 0; i < nn->drc_hashsize; i++) {
 260                 struct nfsd_drc_bucket *b = &nn->drc_hashtbl[i];
 261 
 262                 if (list_empty(&b->lru_head))
 263                         continue;
 264                 spin_lock(&b->cache_lock);
 265                 freed += prune_bucket(b, nn);
 266                 spin_unlock(&b->cache_lock);
 267         }
 268         return freed;
 269 }
 270 
 271 static unsigned long
 272 nfsd_reply_cache_count(struct shrinker *shrink, struct shrink_control *sc)
 273 {
 274         struct nfsd_net *nn = container_of(shrink,
 275                                 struct nfsd_net, nfsd_reply_cache_shrinker);
 276 
 277         return atomic_read(&nn->num_drc_entries);
 278 }
 279 
 280 static unsigned long
 281 nfsd_reply_cache_scan(struct shrinker *shrink, struct shrink_control *sc)
 282 {
 283         struct nfsd_net *nn = container_of(shrink,
 284                                 struct nfsd_net, nfsd_reply_cache_shrinker);
 285 
 286         return prune_cache_entries(nn);
 287 }
 288 /*
 289  * Walk an xdr_buf and get a CRC for at most the first RC_CSUMLEN bytes
 290  */
 291 static __wsum
 292 nfsd_cache_csum(struct svc_rqst *rqstp)
 293 {
 294         int idx;
 295         unsigned int base;
 296         __wsum csum;
 297         struct xdr_buf *buf = &rqstp->rq_arg;
 298         const unsigned char *p = buf->head[0].iov_base;
 299         size_t csum_len = min_t(size_t, buf->head[0].iov_len + buf->page_len,
 300                                 RC_CSUMLEN);
 301         size_t len = min(buf->head[0].iov_len, csum_len);
 302 
 303         /* rq_arg.head first */
 304         csum = csum_partial(p, len, 0);
 305         csum_len -= len;
 306 
 307         /* Continue into page array */
 308         idx = buf->page_base / PAGE_SIZE;
 309         base = buf->page_base & ~PAGE_MASK;
 310         while (csum_len) {
 311                 p = page_address(buf->pages[idx]) + base;
 312                 len = min_t(size_t, PAGE_SIZE - base, csum_len);
 313                 csum = csum_partial(p, len, csum);
 314                 csum_len -= len;
 315                 base = 0;
 316                 ++idx;
 317         }
 318         return csum;
 319 }
 320 
 321 static int
 322 nfsd_cache_key_cmp(const struct svc_cacherep *key,
 323                         const struct svc_cacherep *rp, struct nfsd_net *nn)
 324 {
 325         if (key->c_key.k_xid == rp->c_key.k_xid &&
 326             key->c_key.k_csum != rp->c_key.k_csum)
 327                 ++nn->payload_misses;
 328 
 329         return memcmp(&key->c_key, &rp->c_key, sizeof(key->c_key));
 330 }
 331 
 332 /*
 333  * Search the request hash for an entry that matches the given rqstp.
 334  * Must be called with cache_lock held. Returns the found entry or
 335  * inserts an empty key on failure.
 336  */
 337 static struct svc_cacherep *
 338 nfsd_cache_insert(struct nfsd_drc_bucket *b, struct svc_cacherep *key,
 339                         struct nfsd_net *nn)
 340 {
 341         struct svc_cacherep     *rp, *ret = key;
 342         struct rb_node          **p = &b->rb_head.rb_node,
 343                                 *parent = NULL;
 344         unsigned int            entries = 0;
 345         int cmp;
 346 
 347         while (*p != NULL) {
 348                 ++entries;
 349                 parent = *p;
 350                 rp = rb_entry(parent, struct svc_cacherep, c_node);
 351 
 352                 cmp = nfsd_cache_key_cmp(key, rp, nn);
 353                 if (cmp < 0)
 354                         p = &parent->rb_left;
 355                 else if (cmp > 0)
 356                         p = &parent->rb_right;
 357                 else {
 358                         ret = rp;
 359                         goto out;
 360                 }
 361         }
 362         rb_link_node(&key->c_node, parent, p);
 363         rb_insert_color(&key->c_node, &b->rb_head);
 364 out:
 365         /* tally hash chain length stats */
 366         if (entries > nn->longest_chain) {
 367                 nn->longest_chain = entries;
 368                 nn->longest_chain_cachesize = atomic_read(&nn->num_drc_entries);
 369         } else if (entries == nn->longest_chain) {
 370                 /* prefer to keep the smallest cachesize possible here */
 371                 nn->longest_chain_cachesize = min_t(unsigned int,
 372                                 nn->longest_chain_cachesize,
 373                                 atomic_read(&nn->num_drc_entries));
 374         }
 375 
 376         lru_put_end(b, ret);
 377         return ret;
 378 }
 379 
 380 /*
 381  * Try to find an entry matching the current call in the cache. When none
 382  * is found, we try to grab the oldest expired entry off the LRU list. If
 383  * a suitable one isn't there, then drop the cache_lock and allocate a
 384  * new one, then search again in case one got inserted while this thread
 385  * didn't hold the lock.
 386  */
 387 int
 388 nfsd_cache_lookup(struct svc_rqst *rqstp)
 389 {
 390         struct nfsd_net *nn = net_generic(SVC_NET(rqstp), nfsd_net_id);
 391         struct svc_cacherep     *rp, *found;
 392         __be32                  xid = rqstp->rq_xid;
 393         __wsum                  csum;
 394         u32 hash = nfsd_cache_hash(xid, nn);
 395         struct nfsd_drc_bucket *b = &nn->drc_hashtbl[hash];
 396         int type = rqstp->rq_cachetype;
 397         int rtn = RC_DOIT;
 398 
 399         rqstp->rq_cacherep = NULL;
 400         if (type == RC_NOCACHE) {
 401                 nfsdstats.rcnocache++;
 402                 return rtn;
 403         }
 404 
 405         csum = nfsd_cache_csum(rqstp);
 406 
 407         /*
 408          * Since the common case is a cache miss followed by an insert,
 409          * preallocate an entry.
 410          */
 411         rp = nfsd_reply_cache_alloc(rqstp, csum, nn);
 412         if (!rp) {
 413                 dprintk("nfsd: unable to allocate DRC entry!\n");
 414                 return rtn;
 415         }
 416 
 417         spin_lock(&b->cache_lock);
 418         found = nfsd_cache_insert(b, rp, nn);
 419         if (found != rp) {
 420                 nfsd_reply_cache_free_locked(NULL, rp, nn);
 421                 rp = found;
 422                 goto found_entry;
 423         }
 424 
 425         nfsdstats.rcmisses++;
 426         rqstp->rq_cacherep = rp;
 427         rp->c_state = RC_INPROG;
 428 
 429         atomic_inc(&nn->num_drc_entries);
 430         nn->drc_mem_usage += sizeof(*rp);
 431 
 432         /* go ahead and prune the cache */
 433         prune_bucket(b, nn);
 434  out:
 435         spin_unlock(&b->cache_lock);
 436         return rtn;
 437 
 438 found_entry:
 439         /* We found a matching entry which is either in progress or done. */
 440         nfsdstats.rchits++;
 441         rtn = RC_DROPIT;
 442 
 443         /* Request being processed */
 444         if (rp->c_state == RC_INPROG)
 445                 goto out;
 446 
 447         /* From the hall of fame of impractical attacks:
 448          * Is this a user who tries to snoop on the cache? */
 449         rtn = RC_DOIT;
 450         if (!test_bit(RQ_SECURE, &rqstp->rq_flags) && rp->c_secure)
 451                 goto out;
 452 
 453         /* Compose RPC reply header */
 454         switch (rp->c_type) {
 455         case RC_NOCACHE:
 456                 break;
 457         case RC_REPLSTAT:
 458                 svc_putu32(&rqstp->rq_res.head[0], rp->c_replstat);
 459                 rtn = RC_REPLY;
 460                 break;
 461         case RC_REPLBUFF:
 462                 if (!nfsd_cache_append(rqstp, &rp->c_replvec))
 463                         goto out;       /* should not happen */
 464                 rtn = RC_REPLY;
 465                 break;
 466         default:
 467                 printk(KERN_WARNING "nfsd: bad repcache type %d\n", rp->c_type);
 468                 nfsd_reply_cache_free_locked(b, rp, nn);
 469         }
 470 
 471         goto out;
 472 }
 473 
 474 /*
 475  * Update a cache entry. This is called from nfsd_dispatch when
 476  * the procedure has been executed and the complete reply is in
 477  * rqstp->rq_res.
 478  *
 479  * We're copying around data here rather than swapping buffers because
 480  * the toplevel loop requires max-sized buffers, which would be a waste
 481  * of memory for a cache with a max reply size of 100 bytes (diropokres).
 482  *
 483  * If we should start to use different types of cache entries tailored
 484  * specifically for attrstat and fh's, we may save even more space.
 485  *
 486  * Also note that a cachetype of RC_NOCACHE can legally be passed when
 487  * nfsd failed to encode a reply that otherwise would have been cached.
 488  * In this case, nfsd_cache_update is called with statp == NULL.
 489  */
 490 void
 491 nfsd_cache_update(struct svc_rqst *rqstp, int cachetype, __be32 *statp)
 492 {
 493         struct nfsd_net *nn = net_generic(SVC_NET(rqstp), nfsd_net_id);
 494         struct svc_cacherep *rp = rqstp->rq_cacherep;
 495         struct kvec     *resv = &rqstp->rq_res.head[0], *cachv;
 496         u32             hash;
 497         struct nfsd_drc_bucket *b;
 498         int             len;
 499         size_t          bufsize = 0;
 500 
 501         if (!rp)
 502                 return;
 503 
 504         hash = nfsd_cache_hash(rp->c_key.k_xid, nn);
 505         b = &nn->drc_hashtbl[hash];
 506 
 507         len = resv->iov_len - ((char*)statp - (char*)resv->iov_base);
 508         len >>= 2;
 509 
 510         /* Don't cache excessive amounts of data and XDR failures */
 511         if (!statp || len > (256 >> 2)) {
 512                 nfsd_reply_cache_free(b, rp, nn);
 513                 return;
 514         }
 515 
 516         switch (cachetype) {
 517         case RC_REPLSTAT:
 518                 if (len != 1)
 519                         printk("nfsd: RC_REPLSTAT/reply len %d!\n",len);
 520                 rp->c_replstat = *statp;
 521                 break;
 522         case RC_REPLBUFF:
 523                 cachv = &rp->c_replvec;
 524                 bufsize = len << 2;
 525                 cachv->iov_base = kmalloc(bufsize, GFP_KERNEL);
 526                 if (!cachv->iov_base) {
 527                         nfsd_reply_cache_free(b, rp, nn);
 528                         return;
 529                 }
 530                 cachv->iov_len = bufsize;
 531                 memcpy(cachv->iov_base, statp, bufsize);
 532                 break;
 533         case RC_NOCACHE:
 534                 nfsd_reply_cache_free(b, rp, nn);
 535                 return;
 536         }
 537         spin_lock(&b->cache_lock);
 538         nn->drc_mem_usage += bufsize;
 539         lru_put_end(b, rp);
 540         rp->c_secure = test_bit(RQ_SECURE, &rqstp->rq_flags);
 541         rp->c_type = cachetype;
 542         rp->c_state = RC_DONE;
 543         spin_unlock(&b->cache_lock);
 544         return;
 545 }
 546 
 547 /*
 548  * Copy cached reply to current reply buffer. Should always fit.
 549  * FIXME as reply is in a page, we should just attach the page, and
 550  * keep a refcount....
 551  */
 552 static int
 553 nfsd_cache_append(struct svc_rqst *rqstp, struct kvec *data)
 554 {
 555         struct kvec     *vec = &rqstp->rq_res.head[0];
 556 
 557         if (vec->iov_len + data->iov_len > PAGE_SIZE) {
 558                 printk(KERN_WARNING "nfsd: cached reply too large (%zd).\n",
 559                                 data->iov_len);
 560                 return 0;
 561         }
 562         memcpy((char*)vec->iov_base + vec->iov_len, data->iov_base, data->iov_len);
 563         vec->iov_len += data->iov_len;
 564         return 1;
 565 }
 566 
 567 /*
 568  * Note that fields may be added, removed or reordered in the future. Programs
 569  * scraping this file for info should test the labels to ensure they're
 570  * getting the correct field.
 571  */
 572 static int nfsd_reply_cache_stats_show(struct seq_file *m, void *v)
 573 {
 574         struct nfsd_net *nn = m->private;
 575 
 576         seq_printf(m, "max entries:           %u\n", nn->max_drc_entries);
 577         seq_printf(m, "num entries:           %u\n",
 578                         atomic_read(&nn->num_drc_entries));
 579         seq_printf(m, "hash buckets:          %u\n", 1 << nn->maskbits);
 580         seq_printf(m, "mem usage:             %u\n", nn->drc_mem_usage);
 581         seq_printf(m, "cache hits:            %u\n", nfsdstats.rchits);
 582         seq_printf(m, "cache misses:          %u\n", nfsdstats.rcmisses);
 583         seq_printf(m, "not cached:            %u\n", nfsdstats.rcnocache);
 584         seq_printf(m, "payload misses:        %u\n", nn->payload_misses);
 585         seq_printf(m, "longest chain len:     %u\n", nn->longest_chain);
 586         seq_printf(m, "cachesize at longest:  %u\n", nn->longest_chain_cachesize);
 587         return 0;
 588 }
 589 
 590 int nfsd_reply_cache_stats_open(struct inode *inode, struct file *file)
 591 {
 592         struct nfsd_net *nn = net_generic(file_inode(file)->i_sb->s_fs_info,
 593                                                                 nfsd_net_id);
 594 
 595         return single_open(file, nfsd_reply_cache_stats_show, nn);
 596 }