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_sd(struct sysfs_dirent *parent_sd,
  25                                    struct kobject *target,
  26                                    const char *name, int warn)
  27 {
  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 || !parent_sd);
  35
  36         /* target->sd can go away beneath us but is protected with
  37          * sysfs_assoc_lock.  Fetch target_sd from it.
  38          */
  39         spin_lock(&sysfs_assoc_lock);
  40         if (target->sd)
  41                 target_sd = sysfs_get(target->sd);
  42         spin_unlock(&sysfs_assoc_lock);
  43
  44         error = -ENOENT;
  45         if (!target_sd)
  46                 goto out_put;
  47
  48         error = -ENOMEM;
  49         sd = sysfs_new_dirent(name, S_IFLNK|S_IRWXUGO, SYSFS_KOBJ_LINK);
  50         if (!sd)
  51                 goto out_put;
  52
  53         ns_type = sysfs_ns_type(parent_sd);
  54         if (ns_type)
  55                 sd->s_ns = target->ktype->namespace(target);
  56         sd->s_symlink.target_sd = target_sd;
  57         target_sd = NULL;       /* reference is now owned by the symlink */
  58
  59         sysfs_addrm_start(&acxt, parent_sd);
  60         /* Symlinks must be between directories with the same ns_type */
  61         if (!ns_type ||
  62             (ns_type == sysfs_ns_type(sd->s_symlink.target_sd->s_parent))) {
  63                 if (warn)
  64                         error = sysfs_add_one(&acxt, sd);
  65                 else
  66                         error = __sysfs_add_one(&acxt, sd);
  67         } else {
  68                 error = -EINVAL;
  69                 WARN(1, KERN_WARNING
  70                         "sysfs: symlink across ns_types %s/%s -> %s/%s\n",
  71                         parent_sd->s_name,
  72                         sd->s_name,
  73                         sd->s_symlink.target_sd->s_parent->s_name,
  74                         sd->s_symlink.target_sd->s_name);
  75         }
  76         sysfs_addrm_finish(&acxt);
  77
  78         if (error)
  79                 goto out_put;
  80
  81         return 0;
  82
  83  out_put:
  84         sysfs_put(target_sd);
  85         sysfs_put(sd);
  86         return error;
  87 }
  88
  89 /**
  90  *      sysfs_create_link_sd - create symlink to a given object.
  91  *      @sd:            directory we're creating the link in.
  92  *      @target:        object we're pointing to.
  93  *      @name:          name of the symlink.
  94  */
  95 int sysfs_create_link_sd(struct sysfs_dirent *sd, struct kobject *target,
  96                          const char *name)
  97 {
  98         return sysfs_do_create_link_sd(sd, target, name, 1);
  99 }
 100
 101 static int sysfs_do_create_link(struct kobject *kobj, struct kobject *target,
 102                                 const char *name, int warn)
 103 {
 104         struct sysfs_dirent *parent_sd = NULL;
 105
 106         if (!kobj)
 107                 parent_sd = &sysfs_root;
 108         else
 109                 parent_sd = kobj->sd;
 110
 111         if (!parent_sd)
 112                 return -EFAULT;
 113
 114         return sysfs_do_create_link_sd(parent_sd, target, name, warn);
 115 }
 116
 117 /**
 118  *      sysfs_create_link - create symlink between two objects.
 119  *      @kobj:  object whose directory we're creating the link in.
 120  *      @target:        object we're pointing to.
 121  *      @name:          name of the symlink.
 122  */
 123 int sysfs_create_link(struct kobject *kobj, struct kobject *target,
 124                       const char *name)
 125 {
 126         return sysfs_do_create_link(kobj, target, name, 1);
 127 }
 128
 129 /**
 130  *      sysfs_create_link_nowarn - create symlink between two objects.
 131  *      @kobj:  object whose directory we're creating the link in.
 132  *      @target:        object we're pointing to.
 133  *      @name:          name of the symlink.
 134  *
 135  *      This function does the same as sysfs_create_link(), but it
 136  *      doesn't warn if the link already exists.
 137  */
 138 int sysfs_create_link_nowarn(struct kobject *kobj, struct kobject *target,
 139                              const char *name)
 140 {
 141         return sysfs_do_create_link(kobj, target, name, 0);
 142 }
 143
 144 /**
 145  *      sysfs_delete_link - remove symlink in object's directory.
 146  *      @kobj:  object we're acting for.
 147  *      @targ:  object we're pointing to.
 148  *      @name:  name of the symlink to remove.
 149  *
 150  *      Unlike sysfs_remove_link sysfs_delete_link has enough information
 151  *      to successfully delete symlinks in tagged directories.
 152  */
 153 void sysfs_delete_link(struct kobject *kobj, struct kobject *targ,
 154                         const char *name)
 155 {
 156         const void *ns = NULL;
 157         spin_lock(&sysfs_assoc_lock);
 158         if (targ->sd && sysfs_ns_type(kobj->sd))
 159                 ns = targ->sd->s_ns;
 160         spin_unlock(&sysfs_assoc_lock);
 161         sysfs_hash_and_remove(kobj->sd, ns, name);
 162 }
 163
 164 /**
 165  *      sysfs_remove_link - remove symlink in object's directory.
 166  *      @kobj:  object we're acting for.
 167  *      @name:  name of the symlink to remove.
 168  */
 169
 170 void sysfs_remove_link(struct kobject * kobj, const char * name)
 171 {
 172         struct sysfs_dirent *parent_sd = NULL;
 173
 174         if (!kobj)
 175                 parent_sd = &sysfs_root;
 176         else
 177                 parent_sd = kobj->sd;
 178
 179         sysfs_hash_and_remove(parent_sd, NULL, name);
 180 }
 181
 182 /**
 183  *      sysfs_rename_link - rename symlink in object's directory.
 184  *      @kobj:  object we're acting for.
 185  *      @targ:  object we're pointing to.
 186  *      @old:   previous name of the symlink.
 187  *      @new:   new name of the symlink.
 188  *
 189  *      A helper function for the common rename symlink idiom.
 190  */
 191 int sysfs_rename_link(struct kobject *kobj, struct kobject *targ,
 192                         const char *old, const char *new)
 193 {
 194         struct sysfs_dirent *parent_sd, *sd = NULL;
 195         const void *old_ns = NULL, *new_ns = NULL;
 196         int result;
 197
 198         if (!kobj)
 199                 parent_sd = &sysfs_root;
 200         else
 201                 parent_sd = kobj->sd;
 202
 203         if (targ->sd)
 204                 old_ns = targ->sd->s_ns;
 205
 206         result = -ENOENT;
 207         sd = sysfs_get_dirent(parent_sd, old_ns, old);
 208         if (!sd)
 209                 goto out;
 210
 211         result = -EINVAL;
 212         if (sysfs_type(sd) != SYSFS_KOBJ_LINK)
 213                 goto out;
 214         if (sd->s_symlink.target_sd->s_dir.kobj != targ)
 215                 goto out;
 216
 217         if (sysfs_ns_type(parent_sd))
 218                 new_ns = targ->ktype->namespace(targ);
 219
 220         result = sysfs_rename(sd, parent_sd, new_ns, new);
 221
 222 out:
 223         sysfs_put(sd);
 224         return result;
 225 }
 226
 227 static int sysfs_get_target_path(struct sysfs_dirent *parent_sd,
 228                                  struct sysfs_dirent *target_sd, char *path)
 229 {
 230         struct sysfs_dirent *base, *sd;
 231         char *s = path;
 232         int len = 0;
 233
 234         /* go up to the root, stop at the base */
 235         base = parent_sd;
 236         while (base->s_parent) {
 237                 sd = target_sd->s_parent;
 238                 while (sd->s_parent && base != sd)
 239                         sd = sd->s_parent;
 240
 241                 if (base == sd)
 242                         break;
 243
 244                 strcpy(s, "../");
 245                 s += 3;
 246                 base = base->s_parent;
 247         }
 248
 249         /* determine end of target string for reverse fillup */
 250         sd = target_sd;
 251         while (sd->s_parent && sd != base) {
 252                 len += strlen(sd->s_name) + 1;
 253                 sd = sd->s_parent;
 254         }
 255
 256         /* check limits */
 257         if (len < 2)
 258                 return -EINVAL;
 259         len--;
 260         if ((s - path) + len > PATH_MAX)
 261                 return -ENAMETOOLONG;
 262
 263         /* reverse fillup of target string from target to base */
 264         sd = target_sd;
 265         while (sd->s_parent && sd != base) {
 266                 int slen = strlen(sd->s_name);
 267
 268                 len -= slen;
 269                 strncpy(s + len, sd->s_name, slen);
 270                 if (len)
 271                         s[--len] = '/';
 272
 273                 sd = sd->s_parent;
 274         }
 275
 276         return 0;
 277 }
 278
 279 static int sysfs_getlink(struct dentry *dentry, char * path)
 280 {
 281         struct sysfs_dirent *sd = dentry->d_fsdata;
 282         struct sysfs_dirent *parent_sd = sd->s_parent;
 283         struct sysfs_dirent *target_sd = sd->s_symlink.target_sd;
 284         int error;
 285
 286         mutex_lock(&sysfs_mutex);
 287         error = sysfs_get_target_path(parent_sd, target_sd, path);
 288         mutex_unlock(&sysfs_mutex);
 289
 290         return error;
 291 }
 292
 293 static void *sysfs_follow_link(struct dentry *dentry, struct nameidata *nd)
 294 {
 295         int error = -ENOMEM;
 296         unsigned long page = get_zeroed_page(GFP_KERNEL);
 297         if (page) {
 298                 error = sysfs_getlink(dentry, (char *) page);
 299                 if (error < 0)
 300                         free_page((unsigned long)page);
 301         }
 302         nd_set_link(nd, error ? ERR_PTR(error) : (char *)page);
 303         return NULL;
 304 }
 305
 306 static void sysfs_put_link(struct dentry *dentry, struct nameidata *nd, void *cookie)
 307 {
 308         char *page = nd_get_link(nd);
 309         if (!IS_ERR(page))
 310                 free_page((unsigned long)page);
 311 }
 312
 313 const struct inode_operations sysfs_symlink_inode_operations = {
 314         .setxattr       = sysfs_setxattr,
 315         .readlink       = generic_readlink,
 316         .follow_link    = sysfs_follow_link,
 317         .put_link       = sysfs_put_link,
 318         .setattr        = sysfs_setattr,
 319         .getattr        = sysfs_getattr,
 320         .permission     = sysfs_permission,
 321 };
 322
 323
 324 EXPORT_SYMBOL_GPL(sysfs_create_link);
 325 EXPORT_SYMBOL_GPL(sysfs_remove_link);
 326 EXPORT_SYMBOL_GPL(sysfs_rename_link);