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/mount.h>
15 #include <linux/module.h>
16 #include <linux/kobject.h>
17 #include <linux/namei.h>
18 #include <linux/mutex.h>
19 #include <linux/security.h>
23 static int sysfs_do_create_link(struct kobject *kobj, struct kobject *target,
24 const char *name, int warn)
26 struct sysfs_dirent *parent_sd = NULL;
27 struct sysfs_dirent *target_sd = NULL;
28 struct sysfs_dirent *sd = NULL;
29 struct sysfs_addrm_cxt acxt;
35 parent_sd = &sysfs_root;
43 /* target->sd can go away beneath us but is protected with
44 * sysfs_assoc_lock. Fetch target_sd from it.
46 spin_lock(&sysfs_assoc_lock);
48 target_sd = sysfs_get(target->sd);
49 spin_unlock(&sysfs_assoc_lock);
56 sd = sysfs_new_dirent(name, S_IFLNK|S_IRWXUGO, SYSFS_KOBJ_LINK);
60 sd->s_symlink.target_sd = target_sd;
61 target_sd = NULL; /* reference is now owned by the symlink */
63 sysfs_addrm_start(&acxt, parent_sd);
65 error = sysfs_add_one(&acxt, sd);
67 error = __sysfs_add_one(&acxt, sd);
68 sysfs_addrm_finish(&acxt);
82 * sysfs_create_link - create symlink between two objects.
83 * @kobj: object whose directory we're creating the link in.
84 * @target: object we're pointing to.
85 * @name: name of the symlink.
87 int sysfs_create_link(struct kobject *kobj, struct kobject *target,
90 return sysfs_do_create_link(kobj, target, name, 1);
94 * sysfs_create_link_nowarn - create symlink between two objects.
95 * @kobj: object whose directory we're creating the link in.
96 * @target: object we're pointing to.
97 * @name: name of the symlink.
99 * This function does the same as sysf_create_link(), but it
100 * doesn't warn if the link already exists.
102 int sysfs_create_link_nowarn(struct kobject *kobj, struct kobject *target,
105 return sysfs_do_create_link(kobj, target, name, 0);
109 * sysfs_remove_link - remove symlink in object's directory.
110 * @kobj: object we're acting for.
111 * @name: name of the symlink to remove.
114 void sysfs_remove_link(struct kobject * kobj, const char * name)
116 struct sysfs_dirent *parent_sd = NULL;
119 parent_sd = &sysfs_root;
121 parent_sd = kobj->sd;
123 sysfs_hash_and_remove(parent_sd, name);
126 static int sysfs_get_target_path(struct sysfs_dirent *parent_sd,
127 struct sysfs_dirent *target_sd, char *path)
129 struct sysfs_dirent *base, *sd;
133 /* go up to the root, stop at the base */
135 while (base->s_parent) {
136 sd = target_sd->s_parent;
137 while (sd->s_parent && base != sd)
145 base = base->s_parent;
148 /* determine end of target string for reverse fillup */
150 while (sd->s_parent && sd != base) {
151 len += strlen(sd->s_name) + 1;
159 if ((s - path) + len > PATH_MAX)
160 return -ENAMETOOLONG;
162 /* reverse fillup of target string from target to base */
164 while (sd->s_parent && sd != base) {
165 int slen = strlen(sd->s_name);
168 strncpy(s + len, sd->s_name, slen);
178 static int sysfs_getlink(struct dentry *dentry, char * path)
180 struct sysfs_dirent *sd = dentry->d_fsdata;
181 struct sysfs_dirent *parent_sd = sd->s_parent;
182 struct sysfs_dirent *target_sd = sd->s_symlink.target_sd;
185 mutex_lock(&sysfs_mutex);
186 error = sysfs_get_target_path(parent_sd, target_sd, path);
187 mutex_unlock(&sysfs_mutex);
192 static void *sysfs_follow_link(struct dentry *dentry, struct nameidata *nd)
195 unsigned long page = get_zeroed_page(GFP_KERNEL);
197 error = sysfs_getlink(dentry, (char *) page);
199 free_page((unsigned long)page);
201 nd_set_link(nd, error ? ERR_PTR(error) : (char *)page);
205 static void sysfs_put_link(struct dentry *dentry, struct nameidata *nd, void *cookie)
207 char *page = nd_get_link(nd);
209 free_page((unsigned long)page);
212 const struct inode_operations sysfs_symlink_inode_operations = {
213 .setxattr = sysfs_setxattr,
214 .readlink = generic_readlink,
215 .follow_link = sysfs_follow_link,
216 .put_link = sysfs_put_link,
220 EXPORT_SYMBOL_GPL(sysfs_create_link);
221 EXPORT_SYMBOL_GPL(sysfs_remove_link);