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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 
 25 static struct hlist_head *      cache_hash;
 26 static struct list_head         lru_head;
 27 static int                      cache_disabled = 1;
 28 
 29 /*
 30  * Calculate the hash index from an XID.
 31  */
 32 static inline u32 request_hash(u32 xid)
 33 {
 34         u32 h = xid;
 35         h ^= (xid >> 24);
 36         return h & (HASHSIZE-1);
 37 }
 38 
 39 static 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  */
 46 static DEFINE_SPINLOCK(cache_lock);
 47 
 48 int 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;
 72 out_nomem:
 73         printk(KERN_ERR "nfsd: failed to allocate reply cache\n");
 74         nfsd_reply_cache_shutdown();
 75         return -ENOMEM;
 76 }
 77 
 78 void 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  */
 99 static void
100 lru_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  */
108 static void
109 hash_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  */
120 int
121 nfsd_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 
203 found_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  */
257 void
258 nfsd_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  */
310 static int
311 nfsd_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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