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b2441318 1// SPDX-License-Identifier: GPL-2.0
1da177e4
LT
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>
68274007
AD
12#include <linux/proc_fs.h>
13#include <linux/seq_file.h>
1da177e4
LT
14#include <linux/kmod.h>
15#include <linux/init.h>
16#include <linux/module.h>
5a0e3ad6 17#include <linux/slab.h>
7c0f6ba6 18#include <linux/uaccess.h>
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LT
19
20/*
21 * Handling of filesystem drivers list.
22 * Rules:
23 * Inclusion to/removals from/scanning of list are protected by spinlock.
24 * During the unload module must call unregister_filesystem().
25 * We can access the fields of list element if:
26 * 1) spinlock is held or
27 * 2) we hold the reference to the module.
28 * The latter can be guaranteed by call of try_module_get(); if it
29 * returned 0 we must skip the element, otherwise we got the reference.
30 * Once the reference is obtained we can drop the spinlock.
31 */
32
33static struct file_system_type *file_systems;
34static DEFINE_RWLOCK(file_systems_lock);
35
36/* WARNING: This can be used only if we _already_ own a reference */
ee416bcd 37struct file_system_type *get_filesystem(struct file_system_type *fs)
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38{
39 __module_get(fs->owner);
ee416bcd 40 return fs;
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LT
41}
42
43void put_filesystem(struct file_system_type *fs)
44{
45 module_put(fs->owner);
46}
47
79c0b2df 48static struct file_system_type **find_filesystem(const char *name, unsigned len)
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LT
49{
50 struct file_system_type **p;
558041d8
AV
51 for (p = &file_systems; *p; p = &(*p)->next)
52 if (strncmp((*p)->name, name, len) == 0 &&
53 !(*p)->name[len])
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LT
54 break;
55 return p;
56}
57
58/**
59 * register_filesystem - register a new filesystem
60 * @fs: the file system structure
61 *
62 * Adds the file system passed to the list of file systems the kernel
63 * is aware of for mount and other syscalls. Returns 0 on success,
64 * or a negative errno code on an error.
65 *
66 * The &struct file_system_type that is passed is linked into the kernel
67 * structures and must not be freed until the file system has been
68 * unregistered.
69 */
70
71int register_filesystem(struct file_system_type * fs)
72{
73 int res = 0;
74 struct file_system_type ** p;
75
79c0b2df 76 BUG_ON(strchr(fs->name, '.'));
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LT
77 if (fs->next)
78 return -EBUSY;
1da177e4 79 write_lock(&file_systems_lock);
79c0b2df 80 p = find_filesystem(fs->name, strlen(fs->name));
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LT
81 if (*p)
82 res = -EBUSY;
83 else
84 *p = fs;
85 write_unlock(&file_systems_lock);
86 return res;
87}
88
89EXPORT_SYMBOL(register_filesystem);
90
91/**
92 * unregister_filesystem - unregister a file system
93 * @fs: filesystem to unregister
94 *
95 * Remove a file system that was previously successfully registered
96 * with the kernel. An error is returned if the file system is not found.
97 * Zero is returned on a success.
98 *
99 * Once this function has returned the &struct file_system_type structure
100 * may be freed or reused.
101 */
102
103int unregister_filesystem(struct file_system_type * fs)
104{
105 struct file_system_type ** tmp;
106
107 write_lock(&file_systems_lock);
108 tmp = &file_systems;
109 while (*tmp) {
110 if (fs == *tmp) {
111 *tmp = fs->next;
112 fs->next = NULL;
113 write_unlock(&file_systems_lock);
fff3e5ad 114 synchronize_rcu();
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115 return 0;
116 }
117 tmp = &(*tmp)->next;
118 }
119 write_unlock(&file_systems_lock);
31e6b01f 120
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121 return -EINVAL;
122}
123
124EXPORT_SYMBOL(unregister_filesystem);
125
6af9f7bf 126#ifdef CONFIG_SYSFS_SYSCALL
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127static int fs_index(const char __user * __name)
128{
129 struct file_system_type * tmp;
91a27b2a 130 struct filename *name;
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LT
131 int err, index;
132
133 name = getname(__name);
134 err = PTR_ERR(name);
135 if (IS_ERR(name))
136 return err;
137
138 err = -EINVAL;
139 read_lock(&file_systems_lock);
140 for (tmp=file_systems, index=0 ; tmp ; tmp=tmp->next, index++) {
91a27b2a 141 if (strcmp(tmp->name, name->name) == 0) {
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LT
142 err = index;
143 break;
144 }
145 }
146 read_unlock(&file_systems_lock);
147 putname(name);
148 return err;
149}
150
151static int fs_name(unsigned int index, char __user * buf)
152{
153 struct file_system_type * tmp;
154 int len, res;
155
156 read_lock(&file_systems_lock);
157 for (tmp = file_systems; tmp; tmp = tmp->next, index--)
158 if (index <= 0 && try_module_get(tmp->owner))
159 break;
160 read_unlock(&file_systems_lock);
161 if (!tmp)
162 return -EINVAL;
163
164 /* OK, we got the reference, so we can safely block */
165 len = strlen(tmp->name) + 1;
166 res = copy_to_user(buf, tmp->name, len) ? -EFAULT : 0;
167 put_filesystem(tmp);
168 return res;
169}
170
171static int fs_maxindex(void)
172{
173 struct file_system_type * tmp;
174 int index;
175
176 read_lock(&file_systems_lock);
177 for (tmp = file_systems, index = 0 ; tmp ; tmp = tmp->next, index++)
178 ;
179 read_unlock(&file_systems_lock);
180 return index;
181}
182
183/*
184 * Whee.. Weird sysv syscall.
185 */
1e7bfb21 186SYSCALL_DEFINE3(sysfs, int, option, unsigned long, arg1, unsigned long, arg2)
1da177e4
LT
187{
188 int retval = -EINVAL;
189
190 switch (option) {
191 case 1:
192 retval = fs_index((const char __user *) arg1);
193 break;
194
195 case 2:
196 retval = fs_name(arg1, (char __user *) arg2);
197 break;
198
199 case 3:
200 retval = fs_maxindex();
201 break;
202 }
203 return retval;
204}
6af9f7bf 205#endif
1da177e4 206
38e23c95 207int __init get_filesystem_list(char *buf)
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LT
208{
209 int len = 0;
210 struct file_system_type * tmp;
211
212 read_lock(&file_systems_lock);
213 tmp = file_systems;
214 while (tmp && len < PAGE_SIZE - 80) {
215 len += sprintf(buf+len, "%s\t%s\n",
216 (tmp->fs_flags & FS_REQUIRES_DEV) ? "" : "nodev",
217 tmp->name);
218 tmp = tmp->next;
219 }
220 read_unlock(&file_systems_lock);
221 return len;
222}
223
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AD
224#ifdef CONFIG_PROC_FS
225static int filesystems_proc_show(struct seq_file *m, void *v)
226{
227 struct file_system_type * tmp;
228
229 read_lock(&file_systems_lock);
230 tmp = file_systems;
231 while (tmp) {
232 seq_printf(m, "%s\t%s\n",
233 (tmp->fs_flags & FS_REQUIRES_DEV) ? "" : "nodev",
234 tmp->name);
235 tmp = tmp->next;
236 }
237 read_unlock(&file_systems_lock);
238 return 0;
239}
240
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AD
241static int __init proc_filesystems_init(void)
242{
3f3942ac 243 proc_create_single("filesystems", 0, NULL, filesystems_proc_show);
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AD
244 return 0;
245}
246module_init(proc_filesystems_init);
247#endif
248
d8e9650d 249static struct file_system_type *__get_fs_type(const char *name, int len)
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LT
250{
251 struct file_system_type *fs;
252
253 read_lock(&file_systems_lock);
79c0b2df 254 fs = *(find_filesystem(name, len));
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LT
255 if (fs && !try_module_get(fs->owner))
256 fs = NULL;
257 read_unlock(&file_systems_lock);
d8e9650d
LZ
258 return fs;
259}
260
261struct file_system_type *get_fs_type(const char *name)
262{
263 struct file_system_type *fs;
264 const char *dot = strchr(name, '.');
265 int len = dot ? dot - name : strlen(name);
266
267 fs = __get_fs_type(name, len);
41124db8 268 if (!fs && (request_module("fs-%.*s", len, name) == 0)) {
d8e9650d 269 fs = __get_fs_type(name, len);
41124db8
LR
270 WARN_ONCE(!fs, "request_module fs-%.*s succeeded, but still no fs?\n", len, name);
271 }
79c0b2df
MS
272
273 if (dot && fs && !(fs->fs_flags & FS_HAS_SUBTYPE)) {
274 put_filesystem(fs);
275 fs = NULL;
276 }
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LT
277 return fs;
278}
279
280EXPORT_SYMBOL(get_fs_type);