filesystems.c

  1// SPDX-License-Identifier: GPL-2.0
  2/*
  3 *  linux/fs/filesystems.c
  4 *
  5 *  Copyright (C) 1991, 1992  Linus Torvalds
  6 *
  7 *  table of configured filesystems
  8 */
  9
 10#include <linux/syscalls.h>
 11#include <linux/fs.h>
 12#include <linux/proc_fs.h>
 13#include <linux/seq_file.h>
 14#include <linux/kmod.h>
 15#include <linux/init.h>
 16#include <linux/module.h>
 17#include <linux/slab.h>
 18#include <linux/uaccess.h>
 19#include <linux/fs_parser.h>
 20
 21/*
 22 * Handling of filesystem drivers list.
 23 * Rules:
 24 *	Inclusion to/removals from/scanning of list are protected by spinlock.
 25 *	During the unload module must call unregister_filesystem().
 26 *	We can access the fields of list element if:
 27 *		1) spinlock is held or
 28 *		2) we hold the reference to the module.
 29 *	The latter can be guaranteed by call of try_module_get(); if it
 30 *	returned 0 we must skip the element, otherwise we got the reference.
 31 *	Once the reference is obtained we can drop the spinlock.
 32 */
 33
 34static struct file_system_type *file_systems;
 35static DEFINE_RWLOCK(file_systems_lock);
 36
 37/* WARNING: This can be used only if we _already_ own a reference */
 38struct file_system_type *get_filesystem(struct file_system_type *fs)
 39{
 40	__module_get(fs->owner);
 41	return fs;
 42}
 43
 44void put_filesystem(struct file_system_type *fs)
 45{
 46	module_put(fs->owner);
 47}
 48
 49static struct file_system_type **find_filesystem(const char *name, unsigned len)
 50{
 51	struct file_system_type **p;
 52	for (p = &file_systems; *p; p = &(*p)->next)
 53		if (strncmp((*p)->name, name, len) == 0 &&
 54		    !(*p)->name[len])
 55			break;
 56	return p;
 57}
 58
 59/**
 60 *	register_filesystem - register a new filesystem
 61 *	@fs: the file system structure
 62 *
 63 *	Adds the file system passed to the list of file systems the kernel
 64 *	is aware of for mount and other syscalls. Returns 0 on success,
 65 *	or a negative errno code on an error.
 66 *
 67 *	The &struct file_system_type that is passed is linked into the kernel 
 68 *	structures and must not be freed until the file system has been
 69 *	unregistered.
 70 */
 71 
 72int register_filesystem(struct file_system_type * fs)
 73{
 74	int res = 0;
 75	struct file_system_type ** p;
 76
 77	if (fs->parameters &&
 78	    !fs_validate_description(fs->name, fs->parameters))
 79		return -EINVAL;
 80
 81	BUG_ON(strchr(fs->name, '.'));
 82	if (fs->next)
 83		return -EBUSY;
 84	write_lock(&file_systems_lock);
 85	p = find_filesystem(fs->name, strlen(fs->name));
 86	if (*p)
 87		res = -EBUSY;
 88	else
 89		*p = fs;
 90	write_unlock(&file_systems_lock);
 91	return res;
 92}
 93
 94EXPORT_SYMBOL(register_filesystem);
 95
 96/**
 97 *	unregister_filesystem - unregister a file system
 98 *	@fs: filesystem to unregister
 99 *
100 *	Remove a file system that was previously successfully registered
101 *	with the kernel. An error is returned if the file system is not found.
102 *	Zero is returned on a success.
103 *	
104 *	Once this function has returned the &struct file_system_type structure
105 *	may be freed or reused.
106 */
107 
108int unregister_filesystem(struct file_system_type * fs)
109{
110	struct file_system_type ** tmp;
111
112	write_lock(&file_systems_lock);
113	tmp = &file_systems;
114	while (*tmp) {
115		if (fs == *tmp) {
116			*tmp = fs->next;
117			fs->next = NULL;
118			write_unlock(&file_systems_lock);
119			synchronize_rcu();
120			return 0;
121		}
122		tmp = &(*tmp)->next;
123	}
124	write_unlock(&file_systems_lock);
125
126	return -EINVAL;
127}
128
129EXPORT_SYMBOL(unregister_filesystem);
130
131#ifdef CONFIG_SYSFS_SYSCALL
132static int fs_index(const char __user * __name)
133{
134	struct file_system_type * tmp;
135	struct filename *name;
136	int err, index;
137
138	name = getname(__name);
139	err = PTR_ERR(name);
140	if (IS_ERR(name))
141		return err;
142
143	err = -EINVAL;
144	read_lock(&file_systems_lock);
145	for (tmp=file_systems, index=0 ; tmp ; tmp=tmp->next, index++) {
146		if (strcmp(tmp->name, name->name) == 0) {
147			err = index;
148			break;
149		}
150	}
151	read_unlock(&file_systems_lock);
152	putname(name);
153	return err;
154}
155
156static int fs_name(unsigned int index, char __user * buf)
157{
158	struct file_system_type * tmp;
159	int len, res = -EINVAL;
160
161	read_lock(&file_systems_lock);
162	for (tmp = file_systems; tmp; tmp = tmp->next, index--) {
163		if (index == 0) {
164			if (try_module_get(tmp->owner))
165				res = 0;
166			break;
167		}
168	}
169	read_unlock(&file_systems_lock);
170	if (res)
171		return res;
172
173	/* OK, we got the reference, so we can safely block */
174	len = strlen(tmp->name) + 1;
175	res = copy_to_user(buf, tmp->name, len) ? -EFAULT : 0;
176	put_filesystem(tmp);
177	return res;
178}
179
180static int fs_maxindex(void)
181{
182	struct file_system_type * tmp;
183	int index;
184
185	read_lock(&file_systems_lock);
186	for (tmp = file_systems, index = 0 ; tmp ; tmp = tmp->next, index++)
187		;
188	read_unlock(&file_systems_lock);
189	return index;
190}
191
192/*
193 * Whee.. Weird sysv syscall. 
194 */
195SYSCALL_DEFINE3(sysfs, int, option, unsigned long, arg1, unsigned long, arg2)
196{
197	int retval = -EINVAL;
198
199	switch (option) {
200		case 1:
201			retval = fs_index((const char __user *) arg1);
202			break;
203
204		case 2:
205			retval = fs_name(arg1, (char __user *) arg2);
206			break;
207
208		case 3:
209			retval = fs_maxindex();
210			break;
211	}
212	return retval;
213}
214#endif
215
216int __init list_bdev_fs_names(char *buf, size_t size)
217{
218	struct file_system_type *p;
219	size_t len;
220	int count = 0;
221
222	read_lock(&file_systems_lock);
223	for (p = file_systems; p; p = p->next) {
224		if (!(p->fs_flags & FS_REQUIRES_DEV))
225			continue;
226		len = strlen(p->name) + 1;
227		if (len > size) {
228			pr_warn("%s: truncating file system list\n", __func__);
229			break;
230		}
231		memcpy(buf, p->name, len);
232		buf += len;
233		size -= len;
234		count++;
235	}
236	read_unlock(&file_systems_lock);
237	return count;
238}
239
240#ifdef CONFIG_PROC_FS
241static int filesystems_proc_show(struct seq_file *m, void *v)
242{
243	struct file_system_type * tmp;
244
245	read_lock(&file_systems_lock);
246	tmp = file_systems;
247	while (tmp) {
248		seq_printf(m, "%s\t%s\n",
249			(tmp->fs_flags & FS_REQUIRES_DEV) ? "" : "nodev",
250			tmp->name);
251		tmp = tmp->next;
252	}
253	read_unlock(&file_systems_lock);
254	return 0;
255}
256
257static int __init proc_filesystems_init(void)
258{
259	proc_create_single("filesystems", 0, NULL, filesystems_proc_show);
260	return 0;
261}
262module_init(proc_filesystems_init);
263#endif
264
265static struct file_system_type *__get_fs_type(const char *name, int len)
266{
267	struct file_system_type *fs;
268
269	read_lock(&file_systems_lock);
270	fs = *(find_filesystem(name, len));
271	if (fs && !try_module_get(fs->owner))
272		fs = NULL;
273	read_unlock(&file_systems_lock);
274	return fs;
275}
276
277struct file_system_type *get_fs_type(const char *name)
278{
279	struct file_system_type *fs;
280	const char *dot = strchr(name, '.');
281	int len = dot ? dot - name : strlen(name);
282
283	fs = __get_fs_type(name, len);
284	if (!fs && (request_module("fs-%.*s", len, name) == 0)) {
285		fs = __get_fs_type(name, len);
286		if (!fs)
287			pr_warn_once("request_module fs-%.*s succeeded, but still no fs?\n",
288				     len, name);
289	}
290
291	if (dot && fs && !(fs->fs_flags & FS_HAS_SUBTYPE)) {
292		put_filesystem(fs);
293		fs = NULL;
294	}
295	return fs;
296}
297
298EXPORT_SYMBOL(get_fs_type);