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