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