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