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/kmod.h>
14 #include <linux/init.h>
15 #include <linux/module.h>
16 #include <linux/slab.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 */
get_filesystem(struct file_system_type * fs)36 void get_filesystem(struct file_system_type *fs)
37 {
38 __module_get(fs->owner);
39 }
40
put_filesystem(struct file_system_type * fs)41 void put_filesystem(struct file_system_type *fs)
42 {
43 module_put(fs->owner);
44 }
45
find_filesystem(const char * name,unsigned len)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
register_filesystem(struct file_system_type * fs)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
unregister_filesystem(struct file_system_type * fs)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 synchronize_rcu();
114 return 0;
115 }
116 tmp = &(*tmp)->next;
117 }
118 write_unlock(&file_systems_lock);
119
120 return -EINVAL;
121 }
122
123 EXPORT_SYMBOL(unregister_filesystem);
124
fs_index(const char __user * __name)125 static int fs_index(const char __user * __name)
126 {
127 struct file_system_type * tmp;
128 char * name;
129 int err, index;
130
131 name = getname(__name);
132 err = PTR_ERR(name);
133 if (IS_ERR(name))
134 return err;
135
136 err = -EINVAL;
137 read_lock(&file_systems_lock);
138 for (tmp=file_systems, index=0 ; tmp ; tmp=tmp->next, index++) {
139 if (strcmp(tmp->name,name) == 0) {
140 err = index;
141 break;
142 }
143 }
144 read_unlock(&file_systems_lock);
145 putname(name);
146 return err;
147 }
148
fs_name(unsigned int index,char __user * buf)149 static int fs_name(unsigned int index, char __user * buf)
150 {
151 struct file_system_type * tmp;
152 int len, res;
153
154 read_lock(&file_systems_lock);
155 for (tmp = file_systems; tmp; tmp = tmp->next, index--)
156 if (index <= 0 && try_module_get(tmp->owner))
157 break;
158 read_unlock(&file_systems_lock);
159 if (!tmp)
160 return -EINVAL;
161
162 /* OK, we got the reference, so we can safely block */
163 len = strlen(tmp->name) + 1;
164 res = copy_to_user(buf, tmp->name, len) ? -EFAULT : 0;
165 put_filesystem(tmp);
166 return res;
167 }
168
fs_maxindex(void)169 static int fs_maxindex(void)
170 {
171 struct file_system_type * tmp;
172 int index;
173
174 read_lock(&file_systems_lock);
175 for (tmp = file_systems, index = 0 ; tmp ; tmp = tmp->next, index++)
176 ;
177 read_unlock(&file_systems_lock);
178 return index;
179 }
180
181 /*
182 * Whee.. Weird sysv syscall.
183 */
SYSCALL_DEFINE3(sysfs,int,option,unsigned long,arg1,unsigned long,arg2)184 SYSCALL_DEFINE3(sysfs, int, option, unsigned long, arg1, unsigned long, arg2)
185 {
186 int retval = -EINVAL;
187
188 switch (option) {
189 case 1:
190 retval = fs_index((const char __user *) arg1);
191 break;
192
193 case 2:
194 retval = fs_name(arg1, (char __user *) arg2);
195 break;
196
197 case 3:
198 retval = fs_maxindex();
199 break;
200 }
201 return retval;
202 }
203
get_filesystem_list(char * buf)204 int __init get_filesystem_list(char *buf)
205 {
206 int len = 0;
207 struct file_system_type * tmp;
208
209 read_lock(&file_systems_lock);
210 tmp = file_systems;
211 while (tmp && len < PAGE_SIZE - 80) {
212 len += sprintf(buf+len, "%s\t%s\n",
213 (tmp->fs_flags & FS_REQUIRES_DEV) ? "" : "nodev",
214 tmp->name);
215 tmp = tmp->next;
216 }
217 read_unlock(&file_systems_lock);
218 return len;
219 }
220
221 #ifdef CONFIG_PROC_FS
filesystems_proc_show(struct seq_file * m,void * v)222 static int filesystems_proc_show(struct seq_file *m, void *v)
223 {
224 struct file_system_type * tmp;
225
226 read_lock(&file_systems_lock);
227 tmp = file_systems;
228 while (tmp) {
229 seq_printf(m, "%s\t%s\n",
230 (tmp->fs_flags & FS_REQUIRES_DEV) ? "" : "nodev",
231 tmp->name);
232 tmp = tmp->next;
233 }
234 read_unlock(&file_systems_lock);
235 return 0;
236 }
237
filesystems_proc_open(struct inode * inode,struct file * file)238 static int filesystems_proc_open(struct inode *inode, struct file *file)
239 {
240 return single_open(file, filesystems_proc_show, NULL);
241 }
242
243 static const struct file_operations filesystems_proc_fops = {
244 .open = filesystems_proc_open,
245 .read = seq_read,
246 .llseek = seq_lseek,
247 .release = single_release,
248 };
249
proc_filesystems_init(void)250 static int __init proc_filesystems_init(void)
251 {
252 proc_create("filesystems", 0, NULL, &filesystems_proc_fops);
253 return 0;
254 }
255 module_init(proc_filesystems_init);
256 #endif
257
__get_fs_type(const char * name,int len)258 static struct file_system_type *__get_fs_type(const char *name, int len)
259 {
260 struct file_system_type *fs;
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 return fs;
268 }
269
get_fs_type(const char * name)270 struct file_system_type *get_fs_type(const char *name)
271 {
272 struct file_system_type *fs;
273 const char *dot = strchr(name, '.');
274 int len = dot ? dot - name : strlen(name);
275
276 fs = __get_fs_type(name, len);
277 if (!fs && (request_module("%.*s", len, name) == 0))
278 fs = __get_fs_type(name, len);
279
280 if (dot && fs && !(fs->fs_flags & FS_HAS_SUBTYPE)) {
281 put_filesystem(fs);
282 fs = NULL;
283 }
284 return fs;
285 }
286
287 EXPORT_SYMBOL(get_fs_type);
288