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/slab.h>
  14 #include <linux/kmod.h>
  15 #include <linux/init.h>
  16 #include <linux/module.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 */
  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 (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
  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         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
  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                         return 0;
 114                 }
 115                 tmp = &(*tmp)->next;
 116         }
 117         write_unlock(&file_systems_lock);
 118         return -EINVAL;
 119 }
 120
 121 EXPORT_SYMBOL(unregister_filesystem);
 122
 123 static int fs_index(const char __user * __name)
 124 {
 125         struct file_system_type * tmp;
 126         char * name;
 127         int err, index;
 128
 129         name = getname(__name);
 130         err = PTR_ERR(name);
 131         if (IS_ERR(name))
 132                 return err;
 133
 134         err = -EINVAL;
 135         read_lock(&file_systems_lock);
 136         for (tmp=file_systems, index=0 ; tmp ; tmp=tmp->next, index++) {
 137                 if (strcmp(tmp->name,name) == 0) {
 138                         err = index;
 139                         break;
 140                 }
 141         }
 142         read_unlock(&file_systems_lock);
 143         putname(name);
 144         return err;
 145 }
 146
 147 static int fs_name(unsigned int index, char __user * buf)
 148 {
 149         struct file_system_type * tmp;
 150         int len, res;
 151
 152         read_lock(&file_systems_lock);
 153         for (tmp = file_systems; tmp; tmp = tmp->next, index--)
 154                 if (index <= 0 && try_module_get(tmp->owner))
 155                         break;
 156         read_unlock(&file_systems_lock);
 157         if (!tmp)
 158                 return -EINVAL;
 159
 160         /* OK, we got the reference, so we can safely block */
 161         len = strlen(tmp->name) + 1;
 162         res = copy_to_user(buf, tmp->name, len) ? -EFAULT : 0;
 163         put_filesystem(tmp);
 164         return res;
 165 }
 166
 167 static int fs_maxindex(void)
 168 {
 169         struct file_system_type * tmp;
 170         int index;
 171
 172         read_lock(&file_systems_lock);
 173         for (tmp = file_systems, index = 0 ; tmp ; tmp = tmp->next, index++)
 174                 ;
 175         read_unlock(&file_systems_lock);
 176         return index;
 177 }
 178
 179 /*
 180  * Whee.. Weird sysv syscall.
 181  */
 182 asmlinkage long sys_sysfs(int option, unsigned long arg1, unsigned long arg2)
 183 {
 184         int retval = -EINVAL;
 185
 186         switch (option) {
 187                 case 1:
 188                         retval = fs_index((const char __user *) arg1);
 189                         break;
 190
 191                 case 2:
 192                         retval = fs_name(arg1, (char __user *) arg2);
 193                         break;
 194
 195                 case 3:
 196                         retval = fs_maxindex();
 197                         break;
 198         }
 199         return retval;
 200 }
 201
 202 int get_filesystem_list(char * buf)
 203 {
 204         int len = 0;
 205         struct file_system_type * tmp;
 206
 207         read_lock(&file_systems_lock);
 208         tmp = file_systems;
 209         while (tmp && len < PAGE_SIZE - 80) {
 210                 len += sprintf(buf+len, "%s\t%s\n",
 211                         (tmp->fs_flags & FS_REQUIRES_DEV) ? "" : "nodev",
 212                         tmp->name);
 213                 tmp = tmp->next;
 214         }
 215         read_unlock(&file_systems_lock);
 216         return len;
 217 }
 218
 219 #ifdef CONFIG_PROC_FS
 220 static int filesystems_proc_show(struct seq_file *m, void *v)
 221 {
 222         struct file_system_type * tmp;
 223
 224         read_lock(&file_systems_lock);
 225         tmp = file_systems;
 226         while (tmp) {
 227                 seq_printf(m, "%s\t%s\n",
 228                         (tmp->fs_flags & FS_REQUIRES_DEV) ? "" : "nodev",
 229                         tmp->name);
 230                 tmp = tmp->next;
 231         }
 232         read_unlock(&file_systems_lock);
 233         return 0;
 234 }
 235
 236 static int filesystems_proc_open(struct inode *inode, struct file *file)
 237 {
 238         return single_open(file, filesystems_proc_show, NULL);
 239 }
 240
 241 static const struct file_operations filesystems_proc_fops = {
 242         .open           = filesystems_proc_open,
 243         .read           = seq_read,
 244         .llseek         = seq_lseek,
 245         .release        = single_release,
 246 };
 247
 248 static int __init proc_filesystems_init(void)
 249 {
 250         proc_create("filesystems", 0, NULL, &filesystems_proc_fops);
 251         return 0;
 252 }
 253 module_init(proc_filesystems_init);
 254 #endif
 255
 256 struct file_system_type *get_fs_type(const char *name)
 257 {
 258         struct file_system_type *fs;
 259         const char *dot = strchr(name, '.');
 260         unsigned len = dot ? dot - name : strlen(name);
 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         if (!fs && (request_module("%.*s", len, name) == 0)) {
 268                 read_lock(&file_systems_lock);
 269                 fs = *(find_filesystem(name, len));
 270                 if (fs && !try_module_get(fs->owner))
 271                         fs = NULL;
 272                 read_unlock(&file_systems_lock);
 273         }
 274
 275         if (dot && fs && !(fs->fs_flags & FS_HAS_SUBTYPE)) {
 276                 put_filesystem(fs);
 277                 fs = NULL;
 278         }
 279         return fs;
 280 }
 281
 282 EXPORT_SYMBOL(get_fs_type);