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        write_lock(&file_systems_lock);
  78        p = find_filesystem(fs->name, strlen(fs->name));
  79        if (*p)
  80                res = -EBUSY;
  81        else
  82                *p = fs;
  83        write_unlock(&file_systems_lock);
  84        return res;
  85}
  86
  87EXPORT_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 
 101int 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                        synchronize_rcu();
 113                        return 0;
 114                }
 115                tmp = &(*tmp)->next;
 116        }
 117        write_unlock(&file_systems_lock);
 118
 119        return -EINVAL;
 120}
 121
 122EXPORT_SYMBOL(unregister_filesystem);
 123
 124static int fs_index(const char __user * __name)
 125{
 126        struct file_system_type * tmp;
 127        char * name;
 128        int err, index;
 129
 130        name = getname(__name);
 131        err = PTR_ERR(name);
 132        if (IS_ERR(name))
 133                return err;
 134
 135        err = -EINVAL;
 136        read_lock(&file_systems_lock);
 137        for (tmp=file_systems, index=0 ; tmp ; tmp=tmp->next, index++) {
 138                if (strcmp(tmp->name,name) == 0) {
 139                        err = index;
 140                        break;
 141                }
 142        }
 143        read_unlock(&file_systems_lock);
 144        putname(name);
 145        return err;
 146}
 147
 148static int fs_name(unsigned int index, char __user * buf)
 149{
 150        struct file_system_type * tmp;
 151        int len, res;
 152
 153        read_lock(&file_systems_lock);
 154        for (tmp = file_systems; tmp; tmp = tmp->next, index--)
 155                if (index <= 0 && try_module_get(tmp->owner))
 156                        break;
 157        read_unlock(&file_systems_lock);
 158        if (!tmp)
 159                return -EINVAL;
 160
 161        /* OK, we got the reference, so we can safely block */
 162        len = strlen(tmp->name) + 1;
 163        res = copy_to_user(buf, tmp->name, len) ? -EFAULT : 0;
 164        put_filesystem(tmp);
 165        return res;
 166}
 167
 168static int fs_maxindex(void)
 169{
 170        struct file_system_type * tmp;
 171        int index;
 172
 173        read_lock(&file_systems_lock);
 174        for (tmp = file_systems, index = 0 ; tmp ; tmp = tmp->next, index++)
 175                ;
 176        read_unlock(&file_systems_lock);
 177        return index;
 178}
 179
 180/*
 181 * Whee.. Weird sysv syscall. 
 182 */
 183SYSCALL_DEFINE3(sysfs, int, option, unsigned long, arg1, unsigned long, arg2)
 184{
 185        int retval = -EINVAL;
 186
 187        switch (option) {
 188                case 1:
 189                        retval = fs_index((const char __user *) arg1);
 190                        break;
 191
 192                case 2:
 193                        retval = fs_name(arg1, (char __user *) arg2);
 194                        break;
 195
 196                case 3:
 197                        retval = fs_maxindex();
 198                        break;
 199        }
 200        return retval;
 201}
 202
 203int __init get_filesystem_list(char *buf)
 204{
 205        int len = 0;
 206        struct file_system_type * tmp;
 207
 208        read_lock(&file_systems_lock);
 209        tmp = file_systems;
 210        while (tmp && len < PAGE_SIZE - 80) {
 211                len += sprintf(buf+len, "%s\t%s\n",
 212                        (tmp->fs_flags & FS_REQUIRES_DEV) ? "" : "nodev",
 213                        tmp->name);
 214                tmp = tmp->next;
 215        }
 216        read_unlock(&file_systems_lock);
 217        return len;
 218}
 219
 220#ifdef CONFIG_PROC_FS
 221static int filesystems_proc_show(struct seq_file *m, void *v)
 222{
 223        struct file_system_type * tmp;
 224
 225        read_lock(&file_systems_lock);
 226        tmp = file_systems;
 227        while (tmp) {
 228                seq_printf(m, "%s\t%s\n",
 229                        (tmp->fs_flags & FS_REQUIRES_DEV) ? "" : "nodev",
 230                        tmp->name);
 231                tmp = tmp->next;
 232        }
 233        read_unlock(&file_systems_lock);
 234        return 0;
 235}
 236
 237static int filesystems_proc_open(struct inode *inode, struct file *file)
 238{
 239        return single_open(file, filesystems_proc_show, NULL);
 240}
 241
 242static const struct file_operations filesystems_proc_fops = {
 243        .open           = filesystems_proc_open,
 244        .read           = seq_read,
 245        .llseek         = seq_lseek,
 246        .release        = single_release,
 247};
 248
 249static int __init proc_filesystems_init(void)
 250{
 251        proc_create("filesystems", 0, NULL, &filesystems_proc_fops);
 252        return 0;
 253}
 254module_init(proc_filesystems_init);
 255#endif
 256
 257static struct file_system_type *__get_fs_type(const char *name, int len)
 258{
 259        struct file_system_type *fs;
 260
 261        read_lock(&file_systems_lock);
 262        fs = *(find_filesystem(name, len));
 263        if (fs && !try_module_get(fs->owner))
 264                fs = NULL;
 265        read_unlock(&file_systems_lock);
 266        return fs;
 267}
 268
 269struct file_system_type *get_fs_type(const char *name)
 270{
 271        struct file_system_type *fs;
 272        const char *dot = strchr(name, '.');
 273        int len = dot ? dot - name : strlen(name);
 274
 275        fs = __get_fs_type(name, len);
 276        if (!fs && (request_module("%.*s", len, name) == 0))
 277                fs = __get_fs_type(name, len);
 278
 279        if (dot && fs && !(fs->fs_flags & FS_HAS_SUBTYPE)) {
 280                put_filesystem(fs);
 281                fs = NULL;
 282        }
 283        return fs;
 284}
 285
 286EXPORT_SYMBOL(get_fs_type);
 287
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