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