3 * Copyright (C) 2011 Novell Inc.
5 * This program is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 as published by
7 * the Free Software Foundation.
10 #include <uapi/linux/magic.h>
12 #include <linux/namei.h>
13 #include <linux/xattr.h>
14 #include <linux/mount.h>
15 #include <linux/parser.h>
16 #include <linux/module.h>
17 #include <linux/statfs.h>
18 #include <linux/seq_file.h>
19 #include <linux/posix_acl_xattr.h>
20 #include "overlayfs.h"
21 #include "ovl_entry.h"
23 MODULE_AUTHOR("Miklos Szeredi <miklos@szeredi.hu>");
24 MODULE_DESCRIPTION("Overlay filesystem");
25 MODULE_LICENSE("GPL");
30 #define OVL_MAX_STACK 500
32 static bool ovl_redirect_dir_def = IS_ENABLED(CONFIG_OVERLAY_FS_REDIRECT_DIR);
33 module_param_named(redirect_dir, ovl_redirect_dir_def, bool, 0644);
34 MODULE_PARM_DESC(ovl_redirect_dir_def,
35 "Default to on or off for the redirect_dir feature");
37 static void ovl_dentry_release(struct dentry *dentry)
39 struct ovl_entry *oe = dentry->d_fsdata;
44 dput(oe->__upperdentry);
46 for (i = 0; i < oe->numlower; i++)
47 dput(oe->lowerstack[i].dentry);
52 static struct dentry *ovl_d_real(struct dentry *dentry,
53 const struct inode *inode,
54 unsigned int open_flags)
58 if (!d_is_reg(dentry)) {
59 if (!inode || inode == d_inode(dentry))
64 if (d_is_negative(dentry))
68 int err = ovl_open_maybe_copy_up(dentry, open_flags);
74 real = ovl_dentry_upper(dentry);
75 if (real && (!inode || inode == d_inode(real)))
78 real = ovl_dentry_lower(dentry);
82 /* Handle recursion */
83 real = d_real(real, inode, open_flags);
85 if (!inode || inode == d_inode(real))
88 WARN(1, "ovl_d_real(%pd4, %s:%lu): real dentry not found\n", dentry,
89 inode ? inode->i_sb->s_id : "NULL", inode ? inode->i_ino : 0);
93 static int ovl_dentry_revalidate(struct dentry *dentry, unsigned int flags)
95 struct ovl_entry *oe = dentry->d_fsdata;
99 for (i = 0; i < oe->numlower; i++) {
100 struct dentry *d = oe->lowerstack[i].dentry;
102 if (d->d_flags & DCACHE_OP_REVALIDATE) {
103 ret = d->d_op->d_revalidate(d, flags);
107 if (!(flags & LOOKUP_RCU))
116 static int ovl_dentry_weak_revalidate(struct dentry *dentry, unsigned int flags)
118 struct ovl_entry *oe = dentry->d_fsdata;
122 for (i = 0; i < oe->numlower; i++) {
123 struct dentry *d = oe->lowerstack[i].dentry;
125 if (d->d_flags & DCACHE_OP_WEAK_REVALIDATE) {
126 ret = d->d_op->d_weak_revalidate(d, flags);
134 static const struct dentry_operations ovl_dentry_operations = {
135 .d_release = ovl_dentry_release,
136 .d_real = ovl_d_real,
139 static const struct dentry_operations ovl_reval_dentry_operations = {
140 .d_release = ovl_dentry_release,
141 .d_real = ovl_d_real,
142 .d_revalidate = ovl_dentry_revalidate,
143 .d_weak_revalidate = ovl_dentry_weak_revalidate,
146 static void ovl_put_super(struct super_block *sb)
148 struct ovl_fs *ufs = sb->s_fs_info;
152 mntput(ufs->upper_mnt);
153 for (i = 0; i < ufs->numlower; i++)
154 mntput(ufs->lower_mnt[i]);
155 kfree(ufs->lower_mnt);
157 kfree(ufs->config.lowerdir);
158 kfree(ufs->config.upperdir);
159 kfree(ufs->config.workdir);
160 put_cred(ufs->creator_cred);
164 static int ovl_sync_fs(struct super_block *sb, int wait)
166 struct ovl_fs *ufs = sb->s_fs_info;
167 struct super_block *upper_sb;
172 upper_sb = ufs->upper_mnt->mnt_sb;
173 if (!upper_sb->s_op->sync_fs)
176 /* real inodes have already been synced by sync_filesystem(ovl_sb) */
177 down_read(&upper_sb->s_umount);
178 ret = upper_sb->s_op->sync_fs(upper_sb, wait);
179 up_read(&upper_sb->s_umount);
185 * @sb: The overlayfs super block
186 * @buf: The struct kstatfs to fill in with stats
188 * Get the filesystem statistics. As writes always target the upper layer
189 * filesystem pass the statfs to the upper filesystem (if it exists)
191 static int ovl_statfs(struct dentry *dentry, struct kstatfs *buf)
193 struct ovl_fs *ofs = dentry->d_sb->s_fs_info;
194 struct dentry *root_dentry = dentry->d_sb->s_root;
198 ovl_path_real(root_dentry, &path);
200 err = vfs_statfs(&path, buf);
202 buf->f_namelen = ofs->namelen;
203 buf->f_type = OVERLAYFS_SUPER_MAGIC;
212 * Prints the mount options for a given superblock.
213 * Returns zero; does not fail.
215 static int ovl_show_options(struct seq_file *m, struct dentry *dentry)
217 struct super_block *sb = dentry->d_sb;
218 struct ovl_fs *ufs = sb->s_fs_info;
220 seq_show_option(m, "lowerdir", ufs->config.lowerdir);
221 if (ufs->config.upperdir) {
222 seq_show_option(m, "upperdir", ufs->config.upperdir);
223 seq_show_option(m, "workdir", ufs->config.workdir);
225 if (ufs->config.default_permissions)
226 seq_puts(m, ",default_permissions");
227 if (ufs->config.redirect_dir != ovl_redirect_dir_def)
228 seq_printf(m, ",redirect_dir=%s",
229 ufs->config.redirect_dir ? "on" : "off");
233 static int ovl_remount(struct super_block *sb, int *flags, char *data)
235 struct ovl_fs *ufs = sb->s_fs_info;
237 if (!(*flags & MS_RDONLY) && (!ufs->upper_mnt || !ufs->workdir))
243 static const struct super_operations ovl_super_operations = {
244 .put_super = ovl_put_super,
245 .sync_fs = ovl_sync_fs,
246 .statfs = ovl_statfs,
247 .show_options = ovl_show_options,
248 .remount_fs = ovl_remount,
249 .drop_inode = generic_delete_inode,
256 OPT_DEFAULT_PERMISSIONS,
258 OPT_REDIRECT_DIR_OFF,
262 static const match_table_t ovl_tokens = {
263 {OPT_LOWERDIR, "lowerdir=%s"},
264 {OPT_UPPERDIR, "upperdir=%s"},
265 {OPT_WORKDIR, "workdir=%s"},
266 {OPT_DEFAULT_PERMISSIONS, "default_permissions"},
267 {OPT_REDIRECT_DIR_ON, "redirect_dir=on"},
268 {OPT_REDIRECT_DIR_OFF, "redirect_dir=off"},
272 static char *ovl_next_opt(char **s)
280 for (p = sbegin; *p; p++) {
285 } else if (*p == ',') {
295 static int ovl_parse_opt(char *opt, struct ovl_config *config)
299 while ((p = ovl_next_opt(&opt)) != NULL) {
301 substring_t args[MAX_OPT_ARGS];
306 token = match_token(p, ovl_tokens, args);
309 kfree(config->upperdir);
310 config->upperdir = match_strdup(&args[0]);
311 if (!config->upperdir)
316 kfree(config->lowerdir);
317 config->lowerdir = match_strdup(&args[0]);
318 if (!config->lowerdir)
323 kfree(config->workdir);
324 config->workdir = match_strdup(&args[0]);
325 if (!config->workdir)
329 case OPT_DEFAULT_PERMISSIONS:
330 config->default_permissions = true;
333 case OPT_REDIRECT_DIR_ON:
334 config->redirect_dir = true;
337 case OPT_REDIRECT_DIR_OFF:
338 config->redirect_dir = false;
342 pr_err("overlayfs: unrecognized mount option \"%s\" or missing value\n", p);
347 /* Workdir is useless in non-upper mount */
348 if (!config->upperdir && config->workdir) {
349 pr_info("overlayfs: option \"workdir=%s\" is useless in a non-upper mount, ignore\n",
351 kfree(config->workdir);
352 config->workdir = NULL;
358 #define OVL_WORKDIR_NAME "work"
360 static struct dentry *ovl_workdir_create(struct vfsmount *mnt,
361 struct dentry *dentry)
363 struct inode *dir = dentry->d_inode;
366 bool retried = false;
368 err = mnt_want_write(mnt);
372 inode_lock_nested(dir, I_MUTEX_PARENT);
374 work = lookup_one_len(OVL_WORKDIR_NAME, dentry,
375 strlen(OVL_WORKDIR_NAME));
378 struct iattr attr = {
379 .ia_valid = ATTR_MODE,
380 .ia_mode = S_IFDIR | 0,
389 ovl_workdir_cleanup(dir, mnt, work, 0);
394 err = ovl_create_real(dir, work,
395 &(struct cattr){.mode = S_IFDIR | 0},
401 * Try to remove POSIX ACL xattrs from workdir. We are good if:
403 * a) success (there was a POSIX ACL xattr and was removed)
404 * b) -ENODATA (there was no POSIX ACL xattr)
405 * c) -EOPNOTSUPP (POSIX ACL xattrs are not supported)
407 * There are various other error values that could effectively
408 * mean that the xattr doesn't exist (e.g. -ERANGE is returned
409 * if the xattr name is too long), but the set of filesystems
410 * allowed as upper are limited to "normal" ones, where checking
411 * for the above two errors is sufficient.
413 err = vfs_removexattr(work, XATTR_NAME_POSIX_ACL_DEFAULT);
414 if (err && err != -ENODATA && err != -EOPNOTSUPP)
417 err = vfs_removexattr(work, XATTR_NAME_POSIX_ACL_ACCESS);
418 if (err && err != -ENODATA && err != -EOPNOTSUPP)
421 /* Clear any inherited mode bits */
422 inode_lock(work->d_inode);
423 err = notify_change(work, &attr, NULL);
424 inode_unlock(work->d_inode);
440 static void ovl_unescape(char *s)
453 static int ovl_mount_dir_noesc(const char *name, struct path *path)
458 pr_err("overlayfs: empty lowerdir\n");
461 err = kern_path(name, LOOKUP_FOLLOW, path);
463 pr_err("overlayfs: failed to resolve '%s': %i\n", name, err);
467 if (ovl_dentry_weird(path->dentry)) {
468 pr_err("overlayfs: filesystem on '%s' not supported\n", name);
471 if (!d_is_dir(path->dentry)) {
472 pr_err("overlayfs: '%s' not a directory\n", name);
483 static int ovl_mount_dir(const char *name, struct path *path)
486 char *tmp = kstrdup(name, GFP_KERNEL);
490 err = ovl_mount_dir_noesc(tmp, path);
493 if (ovl_dentry_remote(path->dentry)) {
494 pr_err("overlayfs: filesystem on '%s' not supported as upperdir\n",
504 static int ovl_check_namelen(struct path *path, struct ovl_fs *ofs,
507 struct kstatfs statfs;
508 int err = vfs_statfs(path, &statfs);
511 pr_err("overlayfs: statfs failed on '%s'\n", name);
513 ofs->namelen = max(ofs->namelen, statfs.f_namelen);
518 static int ovl_lower_dir(const char *name, struct path *path,
519 struct ovl_fs *ofs, int *stack_depth, bool *remote)
523 err = ovl_mount_dir_noesc(name, path);
527 err = ovl_check_namelen(path, ofs, name);
531 *stack_depth = max(*stack_depth, path->mnt->mnt_sb->s_stack_depth);
533 if (ovl_dentry_remote(path->dentry))
544 /* Workdir should not be subdir of upperdir and vice versa */
545 static bool ovl_workdir_ok(struct dentry *workdir, struct dentry *upperdir)
549 if (workdir != upperdir) {
550 ok = (lock_rename(workdir, upperdir) == NULL);
551 unlock_rename(workdir, upperdir);
556 static unsigned int ovl_split_lowerdirs(char *str)
558 unsigned int ctr = 1;
561 for (s = d = str;; s++, d++) {
564 } else if (*s == ':') {
576 static int __maybe_unused
577 ovl_posix_acl_xattr_get(const struct xattr_handler *handler,
578 struct dentry *dentry, struct inode *inode,
579 const char *name, void *buffer, size_t size)
581 return ovl_xattr_get(dentry, handler->name, buffer, size);
584 static int __maybe_unused
585 ovl_posix_acl_xattr_set(const struct xattr_handler *handler,
586 struct dentry *dentry, struct inode *inode,
587 const char *name, const void *value,
588 size_t size, int flags)
590 struct dentry *workdir = ovl_workdir(dentry);
591 struct inode *realinode = ovl_inode_real(inode, NULL);
592 struct posix_acl *acl = NULL;
595 /* Check that everything is OK before copy-up */
597 acl = posix_acl_from_xattr(&init_user_ns, value, size);
602 if (!IS_POSIXACL(d_inode(workdir)))
603 goto out_acl_release;
604 if (!realinode->i_op->set_acl)
605 goto out_acl_release;
606 if (handler->flags == ACL_TYPE_DEFAULT && !S_ISDIR(inode->i_mode)) {
607 err = acl ? -EACCES : 0;
608 goto out_acl_release;
611 if (!inode_owner_or_capable(inode))
612 goto out_acl_release;
614 posix_acl_release(acl);
617 * Check if sgid bit needs to be cleared (actual setacl operation will
618 * be done with mounter's capabilities and so that won't do it for us).
620 if (unlikely(inode->i_mode & S_ISGID) &&
621 handler->flags == ACL_TYPE_ACCESS &&
622 !in_group_p(inode->i_gid) &&
623 !capable_wrt_inode_uidgid(inode, CAP_FSETID)) {
624 struct iattr iattr = { .ia_valid = ATTR_KILL_SGID };
626 err = ovl_setattr(dentry, &iattr);
631 err = ovl_xattr_set(dentry, handler->name, value, size, flags);
633 ovl_copyattr(ovl_inode_real(inode, NULL), inode);
638 posix_acl_release(acl);
642 static int ovl_own_xattr_get(const struct xattr_handler *handler,
643 struct dentry *dentry, struct inode *inode,
644 const char *name, void *buffer, size_t size)
649 static int ovl_own_xattr_set(const struct xattr_handler *handler,
650 struct dentry *dentry, struct inode *inode,
651 const char *name, const void *value,
652 size_t size, int flags)
657 static int ovl_other_xattr_get(const struct xattr_handler *handler,
658 struct dentry *dentry, struct inode *inode,
659 const char *name, void *buffer, size_t size)
661 return ovl_xattr_get(dentry, name, buffer, size);
664 static int ovl_other_xattr_set(const struct xattr_handler *handler,
665 struct dentry *dentry, struct inode *inode,
666 const char *name, const void *value,
667 size_t size, int flags)
669 return ovl_xattr_set(dentry, name, value, size, flags);
672 static const struct xattr_handler __maybe_unused
673 ovl_posix_acl_access_xattr_handler = {
674 .name = XATTR_NAME_POSIX_ACL_ACCESS,
675 .flags = ACL_TYPE_ACCESS,
676 .get = ovl_posix_acl_xattr_get,
677 .set = ovl_posix_acl_xattr_set,
680 static const struct xattr_handler __maybe_unused
681 ovl_posix_acl_default_xattr_handler = {
682 .name = XATTR_NAME_POSIX_ACL_DEFAULT,
683 .flags = ACL_TYPE_DEFAULT,
684 .get = ovl_posix_acl_xattr_get,
685 .set = ovl_posix_acl_xattr_set,
688 static const struct xattr_handler ovl_own_xattr_handler = {
689 .prefix = OVL_XATTR_PREFIX,
690 .get = ovl_own_xattr_get,
691 .set = ovl_own_xattr_set,
694 static const struct xattr_handler ovl_other_xattr_handler = {
695 .prefix = "", /* catch all */
696 .get = ovl_other_xattr_get,
697 .set = ovl_other_xattr_set,
700 static const struct xattr_handler *ovl_xattr_handlers[] = {
701 #ifdef CONFIG_FS_POSIX_ACL
702 &ovl_posix_acl_access_xattr_handler,
703 &ovl_posix_acl_default_xattr_handler,
705 &ovl_own_xattr_handler,
706 &ovl_other_xattr_handler,
710 static int ovl_fill_super(struct super_block *sb, void *data, int silent)
712 struct path upperpath = { NULL, NULL };
713 struct path workpath = { NULL, NULL };
714 struct dentry *root_dentry;
715 struct inode *realinode;
716 struct ovl_entry *oe;
718 struct path *stack = NULL;
721 unsigned int numlower;
722 unsigned int stacklen = 0;
729 ufs = kzalloc(sizeof(struct ovl_fs), GFP_KERNEL);
733 init_waitqueue_head(&ufs->copyup_wq);
734 ufs->config.redirect_dir = ovl_redirect_dir_def;
735 err = ovl_parse_opt((char *) data, &ufs->config);
737 goto out_free_config;
740 if (!ufs->config.lowerdir) {
742 pr_err("overlayfs: missing 'lowerdir'\n");
743 goto out_free_config;
746 sb->s_stack_depth = 0;
747 sb->s_maxbytes = MAX_LFS_FILESIZE;
748 if (ufs->config.upperdir) {
749 if (!ufs->config.workdir) {
750 pr_err("overlayfs: missing 'workdir'\n");
751 goto out_free_config;
754 err = ovl_mount_dir(ufs->config.upperdir, &upperpath);
756 goto out_free_config;
758 /* Upper fs should not be r/o */
759 if (upperpath.mnt->mnt_sb->s_flags & MS_RDONLY) {
760 pr_err("overlayfs: upper fs is r/o, try multi-lower layers mount\n");
762 goto out_put_upperpath;
765 err = ovl_check_namelen(&upperpath, ufs, ufs->config.upperdir);
767 goto out_put_upperpath;
769 err = ovl_mount_dir(ufs->config.workdir, &workpath);
771 goto out_put_upperpath;
774 if (upperpath.mnt != workpath.mnt) {
775 pr_err("overlayfs: workdir and upperdir must reside under the same mount\n");
776 goto out_put_workpath;
778 if (!ovl_workdir_ok(workpath.dentry, upperpath.dentry)) {
779 pr_err("overlayfs: workdir and upperdir must be separate subtrees\n");
780 goto out_put_workpath;
782 sb->s_stack_depth = upperpath.mnt->mnt_sb->s_stack_depth;
785 lowertmp = kstrdup(ufs->config.lowerdir, GFP_KERNEL);
787 goto out_put_workpath;
790 stacklen = ovl_split_lowerdirs(lowertmp);
791 if (stacklen > OVL_MAX_STACK) {
792 pr_err("overlayfs: too many lower directories, limit is %d\n",
794 goto out_free_lowertmp;
795 } else if (!ufs->config.upperdir && stacklen == 1) {
796 pr_err("overlayfs: at least 2 lowerdir are needed while upperdir nonexistent\n");
797 goto out_free_lowertmp;
801 stack = kcalloc(stacklen, sizeof(struct path), GFP_KERNEL);
803 goto out_free_lowertmp;
807 for (numlower = 0; numlower < stacklen; numlower++) {
808 err = ovl_lower_dir(lower, &stack[numlower], ufs,
809 &sb->s_stack_depth, &remote);
811 goto out_put_lowerpath;
813 lower = strchr(lower, '\0') + 1;
818 if (sb->s_stack_depth > FILESYSTEM_MAX_STACK_DEPTH) {
819 pr_err("overlayfs: maximum fs stacking depth exceeded\n");
820 goto out_put_lowerpath;
823 if (ufs->config.upperdir) {
824 ufs->upper_mnt = clone_private_mount(&upperpath);
825 err = PTR_ERR(ufs->upper_mnt);
826 if (IS_ERR(ufs->upper_mnt)) {
827 pr_err("overlayfs: failed to clone upperpath\n");
828 goto out_put_lowerpath;
830 /* Don't inherit atime flags */
831 ufs->upper_mnt->mnt_flags &= ~(MNT_NOATIME | MNT_NODIRATIME | MNT_RELATIME);
833 sb->s_time_gran = ufs->upper_mnt->mnt_sb->s_time_gran;
835 ufs->workdir = ovl_workdir_create(ufs->upper_mnt, workpath.dentry);
836 err = PTR_ERR(ufs->workdir);
837 if (IS_ERR(ufs->workdir)) {
838 pr_warn("overlayfs: failed to create directory %s/%s (errno: %i); mounting read-only\n",
839 ufs->config.workdir, OVL_WORKDIR_NAME, -err);
840 sb->s_flags |= MS_RDONLY;
845 * Upper should support d_type, else whiteouts are visible.
846 * Given workdir and upper are on same fs, we can do
847 * iterate_dir() on workdir. This check requires successful
848 * creation of workdir in previous step.
853 err = ovl_check_d_type_supported(&workpath);
855 goto out_put_workdir;
858 * We allowed this configuration and don't want to
859 * break users over kernel upgrade. So warn instead
863 pr_warn("overlayfs: upper fs needs to support d_type.\n");
865 /* Check if upper/work fs supports O_TMPFILE */
866 temp = ovl_do_tmpfile(ufs->workdir, S_IFREG | 0);
867 ufs->tmpfile = !IS_ERR(temp);
871 pr_warn("overlayfs: upper fs does not support tmpfile.\n");
876 ufs->lower_mnt = kcalloc(numlower, sizeof(struct vfsmount *), GFP_KERNEL);
877 if (ufs->lower_mnt == NULL)
878 goto out_put_workdir;
879 for (i = 0; i < numlower; i++) {
880 struct vfsmount *mnt = clone_private_mount(&stack[i]);
884 pr_err("overlayfs: failed to clone lowerpath\n");
885 goto out_put_lower_mnt;
888 * Make lower_mnt R/O. That way fchmod/fchown on lower file
889 * will fail instead of modifying lower fs.
891 mnt->mnt_flags |= MNT_READONLY | MNT_NOATIME;
893 ufs->lower_mnt[ufs->numlower] = mnt;
897 /* If the upper fs is nonexistent, we mark overlayfs r/o too */
899 sb->s_flags |= MS_RDONLY;
902 sb->s_d_op = &ovl_reval_dentry_operations;
904 sb->s_d_op = &ovl_dentry_operations;
906 ufs->creator_cred = cred = prepare_creds();
908 goto out_put_lower_mnt;
910 /* Never override disk quota limits or use reserved space */
911 cap_lower(cred->cap_effective, CAP_SYS_RESOURCE);
914 oe = ovl_alloc_entry(numlower);
918 sb->s_magic = OVERLAYFS_SUPER_MAGIC;
919 sb->s_op = &ovl_super_operations;
920 sb->s_xattr = ovl_xattr_handlers;
922 sb->s_flags |= MS_POSIXACL | MS_NOREMOTELOCK;
924 root_dentry = d_make_root(ovl_new_inode(sb, S_IFDIR, 0));
928 mntput(upperpath.mnt);
929 for (i = 0; i < numlower; i++)
930 mntput(stack[i].mnt);
934 oe->__upperdentry = upperpath.dentry;
935 for (i = 0; i < numlower; i++) {
936 oe->lowerstack[i].dentry = stack[i].dentry;
937 oe->lowerstack[i].mnt = ufs->lower_mnt[i];
941 root_dentry->d_fsdata = oe;
943 realinode = d_inode(ovl_dentry_real(root_dentry));
944 ovl_inode_init(d_inode(root_dentry), realinode, !!upperpath.dentry);
945 ovl_copyattr(realinode, d_inode(root_dentry));
947 sb->s_root = root_dentry;
954 put_cred(ufs->creator_cred);
956 for (i = 0; i < ufs->numlower; i++)
957 mntput(ufs->lower_mnt[i]);
958 kfree(ufs->lower_mnt);
961 mntput(ufs->upper_mnt);
963 for (i = 0; i < numlower; i++)
971 path_put(&upperpath);
973 kfree(ufs->config.lowerdir);
974 kfree(ufs->config.upperdir);
975 kfree(ufs->config.workdir);
981 static struct dentry *ovl_mount(struct file_system_type *fs_type, int flags,
982 const char *dev_name, void *raw_data)
984 return mount_nodev(fs_type, flags, raw_data, ovl_fill_super);
987 static struct file_system_type ovl_fs_type = {
988 .owner = THIS_MODULE,
991 .kill_sb = kill_anon_super,
993 MODULE_ALIAS_FS("overlay");
995 static int __init ovl_init(void)
997 return register_filesystem(&ovl_fs_type);
1000 static void __exit ovl_exit(void)
1002 unregister_filesystem(&ovl_fs_type);
1005 module_init(ovl_init);
1006 module_exit(ovl_exit);