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(module: fs->owner);
41 return fs;
42}
43
44void put_filesystem(struct file_system_type *fs)
45{
46 module_put(module: 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(name: fs->name, desc: 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(name: 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: __name);
139 err = PTR_ERR(ptr: name);
140 if (IS_ERR(ptr: 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(module: 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(to: buf, from: tmp->name, n: len) ? -EFAULT : 0;
176 put_filesystem(fs: 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(name: (const char __user *) arg1);
202 break;
203
204 case 2:
205 retval = fs_name(index: arg1, buf: (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, fmt: "%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(module: 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);
299

source code of linux/fs/filesystems.c