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	write_lock(&file_systems_lock);
78	p = find_filesystem(fs->name, strlen(fs->name));
79	if (*p)
80		res = -EBUSY;
81	else
82		*p = fs;
83	write_unlock(&file_systems_lock);
84	return res;
85}
86
87EXPORT_SYMBOL(register_filesystem);
88
89/**
90 *	unregister_filesystem - unregister a file system
91 *	@fs: filesystem to unregister
92 *
93 *	Remove a file system that was previously successfully registered
94 *	with the kernel. An error is returned if the file system is not found.
95 *	Zero is returned on a success.
96 *
97 *	Once this function has returned the &struct file_system_type structure
98 *	may be freed or reused.
99 */
100
101int unregister_filesystem(struct file_system_type * fs)
102{
103	struct file_system_type ** tmp;
104
105	write_lock(&file_systems_lock);
106	tmp = &file_systems;
107	while (*tmp) {
108		if (fs == *tmp) {
109			*tmp = fs->next;
110			fs->next = NULL;
111			write_unlock(&file_systems_lock);
112			synchronize_rcu();
113			return 0;
114		}
115		tmp = &(*tmp)->next;
116	}
117	write_unlock(&file_systems_lock);
118
119	return -EINVAL;
120}
121
122EXPORT_SYMBOL(unregister_filesystem);
123
124#ifdef CONFIG_SYSFS_SYSCALL
125static int fs_index(const char __user * __name)
126{
127	struct file_system_type * tmp;
128	struct filename *name;
129	int err, index;
130
131	name = getname(__name);
132	err = PTR_ERR(name);
133	if (IS_ERR(name))
134		return err;
135
136	err = -EINVAL;
137	read_lock(&file_systems_lock);
138	for (tmp=file_systems, index=0 ; tmp ; tmp=tmp->next, index++) {
139		if (strcmp(tmp->name, name->name) == 0) {
140			err = index;
141			break;
142		}
143	}
144	read_unlock(&file_systems_lock);
145	putname(name);
146	return err;
147}
148
149static int fs_name(unsigned int index, char __user * buf)
150{
151	struct file_system_type * tmp;
152	int len, res;
153
154	read_lock(&file_systems_lock);
155	for (tmp = file_systems; tmp; tmp = tmp->next, index--)
156		if (index <= 0 && try_module_get(tmp->owner))
157			break;
158	read_unlock(&file_systems_lock);
159	if (!tmp)
160		return -EINVAL;
161
162	/* OK, we got the reference, so we can safely block */
163	len = strlen(tmp->name) + 1;
164	res = copy_to_user(buf, tmp->name, len) ? -EFAULT : 0;
165	put_filesystem(tmp);
166	return res;
167}
168
169static int fs_maxindex(void)
170{
171	struct file_system_type * tmp;
172	int index;
173
174	read_lock(&file_systems_lock);
175	for (tmp = file_systems, index = 0 ; tmp ; tmp = tmp->next, index++)
176		;
177	read_unlock(&file_systems_lock);
178	return index;
179}
180
181/*
182 * Whee.. Weird sysv syscall.
183 */
184SYSCALL_DEFINE3(sysfs, int, option, unsigned long, arg1, unsigned long, arg2)
185{
186	int retval = -EINVAL;
187
188	switch (option) {
189		case 1:
190			retval = fs_index((const char __user *) arg1);
191			break;
192
193		case 2:
194			retval = fs_name(arg1, (char __user *) arg2);
195			break;
196
197		case 3:
198			retval = fs_maxindex();
199			break;
200	}
201	return retval;
202}
203#endif
204
205int __init get_filesystem_list(char *buf)
206{
207	int len = 0;
208	struct file_system_type * tmp;
209
210	read_lock(&file_systems_lock);
211	tmp = file_systems;
212	while (tmp && len < PAGE_SIZE - 80) {
213		len += sprintf(buf+len, "%s\t%s\n",
214			(tmp->fs_flags & FS_REQUIRES_DEV) ? "" : "nodev",
215			tmp->name);
216		tmp = tmp->next;
217	}
218	read_unlock(&file_systems_lock);
219	return len;
220}
221
222#ifdef CONFIG_PROC_FS
223static int filesystems_proc_show(struct seq_file *m, void *v)
224{
225	struct file_system_type * tmp;
226
227	read_lock(&file_systems_lock);
228	tmp = file_systems;
229	while (tmp) {
230		seq_printf(m, "%s\t%s\n",
231			(tmp->fs_flags & FS_REQUIRES_DEV) ? "" : "nodev",
232			tmp->name);
233		tmp = tmp->next;
234	}
235	read_unlock(&file_systems_lock);
236	return 0;
237}
238
239static int filesystems_proc_open(struct inode *inode, struct file *file)
240{
241	return single_open(file, filesystems_proc_show, NULL);
242}
243
244static const struct file_operations filesystems_proc_fops = {
245	.open		= filesystems_proc_open,
246	.read		= seq_read,
247	.llseek		= seq_lseek,
248	.release	= single_release,
249};
250
251static int __init proc_filesystems_init(void)
252{
253	proc_create("filesystems", 0, NULL, &filesystems_proc_fops);
254	return 0;
255}
256module_init(proc_filesystems_init);
257#endif
258
259static struct file_system_type *__get_fs_type(const char *name, int len)
260{
261	struct file_system_type *fs;
262
263	read_lock(&file_systems_lock);
264	fs = *(find_filesystem(name, len));
265	if (fs && !try_module_get(fs->owner))
266		fs = NULL;
267	read_unlock(&file_systems_lock);
268	return fs;
269}
270
271struct file_system_type *get_fs_type(const char *name)
272{
273	struct file_system_type *fs;
274	const char *dot = strchr(name, '.');
275	int len = dot ? dot - name : strlen(name);
276
277	fs = __get_fs_type(name, len);
278	if (!fs && (request_module("fs-%.*s", len, name) == 0))
279		fs = __get_fs_type(name, len);
280
281	if (dot && fs && !(fs->fs_flags & FS_HAS_SUBTYPE)) {
282		put_filesystem(fs);
283		fs = NULL;
284	}
285	return fs;
286}
287
288EXPORT_SYMBOL(get_fs_type);
289