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1 /*
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/proc_fs.h>
12 #include <linux/seq_file.h>
13 #include <linux/slab.h>
14 #include <linux/kmod.h>
15 #include <linux/init.h>
16 #include <linux/module.h>
17 #include <asm/uaccess.h>
18
19 /*
20 * Handling of filesystem drivers list.
21 * Rules:
22 * Inclusion to/removals from/scanning of list are protected by spinlock.
23 * During the unload module must call unregister_filesystem().
24 * We can access the fields of list element if:
25 * 1) spinlock is held or
26 * 2) we hold the reference to the module.
27 * The latter can be guaranteed by call of try_module_get(); if it
28 * returned 0 we must skip the element, otherwise we got the reference.
29 * Once the reference is obtained we can drop the spinlock.
30 */
31
32 static struct file_system_type *file_systems;
33 static DEFINE_RWLOCK(file_systems_lock);
34
35 /* WARNING: This can be used only if we _already_ own a reference */
36 void get_filesystem(struct file_system_type *fs)
37 {
38 __module_get(fs->owner);
39 }
40
41 void put_filesystem(struct file_system_type *fs)
42 {
43 module_put(fs->owner);
44 }
45
46 static struct file_system_type **find_filesystem(const char *name, unsigned len)
47 {
48 struct file_system_type **p;
49 for (p=&file_systems; *p; p=&(*p)->next)
50 if (strlen((*p)->name) == len &&
51 strncmp((*p)->name, name, len) == 0)
52 break;
53 return p;
54 }
55
56 /**
57 * register_filesystem - register a new filesystem
58 * @fs: the file system structure
59 *
60 * Adds the file system passed to the list of file systems the kernel
61 * is aware of for mount and other syscalls. Returns 0 on success,
62 * or a negative errno code on an error.
63 *
64 * The &struct file_system_type that is passed is linked into the kernel
65 * structures and must not be freed until the file system has been
66 * unregistered.
67 */
68
69 int register_filesystem(struct file_system_type * fs)
70 {
71 int res = 0;
72 struct file_system_type ** p;
73
74 BUG_ON(strchr(fs->name, '.'));
75 if (fs->next)
76 return -EBUSY;
77 INIT_LIST_HEAD(&fs->fs_supers);
78 write_lock(&file_systems_lock);
79 p = find_filesystem(fs->name, strlen(fs->name));
80 if (*p)
81 res = -EBUSY;
82 else
83 *p = fs;
84 write_unlock(&file_systems_lock);
85 return res;
86 }
87
88 EXPORT_SYMBOL(register_filesystem);
89
90 /**
91 * unregister_filesystem - unregister a file system
92 * @fs: filesystem to unregister
93 *
94 * Remove a file system that was previously successfully registered
95 * with the kernel. An error is returned if the file system is not found.
96 * Zero is returned on a success.
97 *
98 * Once this function has returned the &struct file_system_type structure
99 * may be freed or reused.
100 */
101
102 int unregister_filesystem(struct file_system_type * fs)
103 {
104 struct file_system_type ** tmp;
105
106 write_lock(&file_systems_lock);
107 tmp = &file_systems;
108 while (*tmp) {
109 if (fs == *tmp) {
110 *tmp = fs->next;
111 fs->next = NULL;
112 write_unlock(&file_systems_lock);
113 return 0;
114 }
115 tmp = &(*tmp)->next;
116 }
117 write_unlock(&file_systems_lock);
118 return -EINVAL;
119 }
120
121 EXPORT_SYMBOL(unregister_filesystem);
122
123 static int fs_index(const char __user * __name)
124 {
125 struct file_system_type * tmp;
126 char * name;
127 int err, index;
128
129 name = getname(__name);
130 err = PTR_ERR(name);
131 if (IS_ERR(name))
132 return err;
133
134 err = -EINVAL;
135 read_lock(&file_systems_lock);
136 for (tmp=file_systems, index=0 ; tmp ; tmp=tmp->next, index++) {
137 if (strcmp(tmp->name,name) == 0) {
138 err = index;
139 break;
140 }
141 }
142 read_unlock(&file_systems_lock);
143 putname(name);
144 return err;
145 }
146
147 static int fs_name(unsigned int index, char __user * buf)
148 {
149 struct file_system_type * tmp;
150 int len, res;
151
152 read_lock(&file_systems_lock);
153 for (tmp = file_systems; tmp; tmp = tmp->next, index--)
154 if (index <= 0 && try_module_get(tmp->owner))
155 break;
156 read_unlock(&file_systems_lock);
157 if (!tmp)
158 return -EINVAL;
159
160 /* OK, we got the reference, so we can safely block */
161 len = strlen(tmp->name) + 1;
162 res = copy_to_user(buf, tmp->name, len) ? -EFAULT : 0;
163 put_filesystem(tmp);
164 return res;
165 }
166
167 static int fs_maxindex(void)
168 {
169 struct file_system_type * tmp;
170 int index;
171
172 read_lock(&file_systems_lock);
173 for (tmp = file_systems, index = 0 ; tmp ; tmp = tmp->next, index++)
174 ;
175 read_unlock(&file_systems_lock);
176 return index;
177 }
178
179 /*
180 * Whee.. Weird sysv syscall.
181 */
182 asmlinkage long sys_sysfs(int option, unsigned long arg1, unsigned long arg2)
183 {
184 int retval = -EINVAL;
185
186 switch (option) {
187 case 1:
188 retval = fs_index((const char __user *) arg1);
189 break;
190
191 case 2:
192 retval = fs_name(arg1, (char __user *) arg2);
193 break;
194
195 case 3:
196 retval = fs_maxindex();
197 break;
198 }
199 return retval;
200 }
201
202 int get_filesystem_list(char * buf)
203 {
204 int len = 0;
205 struct file_system_type * tmp;
206
207 read_lock(&file_systems_lock);
208 tmp = file_systems;
209 while (tmp && len < PAGE_SIZE - 80) {
210 len += sprintf(buf+len, "%s\t%s\n",
211 (tmp->fs_flags & FS_REQUIRES_DEV) ? "" : "nodev",
212 tmp->name);
213 tmp = tmp->next;
214 }
215 read_unlock(&file_systems_lock);
216 return len;
217 }
218
219 #ifdef CONFIG_PROC_FS
220 static int filesystems_proc_show(struct seq_file *m, void *v)
221 {
222 struct file_system_type * tmp;
223
224 read_lock(&file_systems_lock);
225 tmp = file_systems;
226 while (tmp) {
227 seq_printf(m, "%s\t%s\n",
228 (tmp->fs_flags & FS_REQUIRES_DEV) ? "" : "nodev",
229 tmp->name);
230 tmp = tmp->next;
231 }
232 read_unlock(&file_systems_lock);
233 return 0;
234 }
235
236 static int filesystems_proc_open(struct inode *inode, struct file *file)
237 {
238 return single_open(file, filesystems_proc_show, NULL);
239 }
240
241 static const struct file_operations filesystems_proc_fops = {
242 .open = filesystems_proc_open,
243 .read = seq_read,
244 .llseek = seq_lseek,
245 .release = single_release,
246 };
247
248 static int __init proc_filesystems_init(void)
249 {
250 proc_create("filesystems", 0, NULL, &filesystems_proc_fops);
251 return 0;
252 }
253 module_init(proc_filesystems_init);
254 #endif
255
256 struct file_system_type *get_fs_type(const char *name)
257 {
258 struct file_system_type *fs;
259 const char *dot = strchr(name, '.');
260 unsigned len = dot ? dot - name : strlen(name);
261
262 read_lock(&file_systems_lock);
263 fs = *(find_filesystem(name, len));
264 if (fs && !try_module_get(fs->owner))
265 fs = NULL;
266 read_unlock(&file_systems_lock);
267 if (!fs && (request_module("%.*s", len, name) == 0)) {
268 read_lock(&file_systems_lock);
269 fs = *(find_filesystem(name, len));
270 if (fs && !try_module_get(fs->owner))
271 fs = NULL;
272 read_unlock(&file_systems_lock);
273 }
274
275 if (dot && fs && !(fs->fs_flags & FS_HAS_SUBTYPE)) {
276 put_filesystem(fs);
277 fs = NULL;
278 }
279 return fs;
280 }
281
282 EXPORT_SYMBOL(get_fs_type);