fs/sysfs/symlink.c

   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);