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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 */
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 (strncmp((*p)->name, name, len) == 0 &&
51 		    !(*p)->name[len])
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 	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 
unregister_filesystem(struct file_system_type * fs)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 #ifdef CONFIG_SYSFS_SYSCALL
fs_index(const char __user * __name)125 static int fs_index(const char __user * __name)
126 {
127 	struct file_system_type * tmp;
128 	struct filename *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->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 #endif
204 
get_filesystem_list(char * buf)205 int __init get_filesystem_list(char *buf)
206 {
207 	int len = 0;
208 	struct file_system_type * tmp;
209 
210 	read_lock(&file_systems_lock);
211 	tmp = file_systems;
212 	while (tmp && len < PAGE_SIZE - 80) {
213 		len += sprintf(buf+len, "%s\t%s\n",
214 			(tmp->fs_flags & FS_REQUIRES_DEV) ? "" : "nodev",
215 			tmp->name);
216 		tmp = tmp->next;
217 	}
218 	read_unlock(&file_systems_lock);
219 	return len;
220 }
221 
222 #ifdef CONFIG_PROC_FS
filesystems_proc_show(struct seq_file * m,void * v)223 static int filesystems_proc_show(struct seq_file *m, void *v)
224 {
225 	struct file_system_type * tmp;
226 
227 	read_lock(&file_systems_lock);
228 	tmp = file_systems;
229 	while (tmp) {
230 		seq_printf(m, "%s\t%s\n",
231 			(tmp->fs_flags & FS_REQUIRES_DEV) ? "" : "nodev",
232 			tmp->name);
233 		tmp = tmp->next;
234 	}
235 	read_unlock(&file_systems_lock);
236 	return 0;
237 }
238 
filesystems_proc_open(struct inode * inode,struct file * file)239 static int filesystems_proc_open(struct inode *inode, struct file *file)
240 {
241 	return single_open(file, filesystems_proc_show, NULL);
242 }
243 
244 static const struct file_operations filesystems_proc_fops = {
245 	.open		= filesystems_proc_open,
246 	.read		= seq_read,
247 	.llseek		= seq_lseek,
248 	.release	= single_release,
249 };
250 
proc_filesystems_init(void)251 static int __init proc_filesystems_init(void)
252 {
253 	proc_create("filesystems", 0, NULL, &filesystems_proc_fops);
254 	return 0;
255 }
256 module_init(proc_filesystems_init);
257 #endif
258 
__get_fs_type(const char * name,int len)259 static struct file_system_type *__get_fs_type(const char *name, int len)
260 {
261 	struct file_system_type *fs;
262 
263 	read_lock(&file_systems_lock);
264 	fs = *(find_filesystem(name, len));
265 	if (fs && !try_module_get(fs->owner))
266 		fs = NULL;
267 	read_unlock(&file_systems_lock);
268 	return fs;
269 }
270 
get_fs_type(const char * name)271 struct file_system_type *get_fs_type(const char *name)
272 {
273 	struct file_system_type *fs;
274 	const char *dot = strchr(name, '.');
275 	int len = dot ? dot - name : strlen(name);
276 
277 	fs = __get_fs_type(name, len);
278 	if (!fs && (request_module("fs-%.*s", len, name) == 0))
279 		fs = __get_fs_type(name, len);
280 
281 	if (dot && fs && !(fs->fs_flags & FS_HAS_SUBTYPE)) {
282 		put_filesystem(fs);
283 		fs = NULL;
284 	}
285 	return fs;
286 }
287 
288 EXPORT_SYMBOL(get_fs_type);
289