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 struct file_system_type *get_filesystem(struct file_system_type *fs)
  37 {
  38         __module_get(fs->owner);
  39         return fs;
  40 }
  41
  42 void put_filesystem(struct file_system_type *fs)
  43 {
  44         module_put(fs->owner);
  45 }
  46
  47 static struct file_system_type **find_filesystem(const char *name, unsigned len)
  48 {
  49         struct file_system_type **p;
  50         for (p = &file_systems; *p; p = &(*p)->next)
  51                 if (strncmp((*p)->name, name, len) == 0 &&
  52                     !(*p)->name[len])
  53                         break;
  54         return p;
  55 }
  56
  57 /**
  58  *      register_filesystem - register a new filesystem
  59  *      @fs: the file system structure
  60  *
  61  *      Adds the file system passed to the list of file systems the kernel
  62  *      is aware of for mount and other syscalls. Returns 0 on success,
  63  *      or a negative errno code on an error.
  64  *
  65  *      The &struct file_system_type that is passed is linked into the kernel
  66  *      structures and must not be freed until the file system has been
  67  *      unregistered.
  68  */
  69
  70 int register_filesystem(struct file_system_type * fs)
  71 {
  72         int res = 0;
  73         struct file_system_type ** p;
  74
  75         BUG_ON(strchr(fs->name, '.'));
  76         if (fs->next)
  77                 return -EBUSY;
  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
  88 EXPORT_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
 102 int 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
 123 EXPORT_SYMBOL(unregister_filesystem);
 124
 125 #ifdef CONFIG_SYSFS_SYSCALL
 126 static int fs_index(const char __user * __name)
 127 {
 128         struct file_system_type * tmp;
 129         struct filename *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->name) == 0) {
 141                         err = index;
 142                         break;
 143                 }
 144         }
 145         read_unlock(&file_systems_lock);
 146         putname(name);
 147         return err;
 148 }
 149
 150 static 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
 170 static 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  */
 185 SYSCALL_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 #endif
 205
 206 int __init get_filesystem_list(char *buf)
 207 {
 208         int len = 0;
 209         struct file_system_type * tmp;
 210
 211         read_lock(&file_systems_lock);
 212         tmp = file_systems;
 213         while (tmp && len < PAGE_SIZE - 80) {
 214                 len += sprintf(buf+len, "%s\t%s\n",
 215                         (tmp->fs_flags & FS_REQUIRES_DEV) ? "" : "nodev",
 216                         tmp->name);
 217                 tmp = tmp->next;
 218         }
 219         read_unlock(&file_systems_lock);
 220         return len;
 221 }
 222
 223 #ifdef CONFIG_PROC_FS
 224 static int filesystems_proc_show(struct seq_file *m, void *v)
 225 {
 226         struct file_system_type * tmp;
 227
 228         read_lock(&file_systems_lock);
 229         tmp = file_systems;
 230         while (tmp) {
 231                 seq_printf(m, "%s\t%s\n",
 232                         (tmp->fs_flags & FS_REQUIRES_DEV) ? "" : "nodev",
 233                         tmp->name);
 234                 tmp = tmp->next;
 235         }
 236         read_unlock(&file_systems_lock);
 237         return 0;
 238 }
 239
 240 static int filesystems_proc_open(struct inode *inode, struct file *file)
 241 {
 242         return single_open(file, filesystems_proc_show, NULL);
 243 }
 244
 245 static const struct file_operations filesystems_proc_fops = {
 246         .open           = filesystems_proc_open,
 247         .read           = seq_read,
 248         .llseek         = seq_lseek,
 249         .release        = single_release,
 250 };
 251
 252 static int __init proc_filesystems_init(void)
 253 {
 254         proc_create("filesystems", 0, NULL, &filesystems_proc_fops);
 255         return 0;
 256 }
 257 module_init(proc_filesystems_init);
 258 #endif
 259
 260 static struct file_system_type *__get_fs_type(const char *name, int len)
 261 {
 262         struct file_system_type *fs;
 263
 264         read_lock(&file_systems_lock);
 265         fs = *(find_filesystem(name, len));
 266         if (fs && !try_module_get(fs->owner))
 267                 fs = NULL;
 268         read_unlock(&file_systems_lock);
 269         return fs;
 270 }
 271
 272 struct file_system_type *get_fs_type(const char *name)
 273 {
 274         struct file_system_type *fs;
 275         const char *dot = strchr(name, '.');
 276         int len = dot ? dot - name : strlen(name);
 277
 278         fs = __get_fs_type(name, len);
 279         if (!fs && (request_module("fs-%.*s", len, name) == 0)) {
 280                 fs = __get_fs_type(name, len);
 281                 WARN_ONCE(!fs, "request_module fs-%.*s succeeded, but still no fs?\n", len, name);
 282         }
 283
 284         if (dot && fs && !(fs->fs_flags & FS_HAS_SUBTYPE)) {
 285                 put_filesystem(fs);
 286                 fs = NULL;
 287         }
 288         return fs;
 289 }
 290
 291 EXPORT_SYMBOL(get_fs_type);