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         sd->s_symlink.target_sd = target_sd;
  62         target_sd = NULL;       /* reference is now owned by the symlink */
  63
  64         sysfs_addrm_start(&acxt, parent_sd);
  65         if (warn)
  66                 error = sysfs_add_one(&acxt, sd);
  67         else
  68                 error = __sysfs_add_one(&acxt, sd);
  69         sysfs_addrm_finish(&acxt);
  70
  71         if (error)
  72                 goto out_put;
  73
  74         return 0;
  75
  76  out_put:
  77         sysfs_put(target_sd);
  78         sysfs_put(sd);
  79         return error;
  80 }
  81
  82 /**
  83  *      sysfs_create_link - create symlink between two objects.
  84  *      @kobj:  object whose directory we're creating the link in.
  85  *      @target:        object we're pointing to.
  86  *      @name:          name of the symlink.
  87  */
  88 int sysfs_create_link(struct kobject *kobj, struct kobject *target,
  89                       const char *name)
  90 {
  91         return sysfs_do_create_link(kobj, target, name, 1);
  92 }
  93
  94 /**
  95  *      sysfs_create_link_nowarn - create symlink between two objects.
  96  *      @kobj:  object whose directory we're creating the link in.
  97  *      @target:        object we're pointing to.
  98  *      @name:          name of the symlink.
  99  *
 100  *      This function does the same as sysf_create_link(), but it
 101  *      doesn't warn if the link already exists.
 102  */
 103 int sysfs_create_link_nowarn(struct kobject *kobj, struct kobject *target,
 104                              const char *name)
 105 {
 106         return sysfs_do_create_link(kobj, target, name, 0);
 107 }
 108
 109 /**
 110  *      sysfs_remove_link - remove symlink in object's directory.
 111  *      @kobj:  object we're acting for.
 112  *      @name:  name of the symlink to remove.
 113  */
 114
 115 void sysfs_remove_link(struct kobject * kobj, const char * name)
 116 {
 117         struct sysfs_dirent *parent_sd = NULL;
 118
 119         if (!kobj)
 120                 parent_sd = &sysfs_root;
 121         else
 122                 parent_sd = kobj->sd;
 123
 124         sysfs_hash_and_remove(parent_sd, name);
 125 }
 126
 127 /**
 128  *      sysfs_rename_link - rename symlink in object's directory.
 129  *      @kobj:  object we're acting for.
 130  *      @targ:  object we're pointing to.
 131  *      @old:   previous name of the symlink.
 132  *      @new:   new name of the symlink.
 133  *
 134  *      A helper function for the common rename symlink idiom.
 135  */
 136 int sysfs_rename_link(struct kobject *kobj, struct kobject *targ,
 137                         const char *old, const char *new)
 138 {
 139         struct sysfs_dirent *parent_sd, *sd = NULL;
 140         int result;
 141
 142         if (!kobj)
 143                 parent_sd = &sysfs_root;
 144         else
 145                 parent_sd = kobj->sd;
 146
 147         result = -ENOENT;
 148         sd = sysfs_get_dirent(parent_sd, old);
 149         if (!sd)
 150                 goto out;
 151
 152         result = -EINVAL;
 153         if (sysfs_type(sd) != SYSFS_KOBJ_LINK)
 154                 goto out;
 155         if (sd->s_symlink.target_sd->s_dir.kobj != targ)
 156                 goto out;
 157
 158         result = sysfs_rename(sd, parent_sd, new);
 159
 160 out:
 161         sysfs_put(sd);
 162         return result;
 163 }
 164
 165 static int sysfs_get_target_path(struct sysfs_dirent *parent_sd,
 166                                  struct sysfs_dirent *target_sd, char *path)
 167 {
 168         struct sysfs_dirent *base, *sd;
 169         char *s = path;
 170         int len = 0;
 171
 172         /* go up to the root, stop at the base */
 173         base = parent_sd;
 174         while (base->s_parent) {
 175                 sd = target_sd->s_parent;
 176                 while (sd->s_parent && base != sd)
 177                         sd = sd->s_parent;
 178
 179                 if (base == sd)
 180                         break;
 181
 182                 strcpy(s, "../");
 183                 s += 3;
 184                 base = base->s_parent;
 185         }
 186
 187         /* determine end of target string for reverse fillup */
 188         sd = target_sd;
 189         while (sd->s_parent && sd != base) {
 190                 len += strlen(sd->s_name) + 1;
 191                 sd = sd->s_parent;
 192         }
 193
 194         /* check limits */
 195         if (len < 2)
 196                 return -EINVAL;
 197         len--;
 198         if ((s - path) + len > PATH_MAX)
 199                 return -ENAMETOOLONG;
 200
 201         /* reverse fillup of target string from target to base */
 202         sd = target_sd;
 203         while (sd->s_parent && sd != base) {
 204                 int slen = strlen(sd->s_name);
 205
 206                 len -= slen;
 207                 strncpy(s + len, sd->s_name, slen);
 208                 if (len)
 209                         s[--len] = '/';
 210
 211                 sd = sd->s_parent;
 212         }
 213
 214         return 0;
 215 }
 216
 217 static int sysfs_getlink(struct dentry *dentry, char * path)
 218 {
 219         struct sysfs_dirent *sd = dentry->d_fsdata;
 220         struct sysfs_dirent *parent_sd = sd->s_parent;
 221         struct sysfs_dirent *target_sd = sd->s_symlink.target_sd;
 222         int error;
 223
 224         mutex_lock(&sysfs_mutex);
 225         error = sysfs_get_target_path(parent_sd, target_sd, path);
 226         mutex_unlock(&sysfs_mutex);
 227
 228         return error;
 229 }
 230
 231 static void *sysfs_follow_link(struct dentry *dentry, struct nameidata *nd)
 232 {
 233         int error = -ENOMEM;
 234         unsigned long page = get_zeroed_page(GFP_KERNEL);
 235         if (page) {
 236                 error = sysfs_getlink(dentry, (char *) page);
 237                 if (error < 0)
 238                         free_page((unsigned long)page);
 239         }
 240         nd_set_link(nd, error ? ERR_PTR(error) : (char *)page);
 241         return NULL;
 242 }
 243
 244 static void sysfs_put_link(struct dentry *dentry, struct nameidata *nd, void *cookie)
 245 {
 246         char *page = nd_get_link(nd);
 247         if (!IS_ERR(page))
 248                 free_page((unsigned long)page);
 249 }
 250
 251 const struct inode_operations sysfs_symlink_inode_operations = {
 252         .setxattr       = sysfs_setxattr,
 253         .readlink       = generic_readlink,
 254         .follow_link    = sysfs_follow_link,
 255         .put_link       = sysfs_put_link,
 256         .setattr        = sysfs_setattr,
 257         .getattr        = sysfs_getattr,
 258         .permission     = sysfs_permission,
 259 };
 260
 261
 262 EXPORT_SYMBOL_GPL(sysfs_create_link);
 263 EXPORT_SYMBOL_GPL(sysfs_remove_link);