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 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 */ 65 66 sysfs_addrm_start(&acxt, parent_sd); 67 if (warn) 68 error = sysfs_add_one(&acxt, sd); 69 else 70 error = __sysfs_add_one(&acxt, sd); 71 sysfs_addrm_finish(&acxt); 72 73 if (error) 74 goto out_put; 75 76 return 0; 77 78 out_put: 79 sysfs_put(target_sd); 80 sysfs_put(sd); 81 return error; 82 } 83 84 /** 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. 89 */ 90 int sysfs_create_link(struct kobject *kobj, struct kobject *target, 91 const char *name) 92 { 93 return sysfs_do_create_link(kobj, target, name, 1); 94 } 95 96 /** 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. 101 * 102 * This function does the same as sysf_create_link(), but it 103 * doesn't warn if the link already exists. 104 */ 105 int sysfs_create_link_nowarn(struct kobject *kobj, struct kobject *target, 106 const char *name) 107 { 108 return sysfs_do_create_link(kobj, target, name, 0); 109 } 110 111 /** 112 * sysfs_delete_link - remove symlink in object's directory. 113 * @kobj: object we're acting for. 114 * @targ: object we're pointing to. 115 * @name: name of the symlink to remove. 116 * 117 * Unlike sysfs_remove_link sysfs_delete_link has enough information 118 * to successfully delete symlinks in tagged directories. 119 */ 120 void sysfs_delete_link(struct kobject *kobj, struct kobject *targ, 121 const char *name) 122 { 123 const void *ns = NULL; 124 spin_lock(&sysfs_assoc_lock); 125 if (targ->sd) 126 ns = targ->sd->s_ns; 127 spin_unlock(&sysfs_assoc_lock); 128 sysfs_hash_and_remove(kobj->sd, ns, name); 129 } 130 131 /** 132 * sysfs_remove_link - remove symlink in object's directory. 133 * @kobj: object we're acting for. 134 * @name: name of the symlink to remove. 135 */ 136 137 void sysfs_remove_link(struct kobject * kobj, const char * name) 138 { 139 struct sysfs_dirent *parent_sd = NULL; 140 141 if (!kobj) 142 parent_sd = &sysfs_root; 143 else 144 parent_sd = kobj->sd; 145 146 sysfs_hash_and_remove(parent_sd, NULL, name); 147 } 148 149 /** 150 * sysfs_rename_link - rename symlink in object's directory. 151 * @kobj: object we're acting for. 152 * @targ: object we're pointing to. 153 * @old: previous name of the symlink. 154 * @new: new name of the symlink. 155 * 156 * A helper function for the common rename symlink idiom. 157 */ 158 int sysfs_rename_link(struct kobject *kobj, struct kobject *targ, 159 const char *old, const char *new) 160 { 161 struct sysfs_dirent *parent_sd, *sd = NULL; 162 const void *old_ns = NULL, *new_ns = NULL; 163 int result; 164 165 if (!kobj) 166 parent_sd = &sysfs_root; 167 else 168 parent_sd = kobj->sd; 169 170 if (targ->sd) 171 old_ns = targ->sd->s_ns; 172 173 result = -ENOENT; 174 sd = sysfs_get_dirent(parent_sd, old_ns, old); 175 if (!sd) 176 goto out; 177 178 result = -EINVAL; 179 if (sysfs_type(sd) != SYSFS_KOBJ_LINK) 180 goto out; 181 if (sd->s_symlink.target_sd->s_dir.kobj != targ) 182 goto out; 183 184 if (sysfs_ns_type(parent_sd)) 185 new_ns = targ->ktype->namespace(targ); 186 187 result = sysfs_rename(sd, parent_sd, new_ns, new); 188 189 out: 190 sysfs_put(sd); 191 return result; 192 } 193 194 static int sysfs_get_target_path(struct sysfs_dirent *parent_sd, 195 struct sysfs_dirent *target_sd, char *path) 196 { 197 struct sysfs_dirent *base, *sd; 198 char *s = path; 199 int len = 0; 200 201 /* go up to the root, stop at the base */ 202 base = parent_sd; 203 while (base->s_parent) { 204 sd = target_sd->s_parent; 205 while (sd->s_parent && base != sd) 206 sd = sd->s_parent; 207 208 if (base == sd) 209 break; 210 211 strcpy(s, "../"); 212 s += 3; 213 base = base->s_parent; 214 } 215 216 /* determine end of target string for reverse fillup */ 217 sd = target_sd; 218 while (sd->s_parent && sd != base) { 219 len += strlen(sd->s_name) + 1; 220 sd = sd->s_parent; 221 } 222 223 /* check limits */ 224 if (len < 2) 225 return -EINVAL; 226 len--; 227 if ((s - path) + len > PATH_MAX) 228 return -ENAMETOOLONG; 229 230 /* reverse fillup of target string from target to base */ 231 sd = target_sd; 232 while (sd->s_parent && sd != base) { 233 int slen = strlen(sd->s_name); 234 235 len -= slen; 236 strncpy(s + len, sd->s_name, slen); 237 if (len) 238 s[--len] = '/'; 239 240 sd = sd->s_parent; 241 } 242 243 return 0; 244 } 245 246 static int sysfs_getlink(struct dentry *dentry, char * path) 247 { 248 struct sysfs_dirent *sd = dentry->d_fsdata; 249 struct sysfs_dirent *parent_sd = sd->s_parent; 250 struct sysfs_dirent *target_sd = sd->s_symlink.target_sd; 251 int error; 252 253 mutex_lock(&sysfs_mutex); 254 error = sysfs_get_target_path(parent_sd, target_sd, path); 255 mutex_unlock(&sysfs_mutex); 256 257 return error; 258 } 259 260 static void *sysfs_follow_link(struct dentry *dentry, struct nameidata *nd) 261 { 262 int error = -ENOMEM; 263 unsigned long page = get_zeroed_page(GFP_KERNEL); 264 if (page) { 265 error = sysfs_getlink(dentry, (char *) page); 266 if (error < 0) 267 free_page((unsigned long)page); 268 } 269 nd_set_link(nd, error ? ERR_PTR(error) : (char *)page); 270 return NULL; 271 } 272 273 static void sysfs_put_link(struct dentry *dentry, struct nameidata *nd, void *cookie) 274 { 275 char *page = nd_get_link(nd); 276 if (!IS_ERR(page)) 277 free_page((unsigned long)page); 278 } 279 280 const struct inode_operations sysfs_symlink_inode_operations = { 281 .setxattr = sysfs_setxattr, 282 .readlink = generic_readlink, 283 .follow_link = sysfs_follow_link, 284 .put_link = sysfs_put_link, 285 .setattr = sysfs_setattr, 286 .getattr = sysfs_getattr, 287 .permission = sysfs_permission, 288 }; 289 290 291 EXPORT_SYMBOL_GPL(sysfs_create_link); 292 EXPORT_SYMBOL_GPL(sysfs_remove_link); 293 EXPORT_SYMBOL_GPL(sysfs_rename_link); 294