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         enum kobj_ns_type ns_type;
  32         int error;
  33
  34         BUG_ON(!name);
  35
  36         if (!kobj)
  37                 parent_sd = &sysfs_root;
  38         else
  39                 parent_sd = kobj->sd;
  40
  41         error = -EFAULT;
  42         if (!parent_sd)
  43                 goto out_put;
  44
  45         /* target->sd can go away beneath us but is protected with
  46          * sysfs_assoc_lock.  Fetch target_sd from it.
  47          */
  48         spin_lock(&sysfs_assoc_lock);
  49         if (target->sd)
  50                 target_sd = sysfs_get(target->sd);
  51         spin_unlock(&sysfs_assoc_lock);
  52
  53         error = -ENOENT;
  54         if (!target_sd)
  55                 goto out_put;
  56
  57         error = -ENOMEM;
  58         sd = sysfs_new_dirent(name, S_IFLNK|S_IRWXUGO, SYSFS_KOBJ_LINK);
  59         if (!sd)
  60                 goto out_put;
  61
  62         ns_type = sysfs_ns_type(parent_sd);
  63         if (ns_type)
  64                 sd->s_ns = target->ktype->namespace(target);
  65         sd->s_symlink.target_sd = target_sd;
  66         target_sd = NULL;       /* reference is now owned by the symlink */
  67
  68         sysfs_addrm_start(&acxt, parent_sd);
  69         /* Symlinks must be between directories with the same ns_type */
  70         if (ns_type == sysfs_ns_type(sd->s_symlink.target_sd->s_parent)) {
  71                 if (warn)
  72                         error = sysfs_add_one(&acxt, sd);
  73                 else
  74                         error = __sysfs_add_one(&acxt, sd);
  75         } else {
  76                 error = -EINVAL;
  77                 WARN(1, KERN_WARNING
  78                         "sysfs: symlink across ns_types %s/%s -> %s/%s\n",
  79                         parent_sd->s_name,
  80                         sd->s_name,
  81                         sd->s_symlink.target_sd->s_parent->s_name,
  82                         sd->s_symlink.target_sd->s_name);
  83         }
  84         sysfs_addrm_finish(&acxt);
  85
  86         if (error)
  87                 goto out_put;
  88
  89         return 0;
  90
  91  out_put:
  92         sysfs_put(target_sd);
  93         sysfs_put(sd);
  94         return error;
  95 }
  96
  97 /**
  98  *      sysfs_create_link - create symlink between two objects.
  99  *      @kobj:  object whose directory we're creating the link in.
 100  *      @target:        object we're pointing to.
 101  *      @name:          name of the symlink.
 102  */
 103 int sysfs_create_link(struct kobject *kobj, struct kobject *target,
 104                       const char *name)
 105 {
 106         return sysfs_do_create_link(kobj, target, name, 1);
 107 }
 108
 109 /**
 110  *      sysfs_create_link_nowarn - create symlink between two objects.
 111  *      @kobj:  object whose directory we're creating the link in.
 112  *      @target:        object we're pointing to.
 113  *      @name:          name of the symlink.
 114  *
 115  *      This function does the same as sysf_create_link(), but it
 116  *      doesn't warn if the link already exists.
 117  */
 118 int sysfs_create_link_nowarn(struct kobject *kobj, struct kobject *target,
 119                              const char *name)
 120 {
 121         return sysfs_do_create_link(kobj, target, name, 0);
 122 }
 123
 124 /**
 125  *      sysfs_delete_link - remove symlink in object's directory.
 126  *      @kobj:  object we're acting for.
 127  *      @targ:  object we're pointing to.
 128  *      @name:  name of the symlink to remove.
 129  *
 130  *      Unlike sysfs_remove_link sysfs_delete_link has enough information
 131  *      to successfully delete symlinks in tagged directories.
 132  */
 133 void sysfs_delete_link(struct kobject *kobj, struct kobject *targ,
 134                         const char *name)
 135 {
 136         const void *ns = NULL;
 137         spin_lock(&sysfs_assoc_lock);
 138         if (targ->sd)
 139                 ns = targ->sd->s_ns;
 140         spin_unlock(&sysfs_assoc_lock);
 141         sysfs_hash_and_remove(kobj->sd, ns, name);
 142 }
 143
 144 /**
 145  *      sysfs_remove_link - remove symlink in object's directory.
 146  *      @kobj:  object we're acting for.
 147  *      @name:  name of the symlink to remove.
 148  */
 149
 150 void sysfs_remove_link(struct kobject * kobj, const char * name)
 151 {
 152         struct sysfs_dirent *parent_sd = NULL;
 153
 154         if (!kobj)
 155                 parent_sd = &sysfs_root;
 156         else
 157                 parent_sd = kobj->sd;
 158
 159         sysfs_hash_and_remove(parent_sd, NULL, name);
 160 }
 161
 162 /**
 163  *      sysfs_rename_link - rename symlink in object's directory.
 164  *      @kobj:  object we're acting for.
 165  *      @targ:  object we're pointing to.
 166  *      @old:   previous name of the symlink.
 167  *      @new:   new name of the symlink.
 168  *
 169  *      A helper function for the common rename symlink idiom.
 170  */
 171 int sysfs_rename_link(struct kobject *kobj, struct kobject *targ,
 172                         const char *old, const char *new)
 173 {
 174         struct sysfs_dirent *parent_sd, *sd = NULL;
 175         const void *old_ns = NULL, *new_ns = NULL;
 176         int result;
 177
 178         if (!kobj)
 179                 parent_sd = &sysfs_root;
 180         else
 181                 parent_sd = kobj->sd;
 182
 183         if (targ->sd)
 184                 old_ns = targ->sd->s_ns;
 185
 186         result = -ENOENT;
 187         sd = sysfs_get_dirent(parent_sd, old_ns, old);
 188         if (!sd)
 189                 goto out;
 190
 191         result = -EINVAL;
 192         if (sysfs_type(sd) != SYSFS_KOBJ_LINK)
 193                 goto out;
 194         if (sd->s_symlink.target_sd->s_dir.kobj != targ)
 195                 goto out;
 196
 197         if (sysfs_ns_type(parent_sd))
 198                 new_ns = targ->ktype->namespace(targ);
 199
 200         result = sysfs_rename(sd, parent_sd, new_ns, new);
 201
 202 out:
 203         sysfs_put(sd);
 204         return result;
 205 }
 206
 207 static int sysfs_get_target_path(struct sysfs_dirent *parent_sd,
 208                                  struct sysfs_dirent *target_sd, char *path)
 209 {
 210         struct sysfs_dirent *base, *sd;
 211         char *s = path;
 212         int len = 0;
 213
 214         /* go up to the root, stop at the base */
 215         base = parent_sd;
 216         while (base->s_parent) {
 217                 sd = target_sd->s_parent;
 218                 while (sd->s_parent && base != sd)
 219                         sd = sd->s_parent;
 220
 221                 if (base == sd)
 222                         break;
 223
 224                 strcpy(s, "../");
 225                 s += 3;
 226                 base = base->s_parent;
 227         }
 228
 229         /* determine end of target string for reverse fillup */
 230         sd = target_sd;
 231         while (sd->s_parent && sd != base) {
 232                 len += strlen(sd->s_name) + 1;
 233                 sd = sd->s_parent;
 234         }
 235
 236         /* check limits */
 237         if (len < 2)
 238                 return -EINVAL;
 239         len--;
 240         if ((s - path) + len > PATH_MAX)
 241                 return -ENAMETOOLONG;
 242
 243         /* reverse fillup of target string from target to base */
 244         sd = target_sd;
 245         while (sd->s_parent && sd != base) {
 246                 int slen = strlen(sd->s_name);
 247
 248                 len -= slen;
 249                 strncpy(s + len, sd->s_name, slen);
 250                 if (len)
 251                         s[--len] = '/';
 252
 253                 sd = sd->s_parent;
 254         }
 255
 256         return 0;
 257 }
 258
 259 static int sysfs_getlink(struct dentry *dentry, char * path)
 260 {
 261         struct sysfs_dirent *sd = dentry->d_fsdata;
 262         struct sysfs_dirent *parent_sd = sd->s_parent;
 263         struct sysfs_dirent *target_sd = sd->s_symlink.target_sd;
 264         int error;
 265
 266         mutex_lock(&sysfs_mutex);
 267         error = sysfs_get_target_path(parent_sd, target_sd, path);
 268         mutex_unlock(&sysfs_mutex);
 269
 270         return error;
 271 }
 272
 273 static void *sysfs_follow_link(struct dentry *dentry, struct nameidata *nd)
 274 {
 275         int error = -ENOMEM;
 276         unsigned long page = get_zeroed_page(GFP_KERNEL);
 277         if (page) {
 278                 error = sysfs_getlink(dentry, (char *) page);
 279                 if (error < 0)
 280                         free_page((unsigned long)page);
 281         }
 282         nd_set_link(nd, error ? ERR_PTR(error) : (char *)page);
 283         return NULL;
 284 }
 285
 286 static void sysfs_put_link(struct dentry *dentry, struct nameidata *nd, void *cookie)
 287 {
 288         char *page = nd_get_link(nd);
 289         if (!IS_ERR(page))
 290                 free_page((unsigned long)page);
 291 }
 292
 293 const struct inode_operations sysfs_symlink_inode_operations = {
 294         .setxattr       = sysfs_setxattr,
 295         .readlink       = generic_readlink,
 296         .follow_link    = sysfs_follow_link,
 297         .put_link       = sysfs_put_link,
 298         .setattr        = sysfs_setattr,
 299         .getattr        = sysfs_getattr,
 300         .permission     = sysfs_permission,
 301 };
 302
 303
 304 EXPORT_SYMBOL_GPL(sysfs_create_link);
 305 EXPORT_SYMBOL_GPL(sysfs_remove_link);
 306 EXPORT_SYMBOL_GPL(sysfs_rename_link);