Root/fs/nfsd/nfscache.c

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, int type)
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 rtn;
132
133    rqstp->rq_cacherep = NULL;
134    if (cache_disabled || type == RC_NOCACHE) {
135        nfsdstats.rcnocache++;
136        return RC_DOIT;
137    }
138
139    spin_lock(&cache_lock);
140    rtn = RC_DOIT;
141
142    rh = &cache_hash[request_hash(xid)];
143    hlist_for_each_entry(rp, hn, rh, c_hash) {
144        if (rp->c_state != RC_UNUSED &&
145            xid == rp->c_xid && proc == rp->c_proc &&
146            proto == rp->c_prot && vers == rp->c_vers &&
147            time_before(jiffies, rp->c_timestamp + 120*HZ) &&
148            memcmp((char*)&rqstp->rq_addr, (char*)&rp->c_addr, sizeof(rp->c_addr))==0) {
149            nfsdstats.rchits++;
150            goto found_entry;
151        }
152    }
153    nfsdstats.rcmisses++;
154
155    /* This loop shouldn't take more than a few iterations normally */
156    {
157    int safe = 0;
158    list_for_each_entry(rp, &lru_head, c_lru) {
159        if (rp->c_state != RC_INPROG)
160            break;
161        if (safe++ > CACHESIZE) {
162            printk("nfsd: loop in repcache LRU list\n");
163            cache_disabled = 1;
164            goto out;
165        }
166    }
167    }
168
169    /* All entries on the LRU are in-progress. This should not happen */
170    if (&rp->c_lru == &lru_head) {
171        static int complaints;
172
173        printk(KERN_WARNING "nfsd: all repcache entries locked!\n");
174        if (++complaints > 5) {
175            printk(KERN_WARNING "nfsd: disabling repcache.\n");
176            cache_disabled = 1;
177        }
178        goto out;
179    }
180
181    rqstp->rq_cacherep = rp;
182    rp->c_state = RC_INPROG;
183    rp->c_xid = xid;
184    rp->c_proc = proc;
185    memcpy(&rp->c_addr, svc_addr_in(rqstp), sizeof(rp->c_addr));
186    rp->c_prot = proto;
187    rp->c_vers = vers;
188    rp->c_timestamp = jiffies;
189
190    hash_refile(rp);
191
192    /* release any buffer */
193    if (rp->c_type == RC_REPLBUFF) {
194        kfree(rp->c_replvec.iov_base);
195        rp->c_replvec.iov_base = NULL;
196    }
197    rp->c_type = RC_NOCACHE;
198 out:
199    spin_unlock(&cache_lock);
200    return rtn;
201
202found_entry:
203    /* We found a matching entry which is either in progress or done. */
204    age = jiffies - rp->c_timestamp;
205    rp->c_timestamp = jiffies;
206    lru_put_end(rp);
207
208    rtn = RC_DROPIT;
209    /* Request being processed or excessive rexmits */
210    if (rp->c_state == RC_INPROG || age < RC_DELAY)
211        goto out;
212
213    /* From the hall of fame of impractical attacks:
214     * Is this a user who tries to snoop on the cache? */
215    rtn = RC_DOIT;
216    if (!rqstp->rq_secure && rp->c_secure)
217        goto out;
218
219    /* Compose RPC reply header */
220    switch (rp->c_type) {
221    case RC_NOCACHE:
222        break;
223    case RC_REPLSTAT:
224        svc_putu32(&rqstp->rq_res.head[0], rp->c_replstat);
225        rtn = RC_REPLY;
226        break;
227    case RC_REPLBUFF:
228        if (!nfsd_cache_append(rqstp, &rp->c_replvec))
229            goto out; /* should not happen */
230        rtn = RC_REPLY;
231        break;
232    default:
233        printk(KERN_WARNING "nfsd: bad repcache type %d\n", rp->c_type);
234        rp->c_state = RC_UNUSED;
235    }
236
237    goto out;
238}
239
240/*
241 * Update a cache entry. This is called from nfsd_dispatch when
242 * the procedure has been executed and the complete reply is in
243 * rqstp->rq_res.
244 *
245 * We're copying around data here rather than swapping buffers because
246 * the toplevel loop requires max-sized buffers, which would be a waste
247 * of memory for a cache with a max reply size of 100 bytes (diropokres).
248 *
249 * If we should start to use different types of cache entries tailored
250 * specifically for attrstat and fh's, we may save even more space.
251 *
252 * Also note that a cachetype of RC_NOCACHE can legally be passed when
253 * nfsd failed to encode a reply that otherwise would have been cached.
254 * In this case, nfsd_cache_update is called with statp == NULL.
255 */
256void
257nfsd_cache_update(struct svc_rqst *rqstp, int cachetype, __be32 *statp)
258{
259    struct svc_cacherep *rp;
260    struct kvec *resv = &rqstp->rq_res.head[0], *cachv;
261    int len;
262
263    if (!(rp = rqstp->rq_cacherep) || cache_disabled)
264        return;
265
266    len = resv->iov_len - ((char*)statp - (char*)resv->iov_base);
267    len >>= 2;
268
269    /* Don't cache excessive amounts of data and XDR failures */
270    if (!statp || len > (256 >> 2)) {
271        rp->c_state = RC_UNUSED;
272        return;
273    }
274
275    switch (cachetype) {
276    case RC_REPLSTAT:
277        if (len != 1)
278            printk("nfsd: RC_REPLSTAT/reply len %d!\n",len);
279        rp->c_replstat = *statp;
280        break;
281    case RC_REPLBUFF:
282        cachv = &rp->c_replvec;
283        cachv->iov_base = kmalloc(len << 2, GFP_KERNEL);
284        if (!cachv->iov_base) {
285            spin_lock(&cache_lock);
286            rp->c_state = RC_UNUSED;
287            spin_unlock(&cache_lock);
288            return;
289        }
290        cachv->iov_len = len << 2;
291        memcpy(cachv->iov_base, statp, len << 2);
292        break;
293    }
294    spin_lock(&cache_lock);
295    lru_put_end(rp);
296    rp->c_secure = rqstp->rq_secure;
297    rp->c_type = cachetype;
298    rp->c_state = RC_DONE;
299    rp->c_timestamp = jiffies;
300    spin_unlock(&cache_lock);
301    return;
302}
303
304/*
305 * Copy cached reply to current reply buffer. Should always fit.
306 * FIXME as reply is in a page, we should just attach the page, and
307 * keep a refcount....
308 */
309static int
310nfsd_cache_append(struct svc_rqst *rqstp, struct kvec *data)
311{
312    struct kvec *vec = &rqstp->rq_res.head[0];
313
314    if (vec->iov_len + data->iov_len > PAGE_SIZE) {
315        printk(KERN_WARNING "nfsd: cached reply too large (%Zd).\n",
316                data->iov_len);
317        return 0;
318    }
319    memcpy((char*)vec->iov_base + vec->iov_len, data->iov_base, data->iov_len);
320    vec->iov_len += data->iov_len;
321    return 1;
322}
323

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