1/*
2 *  linux/fs/filesystems.c
3 *
4 *  Copyright (C) 1991, 1992  Linus Torvalds
5 *
6 *  table of configured filesystems
7 */
8
9#include <linux/syscalls.h>
10#include <linux/fs.h>
11#include <linux/proc_fs.h>
12#include <linux/seq_file.h>
13#include <linux/kmod.h>
14#include <linux/init.h>
15#include <linux/module.h>
16#include <linux/slab.h>
17#include <asm/uaccess.h>
18
19/*
20 * Handling of filesystem drivers list.
21 * Rules:
22 *	Inclusion to/removals from/scanning of list are protected by spinlock.
23 *	During the unload module must call unregister_filesystem().
24 *	We can access the fields of list element if:
25 *		1) spinlock is held or
26 *		2) we hold the reference to the module.
27 *	The latter can be guaranteed by call of try_module_get(); if it
28 *	returned 0 we must skip the element, otherwise we got the reference.
29 *	Once the reference is obtained we can drop the spinlock.
30 */
31
32static struct file_system_type *file_systems;
33static DEFINE_RWLOCK(file_systems_lock);
34
35/* WARNING: This can be used only if we _already_ own a reference */
36void get_filesystem(struct file_system_type *fs)
37{
38	__module_get(fs->owner);
39}
40
41void put_filesystem(struct file_system_type *fs)
42{
43	module_put(fs->owner);
44}
45
46static struct file_system_type **find_filesystem(const char *name, unsigned len)
47{
48	struct file_system_type **p;
49	for (p=&file_systems; *p; p=&(*p)->next)
50		if (strlen((*p)->name) == len &&
51		    strncmp((*p)->name, name, len) == 0)
52			break;
53	return p;
54}
55
56/**
57 *	register_filesystem - register a new filesystem
58 *	@fs: the file system structure
59 *
60 *	Adds the file system passed to the list of file systems the kernel
61 *	is aware of for mount and other syscalls. Returns 0 on success,
62 *	or a negative errno code on an error.
63 *
64 *	The &struct file_system_type that is passed is linked into the kernel
65 *	structures and must not be freed until the file system has been
66 *	unregistered.
67 */
68
69int register_filesystem(struct file_system_type * fs)
70{
71	int res = 0;
72	struct file_system_type ** p;
73
74	BUG_ON(strchr(fs->name, '.'));
75	if (fs->next)
76		return -EBUSY;
77	INIT_LIST_HEAD(&fs->fs_supers);
78	write_lock(&file_systems_lock);
79	p = find_filesystem(fs->name, strlen(fs->name));
80	if (*p)
81		res = -EBUSY;
82	else
83		*p = fs;
84	write_unlock(&file_systems_lock);
85	return res;
86}
87
88EXPORT_SYMBOL(register_filesystem);
89
90/**
91 *	unregister_filesystem - unregister a file system
92 *	@fs: filesystem to unregister
93 *
94 *	Remove a file system that was previously successfully registered
95 *	with the kernel. An error is returned if the file system is not found.
96 *	Zero is returned on a success.
97 *
98 *	Once this function has returned the &struct file_system_type structure
99 *	may be freed or reused.
100 */
101
102int unregister_filesystem(struct file_system_type * fs)
103{
104	struct file_system_type ** tmp;
105
106	write_lock(&file_systems_lock);
107	tmp = &file_systems;
108	while (*tmp) {
109		if (fs == *tmp) {
110			*tmp = fs->next;
111			fs->next = NULL;
112			write_unlock(&file_systems_lock);
113			return 0;
114		}
115		tmp = &(*tmp)->next;
116	}
117	write_unlock(&file_systems_lock);
118	return -EINVAL;
119}
120
121EXPORT_SYMBOL(unregister_filesystem);
122
123static int fs_index(const char __user * __name)
124{
125	struct file_system_type * tmp;
126	char * name;
127	int err, index;
128
129	name = getname(__name);
130	err = PTR_ERR(name);
131	if (IS_ERR(name))
132		return err;
133
134	err = -EINVAL;
135	read_lock(&file_systems_lock);
136	for (tmp=file_systems, index=0 ; tmp ; tmp=tmp->next, index++) {
137		if (strcmp(tmp->name,name) == 0) {
138			err = index;
139			break;
140		}
141	}
142	read_unlock(&file_systems_lock);
143	putname(name);
144	return err;
145}
146
147static int fs_name(unsigned int index, char __user * buf)
148{
149	struct file_system_type * tmp;
150	int len, res;
151
152	read_lock(&file_systems_lock);
153	for (tmp = file_systems; tmp; tmp = tmp->next, index--)
154		if (index <= 0 && try_module_get(tmp->owner))
155			break;
156	read_unlock(&file_systems_lock);
157	if (!tmp)
158		return -EINVAL;
159
160	/* OK, we got the reference, so we can safely block */
161	len = strlen(tmp->name) + 1;
162	res = copy_to_user(buf, tmp->name, len) ? -EFAULT : 0;
163	put_filesystem(tmp);
164	return res;
165}
166
167static int fs_maxindex(void)
168{
169	struct file_system_type * tmp;
170	int index;
171
172	read_lock(&file_systems_lock);
173	for (tmp = file_systems, index = 0 ; tmp ; tmp = tmp->next, index++)
174		;
175	read_unlock(&file_systems_lock);
176	return index;
177}
178
179/*
180 * Whee.. Weird sysv syscall.
181 */
182SYSCALL_DEFINE3(sysfs, int, option, unsigned long, arg1, unsigned long, arg2)
183{
184	int retval = -EINVAL;
185
186	switch (option) {
187		case 1:
188			retval = fs_index((const char __user *) arg1);
189			break;
190
191		case 2:
192			retval = fs_name(arg1, (char __user *) arg2);
193			break;
194
195		case 3:
196			retval = fs_maxindex();
197			break;
198	}
199	return retval;
200}
201
202int __init get_filesystem_list(char *buf)
203{
204	int len = 0;
205	struct file_system_type * tmp;
206
207	read_lock(&file_systems_lock);
208	tmp = file_systems;
209	while (tmp && len < PAGE_SIZE - 80) {
210		len += sprintf(buf+len, "%s\t%s\n",
211			(tmp->fs_flags & FS_REQUIRES_DEV) ? "" : "nodev",
212			tmp->name);
213		tmp = tmp->next;
214	}
215	read_unlock(&file_systems_lock);
216	return len;
217}
218
219#ifdef CONFIG_PROC_FS
220static int filesystems_proc_show(struct seq_file *m, void *v)
221{
222	struct file_system_type * tmp;
223
224	read_lock(&file_systems_lock);
225	tmp = file_systems;
226	while (tmp) {
227		seq_printf(m, "%s\t%s\n",
228			(tmp->fs_flags & FS_REQUIRES_DEV) ? "" : "nodev",
229			tmp->name);
230		tmp = tmp->next;
231	}
232	read_unlock(&file_systems_lock);
233	return 0;
234}
235
236static int filesystems_proc_open(struct inode *inode, struct file *file)
237{
238	return single_open(file, filesystems_proc_show, NULL);
239}
240
241static const struct file_operations filesystems_proc_fops = {
242	.open		= filesystems_proc_open,
243	.read		= seq_read,
244	.llseek		= seq_lseek,
245	.release	= single_release,
246};
247
248static int __init proc_filesystems_init(void)
249{
250	proc_create("filesystems", 0, NULL, &filesystems_proc_fops);
251	return 0;
252}
253module_init(proc_filesystems_init);
254#endif
255
256static struct file_system_type *__get_fs_type(const char *name, int len)
257{
258	struct file_system_type *fs;
259
260	read_lock(&file_systems_lock);
261	fs = *(find_filesystem(name, len));
262	if (fs && !try_module_get(fs->owner))
263		fs = NULL;
264	read_unlock(&file_systems_lock);
265	return fs;
266}
267
268struct file_system_type *get_fs_type(const char *name)
269{
270	struct file_system_type *fs;
271	const char *dot = strchr(name, '.');
272	int len = dot ? dot - name : strlen(name);
273
274	fs = __get_fs_type(name, len);
275	if (!fs && (request_module("%.*s", len, name) == 0))
276		fs = __get_fs_type(name, len);
277
278	if (dot && fs && !(fs->fs_flags & FS_HAS_SUBTYPE)) {
279		put_filesystem(fs);
280		fs = NULL;
281	}
282	return fs;
283}
284
285EXPORT_SYMBOL(get_fs_type);
286