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                 WARN_ONCE(!fs, "request_module fs-%.*s succeeded, but still no fs?\n", len, name);
 281         }
 282
 283         if (dot && fs && !(fs->fs_flags & FS_HAS_SUBTYPE)) {
 284                 put_filesystem(fs);
 285                 fs = NULL;
 286         }
 287         return fs;
 288 }
 289
 290 EXPORT_SYMBOL(get_fs_type);