shrink struct dentry
[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 asmlinkage long sys_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
202
203 static int dcookie_init(void)
204 {
205         struct list_head * d;
206         unsigned int i, hash_bits;
207         int err = -ENOMEM;
208
209         dcookie_cache = kmem_cache_create("dcookie_cache",
210                 sizeof(struct dcookie_struct),
211                 0, 0, NULL);
212
213         if (!dcookie_cache)
214                 goto out;
215
216         dcookie_hashtable = kmalloc(PAGE_SIZE, GFP_KERNEL);
217         if (!dcookie_hashtable)
218                 goto out_kmem;
219
220         err = 0;
221
222         /*
223          * Find the power-of-two list-heads that can fit into the allocation..
224          * We don't guarantee that "sizeof(struct list_head)" is necessarily
225          * a power-of-two.
226          */
227         hash_size = PAGE_SIZE / sizeof(struct list_head);
228         hash_bits = 0;
229         do {
230                 hash_bits++;
231         } while ((hash_size >> hash_bits) != 0);
232         hash_bits--;
233
234         /*
235          * Re-calculate the actual number of entries and the mask
236          * from the number of bits we can fit.
237          */
238         hash_size = 1UL << hash_bits;
239
240         /* And initialize the newly allocated array */
241         d = dcookie_hashtable;
242         i = hash_size;
243         do {
244                 INIT_LIST_HEAD(d);
245                 d++;
246                 i--;
247         } while (i);
248
249 out:
250         return err;
251 out_kmem:
252         kmem_cache_destroy(dcookie_cache);
253         goto out;
254 }
255
256
257 static void free_dcookie(struct dcookie_struct * dcs)
258 {
259         struct dentry *d = dcs->path.dentry;
260
261         spin_lock(&d->d_lock);
262         d->d_flags &= ~DCACHE_COOKIE;
263         spin_unlock(&d->d_lock);
264
265         path_put(&dcs->path);
266         kmem_cache_free(dcookie_cache, dcs);
267 }
268
269
270 static void dcookie_exit(void)
271 {
272         struct list_head * list;
273         struct list_head * pos;
274         struct list_head * pos2;
275         struct dcookie_struct * dcs;
276         size_t i;
277
278         for (i = 0; i < hash_size; ++i) {
279                 list = dcookie_hashtable + i;
280                 list_for_each_safe(pos, pos2, list) {
281                         dcs = list_entry(pos, struct dcookie_struct, hash_list);
282                         list_del(&dcs->hash_list);
283                         free_dcookie(dcs);
284                 }
285         }
286
287         kfree(dcookie_hashtable);
288         kmem_cache_destroy(dcookie_cache);
289 }
290
291
292 struct dcookie_user {
293         struct list_head next;
294 };
295  
296 struct dcookie_user * dcookie_register(void)
297 {
298         struct dcookie_user * user;
299
300         mutex_lock(&dcookie_mutex);
301
302         user = kmalloc(sizeof(struct dcookie_user), GFP_KERNEL);
303         if (!user)
304                 goto out;
305
306         if (!is_live() && dcookie_init())
307                 goto out_free;
308
309         list_add(&user->next, &dcookie_users);
310
311 out:
312         mutex_unlock(&dcookie_mutex);
313         return user;
314 out_free:
315         kfree(user);
316         user = NULL;
317         goto out;
318 }
319
320
321 void dcookie_unregister(struct dcookie_user * user)
322 {
323         mutex_lock(&dcookie_mutex);
324
325         list_del(&user->next);
326         kfree(user);
327
328         if (!is_live())
329                 dcookie_exit();
330
331         mutex_unlock(&dcookie_mutex);
332 }
333
334 EXPORT_SYMBOL_GPL(dcookie_register);
335 EXPORT_SYMBOL_GPL(dcookie_unregister);
336 EXPORT_SYMBOL_GPL(get_dcookie);