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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>
Tim Schmielau4e57b682005-10-30 15:03:48 -080015#include <linux/sched.h> /* for 'current' */
Linus Torvalds1da177e2005-04-16 15:20:36 -070016#include <asm/uaccess.h>
17
18/*
19 * Handling of filesystem drivers list.
20 * Rules:
21 * Inclusion to/removals from/scanning of list are protected by spinlock.
22 * During the unload module must call unregister_filesystem().
23 * We can access the fields of list element if:
24 * 1) spinlock is held or
25 * 2) we hold the reference to the module.
26 * The latter can be guaranteed by call of try_module_get(); if it
27 * returned 0 we must skip the element, otherwise we got the reference.
28 * Once the reference is obtained we can drop the spinlock.
29 */
30
31static struct file_system_type *file_systems;
32static DEFINE_RWLOCK(file_systems_lock);
33
34/* WARNING: This can be used only if we _already_ own a reference */
35void get_filesystem(struct file_system_type *fs)
36{
37 __module_get(fs->owner);
38}
39
40void put_filesystem(struct file_system_type *fs)
41{
42 module_put(fs->owner);
43}
44
45static struct file_system_type **find_filesystem(const char *name)
46{
47 struct file_system_type **p;
48 for (p=&file_systems; *p; p=&(*p)->next)
49 if (strcmp((*p)->name,name) == 0)
50 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
Linus Torvalds1da177e2005-04-16 15:20:36 -070072 if (fs->next)
73 return -EBUSY;
74 INIT_LIST_HEAD(&fs->fs_supers);
75 write_lock(&file_systems_lock);
76 p = find_filesystem(fs->name);
77 if (*p)
78 res = -EBUSY;
79 else
80 *p = fs;
81 write_unlock(&file_systems_lock);
82 return res;
83}
84
85EXPORT_SYMBOL(register_filesystem);
86
87/**
88 * unregister_filesystem - unregister a file system
89 * @fs: filesystem to unregister
90 *
91 * Remove a file system that was previously successfully registered
92 * with the kernel. An error is returned if the file system is not found.
93 * Zero is returned on a success.
94 *
95 * Once this function has returned the &struct file_system_type structure
96 * may be freed or reused.
97 */
98
99int unregister_filesystem(struct file_system_type * fs)
100{
101 struct file_system_type ** tmp;
102
103 write_lock(&file_systems_lock);
104 tmp = &file_systems;
105 while (*tmp) {
106 if (fs == *tmp) {
107 *tmp = fs->next;
108 fs->next = NULL;
109 write_unlock(&file_systems_lock);
110 return 0;
111 }
112 tmp = &(*tmp)->next;
113 }
114 write_unlock(&file_systems_lock);
115 return -EINVAL;
116}
117
118EXPORT_SYMBOL(unregister_filesystem);
119
120static int fs_index(const char __user * __name)
121{
122 struct file_system_type * tmp;
123 char * name;
124 int err, index;
125
126 name = getname(__name);
127 err = PTR_ERR(name);
128 if (IS_ERR(name))
129 return err;
130
131 err = -EINVAL;
132 read_lock(&file_systems_lock);
133 for (tmp=file_systems, index=0 ; tmp ; tmp=tmp->next, index++) {
134 if (strcmp(tmp->name,name) == 0) {
135 err = index;
136 break;
137 }
138 }
139 read_unlock(&file_systems_lock);
140 putname(name);
141 return err;
142}
143
144static int fs_name(unsigned int index, char __user * buf)
145{
146 struct file_system_type * tmp;
147 int len, res;
148
149 read_lock(&file_systems_lock);
150 for (tmp = file_systems; tmp; tmp = tmp->next, index--)
151 if (index <= 0 && try_module_get(tmp->owner))
152 break;
153 read_unlock(&file_systems_lock);
154 if (!tmp)
155 return -EINVAL;
156
157 /* OK, we got the reference, so we can safely block */
158 len = strlen(tmp->name) + 1;
159 res = copy_to_user(buf, tmp->name, len) ? -EFAULT : 0;
160 put_filesystem(tmp);
161 return res;
162}
163
164static int fs_maxindex(void)
165{
166 struct file_system_type * tmp;
167 int index;
168
169 read_lock(&file_systems_lock);
170 for (tmp = file_systems, index = 0 ; tmp ; tmp = tmp->next, index++)
171 ;
172 read_unlock(&file_systems_lock);
173 return index;
174}
175
176/*
177 * Whee.. Weird sysv syscall.
178 */
179asmlinkage long sys_sysfs(int option, unsigned long arg1, unsigned long arg2)
180{
181 int retval = -EINVAL;
182
183 switch (option) {
184 case 1:
185 retval = fs_index((const char __user *) arg1);
186 break;
187
188 case 2:
189 retval = fs_name(arg1, (char __user *) arg2);
190 break;
191
192 case 3:
193 retval = fs_maxindex();
194 break;
195 }
196 return retval;
197}
198
199int get_filesystem_list(char * buf)
200{
201 int len = 0;
202 struct file_system_type * tmp;
203
204 read_lock(&file_systems_lock);
205 tmp = file_systems;
206 while (tmp && len < PAGE_SIZE - 80) {
207 len += sprintf(buf+len, "%s\t%s\n",
208 (tmp->fs_flags & FS_REQUIRES_DEV) ? "" : "nodev",
209 tmp->name);
210 tmp = tmp->next;
211 }
212 read_unlock(&file_systems_lock);
213 return len;
214}
215
216struct file_system_type *get_fs_type(const char *name)
217{
218 struct file_system_type *fs;
219
220 read_lock(&file_systems_lock);
221 fs = *(find_filesystem(name));
222 if (fs && !try_module_get(fs->owner))
223 fs = NULL;
224 read_unlock(&file_systems_lock);
225 if (!fs && (request_module("%s", name) == 0)) {
226 read_lock(&file_systems_lock);
227 fs = *(find_filesystem(name));
228 if (fs && !try_module_get(fs->owner))
229 fs = NULL;
230 read_unlock(&file_systems_lock);
231 }
232 return fs;
233}
234
235EXPORT_SYMBOL(get_fs_type);