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