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