fs/configfs/symlink.c

   1 /* -*- mode: c; c-basic-offset: 8; -*-
   2  * vim: noexpandtab sw=8 ts=8 sts=0:
   3  *
   4  * symlink.c - operations for configfs symlinks.
   5  *
   6  * This program is free software; you can redistribute it and/or
   7  * modify it under the terms of the GNU General Public
   8  * License as published by the Free Software Foundation; either
   9  * version 2 of the License, or (at your option) any later version.
  10  *
  11  * This program is distributed in the hope that it will be useful,
  12  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  13  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  14  * General Public License for more details.
  15  *
  16  * You should have received a copy of the GNU General Public
  17  * License along with this program; if not, write to the
  18  * Free Software Foundation, Inc., 59 Temple Place - Suite 330,
  19  * Boston, MA 021110-1307, USA.
  20  *
  21  * Based on sysfs:
  22  *      sysfs is Copyright (C) 2001, 2002, 2003 Patrick Mochel
  23  *
  24  * configfs Copyright (C) 2005 Oracle.  All rights reserved.
  25  */
  26
  27 #include <linux/fs.h>
  28 #include <linux/module.h>
  29 #include <linux/namei.h>
  30
  31 #include <linux/configfs.h>
  32 #include "configfs_internal.h"
  33
  34 /* Protects attachments of new symlinks */
  35 DEFINE_MUTEX(configfs_symlink_mutex);
  36
  37 static int item_depth(struct config_item * item)
  38 {
  39         struct config_item * p = item;
  40         int depth = 0;
  41         do { depth++; } while ((p = p->ci_parent) && !configfs_is_root(p));
  42         return depth;
  43 }
  44
  45 static int item_path_length(struct config_item * item)
  46 {
  47         struct config_item * p = item;
  48         int length = 1;
  49         do {
  50                 length += strlen(config_item_name(p)) + 1;
  51                 p = p->ci_parent;
  52         } while (p && !configfs_is_root(p));
  53         return length;
  54 }
  55
  56 static void fill_item_path(struct config_item * item, char * buffer, int length)
  57 {
  58         struct config_item * p;
  59
  60         --length;
  61         for (p = item; p && !configfs_is_root(p); p = p->ci_parent) {
  62                 int cur = strlen(config_item_name(p));
  63
  64                 /* back up enough to print this bus id with '/' */
  65                 length -= cur;
  66                 strncpy(buffer + length,config_item_name(p),cur);
  67                 *(buffer + --length) = '/';
  68         }
  69 }
  70
  71 static int create_link(struct config_item *parent_item,
  72                        struct config_item *item,
  73                        struct dentry *dentry)
  74 {
  75         struct configfs_dirent *target_sd = item->ci_dentry->d_fsdata;
  76         struct configfs_symlink *sl;
  77         int ret;
  78
  79         ret = -ENOENT;
  80         if (!configfs_dirent_is_ready(target_sd))
  81                 goto out;
  82         ret = -ENOMEM;
  83         sl = kmalloc(sizeof(struct configfs_symlink), GFP_KERNEL);
  84         if (sl) {
  85                 sl->sl_target = config_item_get(item);
  86                 spin_lock(&configfs_dirent_lock);
  87                 if (target_sd->s_type & CONFIGFS_USET_DROPPING) {
  88                         spin_unlock(&configfs_dirent_lock);
  89                         config_item_put(item);
  90                         kfree(sl);
  91                         return -ENOENT;
  92                 }
  93                 list_add(&sl->sl_list, &target_sd->s_links);
  94                 spin_unlock(&configfs_dirent_lock);
  95                 ret = configfs_create_link(sl, parent_item->ci_dentry,
  96                                            dentry);
  97                 if (ret) {
  98                         spin_lock(&configfs_dirent_lock);
  99                         list_del_init(&sl->sl_list);
 100                         spin_unlock(&configfs_dirent_lock);
 101                         config_item_put(item);
 102                         kfree(sl);
 103                 }
 104         }
 105
 106 out:
 107         return ret;
 108 }
 109
 110
 111 static int get_target(const char *symname, struct path *path,
 112                       struct config_item **target)
 113 {
 114         int ret;
 115
 116         ret = kern_path(symname, LOOKUP_FOLLOW|LOOKUP_DIRECTORY, path);
 117         if (!ret) {
 118                 if (path->dentry->d_sb == configfs_sb) {
 119                         *target = configfs_get_config_item(path->dentry);
 120                         if (!*target) {
 121                                 ret = -ENOENT;
 122                                 path_put(path);
 123                         }
 124                 } else
 125                         ret = -EPERM;
 126         }
 127
 128         return ret;
 129 }
 130
 131
 132 int configfs_symlink(struct inode *dir, struct dentry *dentry, const char *symname)
 133 {
 134         int ret;
 135         struct path path;
 136         struct configfs_dirent *sd;
 137         struct config_item *parent_item;
 138         struct config_item *target_item = NULL;
 139         struct config_item_type *type;
 140
 141         ret = -EPERM;  /* What lack-of-symlink returns */
 142         if (dentry->d_parent == configfs_sb->s_root)
 143                 goto out;
 144
 145         sd = dentry->d_parent->d_fsdata;
 146         /*
 147          * Fake invisibility if dir belongs to a group/default groups hierarchy
 148          * being attached
 149          */
 150         ret = -ENOENT;
 151         if (!configfs_dirent_is_ready(sd))
 152                 goto out;
 153
 154         parent_item = configfs_get_config_item(dentry->d_parent);
 155         type = parent_item->ci_type;
 156
 157         ret = -EPERM;
 158         if (!type || !type->ct_item_ops ||
 159             !type->ct_item_ops->allow_link)
 160                 goto out_put;
 161
 162         ret = get_target(symname, &path, &target_item);
 163         if (ret)
 164                 goto out_put;
 165
 166         ret = type->ct_item_ops->allow_link(parent_item, target_item);
 167         if (!ret) {
 168                 mutex_lock(&configfs_symlink_mutex);
 169                 ret = create_link(parent_item, target_item, dentry);
 170                 mutex_unlock(&configfs_symlink_mutex);
 171                 if (ret && type->ct_item_ops->drop_link)
 172                         type->ct_item_ops->drop_link(parent_item,
 173                                                      target_item);
 174         }
 175
 176         config_item_put(target_item);
 177         path_put(&path);
 178
 179 out_put:
 180         config_item_put(parent_item);
 181
 182 out:
 183         return ret;
 184 }
 185
 186 int configfs_unlink(struct inode *dir, struct dentry *dentry)
 187 {
 188         struct configfs_dirent *sd = dentry->d_fsdata;
 189         struct configfs_symlink *sl;
 190         struct config_item *parent_item;
 191         struct config_item_type *type;
 192         int ret;
 193
 194         ret = -EPERM;  /* What lack-of-symlink returns */
 195         if (!(sd->s_type & CONFIGFS_ITEM_LINK))
 196                 goto out;
 197
 198         BUG_ON(dentry->d_parent == configfs_sb->s_root);
 199
 200         sl = sd->s_element;
 201
 202         parent_item = configfs_get_config_item(dentry->d_parent);
 203         type = parent_item->ci_type;
 204
 205         spin_lock(&configfs_dirent_lock);
 206         list_del_init(&sd->s_sibling);
 207         spin_unlock(&configfs_dirent_lock);
 208         configfs_drop_dentry(sd, dentry->d_parent);
 209         dput(dentry);
 210         configfs_put(sd);
 211
 212         /*
 213          * drop_link() must be called before
 214          * list_del_init(&sl->sl_list), so that the order of
 215          * drop_link(this, target) and drop_item(target) is preserved.
 216          */
 217         if (type && type->ct_item_ops &&
 218             type->ct_item_ops->drop_link)
 219                 type->ct_item_ops->drop_link(parent_item,
 220                                                sl->sl_target);
 221
 222         spin_lock(&configfs_dirent_lock);
 223         list_del_init(&sl->sl_list);
 224         spin_unlock(&configfs_dirent_lock);
 225
 226         /* Put reference from create_link() */
 227         config_item_put(sl->sl_target);
 228         kfree(sl);
 229
 230         config_item_put(parent_item);
 231
 232         ret = 0;
 233
 234 out:
 235         return ret;
 236 }
 237
 238 static int configfs_get_target_path(struct config_item * item, struct config_item * target,
 239                                    char *path)
 240 {
 241         char * s;
 242         int depth, size;
 243
 244         depth = item_depth(item);
 245         size = item_path_length(target) + depth * 3 - 1;
 246         if (size > PATH_MAX)
 247                 return -ENAMETOOLONG;
 248
 249         pr_debug("%s: depth = %d, size = %d\n", __func__, depth, size);
 250
 251         for (s = path; depth--; s += 3)
 252                 strcpy(s,"../");
 253
 254         fill_item_path(target, path, size);
 255         pr_debug("%s: path = '%s'\n", __func__, path);
 256
 257         return 0;
 258 }
 259
 260 static int configfs_getlink(struct dentry *dentry, char * path)
 261 {
 262         struct config_item *item, *target_item;
 263         int error = 0;
 264
 265         item = configfs_get_config_item(dentry->d_parent);
 266         if (!item)
 267                 return -EINVAL;
 268
 269         target_item = configfs_get_config_item(dentry);
 270         if (!target_item) {
 271                 config_item_put(item);
 272                 return -EINVAL;
 273         }
 274
 275         down_read(&configfs_rename_sem);
 276         error = configfs_get_target_path(item, target_item, path);
 277         up_read(&configfs_rename_sem);
 278
 279         config_item_put(item);
 280         config_item_put(target_item);
 281         return error;
 282
 283 }
 284
 285 static void *configfs_follow_link(struct dentry *dentry, struct nameidata *nd)
 286 {
 287         int error = -ENOMEM;
 288         unsigned long page = get_zeroed_page(GFP_KERNEL);
 289
 290         if (page) {
 291                 error = configfs_getlink(dentry, (char *)page);
 292                 if (!error) {
 293                         nd_set_link(nd, (char *)page);
 294                         return (void *)page;
 295                 }
 296         }
 297
 298         nd_set_link(nd, ERR_PTR(error));
 299         return NULL;
 300 }
 301
 302 static void configfs_put_link(struct dentry *dentry, struct nameidata *nd,
 303                               void *cookie)
 304 {
 305         if (cookie) {
 306                 unsigned long page = (unsigned long)cookie;
 307                 free_page(page);
 308         }
 309 }
 310
 311 const struct inode_operations configfs_symlink_inode_operations = {
 312         .follow_link = configfs_follow_link,
 313         .readlink = generic_readlink,
 314         .put_link = configfs_put_link,
 315         .setattr = configfs_setattr,
 316 };
 317