Root/fs/filesystems.c

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
32static struct file_system_type *file_systems;
33static DEFINE_RWLOCK(file_systems_lock);
34
35/* WARNING: This can be used only if we _already_ own a reference */
36void get_filesystem(struct file_system_type *fs)
37{
38    __module_get(fs->owner);
39}
40
41void put_filesystem(struct file_system_type *fs)
42{
43    module_put(fs->owner);
44}
45
46static 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 
69int 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
88EXPORT_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 
102int 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            return 0;
114        }
115        tmp = &(*tmp)->next;
116    }
117    write_unlock(&file_systems_lock);
118
119    synchronize_rcu();
120
121    return -EINVAL;
122}
123
124EXPORT_SYMBOL(unregister_filesystem);
125
126static int fs_index(const char __user * __name)
127{
128    struct file_system_type * tmp;
129    char * name;
130    int err, index;
131
132    name = getname(__name);
133    err = PTR_ERR(name);
134    if (IS_ERR(name))
135        return err;
136
137    err = -EINVAL;
138    read_lock(&file_systems_lock);
139    for (tmp=file_systems, index=0 ; tmp ; tmp=tmp->next, index++) {
140        if (strcmp(tmp->name,name) == 0) {
141            err = index;
142            break;
143        }
144    }
145    read_unlock(&file_systems_lock);
146    putname(name);
147    return err;
148}
149
150static int fs_name(unsigned int index, char __user * buf)
151{
152    struct file_system_type * tmp;
153    int len, res;
154
155    read_lock(&file_systems_lock);
156    for (tmp = file_systems; tmp; tmp = tmp->next, index--)
157        if (index <= 0 && try_module_get(tmp->owner))
158            break;
159    read_unlock(&file_systems_lock);
160    if (!tmp)
161        return -EINVAL;
162
163    /* OK, we got the reference, so we can safely block */
164    len = strlen(tmp->name) + 1;
165    res = copy_to_user(buf, tmp->name, len) ? -EFAULT : 0;
166    put_filesystem(tmp);
167    return res;
168}
169
170static int fs_maxindex(void)
171{
172    struct file_system_type * tmp;
173    int index;
174
175    read_lock(&file_systems_lock);
176    for (tmp = file_systems, index = 0 ; tmp ; tmp = tmp->next, index++)
177        ;
178    read_unlock(&file_systems_lock);
179    return index;
180}
181
182/*
183 * Whee.. Weird sysv syscall.
184 */
185SYSCALL_DEFINE3(sysfs, int, option, unsigned long, arg1, unsigned long, arg2)
186{
187    int retval = -EINVAL;
188
189    switch (option) {
190        case 1:
191            retval = fs_index((const char __user *) arg1);
192            break;
193
194        case 2:
195            retval = fs_name(arg1, (char __user *) arg2);
196            break;
197
198        case 3:
199            retval = fs_maxindex();
200            break;
201    }
202    return retval;
203}
204
205int __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
223static 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
239static int filesystems_proc_open(struct inode *inode, struct file *file)
240{
241    return single_open(file, filesystems_proc_show, NULL);
242}
243
244static 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
251static int __init proc_filesystems_init(void)
252{
253    proc_create("filesystems", 0, NULL, &filesystems_proc_fops);
254    return 0;
255}
256module_init(proc_filesystems_init);
257#endif
258
259static 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
271struct 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("%.*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
288EXPORT_SYMBOL(get_fs_type);
289

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