Linux Kernel  3.7.1
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filesystems.c
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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 
32 static struct file_system_type *file_systems;
33 static DEFINE_RWLOCK(file_systems_lock);
34 
35 /* WARNING: This can be used only if we _already_ own a reference */
37 {
38  __module_get(fs->owner);
39 }
40 
42 {
43  module_put(fs->owner);
44 }
45 
46 static 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 
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  write_lock(&file_systems_lock);
78  p = find_filesystem(fs->name, strlen(fs->name));
79  if (*p)
80  res = -EBUSY;
81  else
82  *p = fs;
83  write_unlock(&file_systems_lock);
84  return res;
85 }
86 
88 
102 {
103  struct file_system_type ** tmp;
104 
105  write_lock(&file_systems_lock);
106  tmp = &file_systems;
107  while (*tmp) {
108  if (fs == *tmp) {
109  *tmp = fs->next;
110  fs->next = NULL;
111  write_unlock(&file_systems_lock);
112  synchronize_rcu();
113  return 0;
114  }
115  tmp = &(*tmp)->next;
116  }
117  write_unlock(&file_systems_lock);
118 
119  return -EINVAL;
120 }
121 
123 
124 static int fs_index(const char __user * __name)
125 {
126  struct file_system_type * tmp;
127  struct filename *name;
128  int err, index;
129 
130  name = getname(__name);
131  err = PTR_ERR(name);
132  if (IS_ERR(name))
133  return err;
134 
135  err = -EINVAL;
136  read_lock(&file_systems_lock);
137  for (tmp=file_systems, index=0 ; tmp ; tmp=tmp->next, index++) {
138  if (strcmp(tmp->name, name->name) == 0) {
139  err = index;
140  break;
141  }
142  }
143  read_unlock(&file_systems_lock);
144  putname(name);
145  return err;
146 }
147 
148 static int fs_name(unsigned int index, char __user * buf)
149 {
150  struct file_system_type * tmp;
151  int len, res;
152 
153  read_lock(&file_systems_lock);
154  for (tmp = file_systems; tmp; tmp = tmp->next, index--)
155  if (index <= 0 && try_module_get(tmp->owner))
156  break;
157  read_unlock(&file_systems_lock);
158  if (!tmp)
159  return -EINVAL;
160 
161  /* OK, we got the reference, so we can safely block */
162  len = strlen(tmp->name) + 1;
163  res = copy_to_user(buf, tmp->name, len) ? -EFAULT : 0;
164  put_filesystem(tmp);
165  return res;
166 }
167 
168 static int fs_maxindex(void)
169 {
170  struct file_system_type * tmp;
171  int index;
172 
173  read_lock(&file_systems_lock);
174  for (tmp = file_systems, index = 0 ; tmp ; tmp = tmp->next, index++)
175  ;
176  read_unlock(&file_systems_lock);
177  return index;
178 }
179 
180 /*
181  * Whee.. Weird sysv syscall.
182  */
183 SYSCALL_DEFINE3(sysfs, int, option, unsigned long, arg1, unsigned long, arg2)
184 {
185  int retval = -EINVAL;
186 
187  switch (option) {
188  case 1:
189  retval = fs_index((const char __user *) arg1);
190  break;
191 
192  case 2:
193  retval = fs_name(arg1, (char __user *) arg2);
194  break;
195 
196  case 3:
197  retval = fs_maxindex();
198  break;
199  }
200  return retval;
201 }
202 
204 {
205  int len = 0;
206  struct file_system_type * tmp;
207 
208  read_lock(&file_systems_lock);
209  tmp = file_systems;
210  while (tmp && len < PAGE_SIZE - 80) {
211  len += sprintf(buf+len, "%s\t%s\n",
212  (tmp->fs_flags & FS_REQUIRES_DEV) ? "" : "nodev",
213  tmp->name);
214  tmp = tmp->next;
215  }
216  read_unlock(&file_systems_lock);
217  return len;
218 }
219 
220 #ifdef CONFIG_PROC_FS
221 static int filesystems_proc_show(struct seq_file *m, void *v)
222 {
223  struct file_system_type * tmp;
224 
225  read_lock(&file_systems_lock);
226  tmp = file_systems;
227  while (tmp) {
228  seq_printf(m, "%s\t%s\n",
229  (tmp->fs_flags & FS_REQUIRES_DEV) ? "" : "nodev",
230  tmp->name);
231  tmp = tmp->next;
232  }
233  read_unlock(&file_systems_lock);
234  return 0;
235 }
236 
237 static int filesystems_proc_open(struct inode *inode, struct file *file)
238 {
239  return single_open(file, filesystems_proc_show, NULL);
240 }
241 
242 static const struct file_operations filesystems_proc_fops = {
243  .open = filesystems_proc_open,
244  .read = seq_read,
245  .llseek = seq_lseek,
246  .release = single_release,
247 };
248 
249 static int __init proc_filesystems_init(void)
250 {
251  proc_create("filesystems", 0, NULL, &filesystems_proc_fops);
252  return 0;
253 }
254 module_init(proc_filesystems_init);
255 #endif
256 
257 static struct file_system_type *__get_fs_type(const char *name, int len)
258 {
259  struct file_system_type *fs;
260 
261  read_lock(&file_systems_lock);
262  fs = *(find_filesystem(name, len));
263  if (fs && !try_module_get(fs->owner))
264  fs = NULL;
265  read_unlock(&file_systems_lock);
266  return fs;
267 }
268 
269 struct file_system_type *get_fs_type(const char *name)
270 {
271  struct file_system_type *fs;
272  const char *dot = strchr(name, '.');
273  int len = dot ? dot - name : strlen(name);
274 
275  fs = __get_fs_type(name, len);
276  if (!fs && (request_module("%.*s", len, name) == 0))
277  fs = __get_fs_type(name, len);
278 
279  if (dot && fs && !(fs->fs_flags & FS_HAS_SUBTYPE)) {
280  put_filesystem(fs);
281  fs = NULL;
282  }
283  return fs;
284 }
285