blob: 7a4f61aa05f8a63697be13231d69316ef5c365a9 [file] [log] [blame]
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
44static struct file_system_type **find_filesystem(const char *name)
45{
46 struct file_system_type **p;
47 for (p=&file_systems; *p; p=&(*p)->next)
48 if (strcmp((*p)->name,name) == 0)
49 break;
50 return p;
51}
52
53/**
54 * register_filesystem - register a new filesystem
55 * @fs: the file system structure
56 *
57 * Adds the file system passed to the list of file systems the kernel
58 * is aware of for mount and other syscalls. Returns 0 on success,
59 * or a negative errno code on an error.
60 *
61 * The &struct file_system_type that is passed is linked into the kernel
62 * structures and must not be freed until the file system has been
63 * unregistered.
64 */
65
66int register_filesystem(struct file_system_type * fs)
67{
68 int res = 0;
69 struct file_system_type ** p;
70
Linus Torvalds1da177e2005-04-16 15:20:36 -070071 if (fs->next)
72 return -EBUSY;
73 INIT_LIST_HEAD(&fs->fs_supers);
74 write_lock(&file_systems_lock);
75 p = find_filesystem(fs->name);
76 if (*p)
77 res = -EBUSY;
78 else
79 *p = fs;
80 write_unlock(&file_systems_lock);
81 return res;
82}
83
84EXPORT_SYMBOL(register_filesystem);
85
86/**
87 * unregister_filesystem - unregister a file system
88 * @fs: filesystem to unregister
89 *
90 * Remove a file system that was previously successfully registered
91 * with the kernel. An error is returned if the file system is not found.
92 * Zero is returned on a success.
93 *
94 * Once this function has returned the &struct file_system_type structure
95 * may be freed or reused.
96 */
97
98int unregister_filesystem(struct file_system_type * fs)
99{
100 struct file_system_type ** tmp;
101
102 write_lock(&file_systems_lock);
103 tmp = &file_systems;
104 while (*tmp) {
105 if (fs == *tmp) {
106 *tmp = fs->next;
107 fs->next = NULL;
108 write_unlock(&file_systems_lock);
109 return 0;
110 }
111 tmp = &(*tmp)->next;
112 }
113 write_unlock(&file_systems_lock);
114 return -EINVAL;
115}
116
117EXPORT_SYMBOL(unregister_filesystem);
118
119static int fs_index(const char __user * __name)
120{
121 struct file_system_type * tmp;
122 char * name;
123 int err, index;
124
125 name = getname(__name);
126 err = PTR_ERR(name);
127 if (IS_ERR(name))
128 return err;
129
130 err = -EINVAL;
131 read_lock(&file_systems_lock);
132 for (tmp=file_systems, index=0 ; tmp ; tmp=tmp->next, index++) {
133 if (strcmp(tmp->name,name) == 0) {
134 err = index;
135 break;
136 }
137 }
138 read_unlock(&file_systems_lock);
139 putname(name);
140 return err;
141}
142
143static int fs_name(unsigned int index, char __user * buf)
144{
145 struct file_system_type * tmp;
146 int len, res;
147
148 read_lock(&file_systems_lock);
149 for (tmp = file_systems; tmp; tmp = tmp->next, index--)
150 if (index <= 0 && try_module_get(tmp->owner))
151 break;
152 read_unlock(&file_systems_lock);
153 if (!tmp)
154 return -EINVAL;
155
156 /* OK, we got the reference, so we can safely block */
157 len = strlen(tmp->name) + 1;
158 res = copy_to_user(buf, tmp->name, len) ? -EFAULT : 0;
159 put_filesystem(tmp);
160 return res;
161}
162
163static int fs_maxindex(void)
164{
165 struct file_system_type * tmp;
166 int index;
167
168 read_lock(&file_systems_lock);
169 for (tmp = file_systems, index = 0 ; tmp ; tmp = tmp->next, index++)
170 ;
171 read_unlock(&file_systems_lock);
172 return index;
173}
174
175/*
176 * Whee.. Weird sysv syscall.
177 */
178asmlinkage long sys_sysfs(int option, unsigned long arg1, unsigned long arg2)
179{
180 int retval = -EINVAL;
181
182 switch (option) {
183 case 1:
184 retval = fs_index((const char __user *) arg1);
185 break;
186
187 case 2:
188 retval = fs_name(arg1, (char __user *) arg2);
189 break;
190
191 case 3:
192 retval = fs_maxindex();
193 break;
194 }
195 return retval;
196}
197
198int get_filesystem_list(char * buf)
199{
200 int len = 0;
201 struct file_system_type * tmp;
202
203 read_lock(&file_systems_lock);
204 tmp = file_systems;
205 while (tmp && len < PAGE_SIZE - 80) {
206 len += sprintf(buf+len, "%s\t%s\n",
207 (tmp->fs_flags & FS_REQUIRES_DEV) ? "" : "nodev",
208 tmp->name);
209 tmp = tmp->next;
210 }
211 read_unlock(&file_systems_lock);
212 return len;
213}
214
215struct file_system_type *get_fs_type(const char *name)
216{
217 struct file_system_type *fs;
218
219 read_lock(&file_systems_lock);
220 fs = *(find_filesystem(name));
221 if (fs && !try_module_get(fs->owner))
222 fs = NULL;
223 read_unlock(&file_systems_lock);
224 if (!fs && (request_module("%s", name) == 0)) {
225 read_lock(&file_systems_lock);
226 fs = *(find_filesystem(name));
227 if (fs && !try_module_get(fs->owner))
228 fs = NULL;
229 read_unlock(&file_systems_lock);
230 }
231 return fs;
232}
233
234EXPORT_SYMBOL(get_fs_type);