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)
  73                 return -EINVAL;
  74         if (fs->next)
  75                 return -EBUSY;
  76         INIT_LIST_HEAD(&fs->fs_supers);
  77         write_lock(&file_systems_lock);
  78         p = find_filesystem(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                         return 0;
 113                 }
 114                 tmp = &(*tmp)->next;
 115         }
 116         write_unlock(&file_systems_lock);
 117         return -EINVAL;
 118 }
 119
 120 EXPORT_SYMBOL(unregister_filesystem);
 121
 122 static int fs_index(const char __user * __name)
 123 {
 124         struct file_system_type * tmp;
 125         char * name;
 126         int err, index;
 127
 128         name = getname(__name);
 129         err = PTR_ERR(name);
 130         if (IS_ERR(name))
 131                 return err;
 132
 133         err = -EINVAL;
 134         read_lock(&file_systems_lock);
 135         for (tmp=file_systems, index=0 ; tmp ; tmp=tmp->next, index++) {
 136                 if (strcmp(tmp->name,name) == 0) {
 137                         err = index;
 138                         break;
 139                 }
 140         }
 141         read_unlock(&file_systems_lock);
 142         putname(name);
 143         return err;
 144 }
 145
 146 static int fs_name(unsigned int index, char __user * buf)
 147 {
 148         struct file_system_type * tmp;
 149         int len, res;
 150
 151         read_lock(&file_systems_lock);
 152         for (tmp = file_systems; tmp; tmp = tmp->next, index--)
 153                 if (index <= 0 && try_module_get(tmp->owner))
 154                         break;
 155         read_unlock(&file_systems_lock);
 156         if (!tmp)
 157                 return -EINVAL;
 158
 159         /* OK, we got the reference, so we can safely block */
 160         len = strlen(tmp->name) + 1;
 161         res = copy_to_user(buf, tmp->name, len) ? -EFAULT : 0;
 162         put_filesystem(tmp);
 163         return res;
 164 }
 165
 166 static int fs_maxindex(void)
 167 {
 168         struct file_system_type * tmp;
 169         int index;
 170
 171         read_lock(&file_systems_lock);
 172         for (tmp = file_systems, index = 0 ; tmp ; tmp = tmp->next, index++)
 173                 ;
 174         read_unlock(&file_systems_lock);
 175         return index;
 176 }
 177
 178 /*
 179  * Whee.. Weird sysv syscall.
 180  */
 181 asmlinkage long sys_sysfs(int option, unsigned long arg1, unsigned long arg2)
 182 {
 183         int retval = -EINVAL;
 184
 185         switch (option) {
 186                 case 1:
 187                         retval = fs_index((const char __user *) arg1);
 188                         break;
 189
 190                 case 2:
 191                         retval = fs_name(arg1, (char __user *) arg2);
 192                         break;
 193
 194                 case 3:
 195                         retval = fs_maxindex();
 196                         break;
 197         }
 198         return retval;
 199 }
 200
 201 int get_filesystem_list(char * buf)
 202 {
 203         int len = 0;
 204         struct file_system_type * tmp;
 205
 206         read_lock(&file_systems_lock);
 207         tmp = file_systems;
 208         while (tmp && len < PAGE_SIZE - 80) {
 209                 len += sprintf(buf+len, "%s\t%s\n",
 210                         (tmp->fs_flags & FS_REQUIRES_DEV) ? "" : "nodev",
 211                         tmp->name);
 212                 tmp = tmp->next;
 213         }
 214         read_unlock(&file_systems_lock);
 215         return len;
 216 }
 217
 218 struct file_system_type *get_fs_type(const char *name)
 219 {
 220         struct file_system_type *fs;
 221
 222         read_lock(&file_systems_lock);
 223         fs = *(find_filesystem(name));
 224         if (fs && !try_module_get(fs->owner))
 225                 fs = NULL;
 226         read_unlock(&file_systems_lock);
 227         if (!fs && (request_module("%s", name) == 0)) {
 228                 read_lock(&file_systems_lock);
 229                 fs = *(find_filesystem(name));
 230                 if (fs && !try_module_get(fs->owner))
 231                         fs = NULL;
 232                 read_unlock(&file_systems_lock);
 233         }
 234         return fs;
 235 }
 236
 237 EXPORT_SYMBOL(get_fs_type);