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
34static struct hlist_head *	hash_list;
35static struct list_head 	lru_head;
36static int			cache_disabled = 1;
37
38static 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 */
45static DEFINE_SPINLOCK(cache_lock);
46
47void
48nfsd_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
80void
81nfsd_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 */
102static void
103lru_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 */
111static void
112hash_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 */
123int
124nfsd_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
205found_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 */
259void
260nfsd_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
307static int
308nfsd_cache_append(struct svc_rqst *rqstp, struct kvec *data)
309{
310	struct kvec	*vec = &rqstp->rq_res.head[0];
311
312	if (vec->iov_len + data->iov_len > PAGE_SIZE) {
313		printk(KERN_WARNING "nfsd: cached reply too large (%Zd).\n",
314				data->iov_len);
315		return 0;
316	}
317	memcpy((char*)vec->iov_base + vec->iov_len, data->iov_base, data->iov_len);
318	vec->iov_len += data->iov_len;
319	return 1;
320}
321