linux/fs/sysfs/symlink.c
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   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
  24static 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 */
  95int 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
 101static 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 */
 123int 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 */
 138int 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 */
 153void 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
 170void 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 */
 191int 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
 222out:
 223        sysfs_put(sd);
 224        return result;
 225}
 226
 227static 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
 279static 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
 293static 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
 306static 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
 313const 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
 324EXPORT_SYMBOL_GPL(sysfs_create_link);
 325EXPORT_SYMBOL_GPL(sysfs_remove_link);
 326EXPORT_SYMBOL_GPL(sysfs_rename_link);
 327
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