2 * fs/sysfs/symlink.c - sysfs symlink implementation
4 * Copyright (c) 2001-3 Patrick Mochel
5 * Copyright (c) 2007 SUSE Linux Products GmbH
6 * Copyright (c) 2007 Tejun Heo <teheo@suse.de>
8 * This file is released under the GPLv2.
10 * Please see Documentation/filesystems/sysfs.txt for more information.
14 #include <linux/gfp.h>
15 #include <linux/mount.h>
16 #include <linux/module.h>
17 #include <linux/kobject.h>
18 #include <linux/namei.h>
19 #include <linux/mutex.h>
20 #include <linux/security.h>
24 static int sysfs_do_create_link(struct kobject *kobj, struct kobject *target,
25 const char *name, int warn)
27 struct sysfs_dirent *parent_sd = NULL;
28 struct sysfs_dirent *target_sd = NULL;
29 struct sysfs_dirent *sd = NULL;
30 struct sysfs_addrm_cxt acxt;
36 parent_sd = &sysfs_root;
44 /* target->sd can go away beneath us but is protected with
45 * sysfs_assoc_lock. Fetch target_sd from it.
47 spin_lock(&sysfs_assoc_lock);
49 target_sd = sysfs_get(target->sd);
50 spin_unlock(&sysfs_assoc_lock);
57 sd = sysfs_new_dirent(name, S_IFLNK|S_IRWXUGO, SYSFS_KOBJ_LINK);
61 if (sysfs_ns_type(parent_sd))
62 sd->s_ns = target->ktype->namespace(target);
63 sd->s_symlink.target_sd = target_sd;
64 target_sd = NULL; /* reference is now owned by the symlink */
66 sysfs_addrm_start(&acxt, parent_sd);
68 error = sysfs_add_one(&acxt, sd);
70 error = __sysfs_add_one(&acxt, sd);
71 sysfs_addrm_finish(&acxt);
85 * sysfs_create_link - create symlink between two objects.
86 * @kobj: object whose directory we're creating the link in.
87 * @target: object we're pointing to.
88 * @name: name of the symlink.
90 int sysfs_create_link(struct kobject *kobj, struct kobject *target,
93 return sysfs_do_create_link(kobj, target, name, 1);
97 * sysfs_create_link_nowarn - create symlink between two objects.
98 * @kobj: object whose directory we're creating the link in.
99 * @target: object we're pointing to.
100 * @name: name of the symlink.
102 * This function does the same as sysf_create_link(), but it
103 * doesn't warn if the link already exists.
105 int sysfs_create_link_nowarn(struct kobject *kobj, struct kobject *target,
108 return sysfs_do_create_link(kobj, target, name, 0);
112 * sysfs_remove_link - remove symlink in object's directory.
113 * @kobj: object we're acting for.
114 * @name: name of the symlink to remove.
117 void sysfs_remove_link(struct kobject * kobj, const char * name)
119 struct sysfs_dirent *parent_sd = NULL;
122 parent_sd = &sysfs_root;
124 parent_sd = kobj->sd;
126 sysfs_hash_and_remove(parent_sd, NULL, name);
130 * sysfs_rename_link - rename symlink in object's directory.
131 * @kobj: object we're acting for.
132 * @targ: object we're pointing to.
133 * @old: previous name of the symlink.
134 * @new: new name of the symlink.
136 * A helper function for the common rename symlink idiom.
138 int sysfs_rename_link(struct kobject *kobj, struct kobject *targ,
139 const char *old, const char *new)
141 struct sysfs_dirent *parent_sd, *sd = NULL;
142 const void *old_ns = NULL, *new_ns = NULL;
146 parent_sd = &sysfs_root;
148 parent_sd = kobj->sd;
151 old_ns = targ->sd->s_ns;
154 sd = sysfs_get_dirent(parent_sd, old_ns, old);
159 if (sysfs_type(sd) != SYSFS_KOBJ_LINK)
161 if (sd->s_symlink.target_sd->s_dir.kobj != targ)
164 if (sysfs_ns_type(parent_sd))
165 new_ns = targ->ktype->namespace(targ);
167 result = sysfs_rename(sd, parent_sd, new_ns, new);
174 static int sysfs_get_target_path(struct sysfs_dirent *parent_sd,
175 struct sysfs_dirent *target_sd, char *path)
177 struct sysfs_dirent *base, *sd;
181 /* go up to the root, stop at the base */
183 while (base->s_parent) {
184 sd = target_sd->s_parent;
185 while (sd->s_parent && base != sd)
193 base = base->s_parent;
196 /* determine end of target string for reverse fillup */
198 while (sd->s_parent && sd != base) {
199 len += strlen(sd->s_name) + 1;
207 if ((s - path) + len > PATH_MAX)
208 return -ENAMETOOLONG;
210 /* reverse fillup of target string from target to base */
212 while (sd->s_parent && sd != base) {
213 int slen = strlen(sd->s_name);
216 strncpy(s + len, sd->s_name, slen);
226 static int sysfs_getlink(struct dentry *dentry, char * path)
228 struct sysfs_dirent *sd = dentry->d_fsdata;
229 struct sysfs_dirent *parent_sd = sd->s_parent;
230 struct sysfs_dirent *target_sd = sd->s_symlink.target_sd;
233 mutex_lock(&sysfs_mutex);
234 error = sysfs_get_target_path(parent_sd, target_sd, path);
235 mutex_unlock(&sysfs_mutex);
240 static void *sysfs_follow_link(struct dentry *dentry, struct nameidata *nd)
243 unsigned long page = get_zeroed_page(GFP_KERNEL);
245 error = sysfs_getlink(dentry, (char *) page);
247 free_page((unsigned long)page);
249 nd_set_link(nd, error ? ERR_PTR(error) : (char *)page);
253 static void sysfs_put_link(struct dentry *dentry, struct nameidata *nd, void *cookie)
255 char *page = nd_get_link(nd);
257 free_page((unsigned long)page);
260 const struct inode_operations sysfs_symlink_inode_operations = {
261 .setxattr = sysfs_setxattr,
262 .readlink = generic_readlink,
263 .follow_link = sysfs_follow_link,
264 .put_link = sysfs_put_link,
265 .setattr = sysfs_setattr,
266 .getattr = sysfs_getattr,
267 .permission = sysfs_permission,
271 EXPORT_SYMBOL_GPL(sysfs_create_link);
272 EXPORT_SYMBOL_GPL(sysfs_remove_link);
273 EXPORT_SYMBOL_GPL(sysfs_rename_link);