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 sd->s_symlink.target_sd = target_sd;
62 target_sd = NULL; /* reference is now owned by the symlink */
64 sysfs_addrm_start(&acxt, parent_sd);
66 error = sysfs_add_one(&acxt, sd);
68 error = __sysfs_add_one(&acxt, sd);
69 sysfs_addrm_finish(&acxt);
83 * sysfs_create_link - create symlink between two objects.
84 * @kobj: object whose directory we're creating the link in.
85 * @target: object we're pointing to.
86 * @name: name of the symlink.
88 int sysfs_create_link(struct kobject *kobj, struct kobject *target,
91 return sysfs_do_create_link(kobj, target, name, 1);
95 * sysfs_create_link_nowarn - create symlink between two objects.
96 * @kobj: object whose directory we're creating the link in.
97 * @target: object we're pointing to.
98 * @name: name of the symlink.
100 * This function does the same as sysf_create_link(), but it
101 * doesn't warn if the link already exists.
103 int sysfs_create_link_nowarn(struct kobject *kobj, struct kobject *target,
106 return sysfs_do_create_link(kobj, target, name, 0);
110 * sysfs_remove_link - remove symlink in object's directory.
111 * @kobj: object we're acting for.
112 * @name: name of the symlink to remove.
115 void sysfs_remove_link(struct kobject * kobj, const char * name)
117 struct sysfs_dirent *parent_sd = NULL;
120 parent_sd = &sysfs_root;
122 parent_sd = kobj->sd;
124 sysfs_hash_and_remove(parent_sd, name);
128 * sysfs_rename_link - rename symlink in object's directory.
129 * @kobj: object we're acting for.
130 * @targ: object we're pointing to.
131 * @old: previous name of the symlink.
132 * @new: new name of the symlink.
134 * A helper function for the common rename symlink idiom.
136 int sysfs_rename_link(struct kobject *kobj, struct kobject *targ,
137 const char *old, const char *new)
139 struct sysfs_dirent *parent_sd, *sd = NULL;
143 parent_sd = &sysfs_root;
145 parent_sd = kobj->sd;
148 sd = sysfs_get_dirent(parent_sd, old);
153 if (sysfs_type(sd) != SYSFS_KOBJ_LINK)
155 if (sd->s_symlink.target_sd->s_dir.kobj != targ)
158 result = sysfs_rename(sd, parent_sd, new);
165 static int sysfs_get_target_path(struct sysfs_dirent *parent_sd,
166 struct sysfs_dirent *target_sd, char *path)
168 struct sysfs_dirent *base, *sd;
172 /* go up to the root, stop at the base */
174 while (base->s_parent) {
175 sd = target_sd->s_parent;
176 while (sd->s_parent && base != sd)
184 base = base->s_parent;
187 /* determine end of target string for reverse fillup */
189 while (sd->s_parent && sd != base) {
190 len += strlen(sd->s_name) + 1;
198 if ((s - path) + len > PATH_MAX)
199 return -ENAMETOOLONG;
201 /* reverse fillup of target string from target to base */
203 while (sd->s_parent && sd != base) {
204 int slen = strlen(sd->s_name);
207 strncpy(s + len, sd->s_name, slen);
217 static int sysfs_getlink(struct dentry *dentry, char * path)
219 struct sysfs_dirent *sd = dentry->d_fsdata;
220 struct sysfs_dirent *parent_sd = sd->s_parent;
221 struct sysfs_dirent *target_sd = sd->s_symlink.target_sd;
224 mutex_lock(&sysfs_mutex);
225 error = sysfs_get_target_path(parent_sd, target_sd, path);
226 mutex_unlock(&sysfs_mutex);
231 static void *sysfs_follow_link(struct dentry *dentry, struct nameidata *nd)
234 unsigned long page = get_zeroed_page(GFP_KERNEL);
236 error = sysfs_getlink(dentry, (char *) page);
238 free_page((unsigned long)page);
240 nd_set_link(nd, error ? ERR_PTR(error) : (char *)page);
244 static void sysfs_put_link(struct dentry *dentry, struct nameidata *nd, void *cookie)
246 char *page = nd_get_link(nd);
248 free_page((unsigned long)page);
251 const struct inode_operations sysfs_symlink_inode_operations = {
252 .setxattr = sysfs_setxattr,
253 .readlink = generic_readlink,
254 .follow_link = sysfs_follow_link,
255 .put_link = sysfs_put_link,
256 .setattr = sysfs_setattr,
257 .getattr = sysfs_getattr,
258 .permission = sysfs_permission,
262 EXPORT_SYMBOL_GPL(sysfs_create_link);
263 EXPORT_SYMBOL_GPL(sysfs_remove_link);