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