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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/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 */ |
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 | write_lock(&file_systems_lock); |
78 | p = find_filesystem(fs->name, strlen(fs->name)); |
79 | if (*p) |
80 | res = -EBUSY; |
81 | else |
82 | *p = fs; |
83 | write_unlock(&file_systems_lock); |
84 | return res; |
85 | } |
86 | |
87 | EXPORT_SYMBOL(register_filesystem); |
88 | |
89 | /** |
90 | * unregister_filesystem - unregister a file system |
91 | * @fs: filesystem to unregister |
92 | * |
93 | * Remove a file system that was previously successfully registered |
94 | * with the kernel. An error is returned if the file system is not found. |
95 | * Zero is returned on a success. |
96 | * |
97 | * Once this function has returned the &struct file_system_type structure |
98 | * may be freed or reused. |
99 | */ |
100 | |
101 | int unregister_filesystem(struct file_system_type * fs) |
102 | { |
103 | struct file_system_type ** tmp; |
104 | |
105 | write_lock(&file_systems_lock); |
106 | tmp = &file_systems; |
107 | while (*tmp) { |
108 | if (fs == *tmp) { |
109 | *tmp = fs->next; |
110 | fs->next = NULL; |
111 | write_unlock(&file_systems_lock); |
112 | synchronize_rcu(); |
113 | return 0; |
114 | } |
115 | tmp = &(*tmp)->next; |
116 | } |
117 | write_unlock(&file_systems_lock); |
118 | |
119 | return -EINVAL; |
120 | } |
121 | |
122 | EXPORT_SYMBOL(unregister_filesystem); |
123 | |
124 | static int fs_index(const char __user * __name) |
125 | { |
126 | struct file_system_type * tmp; |
127 | struct filename *name; |
128 | int err, index; |
129 | |
130 | name = getname(__name); |
131 | err = PTR_ERR(name); |
132 | if (IS_ERR(name)) |
133 | return err; |
134 | |
135 | err = -EINVAL; |
136 | read_lock(&file_systems_lock); |
137 | for (tmp=file_systems, index=0 ; tmp ; tmp=tmp->next, index++) { |
138 | if (strcmp(tmp->name, name->name) == 0) { |
139 | err = index; |
140 | break; |
141 | } |
142 | } |
143 | read_unlock(&file_systems_lock); |
144 | putname(name); |
145 | return err; |
146 | } |
147 | |
148 | static int fs_name(unsigned int index, char __user * buf) |
149 | { |
150 | struct file_system_type * tmp; |
151 | int len, res; |
152 | |
153 | read_lock(&file_systems_lock); |
154 | for (tmp = file_systems; tmp; tmp = tmp->next, index--) |
155 | if (index <= 0 && try_module_get(tmp->owner)) |
156 | break; |
157 | read_unlock(&file_systems_lock); |
158 | if (!tmp) |
159 | return -EINVAL; |
160 | |
161 | /* OK, we got the reference, so we can safely block */ |
162 | len = strlen(tmp->name) + 1; |
163 | res = copy_to_user(buf, tmp->name, len) ? -EFAULT : 0; |
164 | put_filesystem(tmp); |
165 | return res; |
166 | } |
167 | |
168 | static int fs_maxindex(void) |
169 | { |
170 | struct file_system_type * tmp; |
171 | int index; |
172 | |
173 | read_lock(&file_systems_lock); |
174 | for (tmp = file_systems, index = 0 ; tmp ; tmp = tmp->next, index++) |
175 | ; |
176 | read_unlock(&file_systems_lock); |
177 | return index; |
178 | } |
179 | |
180 | /* |
181 | * Whee.. Weird sysv syscall. |
182 | */ |
183 | SYSCALL_DEFINE3(sysfs, int, option, unsigned long, arg1, unsigned long, arg2) |
184 | { |
185 | int retval = -EINVAL; |
186 | |
187 | switch (option) { |
188 | case 1: |
189 | retval = fs_index((const char __user *) arg1); |
190 | break; |
191 | |
192 | case 2: |
193 | retval = fs_name(arg1, (char __user *) arg2); |
194 | break; |
195 | |
196 | case 3: |
197 | retval = fs_maxindex(); |
198 | break; |
199 | } |
200 | return retval; |
201 | } |
202 | |
203 | int __init get_filesystem_list(char *buf) |
204 | { |
205 | int len = 0; |
206 | struct file_system_type * tmp; |
207 | |
208 | read_lock(&file_systems_lock); |
209 | tmp = file_systems; |
210 | while (tmp && len < PAGE_SIZE - 80) { |
211 | len += sprintf(buf+len, "%s\t%s\n", |
212 | (tmp->fs_flags & FS_REQUIRES_DEV) ? "" : "nodev", |
213 | tmp->name); |
214 | tmp = tmp->next; |
215 | } |
216 | read_unlock(&file_systems_lock); |
217 | return len; |
218 | } |
219 | |
220 | #ifdef CONFIG_PROC_FS |
221 | static int filesystems_proc_show(struct seq_file *m, void *v) |
222 | { |
223 | struct file_system_type * tmp; |
224 | |
225 | read_lock(&file_systems_lock); |
226 | tmp = file_systems; |
227 | while (tmp) { |
228 | seq_printf(m, "%s\t%s\n", |
229 | (tmp->fs_flags & FS_REQUIRES_DEV) ? "" : "nodev", |
230 | tmp->name); |
231 | tmp = tmp->next; |
232 | } |
233 | read_unlock(&file_systems_lock); |
234 | return 0; |
235 | } |
236 | |
237 | static int filesystems_proc_open(struct inode *inode, struct file *file) |
238 | { |
239 | return single_open(file, filesystems_proc_show, NULL); |
240 | } |
241 | |
242 | static const struct file_operations filesystems_proc_fops = { |
243 | .open = filesystems_proc_open, |
244 | .read = seq_read, |
245 | .llseek = seq_lseek, |
246 | .release = single_release, |
247 | }; |
248 | |
249 | static int __init proc_filesystems_init(void) |
250 | { |
251 | proc_create("filesystems", 0, NULL, &filesystems_proc_fops); |
252 | return 0; |
253 | } |
254 | module_init(proc_filesystems_init); |
255 | #endif |
256 | |
257 | static struct file_system_type *__get_fs_type(const char *name, int len) |
258 | { |
259 | struct file_system_type *fs; |
260 | |
261 | read_lock(&file_systems_lock); |
262 | fs = *(find_filesystem(name, len)); |
263 | if (fs && !try_module_get(fs->owner)) |
264 | fs = NULL; |
265 | read_unlock(&file_systems_lock); |
266 | return fs; |
267 | } |
268 | |
269 | struct file_system_type *get_fs_type(const char *name) |
270 | { |
271 | struct file_system_type *fs; |
272 | const char *dot = strchr(name, '.'); |
273 | int len = dot ? dot - name : strlen(name); |
274 | |
275 | fs = __get_fs_type(name, len); |
276 | if (!fs && (request_module("fs-%.*s", len, name) == 0)) |
277 | fs = __get_fs_type(name, len); |
278 | |
279 | if (dot && fs && !(fs->fs_flags & FS_HAS_SUBTYPE)) { |
280 | put_filesystem(fs); |
281 | fs = NULL; |
282 | } |
283 | return fs; |
284 | } |
285 | |
286 | EXPORT_SYMBOL(get_fs_type); |
287 |
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