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