move virtrng_remove to .devexit.text
[linux-2.6.git] / fs / dcookies.c
1 /*
2  * dcookies.c
3  *
4  * Copyright 2002 John Levon <levon@movementarian.org>
5  *
6  * Persistent cookie-path mappings. These are used by
7  * profilers to convert a per-task EIP value into something
8  * non-transitory that can be processed at a later date.
9  * This is done by locking the dentry/vfsmnt pair in the
10  * kernel until released by the tasks needing the persistent
11  * objects. The tag is simply an unsigned long that refers
12  * to the pair and can be looked up from userspace.
13  */
14
15 #include <linux/syscalls.h>
16 #include <linux/module.h>
17 #include <linux/slab.h>
18 #include <linux/list.h>
19 #include <linux/mount.h>
20 #include <linux/capability.h>
21 #include <linux/dcache.h>
22 #include <linux/mm.h>
23 #include <linux/err.h>
24 #include <linux/errno.h>
25 #include <linux/dcookies.h>
26 #include <linux/mutex.h>
27 #include <linux/path.h>
28 #include <asm/uaccess.h>
29
30 /* The dcookies are allocated from a kmem_cache and
31  * hashed onto a small number of lists. None of the
32  * code here is particularly performance critical
33  */
34 struct dcookie_struct {
35         struct path path;
36         struct list_head hash_list;
37 };
38
39 static LIST_HEAD(dcookie_users);
40 static DEFINE_MUTEX(dcookie_mutex);
41 static struct kmem_cache *dcookie_cache __read_mostly;
42 static struct list_head *dcookie_hashtable __read_mostly;
43 static size_t hash_size __read_mostly;
44
45 static inline int is_live(void)
46 {
47         return !(list_empty(&dcookie_users));
48 }
49
50
51 /* The dentry is locked, its address will do for the cookie */
52 static inline unsigned long dcookie_value(struct dcookie_struct * dcs)
53 {
54         return (unsigned long)dcs->path.dentry;
55 }
56
57
58 static size_t dcookie_hash(unsigned long dcookie)
59 {
60         return (dcookie >> L1_CACHE_SHIFT) & (hash_size - 1);
61 }
62
63
64 static struct dcookie_struct * find_dcookie(unsigned long dcookie)
65 {
66         struct dcookie_struct *found = NULL;
67         struct dcookie_struct * dcs;
68         struct list_head * pos;
69         struct list_head * list;
70
71         list = dcookie_hashtable + dcookie_hash(dcookie);
72
73         list_for_each(pos, list) {
74                 dcs = list_entry(pos, struct dcookie_struct, hash_list);
75                 if (dcookie_value(dcs) == dcookie) {
76                         found = dcs;
77                         break;
78                 }
79         }
80
81         return found;
82 }
83
84
85 static void hash_dcookie(struct dcookie_struct * dcs)
86 {
87         struct list_head * list = dcookie_hashtable + dcookie_hash(dcookie_value(dcs));
88         list_add(&dcs->hash_list, list);
89 }
90
91
92 static struct dcookie_struct *alloc_dcookie(struct path *path)
93 {
94         struct dcookie_struct *dcs = kmem_cache_alloc(dcookie_cache,
95                                                         GFP_KERNEL);
96         struct dentry *d;
97         if (!dcs)
98                 return NULL;
99
100         d = path->dentry;
101         spin_lock(&d->d_lock);
102         d->d_flags |= DCACHE_COOKIE;
103         spin_unlock(&d->d_lock);
104
105         dcs->path = *path;
106         path_get(path);
107         hash_dcookie(dcs);
108         return dcs;
109 }
110
111
112 /* This is the main kernel-side routine that retrieves the cookie
113  * value for a dentry/vfsmnt pair.
114  */
115 int get_dcookie(struct path *path, unsigned long *cookie)
116 {
117         int err = 0;
118         struct dcookie_struct * dcs;
119
120         mutex_lock(&dcookie_mutex);
121
122         if (!is_live()) {
123                 err = -EINVAL;
124                 goto out;
125         }
126
127         if (path->dentry->d_flags & DCACHE_COOKIE) {
128                 dcs = find_dcookie((unsigned long)path->dentry);
129         } else {
130                 dcs = alloc_dcookie(path);
131                 if (!dcs) {
132                         err = -ENOMEM;
133                         goto out;
134                 }
135         }
136
137         *cookie = dcookie_value(dcs);
138
139 out:
140         mutex_unlock(&dcookie_mutex);
141         return err;
142 }
143
144
145 /* And here is where the userspace process can look up the cookie value
146  * to retrieve the path.
147  */
148 SYSCALL_DEFINE(lookup_dcookie)(u64 cookie64, char __user * buf, size_t len)
149 {
150         unsigned long cookie = (unsigned long)cookie64;
151         int err = -EINVAL;
152         char * kbuf;
153         char * path;
154         size_t pathlen;
155         struct dcookie_struct * dcs;
156
157         /* we could leak path information to users
158          * without dir read permission without this
159          */
160         if (!capable(CAP_SYS_ADMIN))
161                 return -EPERM;
162
163         mutex_lock(&dcookie_mutex);
164
165         if (!is_live()) {
166                 err = -EINVAL;
167                 goto out;
168         }
169
170         if (!(dcs = find_dcookie(cookie)))
171                 goto out;
172
173         err = -ENOMEM;
174         kbuf = kmalloc(PAGE_SIZE, GFP_KERNEL);
175         if (!kbuf)
176                 goto out;
177
178         /* FIXME: (deleted) ? */
179         path = d_path(&dcs->path, kbuf, PAGE_SIZE);
180
181         if (IS_ERR(path)) {
182                 err = PTR_ERR(path);
183                 goto out_free;
184         }
185
186         err = -ERANGE;
187  
188         pathlen = kbuf + PAGE_SIZE - path;
189         if (pathlen <= len) {
190                 err = pathlen;
191                 if (copy_to_user(buf, path, pathlen))
192                         err = -EFAULT;
193         }
194
195 out_free:
196         kfree(kbuf);
197 out:
198         mutex_unlock(&dcookie_mutex);
199         return err;
200 }
201 #ifdef CONFIG_HAVE_SYSCALL_WRAPPERS
202 asmlinkage long SyS_lookup_dcookie(u64 cookie64, long buf, long len)
203 {
204         return SYSC_lookup_dcookie(cookie64, (char __user *) buf, (size_t) len);
205 }
206 SYSCALL_ALIAS(sys_lookup_dcookie, SyS_lookup_dcookie);
207 #endif
208
209 static int dcookie_init(void)
210 {
211         struct list_head * d;
212         unsigned int i, hash_bits;
213         int err = -ENOMEM;
214
215         dcookie_cache = kmem_cache_create("dcookie_cache",
216                 sizeof(struct dcookie_struct),
217                 0, 0, NULL);
218
219         if (!dcookie_cache)
220                 goto out;
221
222         dcookie_hashtable = kmalloc(PAGE_SIZE, GFP_KERNEL);
223         if (!dcookie_hashtable)
224                 goto out_kmem;
225
226         err = 0;
227
228         /*
229          * Find the power-of-two list-heads that can fit into the allocation..
230          * We don't guarantee that "sizeof(struct list_head)" is necessarily
231          * a power-of-two.
232          */
233         hash_size = PAGE_SIZE / sizeof(struct list_head);
234         hash_bits = 0;
235         do {
236                 hash_bits++;
237         } while ((hash_size >> hash_bits) != 0);
238         hash_bits--;
239
240         /*
241          * Re-calculate the actual number of entries and the mask
242          * from the number of bits we can fit.
243          */
244         hash_size = 1UL << hash_bits;
245
246         /* And initialize the newly allocated array */
247         d = dcookie_hashtable;
248         i = hash_size;
249         do {
250                 INIT_LIST_HEAD(d);
251                 d++;
252                 i--;
253         } while (i);
254
255 out:
256         return err;
257 out_kmem:
258         kmem_cache_destroy(dcookie_cache);
259         goto out;
260 }
261
262
263 static void free_dcookie(struct dcookie_struct * dcs)
264 {
265         struct dentry *d = dcs->path.dentry;
266
267         spin_lock(&d->d_lock);
268         d->d_flags &= ~DCACHE_COOKIE;
269         spin_unlock(&d->d_lock);
270
271         path_put(&dcs->path);
272         kmem_cache_free(dcookie_cache, dcs);
273 }
274
275
276 static void dcookie_exit(void)
277 {
278         struct list_head * list;
279         struct list_head * pos;
280         struct list_head * pos2;
281         struct dcookie_struct * dcs;
282         size_t i;
283
284         for (i = 0; i < hash_size; ++i) {
285                 list = dcookie_hashtable + i;
286                 list_for_each_safe(pos, pos2, list) {
287                         dcs = list_entry(pos, struct dcookie_struct, hash_list);
288                         list_del(&dcs->hash_list);
289                         free_dcookie(dcs);
290                 }
291         }
292
293         kfree(dcookie_hashtable);
294         kmem_cache_destroy(dcookie_cache);
295 }
296
297
298 struct dcookie_user {
299         struct list_head next;
300 };
301  
302 struct dcookie_user * dcookie_register(void)
303 {
304         struct dcookie_user * user;
305
306         mutex_lock(&dcookie_mutex);
307
308         user = kmalloc(sizeof(struct dcookie_user), GFP_KERNEL);
309         if (!user)
310                 goto out;
311
312         if (!is_live() && dcookie_init())
313                 goto out_free;
314
315         list_add(&user->next, &dcookie_users);
316
317 out:
318         mutex_unlock(&dcookie_mutex);
319         return user;
320 out_free:
321         kfree(user);
322         user = NULL;
323         goto out;
324 }
325
326
327 void dcookie_unregister(struct dcookie_user * user)
328 {
329         mutex_lock(&dcookie_mutex);
330
331         list_del(&user->next);
332         kfree(user);
333
334         if (!is_live())
335                 dcookie_exit();
336
337         mutex_unlock(&dcookie_mutex);
338 }
339
340 EXPORT_SYMBOL_GPL(dcookie_register);
341 EXPORT_SYMBOL_GPL(dcookie_unregister);
342 EXPORT_SYMBOL_GPL(get_dcookie);