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            synchronize_rcu();
114            return 0;
115        }
116        tmp = &(*tmp)->next;
117    }
118    write_unlock(&file_systems_lock);
119
120    return -EINVAL;
121}
122
123EXPORT_SYMBOL(unregister_filesystem);
124
125static int fs_index(const char __user * __name)
126{
127    struct file_system_type * tmp;
128    char * 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) == 0) {
140            err = index;
141            break;
142        }
143    }
144    read_unlock(&file_systems_lock);
145    putname(name);
146    return err;
147}
148
149static 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
169static 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 */
184SYSCALL_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
204int __init get_filesystem_list(char *buf)
205{
206    int len = 0;
207    struct file_system_type * tmp;
208
209    read_lock(&file_systems_lock);
210    tmp = file_systems;
211    while (tmp && len < PAGE_SIZE - 80) {
212        len += sprintf(buf+len, "%s\t%s\n",
213            (tmp->fs_flags & FS_REQUIRES_DEV) ? "" : "nodev",
214            tmp->name);
215        tmp = tmp->next;
216    }
217    read_unlock(&file_systems_lock);
218    return len;
219}
220
221#ifdef CONFIG_PROC_FS
222static int filesystems_proc_show(struct seq_file *m, void *v)
223{
224    struct file_system_type * tmp;
225
226    read_lock(&file_systems_lock);
227    tmp = file_systems;
228    while (tmp) {
229        seq_printf(m, "%s\t%s\n",
230            (tmp->fs_flags & FS_REQUIRES_DEV) ? "" : "nodev",
231            tmp->name);
232        tmp = tmp->next;
233    }
234    read_unlock(&file_systems_lock);
235    return 0;
236}
237
238static int filesystems_proc_open(struct inode *inode, struct file *file)
239{
240    return single_open(file, filesystems_proc_show, NULL);
241}
242
243static const struct file_operations filesystems_proc_fops = {
244    .open = filesystems_proc_open,
245    .read = seq_read,
246    .llseek = seq_lseek,
247    .release = single_release,
248};
249
250static int __init proc_filesystems_init(void)
251{
252    proc_create("filesystems", 0, NULL, &filesystems_proc_fops);
253    return 0;
254}
255module_init(proc_filesystems_init);
256#endif
257
258static struct file_system_type *__get_fs_type(const char *name, int len)
259{
260    struct file_system_type *fs;
261
262    read_lock(&file_systems_lock);
263    fs = *(find_filesystem(name, len));
264    if (fs && !try_module_get(fs->owner))
265        fs = NULL;
266    read_unlock(&file_systems_lock);
267    return fs;
268}
269
270struct file_system_type *get_fs_type(const char *name)
271{
272    struct file_system_type *fs;
273    const char *dot = strchr(name, '.');
274    int len = dot ? dot - name : strlen(name);
275
276    fs = __get_fs_type(name, len);
277    if (!fs && (request_module("%.*s", len, name) == 0))
278        fs = __get_fs_type(name, len);
279
280    if (dot && fs && !(fs->fs_flags & FS_HAS_SUBTYPE)) {
281        put_filesystem(fs);
282        fs = NULL;
283    }
284    return fs;
285}
286
287EXPORT_SYMBOL(get_fs_type);
288

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