[linux-2.6-block.git] / fs / overlayfs / super.c

/*
 *
 * Copyright (C) 2011 Novell Inc.
 *
 * This program is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 as published by
 * the Free Software Foundation.
 */

#include <linux/fs.h>
#include <linux/namei.h>
#include <linux/xattr.h>
#include <linux/security.h>
#include <linux/mount.h>
#include <linux/slab.h>
#include <linux/parser.h>
#include <linux/module.h>
#include <linux/sched.h>
#include <linux/statfs.h>
#include <linux/seq_file.h>
#include "overlayfs.h"

MODULE_AUTHOR("Miklos Szeredi <miklos@szeredi.hu>");
MODULE_DESCRIPTION("Overlay filesystem");
MODULE_LICENSE("GPL");

#define OVERLAYFS_SUPER_MAGIC 0x794c7630

struct ovl_config {
	char *lowerdir;
	char *upperdir;
	char *workdir;
};

/* private information held for overlayfs's superblock */
struct ovl_fs {
	struct vfsmount *upper_mnt;
	struct vfsmount *lower_mnt;
	struct dentry *workdir;
	long lower_namelen;
	/* pathnames of lower and upper dirs, for show_options */
	struct ovl_config config;
};

struct ovl_dir_cache;

/* private information held for every overlayfs dentry */
struct ovl_entry {
	struct dentry *__upperdentry;
	struct dentry *lowerdentry;
	struct ovl_dir_cache *cache;
	union {
		struct {
			u64 version;
			bool opaque;
		};
		struct rcu_head rcu;
	};
};

const char *ovl_opaque_xattr = "trusted.overlay.opaque";


enum ovl_path_type ovl_path_type(struct dentry *dentry)
{
	struct ovl_entry *oe = dentry->d_fsdata;

	if (oe->__upperdentry) {
		if (oe->lowerdentry) {
			if (S_ISDIR(dentry->d_inode->i_mode))
				return OVL_PATH_MERGE;
			else
				return OVL_PATH_UPPER;
		} else {
			if (oe->opaque)
				return OVL_PATH_UPPER;
			else
				return OVL_PATH_PURE_UPPER;
		}
	} else {
		return OVL_PATH_LOWER;
	}
}

static struct dentry *ovl_upperdentry_dereference(struct ovl_entry *oe)
{
	struct dentry *upperdentry = ACCESS_ONCE(oe->__upperdentry);
	/*
	 * Make sure to order reads to upperdentry wrt ovl_dentry_update()
	 */
	smp_read_barrier_depends();
	return upperdentry;
}

void ovl_path_upper(struct dentry *dentry, struct path *path)
{
	struct ovl_fs *ofs = dentry->d_sb->s_fs_info;
	struct ovl_entry *oe = dentry->d_fsdata;

	path->mnt = ofs->upper_mnt;
	path->dentry = ovl_upperdentry_dereference(oe);
}

enum ovl_path_type ovl_path_real(struct dentry *dentry, struct path *path)
{

	enum ovl_path_type type = ovl_path_type(dentry);

	if (type == OVL_PATH_LOWER)
		ovl_path_lower(dentry, path);
	else
		ovl_path_upper(dentry, path);

	return type;
}

struct dentry *ovl_dentry_upper(struct dentry *dentry)
{
	struct ovl_entry *oe = dentry->d_fsdata;

	return ovl_upperdentry_dereference(oe);
}

struct dentry *ovl_dentry_lower(struct dentry *dentry)
{
	struct ovl_entry *oe = dentry->d_fsdata;

	return oe->lowerdentry;
}

struct dentry *ovl_dentry_real(struct dentry *dentry)
{
	struct ovl_entry *oe = dentry->d_fsdata;
	struct dentry *realdentry;

	realdentry = ovl_upperdentry_dereference(oe);
	if (!realdentry)
		realdentry = oe->lowerdentry;

	return realdentry;
}

struct dentry *ovl_entry_real(struct ovl_entry *oe, bool *is_upper)
{
	struct dentry *realdentry;

	realdentry = ovl_upperdentry_dereference(oe);
	if (realdentry) {
		*is_upper = true;
	} else {
		realdentry = oe->lowerdentry;
		*is_upper = false;
	}
	return realdentry;
}

struct ovl_dir_cache *ovl_dir_cache(struct dentry *dentry)
{
	struct ovl_entry *oe = dentry->d_fsdata;

	return oe->cache;
}

void ovl_set_dir_cache(struct dentry *dentry, struct ovl_dir_cache *cache)
{
	struct ovl_entry *oe = dentry->d_fsdata;

	oe->cache = cache;
}

void ovl_path_lower(struct dentry *dentry, struct path *path)
{
	struct ovl_fs *ofs = dentry->d_sb->s_fs_info;
	struct ovl_entry *oe = dentry->d_fsdata;

	path->mnt = ofs->lower_mnt;
	path->dentry = oe->lowerdentry;
}

int ovl_want_write(struct dentry *dentry)
{
	struct ovl_fs *ofs = dentry->d_sb->s_fs_info;
	return mnt_want_write(ofs->upper_mnt);
}

void ovl_drop_write(struct dentry *dentry)
{
	struct ovl_fs *ofs = dentry->d_sb->s_fs_info;
	mnt_drop_write(ofs->upper_mnt);
}

struct dentry *ovl_workdir(struct dentry *dentry)
{
	struct ovl_fs *ofs = dentry->d_sb->s_fs_info;
	return ofs->workdir;
}

bool ovl_dentry_is_opaque(struct dentry *dentry)
{
	struct ovl_entry *oe = dentry->d_fsdata;
	return oe->opaque;
}

void ovl_dentry_set_opaque(struct dentry *dentry, bool opaque)
{
	struct ovl_entry *oe = dentry->d_fsdata;
	oe->opaque = opaque;
}

void ovl_dentry_update(struct dentry *dentry, struct dentry *upperdentry)
{
	struct ovl_entry *oe = dentry->d_fsdata;

	WARN_ON(!mutex_is_locked(&upperdentry->d_parent->d_inode->i_mutex));
	WARN_ON(oe->__upperdentry);
	BUG_ON(!upperdentry->d_inode);
	/*
	 * Make sure upperdentry is consistent before making it visible to
	 * ovl_upperdentry_dereference().
	 */
	smp_wmb();
	oe->__upperdentry = upperdentry;
}

void ovl_dentry_version_inc(struct dentry *dentry)
{
	struct ovl_entry *oe = dentry->d_fsdata;

	WARN_ON(!mutex_is_locked(&dentry->d_inode->i_mutex));
	oe->version++;
}

u64 ovl_dentry_version_get(struct dentry *dentry)
{
	struct ovl_entry *oe = dentry->d_fsdata;

	WARN_ON(!mutex_is_locked(&dentry->d_inode->i_mutex));
	return oe->version;
}

bool ovl_is_whiteout(struct dentry *dentry)
{
	struct inode *inode = dentry->d_inode;

	return inode && IS_WHITEOUT(inode);
}

static bool ovl_is_opaquedir(struct dentry *dentry)
{
	int res;
	char val;
	struct inode *inode = dentry->d_inode;

	if (!S_ISDIR(inode->i_mode) || !inode->i_op->getxattr)
		return false;

	res = inode->i_op->getxattr(dentry, ovl_opaque_xattr, &val, 1);
	if (res == 1 && val == 'y')
		return true;

	return false;
}

static void ovl_dentry_release(struct dentry *dentry)
{
	struct ovl_entry *oe = dentry->d_fsdata;

	if (oe) {
		dput(oe->__upperdentry);
		dput(oe->lowerdentry);
		kfree_rcu(oe, rcu);
	}
}

static const struct dentry_operations ovl_dentry_operations = {
	.d_release = ovl_dentry_release,
};

static struct ovl_entry *ovl_alloc_entry(void)
{
	return kzalloc(sizeof(struct ovl_entry), GFP_KERNEL);
}

static inline struct dentry *ovl_lookup_real(struct dentry *dir,
					     struct qstr *name)
{
	struct dentry *dentry;

	mutex_lock(&dir->d_inode->i_mutex);
	dentry = lookup_one_len(name->name, dir, name->len);
	mutex_unlock(&dir->d_inode->i_mutex);

	if (IS_ERR(dentry)) {
		if (PTR_ERR(dentry) == -ENOENT)
			dentry = NULL;
	} else if (!dentry->d_inode) {
		dput(dentry);
		dentry = NULL;
	}
	return dentry;
}

struct dentry *ovl_lookup(struct inode *dir, struct dentry *dentry,
			  unsigned int flags)
{
	struct ovl_entry *oe;
	struct dentry *upperdir;
	struct dentry *lowerdir;
	struct dentry *upperdentry = NULL;
	struct dentry *lowerdentry = NULL;
	struct inode *inode = NULL;
	int err;

	err = -ENOMEM;
	oe = ovl_alloc_entry();
	if (!oe)
		goto out;

	upperdir = ovl_dentry_upper(dentry->d_parent);
	lowerdir = ovl_dentry_lower(dentry->d_parent);

	if (upperdir) {
		upperdentry = ovl_lookup_real(upperdir, &dentry->d_name);
		err = PTR_ERR(upperdentry);
		if (IS_ERR(upperdentry))
			goto out_put_dir;

		if (lowerdir && upperdentry) {
			if (ovl_is_whiteout(upperdentry)) {
				dput(upperdentry);
				upperdentry = NULL;
				oe->opaque = true;
			} else if (ovl_is_opaquedir(upperdentry)) {
				oe->opaque = true;
			}
		}
	}
	if (lowerdir && !oe->opaque) {
		lowerdentry = ovl_lookup_real(lowerdir, &dentry->d_name);
		err = PTR_ERR(lowerdentry);
		if (IS_ERR(lowerdentry))
			goto out_dput_upper;
	}

	if (lowerdentry && upperdentry &&
	    (!S_ISDIR(upperdentry->d_inode->i_mode) ||
	     !S_ISDIR(lowerdentry->d_inode->i_mode))) {
		dput(lowerdentry);
		lowerdentry = NULL;
		oe->opaque = true;
	}

	if (lowerdentry || upperdentry) {
		struct dentry *realdentry;

		realdentry = upperdentry ? upperdentry : lowerdentry;
		err = -ENOMEM;
		inode = ovl_new_inode(dentry->d_sb, realdentry->d_inode->i_mode,
				      oe);
		if (!inode)
			goto out_dput;
		ovl_copyattr(realdentry->d_inode, inode);
	}

	oe->__upperdentry = upperdentry;
	oe->lowerdentry = lowerdentry;

	dentry->d_fsdata = oe;
	d_add(dentry, inode);

	return NULL;

out_dput:
	dput(lowerdentry);
out_dput_upper:
	dput(upperdentry);
out_put_dir:
	kfree(oe);
out:
	return ERR_PTR(err);
}

struct file *ovl_path_open(struct path *path, int flags)
{
	return dentry_open(path, flags, current_cred());
}

static void ovl_put_super(struct super_block *sb)
{
	struct ovl_fs *ufs = sb->s_fs_info;

	dput(ufs->workdir);
	mntput(ufs->upper_mnt);
	mntput(ufs->lower_mnt);

	kfree(ufs->config.lowerdir);
	kfree(ufs->config.upperdir);
	kfree(ufs->config.workdir);
	kfree(ufs);
}

/**
 * ovl_statfs
 * @sb: The overlayfs super block
 * @buf: The struct kstatfs to fill in with stats
 *
 * Get the filesystem statistics.  As writes always target the upper layer
 * filesystem pass the statfs to the same filesystem.
 */
static int ovl_statfs(struct dentry *dentry, struct kstatfs *buf)
{
	struct ovl_fs *ofs = dentry->d_sb->s_fs_info;
	struct dentry *root_dentry = dentry->d_sb->s_root;
	struct path path;
	int err;

	ovl_path_upper(root_dentry, &path);

	err = vfs_statfs(&path, buf);
	if (!err) {
		buf->f_namelen = max(buf->f_namelen, ofs->lower_namelen);
		buf->f_type = OVERLAYFS_SUPER_MAGIC;
	}

	return err;
}

/**
 * ovl_show_options
 *
 * Prints the mount options for a given superblock.
 * Returns zero; does not fail.
 */
static int ovl_show_options(struct seq_file *m, struct dentry *dentry)
{
	struct super_block *sb = dentry->d_sb;
	struct ovl_fs *ufs = sb->s_fs_info;

	seq_printf(m, ",lowerdir=%s", ufs->config.lowerdir);
	seq_printf(m, ",upperdir=%s", ufs->config.upperdir);
	seq_printf(m, ",workdir=%s", ufs->config.workdir);
	return 0;
}

static const struct super_operations ovl_super_operations = {
	.put_super	= ovl_put_super,
	.statfs		= ovl_statfs,
	.show_options	= ovl_show_options,
};

enum {
	OPT_LOWERDIR,
	OPT_UPPERDIR,
	OPT_WORKDIR,
	OPT_ERR,
};

static const match_table_t ovl_tokens = {
	{OPT_LOWERDIR,			"lowerdir=%s"},
	{OPT_UPPERDIR,			"upperdir=%s"},
	{OPT_WORKDIR,			"workdir=%s"},
	{OPT_ERR,			NULL}
};

static int ovl_parse_opt(char *opt, struct ovl_config *config)
{
	char *p;

	while ((p = strsep(&opt, ",")) != NULL) {
		int token;
		substring_t args[MAX_OPT_ARGS];

		if (!*p)
			continue;

		token = match_token(p, ovl_tokens, args);
		switch (token) {
		case OPT_UPPERDIR:
			kfree(config->upperdir);
			config->upperdir = match_strdup(&args[0]);
			if (!config->upperdir)
				return -ENOMEM;
			break;

		case OPT_LOWERDIR:
			kfree(config->lowerdir);
			config->lowerdir = match_strdup(&args[0]);
			if (!config->lowerdir)
				return -ENOMEM;
			break;

		case OPT_WORKDIR:
			kfree(config->workdir);
			config->workdir = match_strdup(&args[0]);
			if (!config->workdir)
				return -ENOMEM;
			break;

		default:
			return -EINVAL;
		}
	}
	return 0;
}

#define OVL_WORKDIR_NAME "work"

static struct dentry *ovl_workdir_create(struct vfsmount *mnt,
					 struct dentry *dentry)
{
	struct inode *dir = dentry->d_inode;
	struct dentry *work;
	int err;
	bool retried = false;

	err = mnt_want_write(mnt);
	if (err)
		return ERR_PTR(err);

	mutex_lock_nested(&dir->i_mutex, I_MUTEX_PARENT);
retry:
	work = lookup_one_len(OVL_WORKDIR_NAME, dentry,
			      strlen(OVL_WORKDIR_NAME));

	if (!IS_ERR(work)) {
		struct kstat stat = {
			.mode = S_IFDIR | 0,
		};

		if (work->d_inode) {
			err = -EEXIST;
			if (retried)
				goto out_dput;

			retried = true;
			ovl_cleanup(dir, work);
			dput(work);
			goto retry;
		}

		err = ovl_create_real(dir, work, &stat, NULL, NULL, true);
		if (err)
			goto out_dput;
	}
out_unlock:
	mutex_unlock(&dir->i_mutex);
	mnt_drop_write(mnt);

	return work;

out_dput:
	dput(work);
	work = ERR_PTR(err);
	goto out_unlock;
}

static int ovl_mount_dir(const char *name, struct path *path)
{
	int err;

	err = kern_path(name, LOOKUP_FOLLOW, path);
	if (err) {
		pr_err("overlayfs: failed to resolve '%s': %i\n", name, err);
		err = -EINVAL;
	}
	return err;
}

static bool ovl_is_allowed_fs_type(struct dentry *root)
{
	const struct dentry_operations *dop = root->d_op;

	/*
	 * We don't support:
	 *  - automount filesystems
	 *  - filesystems with revalidate (FIXME for lower layer)
	 *  - filesystems with case insensitive names
	 */
	if (dop &&
	    (dop->d_manage || dop->d_automount ||
	     dop->d_revalidate || dop->d_weak_revalidate ||
	     dop->d_compare || dop->d_hash)) {
		return false;
	}
	return true;
}

/* Workdir should not be subdir of upperdir and vice versa */
static bool ovl_workdir_ok(struct dentry *workdir, struct dentry *upperdir)
{
	bool ok = false;

	if (workdir != upperdir) {
		ok = (lock_rename(workdir, upperdir) == NULL);
		unlock_rename(workdir, upperdir);
	}
	return ok;
}

static int ovl_fill_super(struct super_block *sb, void *data, int silent)
{
	struct path lowerpath;
	struct path upperpath;
	struct path workpath;
	struct inode *root_inode;
	struct dentry *root_dentry;
	struct ovl_entry *oe;
	struct ovl_fs *ufs;
	struct kstatfs statfs;
	int err;

	err = -ENOMEM;
	ufs = kzalloc(sizeof(struct ovl_fs), GFP_KERNEL);
	if (!ufs)
		goto out;

	err = ovl_parse_opt((char *) data, &ufs->config);
	if (err)
		goto out_free_config;

	/* FIXME: workdir is not needed for a R/O mount */
	err = -EINVAL;
	if (!ufs->config.upperdir || !ufs->config.lowerdir ||
	    !ufs->config.workdir) {
		pr_err("overlayfs: missing upperdir or lowerdir or workdir\n");
		goto out_free_config;
	}

	err = -ENOMEM;
	oe = ovl_alloc_entry();
	if (oe == NULL)
		goto out_free_config;

	err = ovl_mount_dir(ufs->config.upperdir, &upperpath);
	if (err)
		goto out_free_oe;

	err = ovl_mount_dir(ufs->config.lowerdir, &lowerpath);
	if (err)
		goto out_put_upperpath;

	err = ovl_mount_dir(ufs->config.workdir, &workpath);
	if (err)
		goto out_put_lowerpath;

	err = -EINVAL;
	if (!S_ISDIR(upperpath.dentry->d_inode->i_mode) ||
	    !S_ISDIR(lowerpath.dentry->d_inode->i_mode) ||
	    !S_ISDIR(workpath.dentry->d_inode->i_mode)) {
		pr_err("overlayfs: upperdir or lowerdir or workdir not a directory\n");
		goto out_put_workpath;
	}

	if (upperpath.mnt != workpath.mnt) {
		pr_err("overlayfs: workdir and upperdir must reside under the same mount\n");
		goto out_put_workpath;
	}
	if (!ovl_workdir_ok(workpath.dentry, upperpath.dentry)) {
		pr_err("overlayfs: workdir and upperdir must be separate subtrees\n");
		goto out_put_workpath;
	}

	if (!ovl_is_allowed_fs_type(upperpath.dentry)) {
		pr_err("overlayfs: filesystem of upperdir is not supported\n");
		goto out_put_workpath;
	}

	if (!ovl_is_allowed_fs_type(lowerpath.dentry)) {
		pr_err("overlayfs: filesystem of lowerdir is not supported\n");
		goto out_put_workpath;
	}

	err = vfs_statfs(&lowerpath, &statfs);
	if (err) {
		pr_err("overlayfs: statfs failed on lowerpath\n");
		goto out_put_workpath;
	}
	ufs->lower_namelen = statfs.f_namelen;

	sb->s_stack_depth = max(upperpath.mnt->mnt_sb->s_stack_depth,
				lowerpath.mnt->mnt_sb->s_stack_depth) + 1;

	err = -EINVAL;
	if (sb->s_stack_depth > FILESYSTEM_MAX_STACK_DEPTH) {
		pr_err("overlayfs: maximum fs stacking depth exceeded\n");
		goto out_put_workpath;
	}

	ufs->upper_mnt = clone_private_mount(&upperpath);
	err = PTR_ERR(ufs->upper_mnt);
	if (IS_ERR(ufs->upper_mnt)) {
		pr_err("overlayfs: failed to clone upperpath\n");
		goto out_put_workpath;
	}

	ufs->lower_mnt = clone_private_mount(&lowerpath);
	err = PTR_ERR(ufs->lower_mnt);
	if (IS_ERR(ufs->lower_mnt)) {
		pr_err("overlayfs: failed to clone lowerpath\n");
		goto out_put_upper_mnt;
	}

	ufs->workdir = ovl_workdir_create(ufs->upper_mnt, workpath.dentry);
	err = PTR_ERR(ufs->workdir);
	if (IS_ERR(ufs->workdir)) {
		pr_err("overlayfs: failed to create directory %s/%s\n",
		       ufs->config.workdir, OVL_WORKDIR_NAME);
		goto out_put_lower_mnt;
	}

	/*
	 * Make lower_mnt R/O.  That way fchmod/fchown on lower file
	 * will fail instead of modifying lower fs.
	 */
	ufs->lower_mnt->mnt_flags |= MNT_READONLY;

	/* If the upper fs is r/o, we mark overlayfs r/o too */
	if (ufs->upper_mnt->mnt_sb->s_flags & MS_RDONLY)
		sb->s_flags |= MS_RDONLY;

	sb->s_d_op = &ovl_dentry_operations;

	err = -ENOMEM;
	root_inode = ovl_new_inode(sb, S_IFDIR, oe);
	if (!root_inode)
		goto out_put_workdir;

	root_dentry = d_make_root(root_inode);
	if (!root_dentry)
		goto out_put_workdir;

	mntput(upperpath.mnt);
	mntput(lowerpath.mnt);
	path_put(&workpath);

	oe->__upperdentry = upperpath.dentry;
	oe->lowerdentry = lowerpath.dentry;

	root_dentry->d_fsdata = oe;

	sb->s_magic = OVERLAYFS_SUPER_MAGIC;
	sb->s_op = &ovl_super_operations;
	sb->s_root = root_dentry;
	sb->s_fs_info = ufs;

	return 0;

out_put_workdir:
	dput(ufs->workdir);
out_put_lower_mnt:
	mntput(ufs->lower_mnt);
out_put_upper_mnt:
	mntput(ufs->upper_mnt);
out_put_workpath:
	path_put(&workpath);
out_put_lowerpath:
	path_put(&lowerpath);
out_put_upperpath:
	path_put(&upperpath);
out_free_oe:
	kfree(oe);
out_free_config:
	kfree(ufs->config.lowerdir);
	kfree(ufs->config.upperdir);
	kfree(ufs->config.workdir);
	kfree(ufs);
out:
	return err;
}

static struct dentry *ovl_mount(struct file_system_type *fs_type, int flags,
				const char *dev_name, void *raw_data)
{
	return mount_nodev(fs_type, flags, raw_data, ovl_fill_super);
}

static struct file_system_type ovl_fs_type = {
	.owner		= THIS_MODULE,
	.name		= "overlay",
	.mount		= ovl_mount,
	.kill_sb	= kill_anon_super,
};
MODULE_ALIAS_FS("overlay");

static int __init ovl_init(void)
{
	return register_filesystem(&ovl_fs_type);
}

static void __exit ovl_exit(void)
{
	unregister_filesystem(&ovl_fs_type);
}

module_init(ovl_init);
module_exit(ovl_exit);
Commit	Line	Data
e9be9d5e MS	1	/*
	2	*
	3	* Copyright (C) 2011 Novell Inc.
	4	*
	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.
	8	*/
	9
	10	#include <linux/fs.h>
	11	#include <linux/namei.h>
	12	#include <linux/xattr.h>
	13	#include <linux/security.h>
	14	#include <linux/mount.h>
	15	#include <linux/slab.h>
	16	#include <linux/parser.h>
	17	#include <linux/module.h>
	18	#include <linux/sched.h>
cc259639	19	#include <linux/statfs.h>
f45827e8	20	#include <linux/seq_file.h>
e9be9d5e MS	21	#include "overlayfs.h"
	22
	23	MODULE_AUTHOR("Miklos Szeredi <miklos@szeredi.hu>");
	24	MODULE_DESCRIPTION("Overlay filesystem");
	25	MODULE_LICENSE("GPL");
	26
ef94b186	27	#define OVERLAYFS_SUPER_MAGIC 0x794c7630
cc259639	28
f45827e8 EZ	29	struct ovl_config {
	30	char *lowerdir;
	31	char *upperdir;
	32	char *workdir;
	33	};
	34
e9be9d5e MS	35	/* private information held for overlayfs's superblock */
	36	struct ovl_fs {
	37	struct vfsmount *upper_mnt;
	38	struct vfsmount *lower_mnt;
	39	struct dentry *workdir;
cc259639	40	long lower_namelen;
f45827e8 EZ	41	/* pathnames of lower and upper dirs, for show_options */
f45827e8 EZ	42	struct ovl_config config;
e9be9d5e MS	43	};
	44
	45	struct ovl_dir_cache;
	46
	47	/* private information held for every overlayfs dentry */
	48	struct ovl_entry {
	49	struct dentry *__upperdentry;
	50	struct dentry *lowerdentry;
	51	struct ovl_dir_cache *cache;
	52	union {
	53	struct {
	54	u64 version;
	55	bool opaque;
	56	};
	57	struct rcu_head rcu;
	58	};
	59	};
	60
	61	const char *ovl_opaque_xattr = "trusted.overlay.opaque";
	62
	63
	64	enum ovl_path_type ovl_path_type(struct dentry *dentry)
	65	{
	66	struct ovl_entry *oe = dentry->d_fsdata;
	67
	68	if (oe->__upperdentry) {
	69	if (oe->lowerdentry) {
	70	if (S_ISDIR(dentry->d_inode->i_mode))
	71	return OVL_PATH_MERGE;
	72	else
	73	return OVL_PATH_UPPER;
	74	} else {
	75	if (oe->opaque)
	76	return OVL_PATH_UPPER;
	77	else
	78	return OVL_PATH_PURE_UPPER;
	79	}
	80	} else {
	81	return OVL_PATH_LOWER;
	82	}
	83	}
	84
	85	static struct dentry ovl_upperdentry_dereference(struct ovl_entry oe)
	86	{
	87	struct dentry *upperdentry = ACCESS_ONCE(oe->__upperdentry);
	88	/*
	89	* Make sure to order reads to upperdentry wrt ovl_dentry_update()
	90	*/
	91	smp_read_barrier_depends();
	92	return upperdentry;
	93	}
	94
	95	void ovl_path_upper(struct dentry dentry, struct path path)
	96	{
	97	struct ovl_fs *ofs = dentry->d_sb->s_fs_info;
	98	struct ovl_entry *oe = dentry->d_fsdata;
	99
	100	path->mnt = ofs->upper_mnt;
	101	path->dentry = ovl_upperdentry_dereference(oe);
	102	}
	103
	104	enum ovl_path_type ovl_path_real(struct dentry dentry, struct path path)
	105	{
	106
107	enum ovl_path_type type = ovl_path_type(dentry);
108
109	if (type == OVL_PATH_LOWER)
110	ovl_path_lower(dentry, path);
111	else
112	ovl_path_upper(dentry, path);
113
114	return type;
115	}
116
117	struct dentry ovl_dentry_upper(struct dentry dentry)
118	{
119	struct ovl_entry *oe = dentry->d_fsdata;
120
121	return ovl_upperdentry_dereference(oe);
122	}
123
124	struct dentry ovl_dentry_lower(struct dentry dentry)
125	{
126	struct ovl_entry *oe = dentry->d_fsdata;
127
128	return oe->lowerdentry;
129	}
130
131	struct dentry ovl_dentry_real(struct dentry dentry)
132	{
133	struct ovl_entry *oe = dentry->d_fsdata;
134	struct dentry *realdentry;
135
136	realdentry = ovl_upperdentry_dereference(oe);
137	if (!realdentry)
138	realdentry = oe->lowerdentry;
139
140	return realdentry;
141	}
142
143	struct dentry ovl_entry_real(struct ovl_entry oe, bool *is_upper)
144	{
145	struct dentry *realdentry;
146
147	realdentry = ovl_upperdentry_dereference(oe);
148	if (realdentry) {
149	*is_upper = true;
150	} else {
151	realdentry = oe->lowerdentry;
152	*is_upper = false;
153	}
154	return realdentry;
155	}
156
157	struct ovl_dir_cache ovl_dir_cache(struct dentry dentry)
158	{
159	struct ovl_entry *oe = dentry->d_fsdata;
160
161	return oe->cache;
162	}
163
164	void ovl_set_dir_cache(struct dentry dentry, struct ovl_dir_cache cache)
165	{
166	struct ovl_entry *oe = dentry->d_fsdata;
167
168	oe->cache = cache;
169	}
170
171	void ovl_path_lower(struct dentry dentry, struct path path)
172	{
173	struct ovl_fs *ofs = dentry->d_sb->s_fs_info;
174	struct ovl_entry *oe = dentry->d_fsdata;
175
176	path->mnt = ofs->lower_mnt;
177	path->dentry = oe->lowerdentry;
178	}
179
180	int ovl_want_write(struct dentry *dentry)
181	{
182	struct ovl_fs *ofs = dentry->d_sb->s_fs_info;
183	return mnt_want_write(ofs->upper_mnt);
184	}
185
186	void ovl_drop_write(struct dentry *dentry)
187	{
188	struct ovl_fs *ofs = dentry->d_sb->s_fs_info;
189	mnt_drop_write(ofs->upper_mnt);
190	}
191
192	struct dentry ovl_workdir(struct dentry dentry)
193	{
194	struct ovl_fs *ofs = dentry->d_sb->s_fs_info;
195	return ofs->workdir;
196	}
197
198	bool ovl_dentry_is_opaque(struct dentry *dentry)
199	{
200	struct ovl_entry *oe = dentry->d_fsdata;
201	return oe->opaque;
202	}
203
204	void ovl_dentry_set_opaque(struct dentry *dentry, bool opaque)
205	{
206	struct ovl_entry *oe = dentry->d_fsdata;
207	oe->opaque = opaque;
208	}
209
210	void ovl_dentry_update(struct dentry dentry, struct dentry upperdentry)
211	{
212	struct ovl_entry *oe = dentry->d_fsdata;
213
214	WARN_ON(!mutex_is_locked(&upperdentry->d_parent->d_inode->i_mutex));
215	WARN_ON(oe->__upperdentry);
216	BUG_ON(!upperdentry->d_inode);
217	/*
218	* Make sure upperdentry is consistent before making it visible to
219	* ovl_upperdentry_dereference().
220	*/
221	smp_wmb();
222	oe->__upperdentry = upperdentry;
223	}
224
225	void ovl_dentry_version_inc(struct dentry *dentry)
226	{
227	struct ovl_entry *oe = dentry->d_fsdata;
228
229	WARN_ON(!mutex_is_locked(&dentry->d_inode->i_mutex));
230	oe->version++;
231	}
232
233	u64 ovl_dentry_version_get(struct dentry *dentry)
234	{
235	struct ovl_entry *oe = dentry->d_fsdata;
236
237	WARN_ON(!mutex_is_locked(&dentry->d_inode->i_mutex));
238	return oe->version;
239	}
240
241	bool ovl_is_whiteout(struct dentry *dentry)
242	{
243	struct inode *inode = dentry->d_inode;
244
245	return inode && IS_WHITEOUT(inode);
246	}
247
248	static bool ovl_is_opaquedir(struct dentry *dentry)
249	{
250	int res;
251	char val;
252	struct inode *inode = dentry->d_inode;
253
254	if (!S_ISDIR(inode->i_mode) \|\| !inode->i_op->getxattr)
255	return false;
256
257	res = inode->i_op->getxattr(dentry, ovl_opaque_xattr, &val, 1);
258	if (res == 1 && val == 'y')
259	return true;
260
261	return false;
262	}
263
264	static void ovl_dentry_release(struct dentry *dentry)
265	{
266	struct ovl_entry *oe = dentry->d_fsdata;
267
268	if (oe) {
269	dput(oe->__upperdentry);
270	dput(oe->lowerdentry);
271	kfree_rcu(oe, rcu);
272	}
273	}
274
275	static const struct dentry_operations ovl_dentry_operations = {
276	.d_release = ovl_dentry_release,
277	};
278
279	static struct ovl_entry *ovl_alloc_entry(void)
280	{
281	return kzalloc(sizeof(struct ovl_entry), GFP_KERNEL);
282	}
283
284	static inline struct dentry ovl_lookup_real(struct dentry dir,
285	struct qstr *name)
286	{
287	struct dentry *dentry;
288
289	mutex_lock(&dir->d_inode->i_mutex);
290	dentry = lookup_one_len(name->name, dir, name->len);
291	mutex_unlock(&dir->d_inode->i_mutex);
292
293	if (IS_ERR(dentry)) {
294	if (PTR_ERR(dentry) == -ENOENT)
295	dentry = NULL;
296	} else if (!dentry->d_inode) {
297	dput(dentry);
298	dentry = NULL;
299	}
300	return dentry;
301	}
302
303	struct dentry ovl_lookup(struct inode dir, struct dentry *dentry,
304	unsigned int flags)
305	{
306	struct ovl_entry *oe;
307	struct dentry *upperdir;
308	struct dentry *lowerdir;
309	struct dentry *upperdentry = NULL;
310	struct dentry *lowerdentry = NULL;
311	struct inode *inode = NULL;
312	int err;
313
314	err = -ENOMEM;
315	oe = ovl_alloc_entry();
316	if (!oe)
317	goto out;
318
319	upperdir = ovl_dentry_upper(dentry->d_parent);
320	lowerdir = ovl_dentry_lower(dentry->d_parent);
321
322	if (upperdir) {
323	upperdentry = ovl_lookup_real(upperdir, &dentry->d_name);
324	err = PTR_ERR(upperdentry);
325	if (IS_ERR(upperdentry))
326	goto out_put_dir;
327
328	if (lowerdir && upperdentry) {
329	if (ovl_is_whiteout(upperdentry)) {
330	dput(upperdentry);
331	upperdentry = NULL;
332	oe->opaque = true;
333	} else if (ovl_is_opaquedir(upperdentry)) {
334	oe->opaque = true;
335	}
336	}
337	}
338	if (lowerdir && !oe->opaque) {
339	lowerdentry = ovl_lookup_real(lowerdir, &dentry->d_name);
340	err = PTR_ERR(lowerdentry);
341	if (IS_ERR(lowerdentry))
342	goto out_dput_upper;
343	}
344
345	if (lowerdentry && upperdentry &&
346	(!S_ISDIR(upperdentry->d_inode->i_mode) \|\|
347	!S_ISDIR(lowerdentry->d_inode->i_mode))) {
348	dput(lowerdentry);
349	lowerdentry = NULL;
350	oe->opaque = true;
351	}
352
353	if (lowerdentry \|\| upperdentry) {
354	struct dentry *realdentry;
355
356	realdentry = upperdentry ? upperdentry : lowerdentry;
357	err = -ENOMEM;
358	inode = ovl_new_inode(dentry->d_sb, realdentry->d_inode->i_mode,
359	oe);
360	if (!inode)
361	goto out_dput;
362	ovl_copyattr(realdentry->d_inode, inode);
363	}
364
365	oe->__upperdentry = upperdentry;
366	oe->lowerdentry = lowerdentry;
367
368	dentry->d_fsdata = oe;
369	d_add(dentry, inode);
370
371	return NULL;
372
373	out_dput:
374	dput(lowerdentry);
375	out_dput_upper:
376	dput(upperdentry);
377	out_put_dir:
378	kfree(oe);
379	out:
380	return ERR_PTR(err);
381	}
382
383	struct file ovl_path_open(struct path path, int flags)
384	{
385	return dentry_open(path, flags, current_cred());
386	}
387
388	static void ovl_put_super(struct super_block *sb)
389	{
390	struct ovl_fs *ufs = sb->s_fs_info;
391
392	dput(ufs->workdir);
393	mntput(ufs->upper_mnt);
394	mntput(ufs->lower_mnt);
395
f45827e8 EZ	396	kfree(ufs->config.lowerdir);
	397	kfree(ufs->config.upperdir);
	398	kfree(ufs->config.workdir);
e9be9d5e MS	399	kfree(ufs);
	400	}
	401
cc259639 AW	402	/**
	403	* ovl_statfs
	404	* @sb: The overlayfs super block
	405	* @buf: The struct kstatfs to fill in with stats
	406	*
	407	* Get the filesystem statistics. As writes always target the upper layer
	408	* filesystem pass the statfs to the same filesystem.
	409	*/
	410	static int ovl_statfs(struct dentry dentry, struct kstatfs buf)
	411	{
	412	struct ovl_fs *ofs = dentry->d_sb->s_fs_info;
	413	struct dentry *root_dentry = dentry->d_sb->s_root;
	414	struct path path;
	415	int err;
	416
	417	ovl_path_upper(root_dentry, &path);
	418
	419	err = vfs_statfs(&path, buf);
	420	if (!err) {
	421	buf->f_namelen = max(buf->f_namelen, ofs->lower_namelen);
	422	buf->f_type = OVERLAYFS_SUPER_MAGIC;
	423	}
	424
	425	return err;
	426	}
	427
f45827e8 EZ	428	/**
	429	* ovl_show_options
	430	*
	431	* Prints the mount options for a given superblock.
	432	* Returns zero; does not fail.
	433	*/
	434	static int ovl_show_options(struct seq_file m, struct dentry dentry)
	435	{
	436	struct super_block *sb = dentry->d_sb;
	437	struct ovl_fs *ufs = sb->s_fs_info;
	438
	439	seq_printf(m, ",lowerdir=%s", ufs->config.lowerdir);
	440	seq_printf(m, ",upperdir=%s", ufs->config.upperdir);
	441	seq_printf(m, ",workdir=%s", ufs->config.workdir);
	442	return 0;
	443	}
	444
e9be9d5e MS	445	static const struct super_operations ovl_super_operations = {
e9be9d5e MS	446	.put_super = ovl_put_super,
cc259639	447	.statfs = ovl_statfs,
f45827e8	448	.show_options = ovl_show_options,
e9be9d5e MS	449	};
	450
	451	enum {
	452	OPT_LOWERDIR,
	453	OPT_UPPERDIR,
	454	OPT_WORKDIR,
	455	OPT_ERR,
	456	};
	457
	458	static const match_table_t ovl_tokens = {
	459	{OPT_LOWERDIR, "lowerdir=%s"},
	460	{OPT_UPPERDIR, "upperdir=%s"},
	461	{OPT_WORKDIR, "workdir=%s"},
	462	{OPT_ERR, NULL}
	463	};
	464
	465	static int ovl_parse_opt(char opt, struct ovl_config config)
	466	{
	467	char *p;
	468
e9be9d5e MS	469	while ((p = strsep(&opt, ",")) != NULL) {
	470	int token;
	471	substring_t args[MAX_OPT_ARGS];
	472
	473	if (!*p)
	474	continue;
	475
	476	token = match_token(p, ovl_tokens, args);
	477	switch (token) {
	478	case OPT_UPPERDIR:
	479	kfree(config->upperdir);
	480	config->upperdir = match_strdup(&args[0]);
	481	if (!config->upperdir)
	482	return -ENOMEM;
	483	break;
	484
	485	case OPT_LOWERDIR:
	486	kfree(config->lowerdir);
	487	config->lowerdir = match_strdup(&args[0]);
	488	if (!config->lowerdir)
	489	return -ENOMEM;
	490	break;
	491
	492	case OPT_WORKDIR:
	493	kfree(config->workdir);
	494	config->workdir = match_strdup(&args[0]);
	495	if (!config->workdir)
	496	return -ENOMEM;
	497	break;
	498
	499	default:
	500	return -EINVAL;
	501	}
	502	}
	503	return 0;
	504	}
	505
	506	#define OVL_WORKDIR_NAME "work"
	507
	508	static struct dentry ovl_workdir_create(struct vfsmount mnt,
	509	struct dentry *dentry)
	510	{
	511	struct inode *dir = dentry->d_inode;
	512	struct dentry *work;
	513	int err;
	514	bool retried = false;
	515
	516	err = mnt_want_write(mnt);
	517	if (err)
	518	return ERR_PTR(err);
	519
	520	mutex_lock_nested(&dir->i_mutex, I_MUTEX_PARENT);
	521	retry:
	522	work = lookup_one_len(OVL_WORKDIR_NAME, dentry,
	523	strlen(OVL_WORKDIR_NAME));
	524
	525	if (!IS_ERR(work)) {
	526	struct kstat stat = {
	527	.mode = S_IFDIR \| 0,
	528	};
	529
	530	if (work->d_inode) {
	531	err = -EEXIST;
	532	if (retried)
533	goto out_dput;
534
535	retried = true;
536	ovl_cleanup(dir, work);
537	dput(work);
538	goto retry;
539	}
540
541	err = ovl_create_real(dir, work, &stat, NULL, NULL, true);
542	if (err)
543	goto out_dput;
544	}
545	out_unlock:
546	mutex_unlock(&dir->i_mutex);
547	mnt_drop_write(mnt);
548
549	return work;
550
551	out_dput:
552	dput(work);
553	work = ERR_PTR(err);
554	goto out_unlock;
555	}
556
557	static int ovl_mount_dir(const char name, struct path path)
558	{
559	int err;
560
561	err = kern_path(name, LOOKUP_FOLLOW, path);
562	if (err) {
563	pr_err("overlayfs: failed to resolve '%s': %i\n", name, err);
564	err = -EINVAL;
565	}
566	return err;
567	}
568
569	static bool ovl_is_allowed_fs_type(struct dentry *root)
570	{
571	const struct dentry_operations *dop = root->d_op;
572
573	/*
574	* We don't support:
575	* - automount filesystems
576	* - filesystems with revalidate (FIXME for lower layer)
577	* - filesystems with case insensitive names
578	*/
579	if (dop &&
580	(dop->d_manage \|\| dop->d_automount \|\|
581	dop->d_revalidate \|\| dop->d_weak_revalidate \|\|
582	dop->d_compare \|\| dop->d_hash)) {
583	return false;
584	}
585	return true;
586	}
587
588	/* Workdir should not be subdir of upperdir and vice versa */
589	static bool ovl_workdir_ok(struct dentry workdir, struct dentry upperdir)
590	{
591	bool ok = false;
592
593	if (workdir != upperdir) {
594	ok = (lock_rename(workdir, upperdir) == NULL);
595	unlock_rename(workdir, upperdir);
596	}
597	return ok;
598	}
599
600	static int ovl_fill_super(struct super_block sb, void data, int silent)
601	{
602	struct path lowerpath;
603	struct path upperpath;
604	struct path workpath;
605	struct inode *root_inode;
606	struct dentry *root_dentry;
607	struct ovl_entry *oe;
608	struct ovl_fs *ufs;
cc259639	609	struct kstatfs statfs;
e9be9d5e MS	610	int err;
e9be9d5e MS	611
f45827e8 EZ	612	err = -ENOMEM;
	613	ufs = kzalloc(sizeof(struct ovl_fs), GFP_KERNEL);
	614	if (!ufs)
e9be9d5e MS	615	goto out;
e9be9d5e MS	616
f45827e8 EZ	617	err = ovl_parse_opt((char *) data, &ufs->config);
	618	if (err)
	619	goto out_free_config;
	620
e9be9d5e MS	621	/* FIXME: workdir is not needed for a R/O mount */
e9be9d5e MS	622	err = -EINVAL;
f45827e8 EZ	623	if (!ufs->config.upperdir \|\| !ufs->config.lowerdir \|\|
f45827e8 EZ	624	!ufs->config.workdir) {
e9be9d5e MS	625	pr_err("overlayfs: missing upperdir or lowerdir or workdir\n");
	626	goto out_free_config;
	627	}
	628
	629	err = -ENOMEM;
e9be9d5e MS	630	oe = ovl_alloc_entry();
e9be9d5e MS	631	if (oe == NULL)
f45827e8	632	goto out_free_config;
e9be9d5e	633
f45827e8	634	err = ovl_mount_dir(ufs->config.upperdir, &upperpath);
e9be9d5e MS	635	if (err)
	636	goto out_free_oe;
	637
f45827e8	638	err = ovl_mount_dir(ufs->config.lowerdir, &lowerpath);
e9be9d5e MS	639	if (err)
	640	goto out_put_upperpath;
	641
f45827e8	642	err = ovl_mount_dir(ufs->config.workdir, &workpath);
e9be9d5e MS	643	if (err)
	644	goto out_put_lowerpath;
	645
	646	err = -EINVAL;
	647	if (!S_ISDIR(upperpath.dentry->d_inode->i_mode) \|\|
	648	!S_ISDIR(lowerpath.dentry->d_inode->i_mode) \|\|
	649	!S_ISDIR(workpath.dentry->d_inode->i_mode)) {
	650	pr_err("overlayfs: upperdir or lowerdir or workdir not a directory\n");
	651	goto out_put_workpath;
	652	}
	653
	654	if (upperpath.mnt != workpath.mnt) {
	655	pr_err("overlayfs: workdir and upperdir must reside under the same mount\n");
	656	goto out_put_workpath;
	657	}
	658	if (!ovl_workdir_ok(workpath.dentry, upperpath.dentry)) {
	659	pr_err("overlayfs: workdir and upperdir must be separate subtrees\n");
	660	goto out_put_workpath;
	661	}
	662
	663	if (!ovl_is_allowed_fs_type(upperpath.dentry)) {
	664	pr_err("overlayfs: filesystem of upperdir is not supported\n");
	665	goto out_put_workpath;
	666	}
	667
	668	if (!ovl_is_allowed_fs_type(lowerpath.dentry)) {
	669	pr_err("overlayfs: filesystem of lowerdir is not supported\n");
	670	goto out_put_workpath;
	671	}
	672
cc259639 AW	673	err = vfs_statfs(&lowerpath, &statfs);
	674	if (err) {
	675	pr_err("overlayfs: statfs failed on lowerpath\n");
	676	goto out_put_workpath;
	677	}
	678	ufs->lower_namelen = statfs.f_namelen;
	679
69c433ed MS	680	sb->s_stack_depth = max(upperpath.mnt->mnt_sb->s_stack_depth,
	681	lowerpath.mnt->mnt_sb->s_stack_depth) + 1;
	682
	683	err = -EINVAL;
	684	if (sb->s_stack_depth > FILESYSTEM_MAX_STACK_DEPTH) {
	685	pr_err("overlayfs: maximum fs stacking depth exceeded\n");
	686	goto out_put_workpath;
	687	}
	688
e9be9d5e MS	689	ufs->upper_mnt = clone_private_mount(&upperpath);
	690	err = PTR_ERR(ufs->upper_mnt);
	691	if (IS_ERR(ufs->upper_mnt)) {
	692	pr_err("overlayfs: failed to clone upperpath\n");
	693	goto out_put_workpath;
	694	}
	695
	696	ufs->lower_mnt = clone_private_mount(&lowerpath);
	697	err = PTR_ERR(ufs->lower_mnt);
	698	if (IS_ERR(ufs->lower_mnt)) {
	699	pr_err("overlayfs: failed to clone lowerpath\n");
	700	goto out_put_upper_mnt;
	701	}
	702
	703	ufs->workdir = ovl_workdir_create(ufs->upper_mnt, workpath.dentry);
	704	err = PTR_ERR(ufs->workdir);
	705	if (IS_ERR(ufs->workdir)) {
	706	pr_err("overlayfs: failed to create directory %s/%s\n",
f45827e8	707	ufs->config.workdir, OVL_WORKDIR_NAME);
e9be9d5e MS	708	goto out_put_lower_mnt;
	709	}
	710
	711	/*
	712	* Make lower_mnt R/O. That way fchmod/fchown on lower file
	713	* will fail instead of modifying lower fs.
	714	*/
	715	ufs->lower_mnt->mnt_flags \|= MNT_READONLY;
	716
	717	/* If the upper fs is r/o, we mark overlayfs r/o too */
	718	if (ufs->upper_mnt->mnt_sb->s_flags & MS_RDONLY)
	719	sb->s_flags \|= MS_RDONLY;
	720
	721	sb->s_d_op = &ovl_dentry_operations;
	722
	723	err = -ENOMEM;
	724	root_inode = ovl_new_inode(sb, S_IFDIR, oe);
	725	if (!root_inode)
	726	goto out_put_workdir;
	727
	728	root_dentry = d_make_root(root_inode);
	729	if (!root_dentry)
	730	goto out_put_workdir;
	731
	732	mntput(upperpath.mnt);
	733	mntput(lowerpath.mnt);
	734	path_put(&workpath);
	735
	736	oe->__upperdentry = upperpath.dentry;
	737	oe->lowerdentry = lowerpath.dentry;
	738
	739	root_dentry->d_fsdata = oe;
	740
cc259639	741	sb->s_magic = OVERLAYFS_SUPER_MAGIC;
e9be9d5e MS	742	sb->s_op = &ovl_super_operations;
	743	sb->s_root = root_dentry;
	744	sb->s_fs_info = ufs;
	745
	746	return 0;
	747
	748	out_put_workdir:
	749	dput(ufs->workdir);
	750	out_put_lower_mnt:
	751	mntput(ufs->lower_mnt);
	752	out_put_upper_mnt:
	753	mntput(ufs->upper_mnt);
	754	out_put_workpath:
	755	path_put(&workpath);
	756	out_put_lowerpath:
	757	path_put(&lowerpath);
	758	out_put_upperpath:
	759	path_put(&upperpath);
	760	out_free_oe:
	761	kfree(oe);
e9be9d5e	762	out_free_config:
f45827e8 EZ	763	kfree(ufs->config.lowerdir);
	764	kfree(ufs->config.upperdir);
	765	kfree(ufs->config.workdir);
	766	kfree(ufs);
e9be9d5e MS	767	out:
	768	return err;
	769	}
	770
	771	static struct dentry ovl_mount(struct file_system_type fs_type, int flags,
	772	const char dev_name, void raw_data)
	773	{
	774	return mount_nodev(fs_type, flags, raw_data, ovl_fill_super);
	775	}
	776
	777	static struct file_system_type ovl_fs_type = {
	778	.owner = THIS_MODULE,
ef94b186	779	.name = "overlay",
e9be9d5e MS	780	.mount = ovl_mount,
	781	.kill_sb = kill_anon_super,
	782	};
ef94b186	783	MODULE_ALIAS_FS("overlay");
e9be9d5e MS	784
	785	static int __init ovl_init(void)
	786	{
	787	return register_filesystem(&ovl_fs_type);
	788	}
	789
	790	static void __exit ovl_exit(void)
	791	{
	792	unregister_filesystem(&ovl_fs_type);
	793	}
	794
	795	module_init(ovl_init);
	796	module_exit(ovl_exit);