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                        return 0;
 114                }
 115                tmp = &(*tmp)->next;
 116        }
 117        write_unlock(&file_systems_lock);
 118        return -EINVAL;
 119}
 120
 121EXPORT_SYMBOL(unregister_filesystem);
 122
 123static 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
 147static 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
 167static 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 */
 182SYSCALL_DEFINE3(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
 202int __init 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
 220static 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
 236static int filesystems_proc_open(struct inode *inode, struct file *file)
 237{
 238        return single_open(file, filesystems_proc_show, NULL);
 239}
 240
 241static 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
 248static int __init proc_filesystems_init(void)
 249{
 250        proc_create("filesystems", 0, NULL, &filesystems_proc_fops);
 251        return 0;
 252}
 253module_init(proc_filesystems_init);
 254#endif
 255
 256static struct file_system_type *__get_fs_type(const char *name, int len)
 257{
 258        struct file_system_type *fs;
 259
 260        read_lock(&file_systems_lock);
 261        fs = *(find_filesystem(name, len));
 262        if (fs && !try_module_get(fs->owner))
 263                fs = NULL;
 264        read_unlock(&file_systems_lock);
 265        return fs;
 266}
 267
 268struct file_system_type *get_fs_type(const char *name)
 269{
 270        struct file_system_type *fs;
 271        const char *dot = strchr(name, '.');
 272        int len = dot ? dot - name : strlen(name);
 273
 274        fs = __get_fs_type(name, len);
 275        if (!fs && (request_module("%.*s", len, name) == 0))
 276                fs = __get_fs_type(name, len);
 277
 278        if (dot && fs && !(fs->fs_flags & FS_HAS_SUBTYPE)) {
 279                put_filesystem(fs);
 280                fs = NULL;
 281        }
 282        return fs;
 283}
 284
 285EXPORT_SYMBOL(get_fs_type);
 286
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