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 */
36DEFINE_MUTEX(configfs_symlink_mutex);
37
38static 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
46static 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
57static 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
72static 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
107out:
108	return ret;
109}
110
111
112static 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
135int 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
178out_put:
179	config_item_put(parent_item);
180
181out:
182	return ret;
183}
184
185int 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
231out:
232	return ret;
233}
234
235static 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
257static 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
282static 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
299static 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
308const 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