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