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 #include <linux/slab.h>
  31
  32 #include <linux/configfs.h>
  33 #include "configfs_internal.h"
  34
  35 /* Protects attachments of new symlinks */
  36 DEFINE_MUTEX(configfs_symlink_mutex);
  37
  38 static int item_depth(struct config_item * item)
  39 {
  40         struct config_item * p = item;
  41         int depth = 0;
  42         do { depth++; } while ((p = p->ci_parent) && !configfs_is_root(p));
  43         return depth;
  44 }
  45
  46 static int item_path_length(struct config_item * item)
  47 {
  48         struct config_item * p = item;
  49         int length = 1;
  50         do {
  51                 length += strlen(config_item_name(p)) + 1;
  52                 p = p->ci_parent;
  53         } while (p && !configfs_is_root(p));
  54         return length;
  55 }
  56
  57 static void fill_item_path(struct config_item * item, char * buffer, int length)
  58 {
  59         struct config_item * p;
  60
  61         --length;
  62         for (p = item; p && !configfs_is_root(p); p = p->ci_parent) {
  63                 int cur = strlen(config_item_name(p));
  64
  65                 /* back up enough to print this bus id with '/' */
  66                 length -= cur;
  67                 memcpy(buffer + length, config_item_name(p), cur);
  68                 *(buffer + --length) = '/';
  69         }
  70 }
  71
  72 static int create_link(struct config_item *parent_item,
  73                        struct config_item *item,
  74                        struct dentry *dentry)
  75 {
  76         struct configfs_dirent *target_sd = item->ci_dentry->d_fsdata;
  77         struct configfs_symlink *sl;
  78         int ret;
  79
  80         ret = -ENOENT;
  81         if (!configfs_dirent_is_ready(target_sd))
  82                 goto out;
  83         ret = -ENOMEM;
  84         sl = kmalloc(sizeof(struct configfs_symlink), GFP_KERNEL);
  85         if (sl) {
  86                 spin_lock(&configfs_dirent_lock);
  87                 if (target_sd->s_type & CONFIGFS_USET_DROPPING) {
  88                         spin_unlock(&configfs_dirent_lock);
  89                         kfree(sl);
  90                         return -ENOENT;
  91                 }
  92                 sl->sl_target = config_item_get(item);
  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, struct super_block *sb)
 113 {
 114         int ret;
 115
 116         ret = kern_path(symname, LOOKUP_FOLLOW|LOOKUP_DIRECTORY, path);
 117         if (!ret) {
 118                 if (path->dentry->d_sb == 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                         path_put(path);
 127                 }
 128         }
 129
 130         return ret;
 131 }
 132
 133
 134 int configfs_symlink(struct inode *dir, struct dentry *dentry, const char *symname)
 135 {
 136         int ret;
 137         struct path path;
 138         struct configfs_dirent *sd;
 139         struct config_item *parent_item;
 140         struct config_item *target_item = NULL;
 141         const struct config_item_type *type;
 142
 143         sd = dentry->d_parent->d_fsdata;
 144         /*
 145          * Fake invisibility if dir belongs to a group/default groups hierarchy
 146          * being attached
 147          */
 148         ret = -ENOENT;
 149         if (!configfs_dirent_is_ready(sd))
 150                 goto out;
 151
 152         parent_item = configfs_get_config_item(dentry->d_parent);
 153         type = parent_item->ci_type;
 154
 155         ret = -EPERM;
 156         if (!type || !type->ct_item_ops ||
 157             !type->ct_item_ops->allow_link)
 158                 goto out_put;
 159
 160         ret = get_target(symname, &path, &target_item, dentry->d_sb);
 161         if (ret)
 162                 goto out_put;
 163
 164         ret = type->ct_item_ops->allow_link(parent_item, target_item);
 165         if (!ret) {
 166                 mutex_lock(&configfs_symlink_mutex);
 167                 ret = create_link(parent_item, target_item, dentry);
 168                 mutex_unlock(&configfs_symlink_mutex);
 169                 if (ret && type->ct_item_ops->drop_link)
 170                         type->ct_item_ops->drop_link(parent_item,
 171                                                      target_item);
 172         }
 173
 174         config_item_put(target_item);
 175         path_put(&path);
 176
 177 out_put:
 178         config_item_put(parent_item);
 179
 180 out:
 181         return ret;
 182 }
 183
 184 int configfs_unlink(struct inode *dir, struct dentry *dentry)
 185 {
 186         struct configfs_dirent *sd = dentry->d_fsdata;
 187         struct configfs_symlink *sl;
 188         struct config_item *parent_item;
 189         const struct config_item_type *type;
 190         int ret;
 191
 192         ret = -EPERM;  /* What lack-of-symlink returns */
 193         if (!(sd->s_type & CONFIGFS_ITEM_LINK))
 194                 goto out;
 195
 196         sl = sd->s_element;
 197
 198         parent_item = configfs_get_config_item(dentry->d_parent);
 199         type = parent_item->ci_type;
 200
 201         spin_lock(&configfs_dirent_lock);
 202         list_del_init(&sd->s_sibling);
 203         spin_unlock(&configfs_dirent_lock);
 204         configfs_drop_dentry(sd, dentry->d_parent);
 205         dput(dentry);
 206         configfs_put(sd);
 207
 208         /*
 209          * drop_link() must be called before
 210          * list_del_init(&sl->sl_list), so that the order of
 211          * drop_link(this, target) and drop_item(target) is preserved.
 212          */
 213         if (type && type->ct_item_ops &&
 214             type->ct_item_ops->drop_link)
 215                 type->ct_item_ops->drop_link(parent_item,
 216                                                sl->sl_target);
 217
 218         spin_lock(&configfs_dirent_lock);
 219         list_del_init(&sl->sl_list);
 220         spin_unlock(&configfs_dirent_lock);
 221
 222         /* Put reference from create_link() */
 223         config_item_put(sl->sl_target);
 224         kfree(sl);
 225
 226         config_item_put(parent_item);
 227
 228         ret = 0;
 229
 230 out:
 231         return ret;
 232 }
 233
 234 static int configfs_get_target_path(struct config_item * item, struct config_item * target,
 235                                    char *path)
 236 {
 237         char * s;
 238         int depth, size;
 239
 240         depth = item_depth(item);
 241         size = item_path_length(target) + depth * 3 - 1;
 242         if (size > PATH_MAX)
 243                 return -ENAMETOOLONG;
 244
 245         pr_debug("%s: depth = %d, size = %d\n", __func__, depth, size);
 246
 247         for (s = path; depth--; s += 3)
 248                 strcpy(s,"../");
 249
 250         fill_item_path(target, path, size);
 251         pr_debug("%s: path = '%s'\n", __func__, path);
 252
 253         return 0;
 254 }
 255
 256 static int configfs_getlink(struct dentry *dentry, char * path)
 257 {
 258         struct config_item *item, *target_item;
 259         int error = 0;
 260
 261         item = configfs_get_config_item(dentry->d_parent);
 262         if (!item)
 263                 return -EINVAL;
 264
 265         target_item = configfs_get_config_item(dentry);
 266         if (!target_item) {
 267                 config_item_put(item);
 268                 return -EINVAL;
 269         }
 270
 271         down_read(&configfs_rename_sem);
 272         error = configfs_get_target_path(item, target_item, path);
 273         up_read(&configfs_rename_sem);
 274
 275         config_item_put(item);
 276         config_item_put(target_item);
 277         return error;
 278
 279 }
 280
 281 static const char *configfs_get_link(struct dentry *dentry,
 282                                      struct inode *inode,
 283                                      struct delayed_call *done)
 284 {
 285         char *body;
 286         int error;
 287
 288         if (!dentry)
 289                 return ERR_PTR(-ECHILD);
 290
 291         body = kzalloc(PAGE_SIZE, GFP_KERNEL);
 292         if (!body)
 293                 return ERR_PTR(-ENOMEM);
 294
 295         error = configfs_getlink(dentry, body);
 296         if (!error) {
 297                 set_delayed_call(done, kfree_link, body);
 298                 return body;
 299         }
 300
 301         kfree(body);
 302         return ERR_PTR(error);
 303 }
 304
 305 const struct inode_operations configfs_symlink_inode_operations = {
 306         .get_link = configfs_get_link,
 307         .setattr = configfs_setattr,
 308 };
 309