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                 strncpy(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                 sl->sl_target = config_item_get(item);
  87                 spin_lock(&configfs_dirent_lock);
  88                 if (target_sd->s_type & CONFIGFS_USET_DROPPING) {
  89                         spin_unlock(&configfs_dirent_lock);
  90                         config_item_put(item);
  91                         kfree(sl);
  92                         return -ENOENT;
  93                 }
  94                 list_add(&sl->sl_list, &target_sd->s_links);
  95                 spin_unlock(&configfs_dirent_lock);
  96                 ret = configfs_create_link(sl, parent_item->ci_dentry,
  97                                            dentry);
  98                 if (ret) {
  99                         spin_lock(&configfs_dirent_lock);
 100                         list_del_init(&sl->sl_list);
 101                         spin_unlock(&configfs_dirent_lock);
 102                         config_item_put(item);
 103                         kfree(sl);
 104                 }
 105         }
 106
 107 out:
 108         return ret;
 109 }
 110
 111
 112 static int get_target(const char *symname, struct path *path,
 113                       struct config_item **target)
 114 {
 115         int ret;
 116
 117         ret = kern_path(symname, LOOKUP_FOLLOW|LOOKUP_DIRECTORY, path);
 118         if (!ret) {
 119                 if (path->dentry->d_sb == configfs_sb) {
 120                         *target = configfs_get_config_item(path->dentry);
 121                         if (!*target) {
 122                                 ret = -ENOENT;
 123                                 path_put(path);
 124                         }
 125                 } else {
 126                         ret = -EPERM;
 127                         path_put(path);
 128                 }
 129         }
 130
 131         return ret;
 132 }
 133
 134
 135 int configfs_symlink(struct inode *dir, struct dentry *dentry, const char *symname)
 136 {
 137         int ret;
 138         struct path path;
 139         struct configfs_dirent *sd;
 140         struct config_item *parent_item;
 141         struct config_item *target_item = NULL;
 142         struct config_item_type *type;
 143
 144         ret = -EPERM;  /* What lack-of-symlink returns */
 145         if (dentry->d_parent == configfs_sb->s_root)
 146                 goto out;
 147
 148         sd = dentry->d_parent->d_fsdata;
 149         /*
 150          * Fake invisibility if dir belongs to a group/default groups hierarchy
 151          * being attached
 152          */
 153         ret = -ENOENT;
 154         if (!configfs_dirent_is_ready(sd))
 155                 goto out;
 156
 157         parent_item = configfs_get_config_item(dentry->d_parent);
 158         type = parent_item->ci_type;
 159
 160         ret = -EPERM;
 161         if (!type || !type->ct_item_ops ||
 162             !type->ct_item_ops->allow_link)
 163                 goto out_put;
 164
 165         ret = get_target(symname, &path, &target_item);
 166         if (ret)
 167                 goto out_put;
 168
 169         ret = type->ct_item_ops->allow_link(parent_item, target_item);
 170         if (!ret) {
 171                 mutex_lock(&configfs_symlink_mutex);
 172                 ret = create_link(parent_item, target_item, dentry);
 173                 mutex_unlock(&configfs_symlink_mutex);
 174                 if (ret && type->ct_item_ops->drop_link)
 175                         type->ct_item_ops->drop_link(parent_item,
 176                                                      target_item);
 177         }
 178
 179         config_item_put(target_item);
 180         path_put(&path);
 181
 182 out_put:
 183         config_item_put(parent_item);
 184
 185 out:
 186         return ret;
 187 }
 188
 189 int configfs_unlink(struct inode *dir, struct dentry *dentry)
 190 {
 191         struct configfs_dirent *sd = dentry->d_fsdata;
 192         struct configfs_symlink *sl;
 193         struct config_item *parent_item;
 194         struct config_item_type *type;
 195         int ret;
 196
 197         ret = -EPERM;  /* What lack-of-symlink returns */
 198         if (!(sd->s_type & CONFIGFS_ITEM_LINK))
 199                 goto out;
 200
 201         BUG_ON(dentry->d_parent == configfs_sb->s_root);
 202
 203         sl = sd->s_element;
 204
 205         parent_item = configfs_get_config_item(dentry->d_parent);
 206         type = parent_item->ci_type;
 207
 208         spin_lock(&configfs_dirent_lock);
 209         list_del_init(&sd->s_sibling);
 210         spin_unlock(&configfs_dirent_lock);
 211         configfs_drop_dentry(sd, dentry->d_parent);
 212         dput(dentry);
 213         configfs_put(sd);
 214
 215         /*
 216          * drop_link() must be called before
 217          * list_del_init(&sl->sl_list), so that the order of
 218          * drop_link(this, target) and drop_item(target) is preserved.
 219          */
 220         if (type && type->ct_item_ops &&
 221             type->ct_item_ops->drop_link)
 222                 type->ct_item_ops->drop_link(parent_item,
 223                                                sl->sl_target);
 224
 225         spin_lock(&configfs_dirent_lock);
 226         list_del_init(&sl->sl_list);
 227         spin_unlock(&configfs_dirent_lock);
 228
 229         /* Put reference from create_link() */
 230         config_item_put(sl->sl_target);
 231         kfree(sl);
 232
 233         config_item_put(parent_item);
 234
 235         ret = 0;
 236
 237 out:
 238         return ret;
 239 }
 240
 241 static int configfs_get_target_path(struct config_item * item, struct config_item * target,
 242                                    char *path)
 243 {
 244         char * s;
 245         int depth, size;
 246
 247         depth = item_depth(item);
 248         size = item_path_length(target) + depth * 3 - 1;
 249         if (size > PATH_MAX)
 250                 return -ENAMETOOLONG;
 251
 252         pr_debug("%s: depth = %d, size = %d\n", __func__, depth, size);
 253
 254         for (s = path; depth--; s += 3)
 255                 strcpy(s,"../");
 256
 257         fill_item_path(target, path, size);
 258         pr_debug("%s: path = '%s'\n", __func__, path);
 259
 260         return 0;
 261 }
 262
 263 static int configfs_getlink(struct dentry *dentry, char * path)
 264 {
 265         struct config_item *item, *target_item;
 266         int error = 0;
 267
 268         item = configfs_get_config_item(dentry->d_parent);
 269         if (!item)
 270                 return -EINVAL;
 271
 272         target_item = configfs_get_config_item(dentry);
 273         if (!target_item) {
 274                 config_item_put(item);
 275                 return -EINVAL;
 276         }
 277
 278         down_read(&configfs_rename_sem);
 279         error = configfs_get_target_path(item, target_item, path);
 280         up_read(&configfs_rename_sem);
 281
 282         config_item_put(item);
 283         config_item_put(target_item);
 284         return error;
 285
 286 }
 287
 288 static void *configfs_follow_link(struct dentry *dentry, struct nameidata *nd)
 289 {
 290         int error = -ENOMEM;
 291         unsigned long page = get_zeroed_page(GFP_KERNEL);
 292
 293         if (page) {
 294                 error = configfs_getlink(dentry, (char *)page);
 295                 if (!error) {
 296                         nd_set_link(nd, (char *)page);
 297                         return (void *)page;
 298                 }
 299         }
 300
 301         nd_set_link(nd, ERR_PTR(error));
 302         return NULL;
 303 }
 304
 305 static void configfs_put_link(struct dentry *dentry, struct nameidata *nd,
 306                               void *cookie)
 307 {
 308         if (cookie) {
 309                 unsigned long page = (unsigned long)cookie;
 310                 free_page(page);
 311         }
 312 }
 313
 314 const struct inode_operations configfs_symlink_inode_operations = {
 315         .follow_link = configfs_follow_link,
 316         .readlink = generic_readlink,
 317         .put_link = configfs_put_link,
 318         .setattr = configfs_setattr,
 319 };
 320