1 /* 2 * fs/sysfs/symlink.c - sysfs symlink implementation 3 * 4 * Copyright (c) 2001-3 Patrick Mochel 5 * Copyright (c) 2007 SUSE Linux Products GmbH 6 * Copyright (c) 2007 Tejun Heo <teheo@suse.de> 7 * 8 * This file is released under the GPLv2. 9 * 10 * Please see Documentation/filesystems/sysfs.txt for more information. 11 */ 12 13 #include <linux/fs.h> 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> 21 22 #include "sysfs.h" 23 24 static int sysfs_do_create_link(struct kobject *kobj, struct kobject *target, 25 const char *name, int warn) 26 { 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; 31 int error; 32 33 BUG_ON(!name); 34 35 if (!kobj) 36 parent_sd = &sysfs_root; 37 else 38 parent_sd = kobj->sd; 39 40 error = -EFAULT; 41 if (!parent_sd) 42 goto out_put; 43 44 /* target->sd can go away beneath us but is protected with 45 * sysfs_assoc_lock. Fetch target_sd from it. 46 */ 47 spin_lock(&sysfs_assoc_lock); 48 if (target->sd) 49 target_sd = sysfs_get(target->sd); 50 spin_unlock(&sysfs_assoc_lock); 51 52 error = -ENOENT; 53 if (!target_sd) 54 goto out_put; 55 56 error = -ENOMEM; 57 sd = sysfs_new_dirent(name, S_IFLNK|S_IRWXUGO, SYSFS_KOBJ_LINK); 58 if (!sd) 59 goto out_put; 60 61 sd->s_symlink.target_sd = target_sd; 62 target_sd = NULL; /* reference is now owned by the symlink */ 63 64 sysfs_addrm_start(&acxt, parent_sd); 65 if (warn) 66 error = sysfs_add_one(&acxt, sd); 67 else 68 error = __sysfs_add_one(&acxt, sd); 69 sysfs_addrm_finish(&acxt); 70 71 if (error) 72 goto out_put; 73 74 return 0; 75 76 out_put: 77 sysfs_put(target_sd); 78 sysfs_put(sd); 79 return error; 80 } 81 82 /** 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. 87 */ 88 int sysfs_create_link(struct kobject *kobj, struct kobject *target, 89 const char *name) 90 { 91 return sysfs_do_create_link(kobj, target, name, 1); 92 } 93 94 /** 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. 99 * 100 * This function does the same as sysf_create_link(), but it 101 * doesn't warn if the link already exists. 102 */ 103 int sysfs_create_link_nowarn(struct kobject *kobj, struct kobject *target, 104 const char *name) 105 { 106 return sysfs_do_create_link(kobj, target, name, 0); 107 } 108 109 /** 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. 113 */ 114 115 void sysfs_remove_link(struct kobject * kobj, const char * name) 116 { 117 struct sysfs_dirent *parent_sd = NULL; 118 119 if (!kobj) 120 parent_sd = &sysfs_root; 121 else 122 parent_sd = kobj->sd; 123 124 sysfs_hash_and_remove(parent_sd, name); 125 } 126 127 /** 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. 133 * 134 * A helper function for the common rename symlink idiom. 135 */ 136 int sysfs_rename_link(struct kobject *kobj, struct kobject *targ, 137 const char *old, const char *new) 138 { 139 struct sysfs_dirent *parent_sd, *sd = NULL; 140 int result; 141 142 if (!kobj) 143 parent_sd = &sysfs_root; 144 else 145 parent_sd = kobj->sd; 146 147 result = -ENOENT; 148 sd = sysfs_get_dirent(parent_sd, old); 149 if (!sd) 150 goto out; 151 152 result = -EINVAL; 153 if (sysfs_type(sd) != SYSFS_KOBJ_LINK) 154 goto out; 155 if (sd->s_symlink.target_sd->s_dir.kobj != targ) 156 goto out; 157 158 result = sysfs_rename(sd, parent_sd, new); 159 160 out: 161 sysfs_put(sd); 162 return result; 163 } 164 165 static int sysfs_get_target_path(struct sysfs_dirent *parent_sd, 166 struct sysfs_dirent *target_sd, char *path) 167 { 168 struct sysfs_dirent *base, *sd; 169 char *s = path; 170 int len = 0; 171 172 /* go up to the root, stop at the base */ 173 base = parent_sd; 174 while (base->s_parent) { 175 sd = target_sd->s_parent; 176 while (sd->s_parent && base != sd) 177 sd = sd->s_parent; 178 179 if (base == sd) 180 break; 181 182 strcpy(s, "../"); 183 s += 3; 184 base = base->s_parent; 185 } 186 187 /* determine end of target string for reverse fillup */ 188 sd = target_sd; 189 while (sd->s_parent && sd != base) { 190 len += strlen(sd->s_name) + 1; 191 sd = sd->s_parent; 192 } 193 194 /* check limits */ 195 if (len < 2) 196 return -EINVAL; 197 len--; 198 if ((s - path) + len > PATH_MAX) 199 return -ENAMETOOLONG; 200 201 /* reverse fillup of target string from target to base */ 202 sd = target_sd; 203 while (sd->s_parent && sd != base) { 204 int slen = strlen(sd->s_name); 205 206 len -= slen; 207 strncpy(s + len, sd->s_name, slen); 208 if (len) 209 s[--len] = '/'; 210 211 sd = sd->s_parent; 212 } 213 214 return 0; 215 } 216 217 static int sysfs_getlink(struct dentry *dentry, char * path) 218 { 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; 222 int error; 223 224 mutex_lock(&sysfs_mutex); 225 error = sysfs_get_target_path(parent_sd, target_sd, path); 226 mutex_unlock(&sysfs_mutex); 227 228 return error; 229 } 230 231 static void *sysfs_follow_link(struct dentry *dentry, struct nameidata *nd) 232 { 233 int error = -ENOMEM; 234 unsigned long page = get_zeroed_page(GFP_KERNEL); 235 if (page) { 236 error = sysfs_getlink(dentry, (char *) page); 237 if (error < 0) 238 free_page((unsigned long)page); 239 } 240 nd_set_link(nd, error ? ERR_PTR(error) : (char *)page); 241 return NULL; 242 } 243 244 static void sysfs_put_link(struct dentry *dentry, struct nameidata *nd, void *cookie) 245 { 246 char *page = nd_get_link(nd); 247 if (!IS_ERR(page)) 248 free_page((unsigned long)page); 249 } 250 251 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, 259 }; 260 261 262 EXPORT_SYMBOL_GPL(sysfs_create_link); 263 EXPORT_SYMBOL_GPL(sysfs_remove_link); 264