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Linux/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 <linux/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 */
 36 void get_filesystem(struct file_system_type *fs)
 37 {
 38         __module_get(fs->owner);
 39 }
 40 
 41 void put_filesystem(struct file_system_type *fs)
 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 (strncmp((*p)->name, name, len) == 0 &&
 51                     !(*p)->name[len])
 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  
 69 int 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         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 
 87 EXPORT_SYMBOL(register_filesystem);
 88 
 89 /**
 90  *      unregister_filesystem - unregister a file system
 91  *      @fs: filesystem to unregister
 92  *
 93  *      Remove a file system that was previously successfully registered
 94  *      with the kernel. An error is returned if the file system is not found.
 95  *      Zero is returned on a success.
 96  *      
 97  *      Once this function has returned the &struct file_system_type structure
 98  *      may be freed or reused.
 99  */
100  
101 int unregister_filesystem(struct file_system_type * fs)
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 
122 EXPORT_SYMBOL(unregister_filesystem);
123 
124 #ifdef CONFIG_SYSFS_SYSCALL
125 static int fs_index(const char __user * __name)
126 {
127         struct file_system_type * tmp;
128         struct filename *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->name) == 0) {
140                         err = index;
141                         break;
142                 }
143         }
144         read_unlock(&file_systems_lock);
145         putname(name);
146         return err;
147 }
148 
149 static 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 
169 static 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  */
184 SYSCALL_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 #endif
204 
205 int __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
223 static 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 
239 static int filesystems_proc_open(struct inode *inode, struct file *file)
240 {
241         return single_open(file, filesystems_proc_show, NULL);
242 }
243 
244 static 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 
251 static int __init proc_filesystems_init(void)
252 {
253         proc_create("filesystems", 0, NULL, &filesystems_proc_fops);
254         return 0;
255 }
256 module_init(proc_filesystems_init);
257 #endif
258 
259 static 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 
271 struct 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("fs-%.*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 
288 EXPORT_SYMBOL(get_fs_type);
289 

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