[linux.git] / fs / dcookies.c

/*
 * dcookies.c
 *
 * Copyright 2002 John Levon <[email protected]>
 *
 * Persistent cookie-path mappings. These are used by
 * profilers to convert a per-task EIP value into something
 * non-transitory that can be processed at a later date.
 * This is done by locking the dentry/vfsmnt pair in the
 * kernel until released by the tasks needing the persistent
 * objects. The tag is simply an unsigned long that refers
 * to the pair and can be looked up from userspace.
 */

#include <linux/config.h>
#include <linux/syscalls.h>
#include <linux/module.h>
#include <linux/slab.h>
#include <linux/list.h>
#include <linux/mount.h>
#include <linux/dcache.h>
#include <linux/mm.h>
#include <linux/errno.h>
#include <linux/dcookies.h>
#include <asm/uaccess.h>

/* The dcookies are allocated from a kmem_cache and
 * hashed onto a small number of lists. None of the
 * code here is particularly performance critical
 */
struct dcookie_struct {
	struct dentry * dentry;
	struct vfsmount * vfsmnt;
	struct list_head hash_list;
};

static LIST_HEAD(dcookie_users);
static DECLARE_MUTEX(dcookie_sem);
static kmem_cache_t * dcookie_cache;
static struct list_head * dcookie_hashtable;
static size_t hash_size;

static inline int is_live(void)
{
	return !(list_empty(&dcookie_users));
}


/* The dentry is locked, its address will do for the cookie */
static inline unsigned long dcookie_value(struct dcookie_struct * dcs)
{
	return (unsigned long)dcs->dentry;
}


static size_t dcookie_hash(unsigned long dcookie)
{
	return (dcookie >> L1_CACHE_SHIFT) & (hash_size - 1);
}


static struct dcookie_struct * find_dcookie(unsigned long dcookie)
{
	struct dcookie_struct *found = NULL;
	struct dcookie_struct * dcs;
	struct list_head * pos;
	struct list_head * list;

	list = dcookie_hashtable + dcookie_hash(dcookie);

	list_for_each(pos, list) {
		dcs = list_entry(pos, struct dcookie_struct, hash_list);
		if (dcookie_value(dcs) == dcookie) {
			found = dcs;
			break;
		}
	}

	return found;
}


static void hash_dcookie(struct dcookie_struct * dcs)
{
	struct list_head * list = dcookie_hashtable + dcookie_hash(dcookie_value(dcs));
	list_add(&dcs->hash_list, list);
}


static struct dcookie_struct * alloc_dcookie(struct dentry * dentry,
	struct vfsmount * vfsmnt)
{
	struct dcookie_struct * dcs = kmem_cache_alloc(dcookie_cache, GFP_KERNEL);
	if (!dcs)
		return NULL;

	dentry->d_cookie = dcs;

	dcs->dentry = dget(dentry);
	dcs->vfsmnt = mntget(vfsmnt);
	hash_dcookie(dcs);

	return dcs;
}


/* This is the main kernel-side routine that retrieves the cookie
 * value for a dentry/vfsmnt pair.
 */
int get_dcookie(struct dentry * dentry, struct vfsmount * vfsmnt,
	unsigned long * cookie)
{
	int err = 0;
	struct dcookie_struct * dcs;

	down(&dcookie_sem);

	if (!is_live()) {
		err = -EINVAL;
		goto out;
	}

	dcs = dentry->d_cookie;

	if (!dcs)
		dcs = alloc_dcookie(dentry, vfsmnt);

	if (!dcs) {
		err = -ENOMEM;
		goto out;
	}

	*cookie = dcookie_value(dcs);

out:
	up(&dcookie_sem);
	return err;
}


/* And here is where the userspace process can look up the cookie value
 * to retrieve the path.
 */
asmlinkage long sys_lookup_dcookie(u64 cookie64, char __user * buf, size_t len)
{
	unsigned long cookie = (unsigned long)cookie64;
	int err = -EINVAL;
	char * kbuf;
	char * path;
	size_t pathlen;
	struct dcookie_struct * dcs;

	/* we could leak path information to users
	 * without dir read permission without this
	 */
	if (!capable(CAP_SYS_ADMIN))
		return -EPERM;

	down(&dcookie_sem);

	if (!is_live()) {
		err = -EINVAL;
		goto out;
	}

	if (!(dcs = find_dcookie(cookie)))
		goto out;

	err = -ENOMEM;
	kbuf = kmalloc(PAGE_SIZE, GFP_KERNEL);
	if (!kbuf)
		goto out;

	/* FIXME: (deleted) ? */
	path = d_path(dcs->dentry, dcs->vfsmnt, kbuf, PAGE_SIZE);

	if (IS_ERR(path)) {
		err = PTR_ERR(path);
		goto out_free;
	}

	err = -ERANGE;
 
	pathlen = kbuf + PAGE_SIZE - path;
	if (pathlen <= len) {
		err = pathlen;
		if (copy_to_user(buf, path, pathlen))
			err = -EFAULT;
	}

out_free:
	kfree(kbuf);
out:
	up(&dcookie_sem);
	return err;
}


static int dcookie_init(void)
{
	struct list_head * d;
	unsigned int i, hash_bits;
	int err = -ENOMEM;

	dcookie_cache = kmem_cache_create("dcookie_cache",
		sizeof(struct dcookie_struct),
		0, 0, NULL, NULL);

	if (!dcookie_cache)
		goto out;

	dcookie_hashtable = kmalloc(PAGE_SIZE, GFP_KERNEL);
	if (!dcookie_hashtable)
		goto out_kmem;

	err = 0;

	/*
	 * Find the power-of-two list-heads that can fit into the allocation..
	 * We don't guarantee that "sizeof(struct list_head)" is necessarily
	 * a power-of-two.
	 */
	hash_size = PAGE_SIZE / sizeof(struct list_head);
	hash_bits = 0;
	do {
		hash_bits++;
	} while ((hash_size >> hash_bits) != 0);
	hash_bits--;

	/*
	 * Re-calculate the actual number of entries and the mask
	 * from the number of bits we can fit.
	 */
	hash_size = 1UL << hash_bits;

	/* And initialize the newly allocated array */
	d = dcookie_hashtable;
	i = hash_size;
	do {
		INIT_LIST_HEAD(d);
		d++;
		i--;
	} while (i);

out:
	return err;
out_kmem:
	kmem_cache_destroy(dcookie_cache);
	goto out;
}


static void free_dcookie(struct dcookie_struct * dcs)
{
	dcs->dentry->d_cookie = NULL;
	dput(dcs->dentry);
	mntput(dcs->vfsmnt);
	kmem_cache_free(dcookie_cache, dcs);
}


static void dcookie_exit(void)
{
	struct list_head * list;
	struct list_head * pos;
	struct list_head * pos2;
	struct dcookie_struct * dcs;
	size_t i;

	for (i = 0; i < hash_size; ++i) {
		list = dcookie_hashtable + i;
		list_for_each_safe(pos, pos2, list) {
			dcs = list_entry(pos, struct dcookie_struct, hash_list);
			list_del(&dcs->hash_list);
			free_dcookie(dcs);
		}
	}

	kfree(dcookie_hashtable);
	kmem_cache_destroy(dcookie_cache);
}


struct dcookie_user {
	struct list_head next;
};
 
struct dcookie_user * dcookie_register(void)
{
	struct dcookie_user * user;

	down(&dcookie_sem);

	user = kmalloc(sizeof(struct dcookie_user), GFP_KERNEL);
	if (!user)
		goto out;

	if (!is_live() && dcookie_init())
		goto out_free;

	list_add(&user->next, &dcookie_users);

out:
	up(&dcookie_sem);
	return user;
out_free:
	kfree(user);
	user = NULL;
	goto out;
}


void dcookie_unregister(struct dcookie_user * user)
{
	down(&dcookie_sem);

	list_del(&user->next);
	kfree(user);

	if (!is_live())
		dcookie_exit();

	up(&dcookie_sem);
}

EXPORT_SYMBOL_GPL(dcookie_register);
EXPORT_SYMBOL_GPL(dcookie_unregister);
EXPORT_SYMBOL_GPL(get_dcookie);
Commit	Line	Data
1da177e4 LT	1	/*
	2	* dcookies.c
	3	*
	4	* Copyright 2002 John Levon <[email protected]>
	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/config.h>
	16	#include <linux/syscalls.h>
	17	#include <linux/module.h>
	18	#include <linux/slab.h>
	19	#include <linux/list.h>
	20	#include <linux/mount.h>
	21	#include <linux/dcache.h>
	22	#include <linux/mm.h>
	23	#include <linux/errno.h>
	24	#include <linux/dcookies.h>
	25	#include <asm/uaccess.h>
	26
	27	/* The dcookies are allocated from a kmem_cache and
	28	* hashed onto a small number of lists. None of the
	29	* code here is particularly performance critical
	30	*/
	31	struct dcookie_struct {
	32	struct dentry * dentry;
	33	struct vfsmount * vfsmnt;
	34	struct list_head hash_list;
	35	};
	36
	37	static LIST_HEAD(dcookie_users);
	38	static DECLARE_MUTEX(dcookie_sem);
	39	static kmem_cache_t * dcookie_cache;
	40	static struct list_head * dcookie_hashtable;
	41	static size_t hash_size;
	42
	43	static inline int is_live(void)
	44	{
	45	return !(list_empty(&dcookie_users));
	46	}
	47
	48
	49	/* The dentry is locked, its address will do for the cookie */
	50	static inline unsigned long dcookie_value(struct dcookie_struct * dcs)
	51	{
	52	return (unsigned long)dcs->dentry;
	53	}
	54
	55
	56	static size_t dcookie_hash(unsigned long dcookie)
	57	{
	58	return (dcookie >> L1_CACHE_SHIFT) & (hash_size - 1);
	59	}
	60
	61
	62	static struct dcookie_struct * find_dcookie(unsigned long dcookie)
	63	{
	64	struct dcookie_struct *found = NULL;
65	struct dcookie_struct * dcs;
66	struct list_head * pos;
67	struct list_head * list;
68
69	list = dcookie_hashtable + dcookie_hash(dcookie);
70
71	list_for_each(pos, list) {
72	dcs = list_entry(pos, struct dcookie_struct, hash_list);
73	if (dcookie_value(dcs) == dcookie) {
74	found = dcs;
75	break;
76	}
77	}
78
79	return found;
80	}
81
82
83	static void hash_dcookie(struct dcookie_struct * dcs)
84	{
85	struct list_head * list = dcookie_hashtable + dcookie_hash(dcookie_value(dcs));
86	list_add(&dcs->hash_list, list);
87	}
88
89
90	static struct dcookie_struct * alloc_dcookie(struct dentry * dentry,
91	struct vfsmount * vfsmnt)
92	{
93	struct dcookie_struct * dcs = kmem_cache_alloc(dcookie_cache, GFP_KERNEL);
94	if (!dcs)
95	return NULL;
96
1da177e4 LT	97	dentry->d_cookie = dcs;
1da177e4 LT	98
732dbef6 MS	99	dcs->dentry = dget(dentry);
732dbef6 MS	100	dcs->vfsmnt = mntget(vfsmnt);
1da177e4 LT	101	hash_dcookie(dcs);
	102
	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 dentry * dentry, struct vfsmount * vfsmnt,
	111	unsigned long * cookie)
	112	{
	113	int err = 0;
	114	struct dcookie_struct * dcs;
	115
	116	down(&dcookie_sem);
	117
	118	if (!is_live()) {
	119	err = -EINVAL;
	120	goto out;
	121	}
	122
	123	dcs = dentry->d_cookie;
	124
	125	if (!dcs)
	126	dcs = alloc_dcookie(dentry, vfsmnt);
	127
	128	if (!dcs) {
	129	err = -ENOMEM;
	130	goto out;
	131	}
	132
	133	*cookie = dcookie_value(dcs);
	134
	135	out:
	136	up(&dcookie_sem);
	137	return err;
	138	}
	139
	140
	141	/* And here is where the userspace process can look up the cookie value
	142	* to retrieve the path.
	143	*/
	144	asmlinkage long sys_lookup_dcookie(u64 cookie64, char __user * buf, size_t len)
	145	{
	146	unsigned long cookie = (unsigned long)cookie64;
	147	int err = -EINVAL;
	148	char * kbuf;
	149	char * path;
	150	size_t pathlen;
	151	struct dcookie_struct * dcs;
	152
	153	/* we could leak path information to users
	154	* without dir read permission without this
	155	*/
	156	if (!capable(CAP_SYS_ADMIN))
	157	return -EPERM;
	158
	159	down(&dcookie_sem);
	160
	161	if (!is_live()) {
	162	err = -EINVAL;
	163	goto out;
	164	}
165
166	if (!(dcs = find_dcookie(cookie)))
167	goto out;
168
169	err = -ENOMEM;
170	kbuf = kmalloc(PAGE_SIZE, GFP_KERNEL);
171	if (!kbuf)
172	goto out;
173
174	/* FIXME: (deleted) ? */
175	path = d_path(dcs->dentry, dcs->vfsmnt, kbuf, PAGE_SIZE);
176
177	if (IS_ERR(path)) {
178	err = PTR_ERR(path);
179	goto out_free;
180	}
181
182	err = -ERANGE;
183
184	pathlen = kbuf + PAGE_SIZE - path;
185	if (pathlen <= len) {
186	err = pathlen;
187	if (copy_to_user(buf, path, pathlen))
188	err = -EFAULT;
189	}
190
191	out_free:
192	kfree(kbuf);
193	out:
194	up(&dcookie_sem);
195	return err;
196	}
197
198
199	static int dcookie_init(void)
200	{
201	struct list_head * d;
202	unsigned int i, hash_bits;
203	int err = -ENOMEM;
204
205	dcookie_cache = kmem_cache_create("dcookie_cache",
206	sizeof(struct dcookie_struct),
207	0, 0, NULL, NULL);
208
209	if (!dcookie_cache)
210	goto out;
211
212	dcookie_hashtable = kmalloc(PAGE_SIZE, GFP_KERNEL);
213	if (!dcookie_hashtable)
214	goto out_kmem;
215
216	err = 0;
217
218	/*
219	* Find the power-of-two list-heads that can fit into the allocation..
220	* We don't guarantee that "sizeof(struct list_head)" is necessarily
221	* a power-of-two.
222	*/
223	hash_size = PAGE_SIZE / sizeof(struct list_head);
224	hash_bits = 0;
225	do {
226	hash_bits++;
227	} while ((hash_size >> hash_bits) != 0);
228	hash_bits--;
229
230	/*
231	* Re-calculate the actual number of entries and the mask
232	* from the number of bits we can fit.
233	*/
234	hash_size = 1UL << hash_bits;
235
236	/* And initialize the newly allocated array */
237	d = dcookie_hashtable;
238	i = hash_size;
239	do {
240	INIT_LIST_HEAD(d);
241	d++;
242	i--;
243	} while (i);
244
245	out:
246	return err;
247	out_kmem:
248	kmem_cache_destroy(dcookie_cache);
249	goto out;
250	}
251
252
253	static void free_dcookie(struct dcookie_struct * dcs)
254	{
255	dcs->dentry->d_cookie = NULL;
256	dput(dcs->dentry);
257	mntput(dcs->vfsmnt);
258	kmem_cache_free(dcookie_cache, dcs);
259	}
260
261
262	static void dcookie_exit(void)
263	{
264	struct list_head * list;
265	struct list_head * pos;
266	struct list_head * pos2;
267	struct dcookie_struct * dcs;
268	size_t i;
269
270	for (i = 0; i < hash_size; ++i) {
271	list = dcookie_hashtable + i;
272	list_for_each_safe(pos, pos2, list) {
273	dcs = list_entry(pos, struct dcookie_struct, hash_list);
274	list_del(&dcs->hash_list);
275	free_dcookie(dcs);
276	}
277	}
278
279	kfree(dcookie_hashtable);
280	kmem_cache_destroy(dcookie_cache);
281	}
282
283
284	struct dcookie_user {
285	struct list_head next;
286	};
287
288	struct dcookie_user * dcookie_register(void)
289	{
290	struct dcookie_user * user;
291
292	down(&dcookie_sem);
293
294	user = kmalloc(sizeof(struct dcookie_user), GFP_KERNEL);
295	if (!user)
296	goto out;
297
298	if (!is_live() && dcookie_init())
299	goto out_free;
300
301	list_add(&user->next, &dcookie_users);
302
303	out:
304	up(&dcookie_sem);
305	return user;
306	out_free:
307	kfree(user);
308	user = NULL;
309	goto out;
310	}
311
312
313	void dcookie_unregister(struct dcookie_user * user)
314	{
315	down(&dcookie_sem);
316
317	list_del(&user->next);
318	kfree(user);
319
320	if (!is_live())
321	dcookie_exit();
322
323	up(&dcookie_sem);
324	}
325
326	EXPORT_SYMBOL_GPL(dcookie_register);
327	EXPORT_SYMBOL_GPL(dcookie_unregister);
328	EXPORT_SYMBOL_GPL(get_dcookie);