fs/nfsd/nfscache.c

   1 /*
   2  * Request reply cache. This is currently a global cache, but this may
   3  * change in the future and be a per-client cache.
   4  *
   5  * This code is heavily inspired by the 44BSD implementation, although
   6  * it does things a bit differently.
   7  *
   8  * Copyright (C) 1995, 1996 Olaf Kirch <okir@monad.swb.de>
   9  */
  10
  11 #include <linux/slab.h>
  12
  13 #include "nfsd.h"
  14 #include "cache.h"
  15
  16 /* Size of reply cache. Common values are:
  17  * 4.3BSD:      128
  18  * 4.4BSD:      256
  19  * Solaris2:    1024
  20  * DEC Unix:    512-4096
  21  */
  22 #define CACHESIZE               1024
  23 #define HASHSIZE                64
  24
  25 static struct hlist_head *      cache_hash;
  26 static struct list_head         lru_head;
  27 static int                      cache_disabled = 1;
  28
  29 /*
  30  * Calculate the hash index from an XID.
  31  */
  32 static inline u32 request_hash(u32 xid)
  33 {
  34         u32 h = xid;
  35         h ^= (xid >> 24);
  36         return h & (HASHSIZE-1);
  37 }
  38
  39 static int      nfsd_cache_append(struct svc_rqst *rqstp, struct kvec *vec);
  40
  41 /*
  42  * locking for the reply cache:
  43  * A cache entry is "single use" if c_state == RC_INPROG
  44  * Otherwise, it when accessing _prev or _next, the lock must be held.
  45  */
  46 static DEFINE_SPINLOCK(cache_lock);
  47
  48 int nfsd_reply_cache_init(void)
  49 {
  50         struct svc_cacherep     *rp;
  51         int                     i;
  52
  53         INIT_LIST_HEAD(&lru_head);
  54         i = CACHESIZE;
  55         while (i) {
  56                 rp = kmalloc(sizeof(*rp), GFP_KERNEL);
  57                 if (!rp)
  58                         goto out_nomem;
  59                 list_add(&rp->c_lru, &lru_head);
  60                 rp->c_state = RC_UNUSED;
  61                 rp->c_type = RC_NOCACHE;
  62                 INIT_HLIST_NODE(&rp->c_hash);
  63                 i--;
  64         }
  65
  66         cache_hash = kcalloc (HASHSIZE, sizeof(struct hlist_head), GFP_KERNEL);
  67         if (!cache_hash)
  68                 goto out_nomem;
  69
  70         cache_disabled = 0;
  71         return 0;
  72 out_nomem:
  73         printk(KERN_ERR "nfsd: failed to allocate reply cache\n");
  74         nfsd_reply_cache_shutdown();
  75         return -ENOMEM;
  76 }
  77
  78 void nfsd_reply_cache_shutdown(void)
  79 {
  80         struct svc_cacherep     *rp;
  81
  82         while (!list_empty(&lru_head)) {
  83                 rp = list_entry(lru_head.next, struct svc_cacherep, c_lru);
  84                 if (rp->c_state == RC_DONE && rp->c_type == RC_REPLBUFF)
  85                         kfree(rp->c_replvec.iov_base);
  86                 list_del(&rp->c_lru);
  87                 kfree(rp);
  88         }
  89
  90         cache_disabled = 1;
  91
  92         kfree (cache_hash);
  93         cache_hash = NULL;
  94 }
  95
  96 /*
  97  * Move cache entry to end of LRU list
  98  */
  99 static void
 100 lru_put_end(struct svc_cacherep *rp)
 101 {
 102         list_move_tail(&rp->c_lru, &lru_head);
 103 }
 104
 105 /*
 106  * Move a cache entry from one hash list to another
 107  */
 108 static void
 109 hash_refile(struct svc_cacherep *rp)
 110 {
 111         hlist_del_init(&rp->c_hash);
 112         hlist_add_head(&rp->c_hash, cache_hash + request_hash(rp->c_xid));
 113 }
 114
 115 /*
 116  * Try to find an entry matching the current call in the cache. When none
 117  * is found, we grab the oldest unlocked entry off the LRU list.
 118  * Note that no operation within the loop may sleep.
 119  */
 120 int
 121 nfsd_cache_lookup(struct svc_rqst *rqstp, int type)
 122 {
 123         struct hlist_node       *hn;
 124         struct hlist_head       *rh;
 125         struct svc_cacherep     *rp;
 126         __be32                  xid = rqstp->rq_xid;
 127         u32                     proto =  rqstp->rq_prot,
 128                                 vers = rqstp->rq_vers,
 129                                 proc = rqstp->rq_proc;
 130         unsigned long           age;
 131         int rtn;
 132
 133         rqstp->rq_cacherep = NULL;
 134         if (cache_disabled || type == RC_NOCACHE) {
 135                 nfsdstats.rcnocache++;
 136                 return RC_DOIT;
 137         }
 138
 139         spin_lock(&cache_lock);
 140         rtn = RC_DOIT;
 141
 142         rh = &cache_hash[request_hash(xid)];
 143         hlist_for_each_entry(rp, hn, rh, c_hash) {
 144                 if (rp->c_state != RC_UNUSED &&
 145                     xid == rp->c_xid && proc == rp->c_proc &&
 146                     proto == rp->c_prot && vers == rp->c_vers &&
 147                     time_before(jiffies, rp->c_timestamp + 120*HZ) &&
 148                     memcmp((char*)&rqstp->rq_addr, (char*)&rp->c_addr, sizeof(rp->c_addr))==0) {
 149                         nfsdstats.rchits++;
 150                         goto found_entry;
 151                 }
 152         }
 153         nfsdstats.rcmisses++;
 154
 155         /* This loop shouldn't take more than a few iterations normally */
 156         {
 157         int     safe = 0;
 158         list_for_each_entry(rp, &lru_head, c_lru) {
 159                 if (rp->c_state != RC_INPROG)
 160                         break;
 161                 if (safe++ > CACHESIZE) {
 162                         printk("nfsd: loop in repcache LRU list\n");
 163                         cache_disabled = 1;
 164                         goto out;
 165                 }
 166         }
 167         }
 168
 169         /* All entries on the LRU are in-progress. This should not happen */
 170         if (&rp->c_lru == &lru_head) {
 171                 static int      complaints;
 172
 173                 printk(KERN_WARNING "nfsd: all repcache entries locked!\n");
 174                 if (++complaints > 5) {
 175                         printk(KERN_WARNING "nfsd: disabling repcache.\n");
 176                         cache_disabled = 1;
 177                 }
 178                 goto out;
 179         }
 180
 181         rqstp->rq_cacherep = rp;
 182         rp->c_state = RC_INPROG;
 183         rp->c_xid = xid;
 184         rp->c_proc = proc;
 185         memcpy(&rp->c_addr, svc_addr_in(rqstp), sizeof(rp->c_addr));
 186         rp->c_prot = proto;
 187         rp->c_vers = vers;
 188         rp->c_timestamp = jiffies;
 189
 190         hash_refile(rp);
 191
 192         /* release any buffer */
 193         if (rp->c_type == RC_REPLBUFF) {
 194                 kfree(rp->c_replvec.iov_base);
 195                 rp->c_replvec.iov_base = NULL;
 196         }
 197         rp->c_type = RC_NOCACHE;
 198  out:
 199         spin_unlock(&cache_lock);
 200         return rtn;
 201
 202 found_entry:
 203         /* We found a matching entry which is either in progress or done. */
 204         age = jiffies - rp->c_timestamp;
 205         rp->c_timestamp = jiffies;
 206         lru_put_end(rp);
 207
 208         rtn = RC_DROPIT;
 209         /* Request being processed or excessive rexmits */
 210         if (rp->c_state == RC_INPROG || age < RC_DELAY)
 211                 goto out;
 212
 213         /* From the hall of fame of impractical attacks:
 214          * Is this a user who tries to snoop on the cache? */
 215         rtn = RC_DOIT;
 216         if (!rqstp->rq_secure && rp->c_secure)
 217                 goto out;
 218
 219         /* Compose RPC reply header */
 220         switch (rp->c_type) {
 221         case RC_NOCACHE:
 222                 break;
 223         case RC_REPLSTAT:
 224                 svc_putu32(&rqstp->rq_res.head[0], rp->c_replstat);
 225                 rtn = RC_REPLY;
 226                 break;
 227         case RC_REPLBUFF:
 228                 if (!nfsd_cache_append(rqstp, &rp->c_replvec))
 229                         goto out;       /* should not happen */
 230                 rtn = RC_REPLY;
 231                 break;
 232         default:
 233                 printk(KERN_WARNING "nfsd: bad repcache type %d\n", rp->c_type);
 234                 rp->c_state = RC_UNUSED;
 235         }
 236
 237         goto out;
 238 }
 239
 240 /*
 241  * Update a cache entry. This is called from nfsd_dispatch when
 242  * the procedure has been executed and the complete reply is in
 243  * rqstp->rq_res.
 244  *
 245  * We're copying around data here rather than swapping buffers because
 246  * the toplevel loop requires max-sized buffers, which would be a waste
 247  * of memory for a cache with a max reply size of 100 bytes (diropokres).
 248  *
 249  * If we should start to use different types of cache entries tailored
 250  * specifically for attrstat and fh's, we may save even more space.
 251  *
 252  * Also note that a cachetype of RC_NOCACHE can legally be passed when
 253  * nfsd failed to encode a reply that otherwise would have been cached.
 254  * In this case, nfsd_cache_update is called with statp == NULL.
 255  */
 256 void
 257 nfsd_cache_update(struct svc_rqst *rqstp, int cachetype, __be32 *statp)
 258 {
 259         struct svc_cacherep *rp;
 260         struct kvec     *resv = &rqstp->rq_res.head[0], *cachv;
 261         int             len;
 262
 263         if (!(rp = rqstp->rq_cacherep) || cache_disabled)
 264                 return;
 265
 266         len = resv->iov_len - ((char*)statp - (char*)resv->iov_base);
 267         len >>= 2;
 268
 269         /* Don't cache excessive amounts of data and XDR failures */
 270         if (!statp || len > (256 >> 2)) {
 271                 rp->c_state = RC_UNUSED;
 272                 return;
 273         }
 274
 275         switch (cachetype) {
 276         case RC_REPLSTAT:
 277                 if (len != 1)
 278                         printk("nfsd: RC_REPLSTAT/reply len %d!\n",len);
 279                 rp->c_replstat = *statp;
 280                 break;
 281         case RC_REPLBUFF:
 282                 cachv = &rp->c_replvec;
 283                 cachv->iov_base = kmalloc(len << 2, GFP_KERNEL);
 284                 if (!cachv->iov_base) {
 285                         spin_lock(&cache_lock);
 286                         rp->c_state = RC_UNUSED;
 287                         spin_unlock(&cache_lock);
 288                         return;
 289                 }
 290                 cachv->iov_len = len << 2;
 291                 memcpy(cachv->iov_base, statp, len << 2);
 292                 break;
 293         }
 294         spin_lock(&cache_lock);
 295         lru_put_end(rp);
 296         rp->c_secure = rqstp->rq_secure;
 297         rp->c_type = cachetype;
 298         rp->c_state = RC_DONE;
 299         rp->c_timestamp = jiffies;
 300         spin_unlock(&cache_lock);
 301         return;
 302 }
 303
 304 /*
 305  * Copy cached reply to current reply buffer. Should always fit.
 306  * FIXME as reply is in a page, we should just attach the page, and
 307  * keep a refcount....
 308  */
 309 static int
 310 nfsd_cache_append(struct svc_rqst *rqstp, struct kvec *data)
 311 {
 312         struct kvec     *vec = &rqstp->rq_res.head[0];
 313
 314         if (vec->iov_len + data->iov_len > PAGE_SIZE) {
 315                 printk(KERN_WARNING "nfsd: cached reply too large (%Zd).\n",
 316                                 data->iov_len);
 317                 return 0;
 318         }
 319         memcpy((char*)vec->iov_base + vec->iov_len, data->iov_base, data->iov_len);
 320         vec->iov_len += data->iov_len;
 321         return 1;
 322 }