fs/nfsd/nfscache.c

   1 /*
   2  * linux/fs/nfsd/nfscache.c
   3  *
   4  * Request reply cache. This is currently a global cache, but this may
   5  * change in the future and be a per-client cache.
   6  *
   7  * This code is heavily inspired by the 44BSD implementation, although
   8  * it does things a bit differently.
   9  *
  10  * Copyright (C) 1995, 1996 Olaf Kirch <okir@monad.swb.de>
  11  */
  12
  13 #include <linux/kernel.h>
  14 #include <linux/time.h>
  15 #include <linux/slab.h>
  16 #include <linux/string.h>
  17 #include <linux/spinlock.h>
  18 #include <linux/list.h>
  19
  20 #include <linux/sunrpc/svc.h>
  21 #include <linux/nfsd/nfsd.h>
  22 #include <linux/nfsd/cache.h>
  23
  24 /* Size of reply cache. Common values are:
  25  * 4.3BSD:      128
  26  * 4.4BSD:      256
  27  * Solaris2:    1024
  28  * DEC Unix:    512-4096
  29  */
  30 #define CACHESIZE               1024
  31 #define HASHSIZE                64
  32
  33 static struct hlist_head *      cache_hash;
  34 static struct list_head         lru_head;
  35 static int                      cache_disabled = 1;
  36
  37 /*
  38  * Calculate the hash index from an XID.
  39  */
  40 static inline u32 request_hash(u32 xid)
  41 {
  42         u32 h = xid;
  43         h ^= (xid >> 24);
  44         return h & (HASHSIZE-1);
  45 }
  46
  47 static int      nfsd_cache_append(struct svc_rqst *rqstp, struct kvec *vec);
  48
  49 /*
  50  * locking for the reply cache:
  51  * A cache entry is "single use" if c_state == RC_INPROG
  52  * Otherwise, it when accessing _prev or _next, the lock must be held.
  53  */
  54 static DEFINE_SPINLOCK(cache_lock);
  55
  56 int nfsd_reply_cache_init(void)
  57 {
  58         struct svc_cacherep     *rp;
  59         int                     i;
  60
  61         INIT_LIST_HEAD(&lru_head);
  62         i = CACHESIZE;
  63         while (i) {
  64                 rp = kmalloc(sizeof(*rp), GFP_KERNEL);
  65                 if (!rp)
  66                         goto out_nomem;
  67                 list_add(&rp->c_lru, &lru_head);
  68                 rp->c_state = RC_UNUSED;
  69                 rp->c_type = RC_NOCACHE;
  70                 INIT_HLIST_NODE(&rp->c_hash);
  71                 i--;
  72         }
  73
  74         cache_hash = kcalloc (HASHSIZE, sizeof(struct hlist_head), GFP_KERNEL);
  75         if (!cache_hash)
  76                 goto out_nomem;
  77
  78         cache_disabled = 0;
  79         return 0;
  80 out_nomem:
  81         printk(KERN_ERR "nfsd: failed to allocate reply cache\n");
  82         nfsd_reply_cache_shutdown();
  83         return -ENOMEM;
  84 }
  85
  86 void nfsd_reply_cache_shutdown(void)
  87 {
  88         struct svc_cacherep     *rp;
  89
  90         while (!list_empty(&lru_head)) {
  91                 rp = list_entry(lru_head.next, struct svc_cacherep, c_lru);
  92                 if (rp->c_state == RC_DONE && rp->c_type == RC_REPLBUFF)
  93                         kfree(rp->c_replvec.iov_base);
  94                 list_del(&rp->c_lru);
  95                 kfree(rp);
  96         }
  97
  98         cache_disabled = 1;
  99
 100         kfree (cache_hash);
 101         cache_hash = NULL;
 102 }
 103
 104 /*
 105  * Move cache entry to end of LRU list
 106  */
 107 static void
 108 lru_put_end(struct svc_cacherep *rp)
 109 {
 110         list_move_tail(&rp->c_lru, &lru_head);
 111 }
 112
 113 /*
 114  * Move a cache entry from one hash list to another
 115  */
 116 static void
 117 hash_refile(struct svc_cacherep *rp)
 118 {
 119         hlist_del_init(&rp->c_hash);
 120         hlist_add_head(&rp->c_hash, cache_hash + request_hash(rp->c_xid));
 121 }
 122
 123 /*
 124  * Try to find an entry matching the current call in the cache. When none
 125  * is found, we grab the oldest unlocked entry off the LRU list.
 126  * Note that no operation within the loop may sleep.
 127  */
 128 int
 129 nfsd_cache_lookup(struct svc_rqst *rqstp, int type)
 130 {
 131         struct hlist_node       *hn;
 132         struct hlist_head       *rh;
 133         struct svc_cacherep     *rp;
 134         __be32                  xid = rqstp->rq_xid;
 135         u32                     proto =  rqstp->rq_prot,
 136                                 vers = rqstp->rq_vers,
 137                                 proc = rqstp->rq_proc;
 138         unsigned long           age;
 139         int rtn;
 140
 141         rqstp->rq_cacherep = NULL;
 142         if (cache_disabled || type == RC_NOCACHE) {
 143                 nfsdstats.rcnocache++;
 144                 return RC_DOIT;
 145         }
 146
 147         spin_lock(&cache_lock);
 148         rtn = RC_DOIT;
 149
 150         rh = &cache_hash[request_hash(xid)];
 151         hlist_for_each_entry(rp, hn, rh, c_hash) {
 152                 if (rp->c_state != RC_UNUSED &&
 153                     xid == rp->c_xid && proc == rp->c_proc &&
 154                     proto == rp->c_prot && vers == rp->c_vers &&
 155                     time_before(jiffies, rp->c_timestamp + 120*HZ) &&
 156                     memcmp((char*)&rqstp->rq_addr, (char*)&rp->c_addr, sizeof(rp->c_addr))==0) {
 157                         nfsdstats.rchits++;
 158                         goto found_entry;
 159                 }
 160         }
 161         nfsdstats.rcmisses++;
 162
 163         /* This loop shouldn't take more than a few iterations normally */
 164         {
 165         int     safe = 0;
 166         list_for_each_entry(rp, &lru_head, c_lru) {
 167                 if (rp->c_state != RC_INPROG)
 168                         break;
 169                 if (safe++ > CACHESIZE) {
 170                         printk("nfsd: loop in repcache LRU list\n");
 171                         cache_disabled = 1;
 172                         goto out;
 173                 }
 174         }
 175         }
 176
 177         /* All entries on the LRU are in-progress. This should not happen */
 178         if (&rp->c_lru == &lru_head) {
 179                 static int      complaints;
 180
 181                 printk(KERN_WARNING "nfsd: all repcache entries locked!\n");
 182                 if (++complaints > 5) {
 183                         printk(KERN_WARNING "nfsd: disabling repcache.\n");
 184                         cache_disabled = 1;
 185                 }
 186                 goto out;
 187         }
 188
 189         rqstp->rq_cacherep = rp;
 190         rp->c_state = RC_INPROG;
 191         rp->c_xid = xid;
 192         rp->c_proc = proc;
 193         memcpy(&rp->c_addr, svc_addr_in(rqstp), sizeof(rp->c_addr));
 194         rp->c_prot = proto;
 195         rp->c_vers = vers;
 196         rp->c_timestamp = jiffies;
 197
 198         hash_refile(rp);
 199
 200         /* release any buffer */
 201         if (rp->c_type == RC_REPLBUFF) {
 202                 kfree(rp->c_replvec.iov_base);
 203                 rp->c_replvec.iov_base = NULL;
 204         }
 205         rp->c_type = RC_NOCACHE;
 206  out:
 207         spin_unlock(&cache_lock);
 208         return rtn;
 209
 210 found_entry:
 211         /* We found a matching entry which is either in progress or done. */
 212         age = jiffies - rp->c_timestamp;
 213         rp->c_timestamp = jiffies;
 214         lru_put_end(rp);
 215
 216         rtn = RC_DROPIT;
 217         /* Request being processed or excessive rexmits */
 218         if (rp->c_state == RC_INPROG || age < RC_DELAY)
 219                 goto out;
 220
 221         /* From the hall of fame of impractical attacks:
 222          * Is this a user who tries to snoop on the cache? */
 223         rtn = RC_DOIT;
 224         if (!rqstp->rq_secure && rp->c_secure)
 225                 goto out;
 226
 227         /* Compose RPC reply header */
 228         switch (rp->c_type) {
 229         case RC_NOCACHE:
 230                 break;
 231         case RC_REPLSTAT:
 232                 svc_putu32(&rqstp->rq_res.head[0], rp->c_replstat);
 233                 rtn = RC_REPLY;
 234                 break;
 235         case RC_REPLBUFF:
 236                 if (!nfsd_cache_append(rqstp, &rp->c_replvec))
 237                         goto out;       /* should not happen */
 238                 rtn = RC_REPLY;
 239                 break;
 240         default:
 241                 printk(KERN_WARNING "nfsd: bad repcache type %d\n", rp->c_type);
 242                 rp->c_state = RC_UNUSED;
 243         }
 244
 245         goto out;
 246 }
 247
 248 /*
 249  * Update a cache entry. This is called from nfsd_dispatch when
 250  * the procedure has been executed and the complete reply is in
 251  * rqstp->rq_res.
 252  *
 253  * We're copying around data here rather than swapping buffers because
 254  * the toplevel loop requires max-sized buffers, which would be a waste
 255  * of memory for a cache with a max reply size of 100 bytes (diropokres).
 256  *
 257  * If we should start to use different types of cache entries tailored
 258  * specifically for attrstat and fh's, we may save even more space.
 259  *
 260  * Also note that a cachetype of RC_NOCACHE can legally be passed when
 261  * nfsd failed to encode a reply that otherwise would have been cached.
 262  * In this case, nfsd_cache_update is called with statp == NULL.
 263  */
 264 void
 265 nfsd_cache_update(struct svc_rqst *rqstp, int cachetype, __be32 *statp)
 266 {
 267         struct svc_cacherep *rp;
 268         struct kvec     *resv = &rqstp->rq_res.head[0], *cachv;
 269         int             len;
 270
 271         if (!(rp = rqstp->rq_cacherep) || cache_disabled)
 272                 return;
 273
 274         len = resv->iov_len - ((char*)statp - (char*)resv->iov_base);
 275         len >>= 2;
 276
 277         /* Don't cache excessive amounts of data and XDR failures */
 278         if (!statp || len > (256 >> 2)) {
 279                 rp->c_state = RC_UNUSED;
 280                 return;
 281         }
 282
 283         switch (cachetype) {
 284         case RC_REPLSTAT:
 285                 if (len != 1)
 286                         printk("nfsd: RC_REPLSTAT/reply len %d!\n",len);
 287                 rp->c_replstat = *statp;
 288                 break;
 289         case RC_REPLBUFF:
 290                 cachv = &rp->c_replvec;
 291                 cachv->iov_base = kmalloc(len << 2, GFP_KERNEL);
 292                 if (!cachv->iov_base) {
 293                         spin_lock(&cache_lock);
 294                         rp->c_state = RC_UNUSED;
 295                         spin_unlock(&cache_lock);
 296                         return;
 297                 }
 298                 cachv->iov_len = len << 2;
 299                 memcpy(cachv->iov_base, statp, len << 2);
 300                 break;
 301         }
 302         spin_lock(&cache_lock);
 303         lru_put_end(rp);
 304         rp->c_secure = rqstp->rq_secure;
 305         rp->c_type = cachetype;
 306         rp->c_state = RC_DONE;
 307         rp->c_timestamp = jiffies;
 308         spin_unlock(&cache_lock);
 309         return;
 310 }
 311
 312 /*
 313  * Copy cached reply to current reply buffer. Should always fit.
 314  * FIXME as reply is in a page, we should just attach the page, and
 315  * keep a refcount....
 316  */
 317 static int
 318 nfsd_cache_append(struct svc_rqst *rqstp, struct kvec *data)
 319 {
 320         struct kvec     *vec = &rqstp->rq_res.head[0];
 321
 322         if (vec->iov_len + data->iov_len > PAGE_SIZE) {
 323                 printk(KERN_WARNING "nfsd: cached reply too large (%Zd).\n",
 324                                 data->iov_len);
 325                 return 0;
 326         }
 327         memcpy((char*)vec->iov_base + vec->iov_len, data->iov_base, data->iov_len);
 328         vec->iov_len += data->iov_len;
 329         return 1;
 330 }