xref: /openbmc/linux/fs/filesystems.c (revision 3fc41476)
1 // SPDX-License-Identifier: GPL-2.0
2 /*
3  *  linux/fs/filesystems.c
4  *
5  *  Copyright (C) 1991, 1992  Linus Torvalds
6  *
7  *  table of configured filesystems
8  */
9 
10 #include <linux/syscalls.h>
11 #include <linux/fs.h>
12 #include <linux/proc_fs.h>
13 #include <linux/seq_file.h>
14 #include <linux/kmod.h>
15 #include <linux/init.h>
16 #include <linux/module.h>
17 #include <linux/slab.h>
18 #include <linux/uaccess.h>
19 #include <linux/fs_parser.h>
20 
21 /*
22  * Handling of filesystem drivers list.
23  * Rules:
24  *	Inclusion to/removals from/scanning of list are protected by spinlock.
25  *	During the unload module must call unregister_filesystem().
26  *	We can access the fields of list element if:
27  *		1) spinlock is held or
28  *		2) we hold the reference to the module.
29  *	The latter can be guaranteed by call of try_module_get(); if it
30  *	returned 0 we must skip the element, otherwise we got the reference.
31  *	Once the reference is obtained we can drop the spinlock.
32  */
33 
34 static struct file_system_type *file_systems;
35 static DEFINE_RWLOCK(file_systems_lock);
36 
37 /* WARNING: This can be used only if we _already_ own a reference */
38 struct file_system_type *get_filesystem(struct file_system_type *fs)
39 {
40 	__module_get(fs->owner);
41 	return fs;
42 }
43 
44 void put_filesystem(struct file_system_type *fs)
45 {
46 	module_put(fs->owner);
47 }
48 
49 static struct file_system_type **find_filesystem(const char *name, unsigned len)
50 {
51 	struct file_system_type **p;
52 	for (p = &file_systems; *p; p = &(*p)->next)
53 		if (strncmp((*p)->name, name, len) == 0 &&
54 		    !(*p)->name[len])
55 			break;
56 	return p;
57 }
58 
59 /**
60  *	register_filesystem - register a new filesystem
61  *	@fs: the file system structure
62  *
63  *	Adds the file system passed to the list of file systems the kernel
64  *	is aware of for mount and other syscalls. Returns 0 on success,
65  *	or a negative errno code on an error.
66  *
67  *	The &struct file_system_type that is passed is linked into the kernel
68  *	structures and must not be freed until the file system has been
69  *	unregistered.
70  */
71 
72 int register_filesystem(struct file_system_type * fs)
73 {
74 	int res = 0;
75 	struct file_system_type ** p;
76 
77 	if (fs->parameters && !fs_validate_description(fs->parameters))
78 		return -EINVAL;
79 
80 	BUG_ON(strchr(fs->name, '.'));
81 	if (fs->next)
82 		return -EBUSY;
83 	write_lock(&file_systems_lock);
84 	p = find_filesystem(fs->name, strlen(fs->name));
85 	if (*p)
86 		res = -EBUSY;
87 	else
88 		*p = fs;
89 	write_unlock(&file_systems_lock);
90 	return res;
91 }
92 
93 EXPORT_SYMBOL(register_filesystem);
94 
95 /**
96  *	unregister_filesystem - unregister a file system
97  *	@fs: filesystem to unregister
98  *
99  *	Remove a file system that was previously successfully registered
100  *	with the kernel. An error is returned if the file system is not found.
101  *	Zero is returned on a success.
102  *
103  *	Once this function has returned the &struct file_system_type structure
104  *	may be freed or reused.
105  */
106 
107 int unregister_filesystem(struct file_system_type * fs)
108 {
109 	struct file_system_type ** tmp;
110 
111 	write_lock(&file_systems_lock);
112 	tmp = &file_systems;
113 	while (*tmp) {
114 		if (fs == *tmp) {
115 			*tmp = fs->next;
116 			fs->next = NULL;
117 			write_unlock(&file_systems_lock);
118 			synchronize_rcu();
119 			return 0;
120 		}
121 		tmp = &(*tmp)->next;
122 	}
123 	write_unlock(&file_systems_lock);
124 
125 	return -EINVAL;
126 }
127 
128 EXPORT_SYMBOL(unregister_filesystem);
129 
130 #ifdef CONFIG_SYSFS_SYSCALL
131 static int fs_index(const char __user * __name)
132 {
133 	struct file_system_type * tmp;
134 	struct filename *name;
135 	int err, index;
136 
137 	name = getname(__name);
138 	err = PTR_ERR(name);
139 	if (IS_ERR(name))
140 		return err;
141 
142 	err = -EINVAL;
143 	read_lock(&file_systems_lock);
144 	for (tmp=file_systems, index=0 ; tmp ; tmp=tmp->next, index++) {
145 		if (strcmp(tmp->name, name->name) == 0) {
146 			err = index;
147 			break;
148 		}
149 	}
150 	read_unlock(&file_systems_lock);
151 	putname(name);
152 	return err;
153 }
154 
155 static int fs_name(unsigned int index, char __user * buf)
156 {
157 	struct file_system_type * tmp;
158 	int len, res;
159 
160 	read_lock(&file_systems_lock);
161 	for (tmp = file_systems; tmp; tmp = tmp->next, index--)
162 		if (index <= 0 && try_module_get(tmp->owner))
163 			break;
164 	read_unlock(&file_systems_lock);
165 	if (!tmp)
166 		return -EINVAL;
167 
168 	/* OK, we got the reference, so we can safely block */
169 	len = strlen(tmp->name) + 1;
170 	res = copy_to_user(buf, tmp->name, len) ? -EFAULT : 0;
171 	put_filesystem(tmp);
172 	return res;
173 }
174 
175 static int fs_maxindex(void)
176 {
177 	struct file_system_type * tmp;
178 	int index;
179 
180 	read_lock(&file_systems_lock);
181 	for (tmp = file_systems, index = 0 ; tmp ; tmp = tmp->next, index++)
182 		;
183 	read_unlock(&file_systems_lock);
184 	return index;
185 }
186 
187 /*
188  * Whee.. Weird sysv syscall.
189  */
190 SYSCALL_DEFINE3(sysfs, int, option, unsigned long, arg1, unsigned long, arg2)
191 {
192 	int retval = -EINVAL;
193 
194 	switch (option) {
195 		case 1:
196 			retval = fs_index((const char __user *) arg1);
197 			break;
198 
199 		case 2:
200 			retval = fs_name(arg1, (char __user *) arg2);
201 			break;
202 
203 		case 3:
204 			retval = fs_maxindex();
205 			break;
206 	}
207 	return retval;
208 }
209 #endif
210 
211 int __init get_filesystem_list(char *buf)
212 {
213 	int len = 0;
214 	struct file_system_type * tmp;
215 
216 	read_lock(&file_systems_lock);
217 	tmp = file_systems;
218 	while (tmp && len < PAGE_SIZE - 80) {
219 		len += sprintf(buf+len, "%s\t%s\n",
220 			(tmp->fs_flags & FS_REQUIRES_DEV) ? "" : "nodev",
221 			tmp->name);
222 		tmp = tmp->next;
223 	}
224 	read_unlock(&file_systems_lock);
225 	return len;
226 }
227 
228 #ifdef CONFIG_PROC_FS
229 static int filesystems_proc_show(struct seq_file *m, void *v)
230 {
231 	struct file_system_type * tmp;
232 
233 	read_lock(&file_systems_lock);
234 	tmp = file_systems;
235 	while (tmp) {
236 		seq_printf(m, "%s\t%s\n",
237 			(tmp->fs_flags & FS_REQUIRES_DEV) ? "" : "nodev",
238 			tmp->name);
239 		tmp = tmp->next;
240 	}
241 	read_unlock(&file_systems_lock);
242 	return 0;
243 }
244 
245 static int __init proc_filesystems_init(void)
246 {
247 	proc_create_single("filesystems", 0, NULL, filesystems_proc_show);
248 	return 0;
249 }
250 module_init(proc_filesystems_init);
251 #endif
252 
253 static struct file_system_type *__get_fs_type(const char *name, int len)
254 {
255 	struct file_system_type *fs;
256 
257 	read_lock(&file_systems_lock);
258 	fs = *(find_filesystem(name, len));
259 	if (fs && !try_module_get(fs->owner))
260 		fs = NULL;
261 	read_unlock(&file_systems_lock);
262 	return fs;
263 }
264 
265 struct file_system_type *get_fs_type(const char *name)
266 {
267 	struct file_system_type *fs;
268 	const char *dot = strchr(name, '.');
269 	int len = dot ? dot - name : strlen(name);
270 
271 	fs = __get_fs_type(name, len);
272 	if (!fs && (request_module("fs-%.*s", len, name) == 0)) {
273 		fs = __get_fs_type(name, len);
274 		WARN_ONCE(!fs, "request_module fs-%.*s succeeded, but still no fs?\n", len, name);
275 	}
276 
277 	if (dot && fs && !(fs->fs_flags & FS_HAS_SUBTYPE)) {
278 		put_filesystem(fs);
279 		fs = NULL;
280 	}
281 	return fs;
282 }
283 
284 EXPORT_SYMBOL(get_fs_type);
285