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 /**
  23  *      sysfs_create_link - create symlink between two objects.
  24  *      @kobj:  object whose directory we're creating the link in.
  25  *      @target:        object we're pointing to.
  26  *      @name:          name of the symlink.
  27  */
  28 int sysfs_create_link(struct kobject * kobj, struct kobject * target, const char * name)
  29 {
  30         struct sysfs_dirent *parent_sd = NULL;
  31         struct sysfs_dirent *target_sd = NULL;
  32         struct sysfs_dirent *sd = NULL;
  33         struct sysfs_addrm_cxt acxt;
  34         int error;
  35
  36         BUG_ON(!name);
  37
  38         if (!kobj)
  39                 parent_sd = &sysfs_root;
  40         else
  41                 parent_sd = kobj->sd;
  42
  43         error = -EFAULT;
  44         if (!parent_sd)
  45                 goto out_put;
  46
  47         /* target->sd can go away beneath us but is protected with
  48          * sysfs_assoc_lock.  Fetch target_sd from it.
  49          */
  50         spin_lock(&sysfs_assoc_lock);
  51         if (target->sd)
  52                 target_sd = sysfs_get(target->sd);
  53         spin_unlock(&sysfs_assoc_lock);
  54
  55         error = -ENOENT;
  56         if (!target_sd)
  57                 goto out_put;
  58
  59         error = -ENOMEM;
  60         sd = sysfs_new_dirent(name, S_IFLNK|S_IRWXUGO, SYSFS_KOBJ_LINK);
  61         if (!sd)
  62                 goto out_put;
  63
  64         sd->s_symlink.target_sd = target_sd;
  65         target_sd = NULL;       /* reference is now owned by the symlink */
  66
  67         sysfs_addrm_start(&acxt, parent_sd);
  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_remove_link - remove symlink in object's directory.
  84  *      @kobj:  object we're acting for.
  85  *      @name:  name of the symlink to remove.
  86  */
  87
  88 void sysfs_remove_link(struct kobject * kobj, const char * name)
  89 {
  90         sysfs_hash_and_remove(kobj->sd, name);
  91 }
  92
  93 static int sysfs_get_target_path(struct sysfs_dirent *parent_sd,
  94                                  struct sysfs_dirent *target_sd, char *path)
  95 {
  96         struct sysfs_dirent *base, *sd;
  97         char *s = path;
  98         int len = 0;
  99
 100         /* go up to the root, stop at the base */
 101         base = parent_sd;
 102         while (base->s_parent) {
 103                 sd = target_sd->s_parent;
 104                 while (sd->s_parent && base != sd)
 105                         sd = sd->s_parent;
 106
 107                 if (base == sd)
 108                         break;
 109
 110                 strcpy(s, "../");
 111                 s += 3;
 112                 base = base->s_parent;
 113         }
 114
 115         /* determine end of target string for reverse fillup */
 116         sd = target_sd;
 117         while (sd->s_parent && sd != base) {
 118                 len += strlen(sd->s_name) + 1;
 119                 sd = sd->s_parent;
 120         }
 121
 122         /* check limits */
 123         if (len < 2)
 124                 return -EINVAL;
 125         len--;
 126         if ((s - path) + len > PATH_MAX)
 127                 return -ENAMETOOLONG;
 128
 129         /* reverse fillup of target string from target to base */
 130         sd = target_sd;
 131         while (sd->s_parent && sd != base) {
 132                 int slen = strlen(sd->s_name);
 133
 134                 len -= slen;
 135                 strncpy(s + len, sd->s_name, slen);
 136                 if (len)
 137                         s[--len] = '/';
 138
 139                 sd = sd->s_parent;
 140         }
 141
 142         return 0;
 143 }
 144
 145 static int sysfs_getlink(struct dentry *dentry, char * path)
 146 {
 147         struct sysfs_dirent *sd = dentry->d_fsdata;
 148         struct sysfs_dirent *parent_sd = sd->s_parent;
 149         struct sysfs_dirent *target_sd = sd->s_symlink.target_sd;
 150         int error;
 151
 152         mutex_lock(&sysfs_mutex);
 153         error = sysfs_get_target_path(parent_sd, target_sd, path);
 154         mutex_unlock(&sysfs_mutex);
 155
 156         return error;
 157 }
 158
 159 static void *sysfs_follow_link(struct dentry *dentry, struct nameidata *nd)
 160 {
 161         int error = -ENOMEM;
 162         unsigned long page = get_zeroed_page(GFP_KERNEL);
 163         if (page)
 164                 error = sysfs_getlink(dentry, (char *) page);
 165         nd_set_link(nd, error ? ERR_PTR(error) : (char *)page);
 166         return NULL;
 167 }
 168
 169 static void sysfs_put_link(struct dentry *dentry, struct nameidata *nd, void *cookie)
 170 {
 171         char *page = nd_get_link(nd);
 172         if (!IS_ERR(page))
 173                 free_page((unsigned long)page);
 174 }
 175
 176 const struct inode_operations sysfs_symlink_inode_operations = {
 177         .readlink = generic_readlink,
 178         .follow_link = sysfs_follow_link,
 179         .put_link = sysfs_put_link,
 180 };
 181
 182
 183 EXPORT_SYMBOL_GPL(sysfs_create_link);
 184 EXPORT_SYMBOL_GPL(sysfs_remove_link);