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)            (((((__force __u32)xid) >> 24) ^ ((__force __u32)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 = kcalloc (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
  77         cache_disabled = 0;
  78 }
  79
  80 void
  81 nfsd_cache_shutdown(void)
  82 {
  83         struct svc_cacherep     *rp;
  84
  85         while (!list_empty(&lru_head)) {
  86                 rp = list_entry(lru_head.next, struct svc_cacherep, c_lru);
  87                 if (rp->c_state == RC_DONE && rp->c_type == RC_REPLBUFF)
  88                         kfree(rp->c_replvec.iov_base);
  89                 list_del(&rp->c_lru);
  90                 kfree(rp);
  91         }
  92
  93         cache_disabled = 1;
  94
  95         kfree (hash_list);
  96         hash_list = NULL;
  97 }
  98
  99 /*
 100  * Move cache entry to end of LRU list
 101  */
 102 static void
 103 lru_put_end(struct svc_cacherep *rp)
 104 {
 105         list_move_tail(&rp->c_lru, &lru_head);
 106 }
 107
 108 /*
 109  * Move a cache entry from one hash list to another
 110  */
 111 static void
 112 hash_refile(struct svc_cacherep *rp)
 113 {
 114         hlist_del_init(&rp->c_hash);
 115         hlist_add_head(&rp->c_hash, hash_list + REQHASH(rp->c_xid));
 116 }
 117
 118 /*
 119  * Try to find an entry matching the current call in the cache. When none
 120  * is found, we grab the oldest unlocked entry off the LRU list.
 121  * Note that no operation within the loop may sleep.
 122  */
 123 int
 124 nfsd_cache_lookup(struct svc_rqst *rqstp, int type)
 125 {
 126         struct hlist_node       *hn;
 127         struct hlist_head       *rh;
 128         struct svc_cacherep     *rp;
 129         __be32                  xid = rqstp->rq_xid;
 130         u32                     proto =  rqstp->rq_prot,
 131                                 vers = rqstp->rq_vers,
 132                                 proc = rqstp->rq_proc;
 133         unsigned long           age;
 134         int rtn;
 135
 136         rqstp->rq_cacherep = NULL;
 137         if (cache_disabled || type == RC_NOCACHE) {
 138                 nfsdstats.rcnocache++;
 139                 return RC_DOIT;
 140         }
 141
 142         spin_lock(&cache_lock);
 143         rtn = RC_DOIT;
 144
 145         rh = &hash_list[REQHASH(xid)];
 146         hlist_for_each_entry(rp, hn, rh, c_hash) {
 147                 if (rp->c_state != RC_UNUSED &&
 148                     xid == rp->c_xid && proc == rp->c_proc &&
 149                     proto == rp->c_prot && vers == rp->c_vers &&
 150                     time_before(jiffies, rp->c_timestamp + 120*HZ) &&
 151                     memcmp((char*)&rqstp->rq_addr, (char*)&rp->c_addr, sizeof(rp->c_addr))==0) {
 152                         nfsdstats.rchits++;
 153                         goto found_entry;
 154                 }
 155         }
 156         nfsdstats.rcmisses++;
 157
 158         /* This loop shouldn't take more than a few iterations normally */
 159         {
 160         int     safe = 0;
 161         list_for_each_entry(rp, &lru_head, c_lru) {
 162                 if (rp->c_state != RC_INPROG)
 163                         break;
 164                 if (safe++ > CACHESIZE) {
 165                         printk("nfsd: loop in repcache LRU list\n");
 166                         cache_disabled = 1;
 167                         goto out;
 168                 }
 169         }
 170         }
 171
 172         /* This should not happen */
 173         if (rp == NULL) {
 174                 static int      complaints;
 175
 176                 printk(KERN_WARNING "nfsd: all repcache entries locked!\n");
 177                 if (++complaints > 5) {
 178                         printk(KERN_WARNING "nfsd: disabling repcache.\n");
 179                         cache_disabled = 1;
 180                 }
 181                 goto out;
 182         }
 183
 184         rqstp->rq_cacherep = rp;
 185         rp->c_state = RC_INPROG;
 186         rp->c_xid = xid;
 187         rp->c_proc = proc;
 188         memcpy(&rp->c_addr, svc_addr_in(rqstp), sizeof(rp->c_addr));
 189         rp->c_prot = proto;
 190         rp->c_vers = vers;
 191         rp->c_timestamp = jiffies;
 192
 193         hash_refile(rp);
 194
 195         /* release any buffer */
 196         if (rp->c_type == RC_REPLBUFF) {
 197                 kfree(rp->c_replvec.iov_base);
 198                 rp->c_replvec.iov_base = NULL;
 199         }
 200         rp->c_type = RC_NOCACHE;
 201  out:
 202         spin_unlock(&cache_lock);
 203         return rtn;
 204
 205 found_entry:
 206         /* We found a matching entry which is either in progress or done. */
 207         age = jiffies - rp->c_timestamp;
 208         rp->c_timestamp = jiffies;
 209         lru_put_end(rp);
 210
 211         rtn = RC_DROPIT;
 212         /* Request being processed or excessive rexmits */
 213         if (rp->c_state == RC_INPROG || age < RC_DELAY)
 214                 goto out;
 215
 216         /* From the hall of fame of impractical attacks:
 217          * Is this a user who tries to snoop on the cache? */
 218         rtn = RC_DOIT;
 219         if (!rqstp->rq_secure && rp->c_secure)
 220                 goto out;
 221
 222         /* Compose RPC reply header */
 223         switch (rp->c_type) {
 224         case RC_NOCACHE:
 225                 break;
 226         case RC_REPLSTAT:
 227                 svc_putu32(&rqstp->rq_res.head[0], rp->c_replstat);
 228                 rtn = RC_REPLY;
 229                 break;
 230         case RC_REPLBUFF:
 231                 if (!nfsd_cache_append(rqstp, &rp->c_replvec))
 232                         goto out;       /* should not happen */
 233                 rtn = RC_REPLY;
 234                 break;
 235         default:
 236                 printk(KERN_WARNING "nfsd: bad repcache type %d\n", rp->c_type);
 237                 rp->c_state = RC_UNUSED;
 238         }
 239
 240         goto out;
 241 }
 242
 243 /*
 244  * Update a cache entry. This is called from nfsd_dispatch when
 245  * the procedure has been executed and the complete reply is in
 246  * rqstp->rq_res.
 247  *
 248  * We're copying around data here rather than swapping buffers because
 249  * the toplevel loop requires max-sized buffers, which would be a waste
 250  * of memory for a cache with a max reply size of 100 bytes (diropokres).
 251  *
 252  * If we should start to use different types of cache entries tailored
 253  * specifically for attrstat and fh's, we may save even more space.
 254  *
 255  * Also note that a cachetype of RC_NOCACHE can legally be passed when
 256  * nfsd failed to encode a reply that otherwise would have been cached.
 257  * In this case, nfsd_cache_update is called with statp == NULL.
 258  */
 259 void
 260 nfsd_cache_update(struct svc_rqst *rqstp, int cachetype, __be32 *statp)
 261 {
 262         struct svc_cacherep *rp;
 263         struct kvec     *resv = &rqstp->rq_res.head[0], *cachv;
 264         int             len;
 265
 266         if (!(rp = rqstp->rq_cacherep) || cache_disabled)
 267                 return;
 268
 269         len = resv->iov_len - ((char*)statp - (char*)resv->iov_base);
 270         len >>= 2;
 271
 272         /* Don't cache excessive amounts of data and XDR failures */
 273         if (!statp || len > (256 >> 2)) {
 274                 rp->c_state = RC_UNUSED;
 275                 return;
 276         }
 277
 278         switch (cachetype) {
 279         case RC_REPLSTAT:
 280                 if (len != 1)
 281                         printk("nfsd: RC_REPLSTAT/reply len %d!\n",len);
 282                 rp->c_replstat = *statp;
 283                 break;
 284         case RC_REPLBUFF:
 285                 cachv = &rp->c_replvec;
 286                 cachv->iov_base = kmalloc(len << 2, GFP_KERNEL);
 287                 if (!cachv->iov_base) {
 288                         spin_lock(&cache_lock);
 289                         rp->c_state = RC_UNUSED;
 290                         spin_unlock(&cache_lock);
 291                         return;
 292                 }
 293                 cachv->iov_len = len << 2;
 294                 memcpy(cachv->iov_base, statp, len << 2);
 295                 break;
 296         }
 297         spin_lock(&cache_lock);
 298         lru_put_end(rp);
 299         rp->c_secure = rqstp->rq_secure;
 300         rp->c_type = cachetype;
 301         rp->c_state = RC_DONE;
 302         rp->c_timestamp = jiffies;
 303         spin_unlock(&cache_lock);
 304         return;
 305 }
 306
 307 /*
 308  * Copy cached reply to current reply buffer. Should always fit.
 309  * FIXME as reply is in a page, we should just attach the page, and
 310  * keep a refcount....
 311  */
 312 static int
 313 nfsd_cache_append(struct svc_rqst *rqstp, struct kvec *data)
 314 {
 315         struct kvec     *vec = &rqstp->rq_res.head[0];
 316
 317         if (vec->iov_len + data->iov_len > PAGE_SIZE) {
 318                 printk(KERN_WARNING "nfsd: cached reply too large (%Zd).\n",
 319                                 data->iov_len);
 320                 return 0;
 321         }
 322         memcpy((char*)vec->iov_base + vec->iov_len, data->iov_base, data->iov_len);
 323         vec->iov_len += data->iov_len;
 324         return 1;
 325 }