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