linux/fs/filesystems.c
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   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 <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
  32static struct file_system_type *file_systems;
  33static DEFINE_RWLOCK(file_systems_lock);
  34
  35/* WARNING: This can be used only if we _already_ own a reference */
  36void get_filesystem(struct file_system_type *fs)
  37{
  38        __module_get(fs->owner);
  39}
  40
  41void put_filesystem(struct file_system_type *fs)
  42{
  43        module_put(fs->owner);
  44}
  45
  46static 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 
  69int 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
  88EXPORT_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 
 102int 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                        synchronize_rcu();
 114                        return 0;
 115                }
 116                tmp = &(*tmp)->next;
 117        }
 118        write_unlock(&file_systems_lock);
 119
 120        return -EINVAL;
 121}
 122
 123EXPORT_SYMBOL(unregister_filesystem);
 124
 125static int fs_index(const char __user * __name)
 126{
 127        struct file_system_type * tmp;
 128        char * 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) == 0) {
 140                        err = index;
 141                        break;
 142                }
 143        }
 144        read_unlock(&file_systems_lock);
 145        putname(name);
 146        return err;
 147}
 148
 149static 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
 169static 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 */
 184SYSCALL_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
 204int __init get_filesystem_list(char *buf)
 205{
 206        int len = 0;
 207        struct file_system_type * tmp;
 208
 209        read_lock(&file_systems_lock);
 210        tmp = file_systems;
 211        while (tmp && len < PAGE_SIZE - 80) {
 212                len += sprintf(buf+len, "%s\t%s\n",
 213                        (tmp->fs_flags & FS_REQUIRES_DEV) ? "" : "nodev",
 214                        tmp->name);
 215                tmp = tmp->next;
 216        }
 217        read_unlock(&file_systems_lock);
 218        return len;
 219}
 220
 221#ifdef CONFIG_PROC_FS
 222static int filesystems_proc_show(struct seq_file *m, void *v)
 223{
 224        struct file_system_type * tmp;
 225
 226        read_lock(&file_systems_lock);
 227        tmp = file_systems;
 228        while (tmp) {
 229                seq_printf(m, "%s\t%s\n",
 230                        (tmp->fs_flags & FS_REQUIRES_DEV) ? "" : "nodev",
 231                        tmp->name);
 232                tmp = tmp->next;
 233        }
 234        read_unlock(&file_systems_lock);
 235        return 0;
 236}
 237
 238static int filesystems_proc_open(struct inode *inode, struct file *file)
 239{
 240        return single_open(file, filesystems_proc_show, NULL);
 241}
 242
 243static const struct file_operations filesystems_proc_fops = {
 244        .open           = filesystems_proc_open,
 245        .read           = seq_read,
 246        .llseek         = seq_lseek,
 247        .release        = single_release,
 248};
 249
 250static int __init proc_filesystems_init(void)
 251{
 252        proc_create("filesystems", 0, NULL, &filesystems_proc_fops);
 253        return 0;
 254}
 255module_init(proc_filesystems_init);
 256#endif
 257
 258static struct file_system_type *__get_fs_type(const char *name, int len)
 259{
 260        struct file_system_type *fs;
 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        return fs;
 268}
 269
 270struct file_system_type *get_fs_type(const char *name)
 271{
 272        struct file_system_type *fs;
 273        const char *dot = strchr(name, '.');
 274        int len = dot ? dot - name : strlen(name);
 275
 276        fs = __get_fs_type(name, len);
 277        if (!fs && (request_module("%.*s", len, name) == 0))
 278                fs = __get_fs_type(name, len);
 279
 280        if (dot && fs && !(fs->fs_flags & FS_HAS_SUBTYPE)) {
 281                put_filesystem(fs);
 282                fs = NULL;
 283        }
 284        return fs;
 285}
 286
 287EXPORT_SYMBOL(get_fs_type);
 288
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