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Linus Torvalds1da177e2005-04-16 15:20:36 -07001/*
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/slab.h>
12#include <linux/kmod.h>
13#include <linux/init.h>
14#include <linux/module.h>
Linus Torvalds1da177e2005-04-16 15:20:36 -070015#include <asm/uaccess.h>
16
17/*
18 * Handling of filesystem drivers list.
19 * Rules:
20 * Inclusion to/removals from/scanning of list are protected by spinlock.
21 * During the unload module must call unregister_filesystem().
22 * We can access the fields of list element if:
23 * 1) spinlock is held or
24 * 2) we hold the reference to the module.
25 * The latter can be guaranteed by call of try_module_get(); if it
26 * returned 0 we must skip the element, otherwise we got the reference.
27 * Once the reference is obtained we can drop the spinlock.
28 */
29
30static struct file_system_type *file_systems;
31static DEFINE_RWLOCK(file_systems_lock);
32
33/* WARNING: This can be used only if we _already_ own a reference */
34void get_filesystem(struct file_system_type *fs)
35{
36 __module_get(fs->owner);
37}
38
39void put_filesystem(struct file_system_type *fs)
40{
41 module_put(fs->owner);
42}
43
Miklos Szeredi79c0b2d2007-05-08 00:25:43 -070044static struct file_system_type **find_filesystem(const char *name, unsigned len)
Linus Torvalds1da177e2005-04-16 15:20:36 -070045{
46 struct file_system_type **p;
47 for (p=&file_systems; *p; p=&(*p)->next)
Miklos Szeredi79c0b2d2007-05-08 00:25:43 -070048 if (strlen((*p)->name) == len &&
49 strncmp((*p)->name, name, len) == 0)
Linus Torvalds1da177e2005-04-16 15:20:36 -070050 break;
51 return p;
52}
53
54/**
55 * register_filesystem - register a new filesystem
56 * @fs: the file system structure
57 *
58 * Adds the file system passed to the list of file systems the kernel
59 * is aware of for mount and other syscalls. Returns 0 on success,
60 * or a negative errno code on an error.
61 *
62 * The &struct file_system_type that is passed is linked into the kernel
63 * structures and must not be freed until the file system has been
64 * unregistered.
65 */
66
67int register_filesystem(struct file_system_type * fs)
68{
69 int res = 0;
70 struct file_system_type ** p;
71
Miklos Szeredi79c0b2d2007-05-08 00:25:43 -070072 BUG_ON(strchr(fs->name, '.'));
Linus Torvalds1da177e2005-04-16 15:20:36 -070073 if (fs->next)
74 return -EBUSY;
75 INIT_LIST_HEAD(&fs->fs_supers);
76 write_lock(&file_systems_lock);
Miklos Szeredi79c0b2d2007-05-08 00:25:43 -070077 p = find_filesystem(fs->name, strlen(fs->name));
Linus Torvalds1da177e2005-04-16 15:20:36 -070078 if (*p)
79 res = -EBUSY;
80 else
81 *p = fs;
82 write_unlock(&file_systems_lock);
83 return res;
84}
85
86EXPORT_SYMBOL(register_filesystem);
87
88/**
89 * unregister_filesystem - unregister a file system
90 * @fs: filesystem to unregister
91 *
92 * Remove a file system that was previously successfully registered
93 * with the kernel. An error is returned if the file system is not found.
94 * Zero is returned on a success.
95 *
96 * Once this function has returned the &struct file_system_type structure
97 * may be freed or reused.
98 */
99
100int unregister_filesystem(struct file_system_type * fs)
101{
102 struct file_system_type ** tmp;
103
104 write_lock(&file_systems_lock);
105 tmp = &file_systems;
106 while (*tmp) {
107 if (fs == *tmp) {
108 *tmp = fs->next;
109 fs->next = NULL;
110 write_unlock(&file_systems_lock);
111 return 0;
112 }
113 tmp = &(*tmp)->next;
114 }
115 write_unlock(&file_systems_lock);
116 return -EINVAL;
117}
118
119EXPORT_SYMBOL(unregister_filesystem);
120
121static int fs_index(const char __user * __name)
122{
123 struct file_system_type * tmp;
124 char * name;
125 int err, index;
126
127 name = getname(__name);
128 err = PTR_ERR(name);
129 if (IS_ERR(name))
130 return err;
131
132 err = -EINVAL;
133 read_lock(&file_systems_lock);
134 for (tmp=file_systems, index=0 ; tmp ; tmp=tmp->next, index++) {
135 if (strcmp(tmp->name,name) == 0) {
136 err = index;
137 break;
138 }
139 }
140 read_unlock(&file_systems_lock);
141 putname(name);
142 return err;
143}
144
145static int fs_name(unsigned int index, char __user * buf)
146{
147 struct file_system_type * tmp;
148 int len, res;
149
150 read_lock(&file_systems_lock);
151 for (tmp = file_systems; tmp; tmp = tmp->next, index--)
152 if (index <= 0 && try_module_get(tmp->owner))
153 break;
154 read_unlock(&file_systems_lock);
155 if (!tmp)
156 return -EINVAL;
157
158 /* OK, we got the reference, so we can safely block */
159 len = strlen(tmp->name) + 1;
160 res = copy_to_user(buf, tmp->name, len) ? -EFAULT : 0;
161 put_filesystem(tmp);
162 return res;
163}
164
165static int fs_maxindex(void)
166{
167 struct file_system_type * tmp;
168 int index;
169
170 read_lock(&file_systems_lock);
171 for (tmp = file_systems, index = 0 ; tmp ; tmp = tmp->next, index++)
172 ;
173 read_unlock(&file_systems_lock);
174 return index;
175}
176
177/*
178 * Whee.. Weird sysv syscall.
179 */
180asmlinkage long sys_sysfs(int option, unsigned long arg1, unsigned long arg2)
181{
182 int retval = -EINVAL;
183
184 switch (option) {
185 case 1:
186 retval = fs_index((const char __user *) arg1);
187 break;
188
189 case 2:
190 retval = fs_name(arg1, (char __user *) arg2);
191 break;
192
193 case 3:
194 retval = fs_maxindex();
195 break;
196 }
197 return retval;
198}
199
200int get_filesystem_list(char * buf)
201{
202 int len = 0;
203 struct file_system_type * tmp;
204
205 read_lock(&file_systems_lock);
206 tmp = file_systems;
207 while (tmp && len < PAGE_SIZE - 80) {
208 len += sprintf(buf+len, "%s\t%s\n",
209 (tmp->fs_flags & FS_REQUIRES_DEV) ? "" : "nodev",
210 tmp->name);
211 tmp = tmp->next;
212 }
213 read_unlock(&file_systems_lock);
214 return len;
215}
216
217struct file_system_type *get_fs_type(const char *name)
218{
219 struct file_system_type *fs;
Miklos Szeredi79c0b2d2007-05-08 00:25:43 -0700220 const char *dot = strchr(name, '.');
221 unsigned len = dot ? dot - name : strlen(name);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700222
223 read_lock(&file_systems_lock);
Miklos Szeredi79c0b2d2007-05-08 00:25:43 -0700224 fs = *(find_filesystem(name, len));
Linus Torvalds1da177e2005-04-16 15:20:36 -0700225 if (fs && !try_module_get(fs->owner))
226 fs = NULL;
227 read_unlock(&file_systems_lock);
Miklos Szeredi79c0b2d2007-05-08 00:25:43 -0700228 if (!fs && (request_module("%.*s", len, name) == 0)) {
Linus Torvalds1da177e2005-04-16 15:20:36 -0700229 read_lock(&file_systems_lock);
Miklos Szeredi79c0b2d2007-05-08 00:25:43 -0700230 fs = *(find_filesystem(name, len));
Linus Torvalds1da177e2005-04-16 15:20:36 -0700231 if (fs && !try_module_get(fs->owner))
232 fs = NULL;
233 read_unlock(&file_systems_lock);
234 }
Miklos Szeredi79c0b2d2007-05-08 00:25:43 -0700235
236 if (dot && fs && !(fs->fs_flags & FS_HAS_SUBTYPE)) {
237 put_filesystem(fs);
238 fs = NULL;
239 }
Linus Torvalds1da177e2005-04-16 15:20:36 -0700240 return fs;
241}
242
243EXPORT_SYMBOL(get_fs_type);