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 static int item_depth(struct config_item * item)
  35 {
  36         struct config_item * p = item;
  37         int depth = 0;
  38         do { depth++; } while ((p = p->ci_parent) && !configfs_is_root(p));
  39         return depth;
  40 }
  41
  42 static int item_path_length(struct config_item * item)
  43 {
  44         struct config_item * p = item;
  45         int length = 1;
  46         do {
  47                 length += strlen(config_item_name(p)) + 1;
  48                 p = p->ci_parent;
  49         } while (p && !configfs_is_root(p));
  50         return length;
  51 }
  52
  53 static void fill_item_path(struct config_item * item, char * buffer, int length)
  54 {
  55         struct config_item * p;
  56
  57         --length;
  58         for (p = item; p && !configfs_is_root(p); p = p->ci_parent) {
  59                 int cur = strlen(config_item_name(p));
  60
  61                 /* back up enough to print this bus id with '/' */
  62                 length -= cur;
  63                 strncpy(buffer + length,config_item_name(p),cur);
  64                 *(buffer + --length) = '/';
  65         }
  66 }
  67
  68 static int create_link(struct config_item *parent_item,
  69                        struct config_item *item,
  70                        struct dentry *dentry)
  71 {
  72         struct configfs_dirent *target_sd = item->ci_dentry->d_fsdata;
  73         struct configfs_symlink *sl;
  74         int ret;
  75
  76         ret = -ENOMEM;
  77         sl = kmalloc(sizeof(struct configfs_symlink), GFP_KERNEL);
  78         if (sl) {
  79                 sl->sl_target = config_item_get(item);
  80                 spin_lock(&configfs_dirent_lock);
  81                 if (target_sd->s_type & CONFIGFS_USET_DROPPING) {
  82                         spin_unlock(&configfs_dirent_lock);
  83                         config_item_put(item);
  84                         kfree(sl);
  85                         return -ENOENT;
  86                 }
  87                 list_add(&sl->sl_list, &target_sd->s_links);
  88                 spin_unlock(&configfs_dirent_lock);
  89                 ret = configfs_create_link(sl, parent_item->ci_dentry,
  90                                            dentry);
  91                 if (ret) {
  92                         spin_lock(&configfs_dirent_lock);
  93                         list_del_init(&sl->sl_list);
  94                         spin_unlock(&configfs_dirent_lock);
  95                         config_item_put(item);
  96                         kfree(sl);
  97                 }
  98         }
  99
 100         return ret;
 101 }
 102
 103
 104 static int get_target(const char *symname, struct nameidata *nd,
 105                       struct config_item **target)
 106 {
 107         int ret;
 108
 109         ret = path_lookup(symname, LOOKUP_FOLLOW|LOOKUP_DIRECTORY, nd);
 110         if (!ret) {
 111                 if (nd->path.dentry->d_sb == configfs_sb) {
 112                         *target = configfs_get_config_item(nd->path.dentry);
 113                         if (!*target) {
 114                                 ret = -ENOENT;
 115                                 path_put(&nd->path);
 116                         }
 117                 } else
 118                         ret = -EPERM;
 119         }
 120
 121         return ret;
 122 }
 123
 124
 125 int configfs_symlink(struct inode *dir, struct dentry *dentry, const char *symname)
 126 {
 127         int ret;
 128         struct nameidata nd;
 129         struct config_item *parent_item;
 130         struct config_item *target_item;
 131         struct config_item_type *type;
 132
 133         ret = -EPERM;  /* What lack-of-symlink returns */
 134         if (dentry->d_parent == configfs_sb->s_root)
 135                 goto out;
 136
 137         parent_item = configfs_get_config_item(dentry->d_parent);
 138         type = parent_item->ci_type;
 139
 140         if (!type || !type->ct_item_ops ||
 141             !type->ct_item_ops->allow_link)
 142                 goto out_put;
 143
 144         ret = get_target(symname, &nd, &target_item);
 145         if (ret)
 146                 goto out_put;
 147
 148         ret = type->ct_item_ops->allow_link(parent_item, target_item);
 149         if (!ret) {
 150                 ret = create_link(parent_item, target_item, dentry);
 151                 if (ret && type->ct_item_ops->drop_link)
 152                         type->ct_item_ops->drop_link(parent_item,
 153                                                      target_item);
 154         }
 155
 156         config_item_put(target_item);
 157         path_put(&nd.path);
 158
 159 out_put:
 160         config_item_put(parent_item);
 161
 162 out:
 163         return ret;
 164 }
 165
 166 int configfs_unlink(struct inode *dir, struct dentry *dentry)
 167 {
 168         struct configfs_dirent *sd = dentry->d_fsdata;
 169         struct configfs_symlink *sl;
 170         struct config_item *parent_item;
 171         struct config_item_type *type;
 172         int ret;
 173
 174         ret = -EPERM;  /* What lack-of-symlink returns */
 175         if (!(sd->s_type & CONFIGFS_ITEM_LINK))
 176                 goto out;
 177
 178         BUG_ON(dentry->d_parent == configfs_sb->s_root);
 179
 180         sl = sd->s_element;
 181
 182         parent_item = configfs_get_config_item(dentry->d_parent);
 183         type = parent_item->ci_type;
 184
 185         spin_lock(&configfs_dirent_lock);
 186         list_del_init(&sd->s_sibling);
 187         spin_unlock(&configfs_dirent_lock);
 188         configfs_drop_dentry(sd, dentry->d_parent);
 189         dput(dentry);
 190         configfs_put(sd);
 191
 192         /*
 193          * drop_link() must be called before
 194          * list_del_init(&sl->sl_list), so that the order of
 195          * drop_link(this, target) and drop_item(target) is preserved.
 196          */
 197         if (type && type->ct_item_ops &&
 198             type->ct_item_ops->drop_link)
 199                 type->ct_item_ops->drop_link(parent_item,
 200                                                sl->sl_target);
 201
 202         spin_lock(&configfs_dirent_lock);
 203         list_del_init(&sl->sl_list);
 204         spin_unlock(&configfs_dirent_lock);
 205
 206         /* Put reference from create_link() */
 207         config_item_put(sl->sl_target);
 208         kfree(sl);
 209
 210         config_item_put(parent_item);
 211
 212         ret = 0;
 213
 214 out:
 215         return ret;
 216 }
 217
 218 static int configfs_get_target_path(struct config_item * item, struct config_item * target,
 219                                    char *path)
 220 {
 221         char * s;
 222         int depth, size;
 223
 224         depth = item_depth(item);
 225         size = item_path_length(target) + depth * 3 - 1;
 226         if (size > PATH_MAX)
 227                 return -ENAMETOOLONG;
 228
 229         pr_debug("%s: depth = %d, size = %d\n", __func__, depth, size);
 230
 231         for (s = path; depth--; s += 3)
 232                 strcpy(s,"../");
 233
 234         fill_item_path(target, path, size);
 235         pr_debug("%s: path = '%s'\n", __func__, path);
 236
 237         return 0;
 238 }
 239
 240 static int configfs_getlink(struct dentry *dentry, char * path)
 241 {
 242         struct config_item *item, *target_item;
 243         int error = 0;
 244
 245         item = configfs_get_config_item(dentry->d_parent);
 246         if (!item)
 247                 return -EINVAL;
 248
 249         target_item = configfs_get_config_item(dentry);
 250         if (!target_item) {
 251                 config_item_put(item);
 252                 return -EINVAL;
 253         }
 254
 255         down_read(&configfs_rename_sem);
 256         error = configfs_get_target_path(item, target_item, path);
 257         up_read(&configfs_rename_sem);
 258
 259         config_item_put(item);
 260         config_item_put(target_item);
 261         return error;
 262
 263 }
 264
 265 static void *configfs_follow_link(struct dentry *dentry, struct nameidata *nd)
 266 {
 267         int error = -ENOMEM;
 268         unsigned long page = get_zeroed_page(GFP_KERNEL);
 269
 270         if (page) {
 271                 error = configfs_getlink(dentry, (char *)page);
 272                 if (!error) {
 273                         nd_set_link(nd, (char *)page);
 274                         return (void *)page;
 275                 }
 276         }
 277
 278         nd_set_link(nd, ERR_PTR(error));
 279         return NULL;
 280 }
 281
 282 static void configfs_put_link(struct dentry *dentry, struct nameidata *nd,
 283                               void *cookie)
 284 {
 285         if (cookie) {
 286                 unsigned long page = (unsigned long)cookie;
 287                 free_page(page);
 288         }
 289 }
 290
 291 const struct inode_operations configfs_symlink_inode_operations = {
 292         .follow_link = configfs_follow_link,
 293         .readlink = generic_readlink,
 294         .put_link = configfs_put_link,
 295         .setattr = configfs_setattr,
 296 };
 297