summaryrefslogtreecommitdiff
path: root/fs/sysfs/symlink.c
blob: c5081ad77026e95689e58fda616dc0784b958044 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
/*
 * fs/sysfs/symlink.c - sysfs symlink implementation
 *
 * Copyright (c) 2001-3 Patrick Mochel
 * Copyright (c) 2007 SUSE Linux Products GmbH
 * Copyright (c) 2007 Tejun Heo <teheo@suse.de>
 *
 * This file is released under the GPLv2.
 *
 * Please see Documentation/filesystems/sysfs.txt for more information.
 */

#include <linux/fs.h>
#include <linux/mount.h>
#include <linux/module.h>
#include <linux/kobject.h>
#include <linux/namei.h>
#include <linux/mutex.h>
#include <linux/security.h>

#include "sysfs.h"

static int sysfs_do_create_link(struct kobject *kobj, struct kobject *target,
				const char *name, int warn)
{
	struct sysfs_dirent *parent_sd = NULL;
	struct sysfs_dirent *target_sd = NULL;
	struct sysfs_dirent *sd = NULL;
	struct sysfs_addrm_cxt acxt;
	int error;

	BUG_ON(!name);

	if (!kobj)
		parent_sd = &sysfs_root;
	else
		parent_sd = kobj->sd;

	error = -EFAULT;
	if (!parent_sd)
		goto out_put;

	/* target->sd can go away beneath us but is protected with
	 * sysfs_assoc_lock.  Fetch target_sd from it.
	 */
	spin_lock(&sysfs_assoc_lock);
	if (target->sd)
		target_sd = sysfs_get(target->sd);
	spin_unlock(&sysfs_assoc_lock);

	error = -ENOENT;
	if (!target_sd)
		goto out_put;

	error = -ENOMEM;
	sd = sysfs_new_dirent(name, S_IFLNK|S_IRWXUGO, SYSFS_KOBJ_LINK);
	if (!sd)
		goto out_put;

	sd->s_symlink.target_sd = target_sd;
	target_sd = NULL;	/* reference is now owned by the symlink */

	sysfs_addrm_start(&acxt, parent_sd);
	if (warn)
		error = sysfs_add_one(&acxt, sd);
	else
		error = __sysfs_add_one(&acxt, sd);
	sysfs_addrm_finish(&acxt);

	if (error)
		goto out_put;

	return 0;

 out_put:
	sysfs_put(target_sd);
	sysfs_put(sd);
	return error;
}

/**
 *	sysfs_create_link - create symlink between two objects.
 *	@kobj:	object whose directory we're creating the link in.
 *	@target:	object we're pointing to.
 *	@name:		name of the symlink.
 */
int sysfs_create_link(struct kobject *kobj, struct kobject *target,
		      const char *name)
{
	return sysfs_do_create_link(kobj, target, name, 1);
}

/**
 *	sysfs_create_link_nowarn - create symlink between two objects.
 *	@kobj:	object whose directory we're creating the link in.
 *	@target:	object we're pointing to.
 *	@name:		name of the symlink.
 *
 *	This function does the same as sysf_create_link(), but it
 *	doesn't warn if the link already exists.
 */
int sysfs_create_link_nowarn(struct kobject *kobj, struct kobject *target,
			     const char *name)
{
	return sysfs_do_create_link(kobj, target, name, 0);
}

/**
 *	sysfs_remove_link - remove symlink in object's directory.
 *	@kobj:	object we're acting for.
 *	@name:	name of the symlink to remove.
 */

void sysfs_remove_link(struct kobject * kobj, const char * name)
{
	struct sysfs_dirent *parent_sd = NULL;

	if (!kobj)
		parent_sd = &sysfs_root;
	else
		parent_sd = kobj->sd;

	sysfs_hash_and_remove(parent_sd, name);
}

static int sysfs_get_target_path(struct sysfs_dirent *parent_sd,
				 struct sysfs_dirent *target_sd, char *path)
{
	struct sysfs_dirent *base, *sd;
	char *s = path;
	int len = 0;

	/* go up to the root, stop at the base */
	base = parent_sd;
	while (base->s_parent) {
		sd = target_sd->s_parent;
		while (sd->s_parent && base != sd)
			sd = sd->s_parent;

		if (base == sd)
			break;

		strcpy(s, "../");
		s += 3;
		base = base->s_parent;
	}

	/* determine end of target string for reverse fillup */
	sd = target_sd;
	while (sd->s_parent && sd != base) {
		len += strlen(sd->s_name) + 1;
		sd = sd->s_parent;
	}

	/* check limits */
	if (len < 2)
		return -EINVAL;
	len--;
	if ((s - path) + len > PATH_MAX)
		return -ENAMETOOLONG;

	/* reverse fillup of target string from target to base */
	sd = target_sd;
	while (sd->s_parent && sd != base) {
		int slen = strlen(sd->s_name);

		len -= slen;
		strncpy(s + len, sd->s_name, slen);
		if (len)
			s[--len] = '/';

		sd = sd->s_parent;
	}

	return 0;
}

static int sysfs_getlink(struct dentry *dentry, char * path)
{
	struct sysfs_dirent *sd = dentry->d_fsdata;
	struct sysfs_dirent *parent_sd = sd->s_parent;
	struct sysfs_dirent *target_sd = sd->s_symlink.target_sd;
	int error;

	mutex_lock(&sysfs_mutex);
	error = sysfs_get_target_path(parent_sd, target_sd, path);
	mutex_unlock(&sysfs_mutex);

	return error;
}

static void *sysfs_follow_link(struct dentry *dentry, struct nameidata *nd)
{
	int error = -ENOMEM;
	unsigned long page = get_zeroed_page(GFP_KERNEL);
	if (page) {
		error = sysfs_getlink(dentry, (char *) page); 
		if (error < 0)
			free_page((unsigned long)page);
	}
	nd_set_link(nd, error ? ERR_PTR(error) : (char *)page);
	return NULL;
}

static void sysfs_put_link(struct dentry *dentry, struct nameidata *nd, void *cookie)
{
	char *page = nd_get_link(nd);
	if (!IS_ERR(page))
		free_page((unsigned long)page);
}

const struct inode_operations sysfs_symlink_inode_operations = {
	.setxattr = sysfs_setxattr,
	.readlink = generic_readlink,
	.follow_link = sysfs_follow_link,
	.put_link = sysfs_put_link,
};


EXPORT_SYMBOL_GPL(sysfs_create_link);
EXPORT_SYMBOL_GPL(sysfs_remove_link);