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/slab.h>
14#include <linux/kmod.h>
15#include <linux/init.h>
16#include <linux/module.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    return -EINVAL;
119}
120
121EXPORT_SYMBOL(unregister_filesystem);
122
123static int fs_index(const char __user * __name)
124{
125    struct file_system_type * tmp;
126    char * name;
127    int err, index;
128
129    name = getname(__name);
130    err = PTR_ERR(name);
131    if (IS_ERR(name))
132        return err;
133
134    err = -EINVAL;
135    read_lock(&file_systems_lock);
136    for (tmp=file_systems, index=0 ; tmp ; tmp=tmp->next, index++) {
137        if (strcmp(tmp->name,name) == 0) {
138            err = index;
139            break;
140        }
141    }
142    read_unlock(&file_systems_lock);
143    putname(name);
144    return err;
145}
146
147static int fs_name(unsigned int index, char __user * buf)
148{
149    struct file_system_type * tmp;
150    int len, res;
151
152    read_lock(&file_systems_lock);
153    for (tmp = file_systems; tmp; tmp = tmp->next, index--)
154        if (index <= 0 && try_module_get(tmp->owner))
155            break;
156    read_unlock(&file_systems_lock);
157    if (!tmp)
158        return -EINVAL;
159
160    /* OK, we got the reference, so we can safely block */
161    len = strlen(tmp->name) + 1;
162    res = copy_to_user(buf, tmp->name, len) ? -EFAULT : 0;
163    put_filesystem(tmp);
164    return res;
165}
166
167static int fs_maxindex(void)
168{
169    struct file_system_type * tmp;
170    int index;
171
172    read_lock(&file_systems_lock);
173    for (tmp = file_systems, index = 0 ; tmp ; tmp = tmp->next, index++)
174        ;
175    read_unlock(&file_systems_lock);
176    return index;
177}
178
179/*
180 * Whee.. Weird sysv syscall.
181 */
182SYSCALL_DEFINE3(sysfs, int, option, unsigned long, arg1, unsigned long, arg2)
183{
184    int retval = -EINVAL;
185
186    switch (option) {
187        case 1:
188            retval = fs_index((const char __user *) arg1);
189            break;
190
191        case 2:
192            retval = fs_name(arg1, (char __user *) arg2);
193            break;
194
195        case 3:
196            retval = fs_maxindex();
197            break;
198    }
199    return retval;
200}
201
202int __init get_filesystem_list(char *buf)
203{
204    int len = 0;
205    struct file_system_type * tmp;
206
207    read_lock(&file_systems_lock);
208    tmp = file_systems;
209    while (tmp && len < PAGE_SIZE - 80) {
210        len += sprintf(buf+len, "%s\t%s\n",
211            (tmp->fs_flags & FS_REQUIRES_DEV) ? "" : "nodev",
212            tmp->name);
213        tmp = tmp->next;
214    }
215    read_unlock(&file_systems_lock);
216    return len;
217}
218
219#ifdef CONFIG_PROC_FS
220static int filesystems_proc_show(struct seq_file *m, void *v)
221{
222    struct file_system_type * tmp;
223
224    read_lock(&file_systems_lock);
225    tmp = file_systems;
226    while (tmp) {
227        seq_printf(m, "%s\t%s\n",
228            (tmp->fs_flags & FS_REQUIRES_DEV) ? "" : "nodev",
229            tmp->name);
230        tmp = tmp->next;
231    }
232    read_unlock(&file_systems_lock);
233    return 0;
234}
235
236static int filesystems_proc_open(struct inode *inode, struct file *file)
237{
238    return single_open(file, filesystems_proc_show, NULL);
239}
240
241static const struct file_operations filesystems_proc_fops = {
242    .open = filesystems_proc_open,
243    .read = seq_read,
244    .llseek = seq_lseek,
245    .release = single_release,
246};
247
248static int __init proc_filesystems_init(void)
249{
250    proc_create("filesystems", 0, NULL, &filesystems_proc_fops);
251    return 0;
252}
253module_init(proc_filesystems_init);
254#endif
255
256static struct file_system_type *__get_fs_type(const char *name, int len)
257{
258    struct file_system_type *fs;
259
260    read_lock(&file_systems_lock);
261    fs = *(find_filesystem(name, len));
262    if (fs && !try_module_get(fs->owner))
263        fs = NULL;
264    read_unlock(&file_systems_lock);
265    return fs;
266}
267
268struct file_system_type *get_fs_type(const char *name)
269{
270    struct file_system_type *fs;
271    const char *dot = strchr(name, '.');
272    int len = dot ? dot - name : strlen(name);
273
274    fs = __get_fs_type(name, len);
275    if (!fs && (request_module("%.*s", len, name) == 0))
276        fs = __get_fs_type(name, len);
277
278    if (dot && fs && !(fs->fs_flags & FS_HAS_SUBTYPE)) {
279        put_filesystem(fs);
280        fs = NULL;
281    }
282    return fs;
283}
284
285EXPORT_SYMBOL(get_fs_type);
286

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