d_path: Make d_path() use a struct path
[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         if (!dcs)
97                 return NULL;
98
99         path->dentry->d_cookie = dcs;
100         dcs->path = *path;
101         path_get(path);
102         hash_dcookie(dcs);
103         return dcs;
104 }
105
106
107 /* This is the main kernel-side routine that retrieves the cookie
108  * value for a dentry/vfsmnt pair.
109  */
110 int get_dcookie(struct path *path, unsigned long *cookie)
111 {
112         int err = 0;
113         struct dcookie_struct * dcs;
114
115         mutex_lock(&dcookie_mutex);
116
117         if (!is_live()) {
118                 err = -EINVAL;
119                 goto out;
120         }
121
122         dcs = path->dentry->d_cookie;
123
124         if (!dcs)
125                 dcs = alloc_dcookie(path);
126
127         if (!dcs) {
128                 err = -ENOMEM;
129                 goto out;
130         }
131
132         *cookie = dcookie_value(dcs);
133
134 out:
135         mutex_unlock(&dcookie_mutex);
136         return err;
137 }
138
139
140 /* And here is where the userspace process can look up the cookie value
141  * to retrieve the path.
142  */
143 asmlinkage long sys_lookup_dcookie(u64 cookie64, char __user * buf, size_t len)
144 {
145         unsigned long cookie = (unsigned long)cookie64;
146         int err = -EINVAL;
147         char * kbuf;
148         char * path;
149         size_t pathlen;
150         struct dcookie_struct * dcs;
151
152         /* we could leak path information to users
153          * without dir read permission without this
154          */
155         if (!capable(CAP_SYS_ADMIN))
156                 return -EPERM;
157
158         mutex_lock(&dcookie_mutex);
159
160         if (!is_live()) {
161                 err = -EINVAL;
162                 goto out;
163         }
164
165         if (!(dcs = find_dcookie(cookie)))
166                 goto out;
167
168         err = -ENOMEM;
169         kbuf = kmalloc(PAGE_SIZE, GFP_KERNEL);
170         if (!kbuf)
171                 goto out;
172
173         /* FIXME: (deleted) ? */
174         path = d_path(&dcs->path, kbuf, PAGE_SIZE);
175
176         if (IS_ERR(path)) {
177                 err = PTR_ERR(path);
178                 goto out_free;
179         }
180
181         err = -ERANGE;
182  
183         pathlen = kbuf + PAGE_SIZE - path;
184         if (pathlen <= len) {
185                 err = pathlen;
186                 if (copy_to_user(buf, path, pathlen))
187                         err = -EFAULT;
188         }
189
190 out_free:
191         kfree(kbuf);
192 out:
193         mutex_unlock(&dcookie_mutex);
194         return err;
195 }
196
197
198 static int dcookie_init(void)
199 {
200         struct list_head * d;
201         unsigned int i, hash_bits;
202         int err = -ENOMEM;
203
204         dcookie_cache = kmem_cache_create("dcookie_cache",
205                 sizeof(struct dcookie_struct),
206                 0, 0, NULL);
207
208         if (!dcookie_cache)
209                 goto out;
210
211         dcookie_hashtable = kmalloc(PAGE_SIZE, GFP_KERNEL);
212         if (!dcookie_hashtable)
213                 goto out_kmem;
214
215         err = 0;
216
217         /*
218          * Find the power-of-two list-heads that can fit into the allocation..
219          * We don't guarantee that "sizeof(struct list_head)" is necessarily
220          * a power-of-two.
221          */
222         hash_size = PAGE_SIZE / sizeof(struct list_head);
223         hash_bits = 0;
224         do {
225                 hash_bits++;
226         } while ((hash_size >> hash_bits) != 0);
227         hash_bits--;
228
229         /*
230          * Re-calculate the actual number of entries and the mask
231          * from the number of bits we can fit.
232          */
233         hash_size = 1UL << hash_bits;
234
235         /* And initialize the newly allocated array */
236         d = dcookie_hashtable;
237         i = hash_size;
238         do {
239                 INIT_LIST_HEAD(d);
240                 d++;
241                 i--;
242         } while (i);
243
244 out:
245         return err;
246 out_kmem:
247         kmem_cache_destroy(dcookie_cache);
248         goto out;
249 }
250
251
252 static void free_dcookie(struct dcookie_struct * dcs)
253 {
254         dcs->path.dentry->d_cookie = NULL;
255         path_put(&dcs->path);
256         kmem_cache_free(dcookie_cache, dcs);
257 }
258
259
260 static void dcookie_exit(void)
261 {
262         struct list_head * list;
263         struct list_head * pos;
264         struct list_head * pos2;
265         struct dcookie_struct * dcs;
266         size_t i;
267
268         for (i = 0; i < hash_size; ++i) {
269                 list = dcookie_hashtable + i;
270                 list_for_each_safe(pos, pos2, list) {
271                         dcs = list_entry(pos, struct dcookie_struct, hash_list);
272                         list_del(&dcs->hash_list);
273                         free_dcookie(dcs);
274                 }
275         }
276
277         kfree(dcookie_hashtable);
278         kmem_cache_destroy(dcookie_cache);
279 }
280
281
282 struct dcookie_user {
283         struct list_head next;
284 };
285  
286 struct dcookie_user * dcookie_register(void)
287 {
288         struct dcookie_user * user;
289
290         mutex_lock(&dcookie_mutex);
291
292         user = kmalloc(sizeof(struct dcookie_user), GFP_KERNEL);
293         if (!user)
294                 goto out;
295
296         if (!is_live() && dcookie_init())
297                 goto out_free;
298
299         list_add(&user->next, &dcookie_users);
300
301 out:
302         mutex_unlock(&dcookie_mutex);
303         return user;
304 out_free:
305         kfree(user);
306         user = NULL;
307         goto out;
308 }
309
310
311 void dcookie_unregister(struct dcookie_user * user)
312 {
313         mutex_lock(&dcookie_mutex);
314
315         list_del(&user->next);
316         kfree(user);
317
318         if (!is_live())
319                 dcookie_exit();
320
321         mutex_unlock(&dcookie_mutex);
322 }
323
324 EXPORT_SYMBOL_GPL(dcookie_register);
325 EXPORT_SYMBOL_GPL(dcookie_unregister);
326 EXPORT_SYMBOL_GPL(get_dcookie);