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