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/mount.h>
  15 #include <linux/module.h>
  16 #include <linux/kobject.h>
  17 #include <linux/namei.h>
  18 #include <linux/mutex.h>
  19 #include <linux/security.h>
  20
  21 #include "sysfs.h"
  22
  23 static int sysfs_do_create_link(struct kobject *kobj, struct kobject *target,
  24                                 const char *name, int warn)
  25 {
  26         struct sysfs_dirent *parent_sd = NULL;
  27         struct sysfs_dirent *target_sd = NULL;
  28         struct sysfs_dirent *sd = NULL;
  29         struct sysfs_addrm_cxt acxt;
  30         int error;
  31
  32         BUG_ON(!name);
  33
  34         if (!kobj)
  35                 parent_sd = &sysfs_root;
  36         else
  37                 parent_sd = kobj->sd;
  38
  39         error = -EFAULT;
  40         if (!parent_sd)
  41                 goto out_put;
  42
  43         /* target->sd can go away beneath us but is protected with
  44          * sysfs_assoc_lock.  Fetch target_sd from it.
  45          */
  46         spin_lock(&sysfs_assoc_lock);
  47         if (target->sd)
  48                 target_sd = sysfs_get(target->sd);
  49         spin_unlock(&sysfs_assoc_lock);
  50
  51         error = -ENOENT;
  52         if (!target_sd)
  53                 goto out_put;
  54
  55         error = -ENOMEM;
  56         sd = sysfs_new_dirent(name, S_IFLNK|S_IRWXUGO, SYSFS_KOBJ_LINK);
  57         if (!sd)
  58                 goto out_put;
  59
  60         sd->s_symlink.target_sd = target_sd;
  61         target_sd = NULL;       /* reference is now owned by the symlink */
  62
  63         sysfs_addrm_start(&acxt, parent_sd);
  64         if (warn)
  65                 error = sysfs_add_one(&acxt, sd);
  66         else
  67                 error = __sysfs_add_one(&acxt, sd);
  68         sysfs_addrm_finish(&acxt);
  69
  70         if (error)
  71                 goto out_put;
  72
  73         return 0;
  74
  75  out_put:
  76         sysfs_put(target_sd);
  77         sysfs_put(sd);
  78         return error;
  79 }
  80
  81 /**
  82  *      sysfs_create_link - create symlink between two objects.
  83  *      @kobj:  object whose directory we're creating the link in.
  84  *      @target:        object we're pointing to.
  85  *      @name:          name of the symlink.
  86  */
  87 int sysfs_create_link(struct kobject *kobj, struct kobject *target,
  88                       const char *name)
  89 {
  90         return sysfs_do_create_link(kobj, target, name, 1);
  91 }
  92
  93 /**
  94  *      sysfs_create_link_nowarn - create symlink between two objects.
  95  *      @kobj:  object whose directory we're creating the link in.
  96  *      @target:        object we're pointing to.
  97  *      @name:          name of the symlink.
  98  *
  99  *      This function does the same as sysf_create_link(), but it
 100  *      doesn't warn if the link already exists.
 101  */
 102 int sysfs_create_link_nowarn(struct kobject *kobj, struct kobject *target,
 103                              const char *name)
 104 {
 105         return sysfs_do_create_link(kobj, target, name, 0);
 106 }
 107
 108 /**
 109  *      sysfs_remove_link - remove symlink in object's directory.
 110  *      @kobj:  object we're acting for.
 111  *      @name:  name of the symlink to remove.
 112  */
 113
 114 void sysfs_remove_link(struct kobject * kobj, const char * name)
 115 {
 116         struct sysfs_dirent *parent_sd = NULL;
 117
 118         if (!kobj)
 119                 parent_sd = &sysfs_root;
 120         else
 121                 parent_sd = kobj->sd;
 122
 123         sysfs_hash_and_remove(parent_sd, name);
 124 }
 125
 126 static int sysfs_get_target_path(struct sysfs_dirent *parent_sd,
 127                                  struct sysfs_dirent *target_sd, char *path)
 128 {
 129         struct sysfs_dirent *base, *sd;
 130         char *s = path;
 131         int len = 0;
 132
 133         /* go up to the root, stop at the base */
 134         base = parent_sd;
 135         while (base->s_parent) {
 136                 sd = target_sd->s_parent;
 137                 while (sd->s_parent && base != sd)
 138                         sd = sd->s_parent;
 139
 140                 if (base == sd)
 141                         break;
 142
 143                 strcpy(s, "../");
 144                 s += 3;
 145                 base = base->s_parent;
 146         }
 147
 148         /* determine end of target string for reverse fillup */
 149         sd = target_sd;
 150         while (sd->s_parent && sd != base) {
 151                 len += strlen(sd->s_name) + 1;
 152                 sd = sd->s_parent;
 153         }
 154
 155         /* check limits */
 156         if (len < 2)
 157                 return -EINVAL;
 158         len--;
 159         if ((s - path) + len > PATH_MAX)
 160                 return -ENAMETOOLONG;
 161
 162         /* reverse fillup of target string from target to base */
 163         sd = target_sd;
 164         while (sd->s_parent && sd != base) {
 165                 int slen = strlen(sd->s_name);
 166
 167                 len -= slen;
 168                 strncpy(s + len, sd->s_name, slen);
 169                 if (len)
 170                         s[--len] = '/';
 171
 172                 sd = sd->s_parent;
 173         }
 174
 175         return 0;
 176 }
 177
 178 static int sysfs_getlink(struct dentry *dentry, char * path)
 179 {
 180         struct sysfs_dirent *sd = dentry->d_fsdata;
 181         struct sysfs_dirent *parent_sd = sd->s_parent;
 182         struct sysfs_dirent *target_sd = sd->s_symlink.target_sd;
 183         int error;
 184
 185         mutex_lock(&sysfs_mutex);
 186         error = sysfs_get_target_path(parent_sd, target_sd, path);
 187         mutex_unlock(&sysfs_mutex);
 188
 189         return error;
 190 }
 191
 192 static void *sysfs_follow_link(struct dentry *dentry, struct nameidata *nd)
 193 {
 194         int error = -ENOMEM;
 195         unsigned long page = get_zeroed_page(GFP_KERNEL);
 196         if (page) {
 197                 error = sysfs_getlink(dentry, (char *) page);
 198                 if (error < 0)
 199                         free_page((unsigned long)page);
 200         }
 201         nd_set_link(nd, error ? ERR_PTR(error) : (char *)page);
 202         return NULL;
 203 }
 204
 205 static void sysfs_put_link(struct dentry *dentry, struct nameidata *nd, void *cookie)
 206 {
 207         char *page = nd_get_link(nd);
 208         if (!IS_ERR(page))
 209                 free_page((unsigned long)page);
 210 }
 211
 212 const struct inode_operations sysfs_symlink_inode_operations = {
 213         .setxattr = sysfs_setxattr,
 214         .readlink = generic_readlink,
 215         .follow_link = sysfs_follow_link,
 216         .put_link = sysfs_put_link,
 217 };
 218
 219
 220 EXPORT_SYMBOL_GPL(sysfs_create_link);
 221 EXPORT_SYMBOL_GPL(sysfs_remove_link);