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/slab.h>
  12 #include <linux/kmod.h>
  13 #include <linux/init.h>
  14 #include <linux/module.h>
  15 #include <linux/sched.h>        /* for 'current' */
  16 #include <asm/uaccess.h>
  17
  18 /*
  19  * Handling of filesystem drivers list.
  20  * Rules:
  21  *      Inclusion to/removals from/scanning of list are protected by spinlock.
  22  *      During the unload module must call unregister_filesystem().
  23  *      We can access the fields of list element if:
  24  *              1) spinlock is held or
  25  *              2) we hold the reference to the module.
  26  *      The latter can be guaranteed by call of try_module_get(); if it
  27  *      returned 0 we must skip the element, otherwise we got the reference.
  28  *      Once the reference is obtained we can drop the spinlock.
  29  */
  30
  31 static struct file_system_type *file_systems;
  32 static DEFINE_RWLOCK(file_systems_lock);
  33
  34 /* WARNING: This can be used only if we _already_ own a reference */
  35 void get_filesystem(struct file_system_type *fs)
  36 {
  37         __module_get(fs->owner);
  38 }
  39
  40 void put_filesystem(struct file_system_type *fs)
  41 {
  42         module_put(fs->owner);
  43 }
  44
  45 static struct file_system_type **find_filesystem(const char *name)
  46 {
  47         struct file_system_type **p;
  48         for (p=&file_systems; *p; p=&(*p)->next)
  49                 if (strcmp((*p)->name,name) == 0)
  50                         break;
  51         return p;
  52 }
  53
  54 /**
  55  *      register_filesystem - register a new filesystem
  56  *      @fs: the file system structure
  57  *
  58  *      Adds the file system passed to the list of file systems the kernel
  59  *      is aware of for mount and other syscalls. Returns 0 on success,
  60  *      or a negative errno code on an error.
  61  *
  62  *      The &struct file_system_type that is passed is linked into the kernel
  63  *      structures and must not be freed until the file system has been
  64  *      unregistered.
  65  */
  66
  67 int register_filesystem(struct file_system_type * fs)
  68 {
  69         int res = 0;
  70         struct file_system_type ** p;
  71
  72         if (fs->next)
  73                 return -EBUSY;
  74         INIT_LIST_HEAD(&fs->fs_supers);
  75         write_lock(&file_systems_lock);
  76         p = find_filesystem(fs->name);
  77         if (*p)
  78                 res = -EBUSY;
  79         else
  80                 *p = fs;
  81         write_unlock(&file_systems_lock);
  82         return res;
  83 }
  84
  85 EXPORT_SYMBOL(register_filesystem);
  86
  87 /**
  88  *      unregister_filesystem - unregister a file system
  89  *      @fs: filesystem to unregister
  90  *
  91  *      Remove a file system that was previously successfully registered
  92  *      with the kernel. An error is returned if the file system is not found.
  93  *      Zero is returned on a success.
  94  *
  95  *      Once this function has returned the &struct file_system_type structure
  96  *      may be freed or reused.
  97  */
  98
  99 int unregister_filesystem(struct file_system_type * fs)
 100 {
 101         struct file_system_type ** tmp;
 102
 103         write_lock(&file_systems_lock);
 104         tmp = &file_systems;
 105         while (*tmp) {
 106                 if (fs == *tmp) {
 107                         *tmp = fs->next;
 108                         fs->next = NULL;
 109                         write_unlock(&file_systems_lock);
 110                         return 0;
 111                 }
 112                 tmp = &(*tmp)->next;
 113         }
 114         write_unlock(&file_systems_lock);
 115         return -EINVAL;
 116 }
 117
 118 EXPORT_SYMBOL(unregister_filesystem);
 119
 120 static int fs_index(const char __user * __name)
 121 {
 122         struct file_system_type * tmp;
 123         char * name;
 124         int err, index;
 125
 126         name = getname(__name);
 127         err = PTR_ERR(name);
 128         if (IS_ERR(name))
 129                 return err;
 130
 131         err = -EINVAL;
 132         read_lock(&file_systems_lock);
 133         for (tmp=file_systems, index=0 ; tmp ; tmp=tmp->next, index++) {
 134                 if (strcmp(tmp->name,name) == 0) {
 135                         err = index;
 136                         break;
 137                 }
 138         }
 139         read_unlock(&file_systems_lock);
 140         putname(name);
 141         return err;
 142 }
 143
 144 static int fs_name(unsigned int index, char __user * buf)
 145 {
 146         struct file_system_type * tmp;
 147         int len, res;
 148
 149         read_lock(&file_systems_lock);
 150         for (tmp = file_systems; tmp; tmp = tmp->next, index--)
 151                 if (index <= 0 && try_module_get(tmp->owner))
 152                         break;
 153         read_unlock(&file_systems_lock);
 154         if (!tmp)
 155                 return -EINVAL;
 156
 157         /* OK, we got the reference, so we can safely block */
 158         len = strlen(tmp->name) + 1;
 159         res = copy_to_user(buf, tmp->name, len) ? -EFAULT : 0;
 160         put_filesystem(tmp);
 161         return res;
 162 }
 163
 164 static int fs_maxindex(void)
 165 {
 166         struct file_system_type * tmp;
 167         int index;
 168
 169         read_lock(&file_systems_lock);
 170         for (tmp = file_systems, index = 0 ; tmp ; tmp = tmp->next, index++)
 171                 ;
 172         read_unlock(&file_systems_lock);
 173         return index;
 174 }
 175
 176 /*
 177  * Whee.. Weird sysv syscall.
 178  */
 179 asmlinkage long sys_sysfs(int option, unsigned long arg1, unsigned long arg2)
 180 {
 181         int retval = -EINVAL;
 182
 183         switch (option) {
 184                 case 1:
 185                         retval = fs_index((const char __user *) arg1);
 186                         break;
 187
 188                 case 2:
 189                         retval = fs_name(arg1, (char __user *) arg2);
 190                         break;
 191
 192                 case 3:
 193                         retval = fs_maxindex();
 194                         break;
 195         }
 196         return retval;
 197 }
 198
 199 int get_filesystem_list(char * buf)
 200 {
 201         int len = 0;
 202         struct file_system_type * tmp;
 203
 204         read_lock(&file_systems_lock);
 205         tmp = file_systems;
 206         while (tmp && len < PAGE_SIZE - 80) {
 207                 len += sprintf(buf+len, "%s\t%s\n",
 208                         (tmp->fs_flags & FS_REQUIRES_DEV) ? "" : "nodev",
 209                         tmp->name);
 210                 tmp = tmp->next;
 211         }
 212         read_unlock(&file_systems_lock);
 213         return len;
 214 }
 215
 216 struct file_system_type *get_fs_type(const char *name)
 217 {
 218         struct file_system_type *fs;
 219
 220         read_lock(&file_systems_lock);
 221         fs = *(find_filesystem(name));
 222         if (fs && !try_module_get(fs->owner))
 223                 fs = NULL;
 224         read_unlock(&file_systems_lock);
 225         if (!fs && (request_module("%s", name) == 0)) {
 226                 read_lock(&file_systems_lock);
 227                 fs = *(find_filesystem(name));
 228                 if (fs && !try_module_get(fs->owner))
 229                         fs = NULL;
 230                 read_unlock(&file_systems_lock);
 231         }
 232         return fs;
 233 }
 234
 235 EXPORT_SYMBOL(get_fs_type);