[PATCH 4/7] overlay filesystem

[Miklos Szeredi]

From: Miklos Szeredi <mszeredi@xxxxxxx>

Overlayfs allows one, usually read-write, directory tree to be
overlaid onto another, read-only directory tree.  All modifications
go to the upper, writable layer.

This type of mechanism is most often used for live CDs but there's a
wide variety of other uses.

The implementation differs from other "union filesystem"
implementations in that after a file is opened all operations go
directly to the underlying, lower or upper, filesystems.  This
simplifies the implementation and allows native performance in these
cases.

The dentry tree is duplicated from the underlying filesystems, this
enables fast cached lookups without adding special support into the
VFS.  This uses slightly more memory than union mounts, but dentries
are relatively small.

Currently inodes are duplicated as well, but it is a possible
optimization to share inodes for non-directories.

Opening non directories results in the open forwarded to the
underlying filesystem.  This makes the behavior very similar to union
mounts (with the same limitations vs. fchmod/fchown on O_RDONLY file
descriptors).

Usage:

  mount -t overlay -olowerdir=/lower,upperdir=/upper overlay /mnt

Supported:

 - all operations

Missing:

 - ensure that filesystems part of the overlay are not modified outside
   the overlay

The following cotributions have been folded into this patch:

Neil Brown <neilb@xxxxxxx>:
 - minimal remount support
 - use correct seek function for directories
 - initialise is_real before use
 - rename ovl_fill_cache to ovl_dir_read

Felix Fietkau <nbd@xxxxxxxxxxx>:
 - fix a deadlock in ovl_dir_read_merged
 - fix a deadlock in ovl_remove_whiteouts

Erez Zadok <ezk@xxxxxxxxxxxxxxxxx>
 - fix cleanup after WARN_ON

Also thanks to the following people for testing and reporting bugs:

  Jordi Pujol <jordipujolp@xxxxxxxxx>
  Andy Whitcroft <apw@xxxxxxxxxxxxx>
  Michal Suchanek <hramrach@xxxxxxxxxx>
  Felix Fietkau <nbd@xxxxxxxxxxx>
  Erez Zadok <ezk@xxxxxxxxxxxxxxxxx>
  Randy Dunlap <rdunlap@xxxxxxxxxxxx>

Signed-off-by: Miklos Szeredi <mszeredi@xxxxxxx>
---
 fs/Kconfig               |    1 +
 fs/Makefile              |    1 +
 fs/overlayfs/Kconfig     |    4 +
 fs/overlayfs/Makefile    |    7 +
 fs/overlayfs/copy_up.c   |  383 +++++++++++++++++++++++++++++
 fs/overlayfs/dir.c       |  607 ++++++++++++++++++++++++++++++++++++++++++++++
 fs/overlayfs/inode.c     |  375 ++++++++++++++++++++++++++++
 fs/overlayfs/overlayfs.h |   62 +++++
 fs/overlayfs/readdir.c   |  558 ++++++++++++++++++++++++++++++++++++++++++
 fs/overlayfs/super.c     |  582 ++++++++++++++++++++++++++++++++++++++++++++
 10 files changed, 2580 insertions(+), 0 deletions(-)
 create mode 100644 fs/overlayfs/Kconfig
 create mode 100644 fs/overlayfs/Makefile
 create mode 100644 fs/overlayfs/copy_up.c
 create mode 100644 fs/overlayfs/dir.c
 create mode 100644 fs/overlayfs/inode.c
 create mode 100644 fs/overlayfs/overlayfs.h
 create mode 100644 fs/overlayfs/readdir.c
 create mode 100644 fs/overlayfs/super.c

diff --git a/fs/Kconfig b/fs/Kconfig
index 19891aa..3badf8f 100644
--- a/fs/Kconfig
+++ b/fs/Kconfig
@@ -63,6 +63,7 @@ source "fs/quota/Kconfig"
 
 source "fs/autofs4/Kconfig"
 source "fs/fuse/Kconfig"
+source "fs/overlayfs/Kconfig"
 
 config CUSE
 	tristate "Character device in Userspace support"
diff --git a/fs/Makefile b/fs/Makefile
index fb68c2b..ac7402a 100644
--- a/fs/Makefile
+++ b/fs/Makefile
@@ -105,6 +105,7 @@ obj-$(CONFIG_QNX4FS_FS)		+= qnx4/
 obj-$(CONFIG_AUTOFS4_FS)	+= autofs4/
 obj-$(CONFIG_ADFS_FS)		+= adfs/
 obj-$(CONFIG_FUSE_FS)		+= fuse/
+obj-$(CONFIG_OVERLAYFS_FS)	+= overlayfs/
 obj-$(CONFIG_UDF_FS)		+= udf/
 obj-$(CONFIG_SUN_OPENPROMFS)	+= openpromfs/
 obj-$(CONFIG_OMFS_FS)		+= omfs/
diff --git a/fs/overlayfs/Kconfig b/fs/overlayfs/Kconfig
new file mode 100644
index 0000000..c4517da
--- /dev/null
+++ b/fs/overlayfs/Kconfig
@@ -0,0 +1,4 @@
+config OVERLAYFS_FS
+	tristate "Overlay filesystem support"
+	help
+	  Add support for overlay filesystem.
diff --git a/fs/overlayfs/Makefile b/fs/overlayfs/Makefile
new file mode 100644
index 0000000..8f91889
--- /dev/null
+++ b/fs/overlayfs/Makefile
@@ -0,0 +1,7 @@
+#
+# Makefile for the overlay filesystem.
+#
+
+obj-$(CONFIG_OVERLAYFS_FS) += overlayfs.o
+
+overlayfs-objs := super.o inode.o dir.o readdir.o copy_up.o
diff --git a/fs/overlayfs/copy_up.c b/fs/overlayfs/copy_up.c
new file mode 100644
index 0000000..308a80a
--- /dev/null
+++ b/fs/overlayfs/copy_up.c
@@ -0,0 +1,383 @@
+/*
+ *
+ * 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/slab.h>
+#include <linux/file.h>
+#include <linux/splice.h>
+#include <linux/xattr.h>
+#include <linux/security.h>
+#include <linux/uaccess.h>
+#include "overlayfs.h"
+
+#define OVL_COPY_UP_CHUNK_SIZE (1 << 20)
+
+static int ovl_copy_up_xattr(struct dentry *old, struct dentry *new)
+{
+	ssize_t list_size, size;
+	char *buf, *name, *value;
+	int error;
+
+	if (!old->d_inode->i_op->getxattr ||
+	    !new->d_inode->i_op->getxattr)
+		return 0;
+
+	list_size = vfs_listxattr(old, NULL, 0);
+	if (list_size <= 0) {
+		if (list_size == -EOPNOTSUPP)
+			return 0;
+		return list_size;
+	}
+
+	buf = kzalloc(list_size, GFP_KERNEL);
+	if (!buf)
+		return -ENOMEM;
+
+	error = -ENOMEM;
+	value = kmalloc(XATTR_SIZE_MAX, GFP_KERNEL);
+	if (!value)
+		goto out;
+
+	list_size = vfs_listxattr(old, buf, list_size);
+	if (list_size <= 0) {
+		error = list_size;
+		goto out_free_value;
+	}
+
+	for (name = buf; name < (buf + list_size); name += strlen(name) + 1) {
+		size = vfs_getxattr(old, name, value, XATTR_SIZE_MAX);
+		if (size <= 0) {
+			error = size;
+			goto out_free_value;
+		}
+		error = vfs_setxattr(new, name, value, size, 0);
+		if (error)
+			goto out_free_value;
+	}
+
+out_free_value:
+	kfree(value);
+out:
+	kfree(buf);
+	return error;
+}
+
+static int ovl_copy_up_data(struct path *old, struct path *new, loff_t len)
+{
+	struct file *old_file;
+	struct file *new_file;
+	int error = 0;
+
+	if (len == 0)
+		return 0;
+
+	old_file = vfs_open(old, O_RDONLY, current_cred());
+	if (IS_ERR(old_file))
+		return PTR_ERR(old_file);
+
+	new_file = vfs_open(new, O_WRONLY, current_cred());
+	if (IS_ERR(new_file)) {
+		error = PTR_ERR(new_file);
+		goto out_fput;
+	}
+
+	/* FIXME: copy up sparse files efficiently */
+	while (len) {
+		loff_t offset = new_file->f_pos;
+		size_t this_len = OVL_COPY_UP_CHUNK_SIZE;
+		long bytes;
+
+		if (len < this_len)
+			this_len = len;
+
+		if (signal_pending_state(TASK_KILLABLE, current)) {
+			error = -EINTR;
+			break;
+		}
+
+		bytes = do_splice_direct(old_file, &offset, new_file, this_len,
+				 SPLICE_F_MOVE);
+		if (bytes <= 0) {
+			error = bytes;
+			break;
+		}
+
+		len -= bytes;
+	}
+
+	fput(new_file);
+out_fput:
+	fput(old_file);
+	return error;
+}
+
+static char *ovl_read_symlink(struct dentry *realdentry)
+{
+	int res;
+	char *buf;
+	struct inode *inode = realdentry->d_inode;
+	mm_segment_t old_fs;
+
+	res = -EINVAL;
+	if (!inode->i_op->readlink)
+		goto err;
+
+	res = -ENOMEM;
+	buf = (char *) __get_free_page(GFP_KERNEL);
+	if (!buf)
+		goto err;
+
+	old_fs = get_fs();
+	set_fs(get_ds());
+	/* The cast to a user pointer is valid due to the set_fs() */
+	res = inode->i_op->readlink(realdentry,
+				    (char __user *)buf, PAGE_SIZE - 1);
+	set_fs(old_fs);
+	if (res < 0) {
+		free_page((unsigned long) buf);
+		goto err;
+	}
+	buf[res] = '\0';
+
+	return buf;
+
+err:
+	return ERR_PTR(res);
+}
+
+static int ovl_set_timestamps(struct dentry *upperdentry, struct kstat *stat)
+{
+	struct iattr attr = {
+		.ia_valid = ATTR_ATIME | ATTR_MTIME | ATTR_ATIME_SET | ATTR_MTIME_SET,
+		.ia_atime = stat->atime,
+		.ia_mtime = stat->mtime,
+	};
+
+	return notify_change(upperdentry, &attr);
+}
+
+static int ovl_set_mode(struct dentry *upperdentry, umode_t mode)
+{
+	struct iattr attr = {
+		.ia_valid = ATTR_MODE,
+		.ia_mode = mode,
+	};
+
+	return notify_change(upperdentry, &attr);
+}
+
+static int ovl_copy_up_locked(struct dentry *upperdir, struct dentry *dentry,
+			      struct path *lowerpath, struct kstat *stat,
+			      const char *link)
+{
+	int err;
+	struct path newpath;
+	umode_t mode = stat->mode;
+
+	/* Can't properly set mode on creation because of the umask */
+	stat->mode &= S_IFMT;
+
+	ovl_path_upper(dentry, &newpath);
+	WARN_ON(newpath.dentry);
+	newpath.dentry = ovl_upper_create(upperdir, dentry, stat, link);
+	if (IS_ERR(newpath.dentry))
+		return PTR_ERR(newpath.dentry);
+
+	if (S_ISREG(stat->mode)) {
+		err = ovl_copy_up_data(lowerpath, &newpath, stat->size);
+		if (err)
+			goto err_remove;
+	}
+
+	err = ovl_copy_up_xattr(lowerpath->dentry, newpath.dentry);
+	if (err)
+		goto err_remove;
+
+	mutex_lock(&newpath.dentry->d_inode->i_mutex);
+	if (!S_ISLNK(stat->mode))
+		err = ovl_set_mode(newpath.dentry, mode);
+	if (!err)
+		err = ovl_set_timestamps(newpath.dentry, stat);
+	mutex_unlock(&newpath.dentry->d_inode->i_mutex);
+	if (err)
+		goto err_remove;
+
+	ovl_dentry_update(dentry, newpath.dentry);
+
+	/*
+	 * Easiest way to get rid of the lower dentry reference is to
+	 * drop this dentry.  This is neither needed nor possible for
+	 * directories.
+	 */
+	if (!S_ISDIR(stat->mode))
+		d_drop(dentry);
+
+	return 0;
+
+err_remove:
+	if (S_ISDIR(stat->mode))
+		vfs_rmdir(upperdir->d_inode, newpath.dentry);
+	else
+		vfs_unlink(upperdir->d_inode, newpath.dentry);
+
+	dput(newpath.dentry);
+
+	return err;
+}
+
+/*
+ * Copy up a single dentry
+ *
+ * Directory renames only allowed on "pure upper" (already created on
+ * upper filesystem, never copied up).  Directories which are on lower or
+ * are merged may not be renamed.  For these -EXDEV is returned and
+ * userspace has to deal with it.  This means, when copying up a
+ * directory we can rely on it and ancestors being stable.
+ *
+ * Non-directory renames start with copy up of source if necessary.  The
+ * actual rename will only proceed once the copy up was successful.  Copy
+ * up uses upper parent i_mutex for exclusion.  Since rename can change
+ * d_parent it is possible that the copy up will lock the old parent.  At
+ * that point the file will have already been copied up anyway.
+ */
+static int ovl_copy_up_one(struct dentry *parent, struct dentry *dentry,
+			   struct path *lowerpath, struct kstat *stat)
+{
+	int err;
+	struct kstat pstat;
+	struct path parentpath;
+	struct dentry *upperdir;
+	const struct cred *old_cred;
+	struct cred *override_cred;
+	char *link = NULL;
+
+	ovl_path_upper(parent, &parentpath);
+	upperdir = parentpath.dentry;
+
+	err = vfs_getattr(parentpath.mnt, parentpath.dentry, &pstat);
+	if (err)
+		return err;
+
+	if (S_ISLNK(stat->mode)) {
+		link = ovl_read_symlink(lowerpath->dentry);
+		if (IS_ERR(link))
+			return PTR_ERR(link);
+	}
+
+	err = -ENOMEM;
+	override_cred = prepare_creds();
+	if (!override_cred)
+		goto out_free_link;
+
+	override_cred->fsuid = stat->uid;
+	override_cred->fsgid = stat->gid;
+	/*
+	 * CAP_SYS_ADMIN for copying up extended attributes
+	 * CAP_DAC_OVERRIDE for create
+	 * CAP_FOWNER for chmod, timestamp update
+	 * CAP_FSETID for chmod
+	 * CAP_MKNOD for mknod
+	 */
+	cap_raise(override_cred->cap_effective, CAP_SYS_ADMIN);
+	cap_raise(override_cred->cap_effective, CAP_DAC_OVERRIDE);
+	cap_raise(override_cred->cap_effective, CAP_FOWNER);
+	cap_raise(override_cred->cap_effective, CAP_FSETID);
+	cap_raise(override_cred->cap_effective, CAP_MKNOD);
+	old_cred = override_creds(override_cred);
+
+	mutex_lock_nested(&upperdir->d_inode->i_mutex, I_MUTEX_PARENT);
+	if (ovl_path_type(dentry) != OVL_PATH_LOWER) {
+		err = 0;
+	} else {
+		err = ovl_copy_up_locked(upperdir, dentry, lowerpath,
+					 stat, link);
+		if (!err) {
+			/* Restore timestamps on parent (best effort) */
+			ovl_set_timestamps(upperdir, &pstat);
+		}
+	}
+
+	mutex_unlock(&upperdir->d_inode->i_mutex);
+
+	revert_creds(old_cred);
+	put_cred(override_cred);
+
+out_free_link:
+	if (link)
+		free_page((unsigned long) link);
+
+	return err;
+}
+
+int ovl_copy_up(struct dentry *dentry)
+{
+	int err;
+
+	err = 0;
+	while (!err) {
+		struct dentry *next;
+		struct dentry *parent;
+		struct path lowerpath;
+		struct kstat stat;
+		enum ovl_path_type type = ovl_path_type(dentry);
+
+		if (type != OVL_PATH_LOWER)
+			break;
+
+		next = dget(dentry);
+		/* find the topmost dentry not yet copied up */
+		for (;;) {
+			parent = dget_parent(next);
+
+			type = ovl_path_type(parent);
+			if (type != OVL_PATH_LOWER)
+				break;
+
+			dput(next);
+			next = parent;
+		}
+
+		ovl_path_lower(next, &lowerpath);
+		err = vfs_getattr(lowerpath.mnt, lowerpath.dentry, &stat);
+		if (!err)
+			err = ovl_copy_up_one(parent, next, &lowerpath, &stat);
+
+		dput(parent);
+		dput(next);
+	}
+
+	return err;
+}
+
+/* Optimize by not copying up the file first and truncating later */
+int ovl_copy_up_truncate(struct dentry *dentry, loff_t size)
+{
+	int err;
+	struct kstat stat;
+	struct path lowerpath;
+	struct dentry *parent = dget_parent(dentry);
+
+	err = ovl_copy_up(parent);
+	if (err)
+		goto out_dput_parent;
+
+	ovl_path_lower(dentry, &lowerpath);
+	err = vfs_getattr(lowerpath.mnt, lowerpath.dentry, &stat);
+	if (err)
+		goto out_dput_parent;
+
+	if (size < stat.size)
+		stat.size = size;
+
+	err = ovl_copy_up_one(parent, dentry, &lowerpath, &stat);
+
+out_dput_parent:
+	dput(parent);
+	return err;
+}
diff --git a/fs/overlayfs/dir.c b/fs/overlayfs/dir.c
new file mode 100644
index 0000000..966db6b
--- /dev/null
+++ b/fs/overlayfs/dir.c
@@ -0,0 +1,607 @@
+/*
+ *
+ * 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 "overlayfs.h"
+
+static const char *ovl_whiteout_symlink = "(overlay-whiteout)";
+
+static struct dentry *ovl_lookup(struct inode *dir, struct dentry *dentry,
+				 struct nameidata *nd)
+{
+	int err = ovl_do_lookup(dentry);
+
+	if (err)
+		return ERR_PTR(err);
+
+	return NULL;
+}
+
+static int ovl_whiteout(struct dentry *upperdir, struct dentry *dentry)
+{
+	int err;
+	struct dentry *newdentry;
+	const struct cred *old_cred;
+	struct cred *override_cred;
+
+	/* FIXME: recheck lower dentry to see if whiteout is really needed */
+
+	err = -ENOMEM;
+	override_cred = prepare_creds();
+	if (!override_cred)
+		goto out;
+
+	/*
+	 * CAP_SYS_ADMIN for setxattr
+	 * CAP_DAC_OVERRIDE for symlink creation
+	 * CAP_FOWNER for unlink in sticky directory
+	 */
+	cap_raise(override_cred->cap_effective, CAP_SYS_ADMIN);
+	cap_raise(override_cred->cap_effective, CAP_DAC_OVERRIDE);
+	cap_raise(override_cred->cap_effective, CAP_FOWNER);
+	override_cred->fsuid = 0;
+	override_cred->fsgid = 0;
+	old_cred = override_creds(override_cred);
+
+	newdentry = lookup_one_len(dentry->d_name.name, upperdir,
+				   dentry->d_name.len);
+	err = PTR_ERR(newdentry);
+	if (IS_ERR(newdentry))
+		goto out_put_cred;
+
+	/* Just been removed within the same locked region */
+	WARN_ON(newdentry->d_inode);
+
+	err = vfs_symlink(upperdir->d_inode, newdentry, ovl_whiteout_symlink);
+	if (err)
+		goto out_dput;
+
+	ovl_dentry_version_inc(dentry->d_parent);
+
+	err = vfs_setxattr(newdentry, ovl_whiteout_xattr, "y", 1, 0);
+	if (err)
+		vfs_unlink(upperdir->d_inode, newdentry);
+
+out_dput:
+	dput(newdentry);
+out_put_cred:
+	revert_creds(old_cred);
+	put_cred(override_cred);
+out:
+	if (err) {
+		/*
+		 * There's no way to recover from failure to whiteout.
+		 * What should we do?  Log a big fat error and... ?
+		 */
+		printk(KERN_ERR "overlayfs: ERROR - failed to whiteout '%s'\n",
+		       dentry->d_name.name);
+	}
+
+	return err;
+}
+
+static struct dentry *ovl_lookup_create(struct dentry *upperdir,
+					struct dentry *template)
+{
+	int err;
+	struct dentry *newdentry;
+	struct qstr *name = &template->d_name;
+
+	newdentry = lookup_one_len(name->name, upperdir, name->len);
+	if (IS_ERR(newdentry))
+		return newdentry;
+
+	if (newdentry->d_inode) {
+		const struct cred *old_cred;
+		struct cred *override_cred;
+
+		/* No need to check whiteout if lower parent is non-existent */
+		err = -EEXIST;
+		if (!ovl_dentry_lower(template->d_parent))
+			goto out_dput;
+
+		if (!S_ISLNK(newdentry->d_inode->i_mode))
+			goto out_dput;
+
+		err = -ENOMEM;
+		override_cred = prepare_creds();
+		if (!override_cred)
+			goto out_dput;
+
+		/*
+		 * CAP_SYS_ADMIN for getxattr
+		 * CAP_FOWNER for unlink in sticky directory
+		 */
+		cap_raise(override_cred->cap_effective, CAP_SYS_ADMIN);
+		cap_raise(override_cred->cap_effective, CAP_FOWNER);
+		old_cred = override_creds(override_cred);
+
+		err = -EEXIST;
+		if (ovl_is_whiteout(newdentry))
+			err = vfs_unlink(upperdir->d_inode, newdentry);
+
+		revert_creds(old_cred);
+		put_cred(override_cred);
+		if (err)
+			goto out_dput;
+
+		dput(newdentry);
+		newdentry = lookup_one_len(name->name, upperdir, name->len);
+		if (IS_ERR(newdentry)) {
+			ovl_whiteout(upperdir, template);
+			return newdentry;
+		}
+
+		/*
+		 * Whiteout just been successfully removed, parent
+		 * i_mutex is still held, there's no way the lookup
+		 * could return positive.
+		 */
+		WARN_ON(newdentry->d_inode);
+	}
+
+	return newdentry;
+
+out_dput:
+	dput(newdentry);
+	return ERR_PTR(err);
+}
+
+struct dentry *ovl_upper_create(struct dentry *upperdir, struct dentry *dentry,
+				struct kstat *stat, const char *link)
+{
+	int err;
+	struct dentry *newdentry;
+	struct inode *dir = upperdir->d_inode;
+
+	newdentry = ovl_lookup_create(upperdir, dentry);
+	if (IS_ERR(newdentry))
+		goto out;
+
+	switch (stat->mode & S_IFMT) {
+	case S_IFREG:
+		err = vfs_create(dir, newdentry, stat->mode, NULL);
+		break;
+
+	case S_IFDIR:
+		err = vfs_mkdir(dir, newdentry, stat->mode);
+		break;
+
+	case S_IFCHR:
+	case S_IFBLK:
+	case S_IFIFO:
+	case S_IFSOCK:
+		err = vfs_mknod(dir, newdentry, stat->mode, stat->rdev);
+		break;
+
+	case S_IFLNK:
+		err = vfs_symlink(dir, newdentry, link);
+		break;
+
+	default:
+		err = -EPERM;
+	}
+	if (err) {
+		if (ovl_dentry_is_opaque(dentry))
+			ovl_whiteout(upperdir, dentry);
+		dput(newdentry);
+		newdentry = ERR_PTR(err);
+	} else if (WARN_ON(!newdentry->d_inode)) {
+		/*
+		 * Not quite sure if non-instantiated dentry is legal or not.
+		 * VFS doesn't seem to care so check and warn here.
+		 */
+		dput(newdentry);
+		newdentry = ERR_PTR(-ENOENT);
+	}
+
+out:
+	return newdentry;
+
+}
+
+static int ovl_set_opaque(struct dentry *upperdentry)
+{
+	int err;
+	const struct cred *old_cred;
+	struct cred *override_cred;
+
+	override_cred = prepare_creds();
+	if (!override_cred)
+		return -ENOMEM;
+
+	/* CAP_SYS_ADMIN for setxattr of "trusted" namespace */
+	cap_raise(override_cred->cap_effective, CAP_SYS_ADMIN);
+	old_cred = override_creds(override_cred);
+	err = vfs_setxattr(upperdentry, ovl_opaque_xattr, "y", 1, 0);
+	revert_creds(old_cred);
+	put_cred(override_cred);
+
+	return err;
+}
+
+static int ovl_remove_opaque(struct dentry *upperdentry)
+{
+	int err;
+	const struct cred *old_cred;
+	struct cred *override_cred;
+
+	override_cred = prepare_creds();
+	if (!override_cred)
+		return -ENOMEM;
+
+	/* CAP_SYS_ADMIN for removexattr of "trusted" namespace */
+	cap_raise(override_cred->cap_effective, CAP_SYS_ADMIN);
+	old_cred = override_creds(override_cred);
+	err = vfs_removexattr(upperdentry, ovl_opaque_xattr);
+	revert_creds(old_cred);
+	put_cred(override_cred);
+
+	return err;
+}
+
+static int ovl_dir_getattr(struct vfsmount *mnt, struct dentry *dentry,
+			 struct kstat *stat)
+{
+	int err;
+	enum ovl_path_type type;
+	struct path realpath;
+
+	type = ovl_path_real(dentry, &realpath);
+	err = vfs_getattr(realpath.mnt, realpath.dentry, stat);
+	if (err)
+		return err;
+
+	stat->dev = dentry->d_sb->s_dev;
+	stat->ino = dentry->d_inode->i_ino;
+
+	/*
+	 * It's probably not worth it to count subdirs to get the
+	 * correct link count.  nlink=1 seems to pacify 'find' and
+	 * other utilities.
+	 */
+	if (type == OVL_PATH_MERGE)
+		stat->nlink = 1;
+
+	return 0;
+}
+
+static int ovl_create_object(struct dentry *dentry, int mode, dev_t rdev,
+			     const char *link)
+{
+	int err;
+	struct dentry *newdentry;
+	struct dentry *upperdir;
+	struct inode *inode;
+	struct kstat stat = {
+		.mode = mode,
+		.rdev = rdev,
+	};
+
+	err = -ENOMEM;
+	inode = ovl_new_inode(dentry->d_sb, mode, dentry->d_fsdata);
+	if (!inode)
+		goto out;
+
+	err = ovl_copy_up(dentry->d_parent);
+	if (err)
+		goto out_iput;
+
+	upperdir = ovl_dentry_upper(dentry->d_parent);
+	mutex_lock_nested(&upperdir->d_inode->i_mutex, I_MUTEX_PARENT);
+
+	newdentry = ovl_upper_create(upperdir, dentry, &stat, link);
+	err = PTR_ERR(newdentry);
+	if (IS_ERR(newdentry))
+		goto out_unlock;
+
+	ovl_dentry_version_inc(dentry->d_parent);
+	if (ovl_dentry_is_opaque(dentry) && S_ISDIR(mode)) {
+		err = ovl_set_opaque(newdentry);
+		if (err) {
+			vfs_rmdir(upperdir->d_inode, newdentry);
+			ovl_whiteout(upperdir, dentry);
+			goto out_dput;
+		}
+	}
+	ovl_dentry_update(dentry, newdentry);
+	d_instantiate(dentry, inode);
+	inode = NULL;
+	newdentry = NULL;
+	err = 0;
+
+out_dput:
+	dput(newdentry);
+out_unlock:
+	mutex_unlock(&upperdir->d_inode->i_mutex);
+out_iput:
+	iput(inode);
+out:
+	return err;
+}
+
+static int ovl_create(struct inode *dir, struct dentry *dentry, int mode,
+			struct nameidata *nd)
+{
+	return ovl_create_object(dentry, (mode & 07777) | S_IFREG, 0, NULL);
+}
+
+static int ovl_mkdir(struct inode *dir, struct dentry *dentry, int mode)
+{
+	return ovl_create_object(dentry, (mode & 07777) | S_IFDIR, 0, NULL);
+}
+
+static int ovl_mknod(struct inode *dir, struct dentry *dentry, int mode,
+		       dev_t rdev)
+{
+	return ovl_create_object(dentry, mode, rdev, NULL);
+}
+
+static int ovl_symlink(struct inode *dir, struct dentry *dentry,
+			 const char *link)
+{
+	return ovl_create_object(dentry, S_IFLNK, 0, link);
+}
+
+static int ovl_do_remove(struct dentry *dentry, bool is_dir)
+{
+	int err;
+	enum ovl_path_type type;
+	struct path realpath;
+	struct dentry *upperdir;
+
+	err = ovl_copy_up(dentry->d_parent);
+	if (err)
+		return err;
+
+	upperdir = ovl_dentry_upper(dentry->d_parent);
+	mutex_lock_nested(&upperdir->d_inode->i_mutex, I_MUTEX_PARENT);
+	type = ovl_path_real(dentry, &realpath);
+	if (type != OVL_PATH_LOWER) {
+		err = -ESTALE;
+		if (realpath.dentry->d_parent != upperdir)
+			goto out_d_drop;
+
+		/* FIXME: create whiteout up front and rename to target */
+
+		if (is_dir)
+			err = vfs_rmdir(upperdir->d_inode, realpath.dentry);
+		else
+			err = vfs_unlink(upperdir->d_inode, realpath.dentry);
+		if (err)
+			goto out_d_drop;
+
+		ovl_dentry_version_inc(dentry->d_parent);
+	}
+
+	if (type != OVL_PATH_UPPER || ovl_dentry_is_opaque(dentry))
+		err = ovl_whiteout(upperdir, dentry);
+
+	/*
+	 * Keeping this dentry hashed would mean having to release
+	 * upperpath/lowerpath, which could only be done if we are the
+	 * sole user of this dentry.  Too tricky...  Just unhash for
+	 * now.
+	 */
+out_d_drop:
+	d_drop(dentry);
+	mutex_unlock(&upperdir->d_inode->i_mutex);
+
+	return err;
+}
+
+static int ovl_unlink(struct inode *dir, struct dentry *dentry)
+{
+	return ovl_do_remove(dentry, false);
+}
+
+
+static int ovl_rmdir(struct inode *dir, struct dentry *dentry)
+{
+	int err;
+	enum ovl_path_type type;
+
+	type = ovl_path_type(dentry);
+	if (type != OVL_PATH_UPPER) {
+		err = ovl_check_empty_and_clear(dentry, type);
+		if (err)
+			return err;
+	}
+
+	return ovl_do_remove(dentry, true);
+}
+
+static int ovl_link(struct dentry *old, struct inode *newdir,
+		    struct dentry *new)
+{
+	int err;
+	struct dentry *olddentry;
+	struct dentry *newdentry;
+	struct dentry *upperdir;
+
+	err = ovl_copy_up(old);
+	if (err)
+		goto out;
+
+	err = ovl_copy_up(new->d_parent);
+	if (err)
+		goto out;
+
+	upperdir = ovl_dentry_upper(new->d_parent);
+	mutex_lock_nested(&upperdir->d_inode->i_mutex, I_MUTEX_PARENT);
+	newdentry = ovl_lookup_create(upperdir, new);
+	err = PTR_ERR(newdentry);
+	if (IS_ERR(newdentry))
+		goto out_unlock;
+
+	olddentry = ovl_dentry_upper(old);
+	err = vfs_link(olddentry, upperdir->d_inode, newdentry);
+	if (!err) {
+		if (WARN_ON(!newdentry->d_inode)) {
+			dput(newdentry);
+			err = -ENOENT;
+			goto out_unlock;
+		}
+
+		ovl_dentry_version_inc(new->d_parent);
+		ovl_dentry_update(new, newdentry);
+
+		ihold(old->d_inode);
+		d_instantiate(new, old->d_inode);
+	} else {
+		if (ovl_dentry_is_opaque(new))
+			ovl_whiteout(upperdir, new);
+		dput(newdentry);
+	}
+out_unlock:
+	mutex_unlock(&upperdir->d_inode->i_mutex);
+out:
+	return err;
+
+}
+
+static int ovl_rename(struct inode *olddir, struct dentry *old,
+			struct inode *newdir, struct dentry *new)
+{
+	int err;
+	enum ovl_path_type old_type;
+	enum ovl_path_type new_type;
+	struct dentry *old_upperdir;
+	struct dentry *new_upperdir;
+	struct dentry *olddentry;
+	struct dentry *newdentry;
+	struct dentry *trap;
+	bool old_opaque;
+	bool new_opaque;
+	bool new_create = false;
+	bool is_dir = S_ISDIR(old->d_inode->i_mode);
+
+	/* Don't copy up directory trees */
+	old_type = ovl_path_type(old);
+	if (old_type != OVL_PATH_UPPER && is_dir)
+		return -EXDEV;
+
+	if (new->d_inode) {
+		new_type = ovl_path_type(new);
+
+		if (new_type == OVL_PATH_LOWER && old_type == OVL_PATH_LOWER) {
+			if (ovl_dentry_lower(old)->d_inode ==
+			    ovl_dentry_lower(new)->d_inode)
+				return 0;
+		}
+		if (new_type != OVL_PATH_LOWER && old_type != OVL_PATH_LOWER) {
+			if (ovl_dentry_upper(old)->d_inode ==
+			    ovl_dentry_upper(new)->d_inode)
+				return 0;
+		}
+
+		if (new_type != OVL_PATH_UPPER &&
+		    S_ISDIR(new->d_inode->i_mode)) {
+			err = ovl_check_empty_and_clear(new, new_type);
+			if (err)
+				return err;
+		}
+	} else {
+		new_type = OVL_PATH_UPPER;
+	}
+
+	err = ovl_copy_up(old);
+	if (err)
+		return err;
+
+	err = ovl_copy_up(new->d_parent);
+	if (err)
+		return err;
+
+	old_upperdir = ovl_dentry_upper(old->d_parent);
+	new_upperdir = ovl_dentry_upper(new->d_parent);
+
+	trap = lock_rename(new_upperdir, old_upperdir);
+
+	olddentry = ovl_dentry_upper(old);
+	newdentry = ovl_dentry_upper(new);
+	if (newdentry) {
+		dget(newdentry);
+	} else {
+		new_create = true;
+		newdentry = ovl_lookup_create(new_upperdir, new);
+		err = PTR_ERR(newdentry);
+		if (IS_ERR(newdentry))
+			goto out_unlock;
+	}
+
+	err = -ESTALE;
+	if (olddentry->d_parent != old_upperdir)
+		goto out_dput;
+	if (newdentry->d_parent != new_upperdir)
+		goto out_dput;
+	if (olddentry == trap)
+		goto out_dput;
+	if (newdentry == trap)
+		goto out_dput;
+
+	old_opaque = ovl_dentry_is_opaque(old);
+	new_opaque = ovl_dentry_is_opaque(new) || new_type != OVL_PATH_UPPER;
+
+	if (is_dir && !old_opaque && new_opaque) {
+		err = ovl_set_opaque(olddentry);
+		if (err)
+			goto out_dput;
+	}
+
+	err = vfs_rename(old_upperdir->d_inode, olddentry,
+			 new_upperdir->d_inode, newdentry);
+
+	if (err) {
+		if (new_create && ovl_dentry_is_opaque(new))
+			ovl_whiteout(new_upperdir, new);
+		if (is_dir && !old_opaque && new_opaque)
+			ovl_remove_opaque(olddentry);
+		goto out_dput;
+	}
+
+	if (old_type != OVL_PATH_UPPER || old_opaque)
+		err = ovl_whiteout(old_upperdir, old);
+	if (is_dir && old_opaque && !new_opaque)
+		ovl_remove_opaque(olddentry);
+
+	if (old_opaque != new_opaque)
+		ovl_dentry_set_opaque(old, new_opaque);
+
+	ovl_dentry_version_inc(old->d_parent);
+	ovl_dentry_version_inc(new->d_parent);
+
+out_dput:
+	dput(newdentry);
+out_unlock:
+	unlock_rename(new_upperdir, old_upperdir);
+	return err;
+}
+
+const struct inode_operations ovl_dir_inode_operations = {
+	.lookup		= ovl_lookup,
+	.mkdir		= ovl_mkdir,
+	.symlink	= ovl_symlink,
+	.unlink		= ovl_unlink,
+	.rmdir		= ovl_rmdir,
+	.rename		= ovl_rename,
+	.link		= ovl_link,
+	.setattr	= ovl_setattr,
+	.create		= ovl_create,
+	.mknod		= ovl_mknod,
+	.permission	= ovl_permission,
+	.getattr	= ovl_dir_getattr,
+	.setxattr	= ovl_setxattr,
+	.getxattr	= ovl_getxattr,
+	.listxattr	= ovl_listxattr,
+	.removexattr	= ovl_removexattr,
+};
diff --git a/fs/overlayfs/inode.c b/fs/overlayfs/inode.c
new file mode 100644
index 0000000..289006e
--- /dev/null
+++ b/fs/overlayfs/inode.c
@@ -0,0 +1,375 @@
+/*
+ *
+ * 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/slab.h>
+#include <linux/xattr.h>
+#include "overlayfs.h"
+
+int ovl_setattr(struct dentry *dentry, struct iattr *attr)
+{
+	struct dentry *upperdentry;
+	int err;
+
+	if ((attr->ia_valid & ATTR_SIZE) && !ovl_dentry_upper(dentry))
+		err = ovl_copy_up_truncate(dentry, attr->ia_size);
+	else
+		err = ovl_copy_up(dentry);
+	if (err)
+		return err;
+
+	upperdentry = ovl_dentry_upper(dentry);
+
+	if (attr->ia_valid & (ATTR_KILL_SUID|ATTR_KILL_SGID))
+		attr->ia_valid &= ~ATTR_MODE;
+
+	mutex_lock(&upperdentry->d_inode->i_mutex);
+	err = notify_change(upperdentry, attr);
+	mutex_unlock(&upperdentry->d_inode->i_mutex);
+
+	return err;
+}
+
+static int ovl_getattr(struct vfsmount *mnt, struct dentry *dentry,
+			 struct kstat *stat)
+{
+	struct path realpath;
+
+	ovl_path_real(dentry, &realpath);
+	return vfs_getattr(realpath.mnt, realpath.dentry, stat);
+}
+
+int ovl_permission(struct inode *inode, int mask, unsigned int flags)
+{
+	struct ovl_entry *oe;
+	struct dentry *alias = NULL;
+	struct inode *realinode;
+	struct dentry *realdentry;
+	bool is_upper;
+	int err;
+
+	if (S_ISDIR(inode->i_mode)) {
+		oe = inode->i_private;
+	} else if (flags & IPERM_FLAG_RCU) {
+		return -ECHILD;
+	} else {
+		/*
+		 * For non-directories find an alias and get the info
+		 * from there.
+		 */
+		spin_lock(&inode->i_lock);
+		if (WARN_ON(list_empty(&inode->i_dentry))) {
+			spin_unlock(&inode->i_lock);
+			return -ENOENT;
+		}
+		alias = list_entry(inode->i_dentry.next, struct dentry, d_alias);
+		dget(alias);
+		spin_unlock(&inode->i_lock);
+		oe = alias->d_fsdata;
+	}
+
+	realdentry = ovl_entry_real(oe, &is_upper);
+
+	/* Careful in RCU walk mode */
+	realinode = ACCESS_ONCE(realdentry->d_inode);
+	if (!realinode) {
+		WARN_ON(!(flags & IPERM_FLAG_RCU));
+		err = -ENOENT;
+		goto out_dput;
+	}
+
+	if (mask & MAY_WRITE) {
+		umode_t mode = realinode->i_mode;
+
+		/*
+		 * Writes will always be redirected to upper layer, so
+		 * ignore lower layer being read-only.
+		 */
+		err = -EROFS;
+		if (is_upper && IS_RDONLY(realinode) &&
+		    (S_ISREG(mode) || S_ISDIR(mode) || S_ISLNK(mode)))
+			goto out_dput;
+
+		/*
+		 * Nobody gets write access to an immutable file.
+		 */
+		err = -EACCES;
+		if (IS_IMMUTABLE(realinode))
+			goto out_dput;
+	}
+
+	if (realinode->i_op->permission)
+		err = realinode->i_op->permission(realinode, mask, flags);
+	else
+		err = generic_permission(realinode, mask, flags,
+					 realinode->i_op->check_acl);
+out_dput:
+	dput(alias);
+	return err;
+}
+
+
+struct ovl_link_data {
+	struct dentry *realdentry;
+	void *cookie;
+};
+
+static void *ovl_follow_link(struct dentry *dentry, struct nameidata *nd)
+{
+	void *ret;
+	struct dentry *realdentry;
+	struct inode *realinode;
+
+	realdentry = ovl_dentry_real(dentry);
+	realinode = realdentry->d_inode;
+
+	if (WARN_ON(!realinode->i_op->follow_link))
+		return ERR_PTR(-EPERM);
+
+	ret = realinode->i_op->follow_link(realdentry, nd);
+	if (IS_ERR(ret))
+		return ret;
+
+	if (realinode->i_op->put_link) {
+		struct ovl_link_data *data;
+
+		data = kmalloc(sizeof(struct ovl_link_data), GFP_KERNEL);
+		if (!data) {
+			realinode->i_op->put_link(realdentry, nd, ret);
+			return ERR_PTR(-ENOMEM);
+		}
+		data->realdentry = realdentry;
+		data->cookie = ret;
+
+		return data;
+	} else {
+		return NULL;
+	}
+}
+
+static void ovl_put_link(struct dentry *dentry, struct nameidata *nd, void *c)
+{
+	struct inode *realinode;
+	struct ovl_link_data *data = c;
+
+	if (!data)
+		return;
+
+	realinode = data->realdentry->d_inode;
+	realinode->i_op->put_link(data->realdentry, nd, data->cookie);
+	kfree(data);
+}
+
+static int ovl_readlink(struct dentry *dentry, char __user *buf, int bufsiz)
+{
+	struct path realpath;
+	struct inode *realinode;
+
+	ovl_path_real(dentry, &realpath);
+	realinode = realpath.dentry->d_inode;
+
+	if (!realinode->i_op->readlink)
+		return -EINVAL;
+
+	touch_atime(realpath.mnt, realpath.dentry);
+
+	return realinode->i_op->readlink(realpath.dentry, buf, bufsiz);
+}
+
+
+static bool ovl_is_private_xattr(const char *name)
+{
+	return strncmp(name, "trusted.overlay.", 14) == 0;
+}
+
+int ovl_setxattr(struct dentry *dentry, const char *name,
+		 const void *value, size_t size, int flags)
+{
+	int err;
+	struct dentry *upperdentry;
+
+	if (ovl_is_private_xattr(name))
+		return -EPERM;
+
+	err = ovl_copy_up(dentry);
+	if (err)
+		return err;
+
+	upperdentry = ovl_dentry_upper(dentry);
+	return  vfs_setxattr(upperdentry, name, value, size, flags);
+}
+
+ssize_t ovl_getxattr(struct dentry *dentry, const char *name,
+		     void *value, size_t size)
+{
+	if (ovl_path_type(dentry->d_parent) == OVL_PATH_MERGE &&
+	    ovl_is_private_xattr(name))
+		return -ENODATA;
+
+	return vfs_getxattr(ovl_dentry_real(dentry), name, value, size);
+}
+
+ssize_t ovl_listxattr(struct dentry *dentry, char *list, size_t size)
+{
+	ssize_t res;
+	int off;
+
+	res = vfs_listxattr(ovl_dentry_real(dentry), list, size);
+	if (res <= 0 || size == 0)
+		return res;
+
+	if (ovl_path_type(dentry->d_parent) != OVL_PATH_MERGE)
+		return res;
+
+	/* filter out private xattrs */
+	for (off = 0; off < res;) {
+		char *s = list + off;
+		size_t slen = strlen(s) + 1;
+
+		BUG_ON(off + slen > res);
+
+		if (ovl_is_private_xattr(s)) {
+			res -= slen;
+			memmove(s, s + slen, res - off);
+		} else {
+			off += slen;
+		}
+	}
+
+	return res;
+}
+
+int ovl_removexattr(struct dentry *dentry, const char *name)
+{
+	int err;
+	struct path realpath;
+	enum ovl_path_type type;
+
+	if (ovl_path_type(dentry->d_parent) == OVL_PATH_MERGE &&
+	    ovl_is_private_xattr(name))
+		return -ENODATA;
+
+	type = ovl_path_real(dentry, &realpath);
+	if (type == OVL_PATH_LOWER) {
+		err = vfs_getxattr(realpath.dentry, name, NULL, 0);
+		if (err < 0)
+			return err;
+
+		err = ovl_copy_up(dentry);
+		if (err)
+			return err;
+
+		ovl_path_upper(dentry, &realpath);
+	}
+
+	return vfs_removexattr(realpath.dentry, name);
+}
+
+static bool ovl_open_need_copy_up(int flags, enum ovl_path_type type,
+				  struct dentry *realdentry)
+{
+	if (type != OVL_PATH_LOWER)
+		return false;
+
+	if (special_file(realdentry->d_inode->i_mode))
+		return false;
+
+	if (!(OPEN_FMODE(flags) & FMODE_WRITE) && !(flags & O_TRUNC))
+		return false;
+
+	return true;
+}
+
+static struct file *ovl_open(struct dentry *dentry, int flags,
+			     const struct cred *cred)
+{
+	int err;
+	struct path realpath;
+	enum ovl_path_type type;
+
+	type = ovl_path_real(dentry, &realpath);
+	if (ovl_open_need_copy_up(flags, type, realpath.dentry)) {
+		if (flags & O_TRUNC)
+			err = ovl_copy_up_truncate(dentry, 0);
+		else
+			err = ovl_copy_up(dentry);
+		if (err)
+			return ERR_PTR(err);
+
+		ovl_path_upper(dentry, &realpath);
+	}
+
+	return vfs_open(&realpath, flags, cred);
+}
+
+static const struct inode_operations ovl_file_inode_operations = {
+	.setattr	= ovl_setattr,
+	.permission	= ovl_permission,
+	.getattr	= ovl_getattr,
+	.setxattr	= ovl_setxattr,
+	.getxattr	= ovl_getxattr,
+	.listxattr	= ovl_listxattr,
+	.removexattr	= ovl_removexattr,
+	.open		= ovl_open,
+};
+
+static const struct inode_operations ovl_symlink_inode_operations = {
+	.setattr	= ovl_setattr,
+	.follow_link	= ovl_follow_link,
+	.put_link	= ovl_put_link,
+	.readlink	= ovl_readlink,
+	.getattr	= ovl_getattr,
+	.setxattr	= ovl_setxattr,
+	.getxattr	= ovl_getxattr,
+	.listxattr	= ovl_listxattr,
+	.removexattr	= ovl_removexattr,
+};
+
+struct inode *ovl_new_inode(struct super_block *sb, umode_t mode,
+			    struct ovl_entry *oe)
+{
+	struct inode *inode;
+
+	inode = new_inode(sb);
+	if (!inode)
+		return NULL;
+
+	mode &= S_IFMT;
+
+	inode->i_ino = get_next_ino();
+	inode->i_mode = mode;
+	inode->i_flags |= S_NOATIME | S_NOCMTIME;
+
+	switch (mode) {
+	case S_IFDIR:
+		inode->i_private = oe;
+		inode->i_op = &ovl_dir_inode_operations;
+		inode->i_fop = &ovl_dir_operations;
+		break;
+
+	case S_IFLNK:
+		inode->i_op = &ovl_symlink_inode_operations;
+		break;
+
+	case S_IFREG:
+	case S_IFSOCK:
+	case S_IFBLK:
+	case S_IFCHR:
+	case S_IFIFO:
+		inode->i_op = &ovl_file_inode_operations;
+		break;
+
+	default:
+		WARN(1, "illegal file type: %i\n", mode);
+		inode = NULL;
+	}
+
+	return inode;
+
+}
diff --git a/fs/overlayfs/overlayfs.h b/fs/overlayfs/overlayfs.h
new file mode 100644
index 0000000..10c4c36
--- /dev/null
+++ b/fs/overlayfs/overlayfs.h
@@ -0,0 +1,62 @@
+/*
+ *
+ * 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.
+ */
+
+struct ovl_entry;
+
+enum ovl_path_type {
+	OVL_PATH_UPPER,
+	OVL_PATH_MERGE,
+	OVL_PATH_LOWER,
+};
+
+extern const char *ovl_opaque_xattr;
+extern const char *ovl_whiteout_xattr;
+extern const struct dentry_operations ovl_dentry_operations;
+
+enum ovl_path_type ovl_path_type(struct dentry *dentry);
+u64 ovl_dentry_version_get(struct dentry *dentry);
+void ovl_dentry_version_inc(struct dentry *dentry);
+void ovl_path_upper(struct dentry *dentry, struct path *path);
+void ovl_path_lower(struct dentry *dentry, struct path *path);
+enum ovl_path_type ovl_path_real(struct dentry *dentry, struct path *path);
+struct dentry *ovl_dentry_upper(struct dentry *dentry);
+struct dentry *ovl_dentry_lower(struct dentry *dentry);
+struct dentry *ovl_dentry_real(struct dentry *dentry);
+struct dentry *ovl_entry_real(struct ovl_entry *oe, bool *is_upper);
+bool ovl_dentry_is_opaque(struct dentry *dentry);
+void ovl_dentry_set_opaque(struct dentry *dentry, bool opaque);
+bool ovl_is_whiteout(struct dentry *dentry);
+void ovl_dentry_update(struct dentry *dentry, struct dentry *upperdentry);
+int ovl_do_lookup(struct dentry *dentry);
+
+struct dentry *ovl_upper_create(struct dentry *upperdir, struct dentry *dentry,
+				struct kstat *stat, const char *link);
+
+/* readdir.c */
+extern const struct file_operations ovl_dir_operations;
+int ovl_check_empty_and_clear(struct dentry *dentry, enum ovl_path_type type);
+
+/* inode.c */
+int ovl_setattr(struct dentry *dentry, struct iattr *attr);
+int ovl_permission(struct inode *inode, int mask, unsigned int flags);
+int ovl_setxattr(struct dentry *dentry, const char *name,
+		 const void *value, size_t size, int flags);
+ssize_t ovl_getxattr(struct dentry *dentry, const char *name,
+		     void *value, size_t size);
+ssize_t ovl_listxattr(struct dentry *dentry, char *list, size_t size);
+int ovl_removexattr(struct dentry *dentry, const char *name);
+
+struct inode *ovl_new_inode(struct super_block *sb, umode_t mode,
+			    struct ovl_entry *oe);
+/* dir.c */
+extern const struct inode_operations ovl_dir_inode_operations;
+
+/* copy_up.c */
+int ovl_copy_up(struct dentry *dentry);
+int ovl_copy_up_truncate(struct dentry *dentry, loff_t size);
diff --git a/fs/overlayfs/readdir.c b/fs/overlayfs/readdir.c
new file mode 100644
index 0000000..4f0a51c
--- /dev/null
+++ b/fs/overlayfs/readdir.c
@@ -0,0 +1,558 @@
+/*
+ *
+ * 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/slab.h>
+#include <linux/namei.h>
+#include <linux/file.h>
+#include <linux/xattr.h>
+#include <linux/rbtree.h>
+#include <linux/security.h>
+#include "overlayfs.h"
+
+struct ovl_cache_entry {
+	const char *name;
+	unsigned int len;
+	unsigned int type;
+	u64 ino;
+	bool is_whiteout;
+	struct list_head l_node;
+	struct rb_node node;
+};
+
+struct ovl_readdir_data {
+	struct rb_root *root;
+	struct list_head *list;
+	struct list_head *middle;
+	struct dentry *dir;
+	int count;
+	int err;
+};
+
+struct ovl_dir_file {
+	bool is_real;
+	bool is_cached;
+	struct list_head cursor;
+	u64 cache_version;
+	struct list_head cache;
+	struct file *realfile;
+};
+
+static struct ovl_cache_entry *ovl_cache_entry_from_node(struct rb_node *n)
+{
+	return container_of(n, struct ovl_cache_entry, node);
+}
+
+static struct ovl_cache_entry *ovl_cache_entry_find(struct rb_root *root,
+						    const char *name, int len)
+{
+	struct rb_node *node = root->rb_node;
+	int cmp;
+
+	while (node) {
+		struct ovl_cache_entry *p = ovl_cache_entry_from_node(node);
+
+		cmp = strncmp(name, p->name, len);
+		if (cmp > 0)
+			node = p->node.rb_right;
+		else if (cmp < 0 || len < p->len)
+			node = p->node.rb_left;
+		else
+			return p;
+	}
+
+	return NULL;
+}
+
+static struct ovl_cache_entry *ovl_cache_entry_new(const char *name, int len,
+						   u64 ino, unsigned int d_type)
+{
+	struct ovl_cache_entry *p;
+
+	p = kmalloc(sizeof(*p) + len + 1, GFP_KERNEL);
+	if (p) {
+		char *name_copy = (char *) (p + 1);
+		memcpy(name_copy, name, len);
+		name_copy[len] = '\0';
+		p->name = name_copy;
+		p->len = len;
+		p->type = d_type;
+		p->ino = ino;
+		p->is_whiteout = false;
+	}
+
+	return p;
+}
+
+static int ovl_cache_entry_add_rb(struct ovl_readdir_data *rdd,
+				  const char *name, int len, u64 ino,
+				  unsigned int d_type)
+{
+	struct rb_node **newp = &rdd->root->rb_node;
+	struct rb_node *parent = NULL;
+	struct ovl_cache_entry *p;
+
+	while (*newp) {
+		int cmp;
+		struct ovl_cache_entry *tmp;
+
+		parent = *newp;
+		tmp = ovl_cache_entry_from_node(*newp);
+		cmp = strncmp(name, tmp->name, len);
+		if (cmp > 0)
+			newp = &tmp->node.rb_right;
+		else if (cmp < 0 || len < tmp->len)
+			newp = &tmp->node.rb_left;
+		else
+			return 0;
+	}
+
+	p = ovl_cache_entry_new(name, len, ino, d_type);
+	if (p == NULL)
+		return -ENOMEM;
+
+	list_add_tail(&p->l_node, rdd->list);
+	rb_link_node(&p->node, parent, newp);
+	rb_insert_color(&p->node, rdd->root);
+
+	return 0;
+}
+
+static int ovl_fill_lower(void *buf, const char *name, int namelen,
+			    loff_t offset, u64 ino, unsigned int d_type)
+{
+	struct ovl_readdir_data *rdd = buf;
+	struct ovl_cache_entry *p;
+
+	rdd->count++;
+	p = ovl_cache_entry_find(rdd->root, name, namelen);
+	if (p) {
+		list_move_tail(&p->l_node, rdd->middle);
+	} else {
+		p = ovl_cache_entry_new(name, namelen, ino, d_type);
+		if (p == NULL)
+			rdd->err = -ENOMEM;
+		else
+			list_add_tail(&p->l_node, rdd->middle);
+	}
+
+	return rdd->err;
+}
+
+static void ovl_cache_free(struct list_head *list)
+{
+	struct ovl_cache_entry *p;
+	struct ovl_cache_entry *n;
+
+	list_for_each_entry_safe(p, n, list, l_node)
+		kfree(p);
+
+	INIT_LIST_HEAD(list);
+}
+
+static int ovl_fill_upper(void *buf, const char *name, int namelen,
+			  loff_t offset, u64 ino, unsigned int d_type)
+{
+	struct ovl_readdir_data *rdd = buf;
+
+	rdd->count++;
+	return ovl_cache_entry_add_rb(rdd, name, namelen, ino, d_type);
+}
+
+static int ovl_dir_read(struct path *realpath, struct ovl_readdir_data *rdd,
+			  filldir_t filler)
+{
+	struct file *realfile;
+	int err;
+
+	realfile = vfs_open(realpath, O_RDONLY | O_DIRECTORY, current_cred());
+	if (IS_ERR(realfile))
+		return PTR_ERR(realfile);
+
+	do {
+		rdd->count = 0;
+		rdd->err = 0;
+		err = vfs_readdir(realfile, filler, rdd);
+		if (err >= 0)
+			err = rdd->err;
+	} while (!err && rdd->count);
+	fput(realfile);
+
+	return 0;
+}
+
+static void ovl_dir_reset(struct file *file)
+{
+	struct ovl_dir_file *od = file->private_data;
+	enum ovl_path_type type = ovl_path_type(file->f_path.dentry);
+
+	if (ovl_dentry_version_get(file->f_path.dentry) != od->cache_version) {
+		list_del_init(&od->cursor);
+		ovl_cache_free(&od->cache);
+		od->is_cached = false;
+	}
+	WARN_ON(!od->is_real && type != OVL_PATH_MERGE);
+	if (od->is_real && type == OVL_PATH_MERGE) {
+		fput(od->realfile);
+		od->realfile = NULL;
+		od->is_real = false;
+	}
+}
+
+static int ovl_dir_mark_whiteouts(struct ovl_readdir_data *rdd)
+{
+	struct ovl_cache_entry *p;
+	struct dentry *dentry;
+	const struct cred *old_cred;
+	struct cred *override_cred;
+
+	override_cred = prepare_creds();
+	if (!override_cred) {
+		ovl_cache_free(rdd->list);
+		return -ENOMEM;
+	}
+
+	/*
+	 * CAP_SYS_ADMIN for getxattr
+	 * CAP_DAC_OVERRIDE for lookup
+	 */
+	cap_raise(override_cred->cap_effective, CAP_SYS_ADMIN);
+	cap_raise(override_cred->cap_effective, CAP_DAC_OVERRIDE);
+	old_cred = override_creds(override_cred);
+
+	mutex_lock(&rdd->dir->d_inode->i_mutex);
+	list_for_each_entry(p, rdd->list, l_node) {
+		if (p->type != DT_LNK)
+			continue;
+
+		dentry = lookup_one_len(p->name, rdd->dir, p->len);
+		if (IS_ERR(dentry))
+			continue;
+
+		p->is_whiteout = ovl_is_whiteout(dentry);
+		dput(dentry);
+	}
+	mutex_unlock(&rdd->dir->d_inode->i_mutex);
+
+	revert_creds(old_cred);
+	put_cred(override_cred);
+
+	return 0;
+}
+
+static int ovl_dir_read_merged(struct path *upperpath, struct path *lowerpath,
+			       struct ovl_readdir_data *rdd)
+{
+	int err;
+	struct rb_root root = RB_ROOT;
+	struct list_head middle;
+
+	rdd->root = &root;
+	if (upperpath->dentry) {
+		rdd->dir = upperpath->dentry;
+		err = ovl_dir_read(upperpath, rdd, ovl_fill_upper);
+		if (err)
+			goto out;
+
+		err = ovl_dir_mark_whiteouts(rdd);
+		if (err)
+			goto out;
+	}
+	/*
+	 * Insert lowerpath entries before upperpath ones, this allows
+	 * offsets to be reasonably constant
+	 */
+	list_add(&middle, rdd->list);
+	rdd->middle = &middle;
+	err = ovl_dir_read(lowerpath, rdd, ovl_fill_lower);
+	list_del(&middle);
+out:
+	rdd->root = NULL;
+
+	return err;
+}
+
+static void ovl_seek_cursor(struct ovl_dir_file *od, loff_t pos)
+{
+	struct list_head *l;
+	loff_t off;
+
+	l = od->cache.next;
+	for (off = 0; off < pos; off++) {
+		if (l == &od->cache)
+			break;
+		l = l->next;
+	}
+	list_move_tail(&od->cursor, l);
+}
+
+static int ovl_readdir(struct file *file, void *buf, filldir_t filler)
+{
+	struct ovl_dir_file *od = file->private_data;
+	int res;
+
+	if (!file->f_pos)
+		ovl_dir_reset(file);
+
+	if (od->is_real) {
+		res = vfs_readdir(od->realfile, filler, buf);
+		file->f_pos = od->realfile->f_pos;
+
+		return res;
+	}
+
+	if (!od->is_cached) {
+		struct path lowerpath;
+		struct path upperpath;
+		struct ovl_readdir_data rdd = { .list = &od->cache };
+
+		ovl_path_lower(file->f_path.dentry, &lowerpath);
+		ovl_path_upper(file->f_path.dentry, &upperpath);
+
+		res = ovl_dir_read_merged(&upperpath, &lowerpath, &rdd);
+		if (res) {
+			ovl_cache_free(rdd.list);
+			return res;
+		}
+
+		od->cache_version = ovl_dentry_version_get(file->f_path.dentry);
+		od->is_cached = true;
+
+		ovl_seek_cursor(od, file->f_pos);
+	}
+
+	while (od->cursor.next != &od->cache) {
+		int over;
+		loff_t off;
+		struct ovl_cache_entry *p;
+
+		p = list_entry(od->cursor.next, struct ovl_cache_entry, l_node);
+		off = file->f_pos;
+		if (!p->is_whiteout) {
+			over = filler(buf, p->name, p->len, off, p->ino, p->type);
+			if (over)
+				break;
+		}
+		file->f_pos++;
+		list_move(&od->cursor, &p->l_node);
+	}
+
+	return 0;
+}
+
+static loff_t ovl_dir_llseek(struct file *file, loff_t offset, int origin)
+{
+	loff_t res;
+	struct ovl_dir_file *od = file->private_data;
+
+	mutex_lock(&file->f_dentry->d_inode->i_mutex);
+	if (!file->f_pos)
+		ovl_dir_reset(file);
+
+	if (od->is_real) {
+		res = vfs_llseek(od->realfile, offset, origin);
+		file->f_pos = od->realfile->f_pos;
+	} else {
+		res = -EINVAL;
+
+		switch (origin) {
+		case SEEK_CUR:
+			offset += file->f_pos;
+			break;
+		case SEEK_SET:
+			break;
+		default:
+			goto out_unlock;
+		}
+		if (offset < 0)
+			goto out_unlock;
+
+		if (offset != file->f_pos) {
+			file->f_pos = offset;
+			if (od->is_cached)
+				ovl_seek_cursor(od, offset);
+		}
+		res = offset;
+	}
+out_unlock:
+	mutex_unlock(&file->f_dentry->d_inode->i_mutex);
+
+	return res;
+}
+
+static int ovl_dir_fsync(struct file *file, int datasync)
+{
+	struct ovl_dir_file *od = file->private_data;
+
+	/* May need to reopen directory if it got copied up */
+	if (!od->realfile) {
+		struct path upperpath;
+
+		ovl_path_upper(file->f_path.dentry, &upperpath);
+		od->realfile = vfs_open(&upperpath, O_RDONLY, current_cred());
+		if (IS_ERR(od->realfile))
+			return PTR_ERR(od->realfile);
+	}
+
+	return vfs_fsync(od->realfile, datasync);
+}
+
+static int ovl_dir_release(struct inode *inode, struct file *file)
+{
+	struct ovl_dir_file *od = file->private_data;
+
+	list_del(&od->cursor);
+	ovl_cache_free(&od->cache);
+	if (od->realfile)
+		fput(od->realfile);
+	kfree(od);
+
+	return 0;
+}
+
+static int ovl_dir_open(struct inode *inode, struct file *file)
+{
+	struct path realpath;
+	struct file *realfile;
+	struct ovl_dir_file *od;
+	enum ovl_path_type type;
+
+	od = kzalloc(sizeof(struct ovl_dir_file), GFP_KERNEL);
+	if (!od)
+		return -ENOMEM;
+
+	type = ovl_path_real(file->f_path.dentry, &realpath);
+	realfile = vfs_open(&realpath, file->f_flags, current_cred());
+	if (IS_ERR(realfile)) {
+		kfree(od);
+		return PTR_ERR(realfile);
+	}
+	INIT_LIST_HEAD(&od->cache);
+	INIT_LIST_HEAD(&od->cursor);
+	od->is_cached = false;
+	od->realfile = realfile;
+	od->is_real = (type != OVL_PATH_MERGE);
+	file->private_data = od;
+
+	return 0;
+}
+
+const struct file_operations ovl_dir_operations = {
+	.read		= generic_read_dir,
+	.open		= ovl_dir_open,
+	.readdir	= ovl_readdir,
+	.llseek		= ovl_dir_llseek,
+	.fsync		= ovl_dir_fsync,
+	.release	= ovl_dir_release,
+};
+
+static int ovl_check_empty_dir(struct dentry *dentry, struct list_head *list)
+{
+	int err;
+	struct path lowerpath;
+	struct path upperpath;
+	struct ovl_cache_entry *p;
+	struct ovl_readdir_data rdd = { .list = list };
+
+	ovl_path_upper(dentry, &upperpath);
+	ovl_path_lower(dentry, &lowerpath);
+
+	err = ovl_dir_read_merged(&upperpath, &lowerpath, &rdd);
+	if (err)
+		return err;
+
+	err = 0;
+
+	list_for_each_entry(p, list, l_node) {
+		if (p->is_whiteout)
+			continue;
+
+		if (p->name[0] == '.') {
+			if (p->len == 1)
+				continue;
+			if (p->len == 2 && p->name[1] == '.')
+				continue;
+		}
+		err = -ENOTEMPTY;
+		break;
+	}
+
+	return err;
+}
+
+static int ovl_remove_whiteouts(struct dentry *dir, struct list_head *list)
+{
+	struct path upperpath;
+	struct dentry *upperdir;
+	struct ovl_cache_entry *p;
+	const struct cred *old_cred;
+	struct cred *override_cred;
+	int err;
+
+	ovl_path_upper(dir, &upperpath);
+	upperdir = upperpath.dentry;
+
+	override_cred = prepare_creds();
+	if (!override_cred)
+		return -ENOMEM;
+
+	/*
+	 * CAP_DAC_OVERRIDE for lookup and unlink
+	 * CAP_SYS_ADMIN for setxattr of "trusted" namespace
+	 * CAP_FOWNER for unlink in sticky directory
+	 */
+	cap_raise(override_cred->cap_effective, CAP_DAC_OVERRIDE);
+	cap_raise(override_cred->cap_effective, CAP_SYS_ADMIN);
+	cap_raise(override_cred->cap_effective, CAP_FOWNER);
+	old_cred = override_creds(override_cred);
+
+	err = vfs_setxattr(upperdir, ovl_opaque_xattr, "y", 1, 0);
+	if (err)
+		goto out_revert_creds;
+
+	mutex_lock_nested(&upperdir->d_inode->i_mutex, I_MUTEX_PARENT);
+	list_for_each_entry(p, list, l_node) {
+		struct dentry *dentry;
+		int ret;
+
+		if (!p->is_whiteout)
+			continue;
+
+		dentry = lookup_one_len(p->name, upperdir, p->len);
+		if (IS_ERR(dentry)) {
+			printk(KERN_WARNING "overlayfs: failed to lookup whiteout %.*s: %li\n", p->len, p->name, PTR_ERR(dentry));
+			continue;
+		}
+		ret = vfs_unlink(upperdir->d_inode, dentry);
+		dput(dentry);
+		if (ret)
+			printk(KERN_WARNING "overlayfs: failed to unlink whiteout %.*s: %i\n", p->len, p->name, ret);
+	}
+	mutex_unlock(&upperdir->d_inode->i_mutex);
+
+out_revert_creds:
+	revert_creds(old_cred);
+	put_cred(override_cred);
+
+	return err;
+}
+
+int ovl_check_empty_and_clear(struct dentry *dentry, enum ovl_path_type type)
+{
+	int err;
+	LIST_HEAD(list);
+
+	err = ovl_check_empty_dir(dentry, &list);
+	if (!err && type == OVL_PATH_MERGE)
+		err = ovl_remove_whiteouts(dentry, &list);
+
+	ovl_cache_free(&list);
+
+	return err;
+}
diff --git a/fs/overlayfs/super.c b/fs/overlayfs/super.c
new file mode 100644
index 0000000..a344b42
--- /dev/null
+++ b/fs/overlayfs/super.c
@@ -0,0 +1,582 @@
+/*
+ *
+ * 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 "overlayfs.h"
+
+MODULE_AUTHOR("Miklos Szeredi <miklos@xxxxxxxxxx>");
+MODULE_DESCRIPTION("Overlay filesystem");
+MODULE_LICENSE("GPL");
+
+struct ovl_fs {
+	struct vfsmount *upper_mnt;
+	struct vfsmount *lower_mnt;
+};
+
+struct ovl_entry {
+	/*
+	 * Keep "double reference" on upper dentries, so that
+	 * d_delete() doesn't think it's OK to reset d_inode to NULL.
+	 */
+	struct dentry *__upperdentry;
+	struct dentry *lowerdentry;
+	union {
+		struct {
+			u64 version;
+			bool opaque;
+		};
+		struct rcu_head rcu;
+	};
+};
+
+const char *ovl_whiteout_xattr = "trusted.overlay.whiteout";
+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 && S_ISDIR(dentry->d_inode->i_mode))
+			return OVL_PATH_MERGE;
+		else
+			return OVL_PATH_UPPER;
+	} else {
+		return OVL_PATH_LOWER;
+	}
+}
+
+static struct dentry *ovl_upperdentry_dereference(struct ovl_entry *oe)
+{
+	struct dentry *upperdentry = ACCESS_ONCE(oe->__upperdentry);
+	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);
+}
+
+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;
+}
+
+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;
+}
+
+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);
+	smp_wmb();
+	oe->__upperdentry = dget(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)
+{
+	int res;
+	char val;
+
+	if (!dentry)
+		return false;
+	if (!dentry->d_inode)
+		return false;
+	if (!S_ISLNK(dentry->d_inode->i_mode))
+		return false;
+
+	res = vfs_getxattr(dentry, ovl_whiteout_xattr, &val, 1);
+	if (res == 1 && val == 'y')
+		return true;
+
+	return false;
+}
+
+static bool ovl_is_opaquedir(struct dentry *dentry)
+{
+	int res;
+	char val;
+
+	if (!S_ISDIR(dentry->d_inode->i_mode))
+		return false;
+
+	res = vfs_getxattr(dentry, ovl_opaque_xattr, &val, 1);
+	if (res == 1 && val == 'y')
+		return true;
+
+	return false;
+}
+
+static void ovl_entry_free(struct rcu_head *head)
+{
+	struct ovl_entry *oe = container_of(head, struct ovl_entry, rcu);
+	kfree(oe);
+}
+
+static void ovl_dentry_release(struct dentry *dentry)
+{
+	struct ovl_entry *oe = dentry->d_fsdata;
+
+	if (oe) {
+		dput(oe->__upperdentry);
+		dput(oe->__upperdentry);
+		dput(oe->lowerdentry);
+		call_rcu(&oe->rcu, ovl_entry_free);
+	}
+}
+
+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 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;
+}
+
+int ovl_do_lookup(struct dentry *dentry)
+{
+	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 &&
+		    (S_ISLNK(upperdentry->d_inode->i_mode) ||
+		     S_ISDIR(upperdentry->d_inode->i_mode))) {
+			const struct cred *old_cred;
+			struct cred *override_cred;
+
+			err = -ENOMEM;
+			override_cred = prepare_creds();
+			if (!override_cred)
+				goto out_dput_upper;
+
+			/* CAP_SYS_ADMIN needed for getxattr */
+			cap_raise(override_cred->cap_effective, CAP_SYS_ADMIN);
+			old_cred = override_creds(override_cred);
+
+			if (ovl_is_opaquedir(upperdentry)) {
+				oe->opaque = true;
+			} else if (ovl_is_whiteout(upperdentry)) {
+				dput(upperdentry);
+				upperdentry = NULL;
+				oe->opaque = true;
+			}
+			revert_creds(old_cred);
+			put_cred(override_cred);
+		}
+	}
+	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;
+	}
+
+	if (upperdentry)
+		oe->__upperdentry = dget(upperdentry);
+
+	if (lowerdentry)
+		oe->lowerdentry = lowerdentry;
+
+	dentry->d_fsdata = oe;
+	dentry->d_op = &ovl_dentry_operations;
+	d_add(dentry, inode);
+
+	return 0;
+
+out_dput:
+	dput(lowerdentry);
+out_dput_upper:
+	dput(upperdentry);
+out_put_dir:
+	kfree(oe);
+out:
+	return err;
+}
+
+static void ovl_put_super(struct super_block *sb)
+{
+	struct ovl_fs *ufs = sb->s_fs_info;
+
+	if (!(sb->s_flags & MS_RDONLY))
+		mnt_drop_write(ufs->upper_mnt);
+
+	mntput(ufs->upper_mnt);
+	mntput(ufs->lower_mnt);
+
+	kfree(ufs);
+}
+
+static int ovl_remount_fs(struct super_block *sb, int *flagsp, char *data)
+{
+	int flags = *flagsp;
+	struct ovl_fs *ufs = sb->s_fs_info;
+
+	/* When remounting rw or ro, we need to adjust the write access to the
+	 * upper fs.
+	 */
+	if (((flags ^ sb->s_flags) & MS_RDONLY) == 0)
+		/* No change to readonly status */
+		return 0;
+
+	if (flags & MS_RDONLY) {
+		mnt_drop_write(ufs->upper_mnt);
+		return 0;
+	} else
+		return mnt_want_write(ufs->upper_mnt);
+}
+
+static const struct super_operations ovl_super_operations = {
+	.put_super	= ovl_put_super,
+	.remount_fs	= ovl_remount_fs,
+};
+
+struct ovl_config {
+	char *lowerdir;
+	char *upperdir;
+};
+
+enum {
+	Opt_lowerdir,
+	Opt_upperdir,
+	Opt_err,
+};
+
+static const match_table_t ovl_tokens = {
+	{Opt_lowerdir,			"lowerdir=%s"},
+	{Opt_upperdir,			"upperdir=%s"},
+	{Opt_err,			NULL}
+};
+
+static int ovl_parse_opt(char *opt, struct ovl_config *config)
+{
+	char *p;
+
+	config->upperdir = NULL;
+	config->lowerdir = NULL;
+
+	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;
+
+		default:
+			return -EINVAL;
+		}
+	}
+	return 0;
+}
+
+static int ovl_fill_super(struct super_block *sb, void *data, int silent)
+{
+	struct path lowerpath;
+	struct path upperpath;
+	struct inode *root_inode;
+	struct dentry *root_dentry;
+	struct ovl_entry *oe;
+	struct ovl_fs *ufs;
+	struct ovl_config config;
+	int err;
+
+	err = ovl_parse_opt((char *) data, &config);
+	if (err)
+		goto out;
+
+	err = -EINVAL;
+	if (!config.upperdir || !config.lowerdir) {
+		printk(KERN_ERR "overlayfs: missing upperdir or lowerdir\n");
+		goto out_free_config;
+	}
+
+	err = -ENOMEM;
+	ufs = kmalloc(sizeof(struct ovl_fs), GFP_KERNEL);
+	if (!ufs)
+		goto out_free_config;
+
+	oe = ovl_alloc_entry();
+	if (oe == NULL)
+		goto out_free_ufs;
+
+	root_inode = ovl_new_inode(sb, S_IFDIR, oe);
+	if (!root_inode)
+		goto out_free_oe;
+
+	err = kern_path(config.upperdir, LOOKUP_FOLLOW, &upperpath);
+	if (err)
+		goto out_put_root;
+
+	err = kern_path(config.lowerdir, LOOKUP_FOLLOW, &lowerpath);
+	if (err)
+		goto out_put_upperpath;
+
+	err = -ENOTDIR;
+	if (!S_ISDIR(upperpath.dentry->d_inode->i_mode) ||
+	    !S_ISDIR(lowerpath.dentry->d_inode->i_mode))
+		goto out_put_lowerpath;
+
+	ufs->upper_mnt = clone_private_mount(&upperpath);
+	err = PTR_ERR(ufs->upper_mnt);
+	if (IS_ERR(ufs->upper_mnt)) {
+		printk(KERN_ERR "overlayfs: failed to clone upperpath\n");
+		goto out_put_lowerpath;
+	}
+
+	ufs->lower_mnt = clone_private_mount(&lowerpath);
+	err = PTR_ERR(ufs->lower_mnt);
+	if (IS_ERR(ufs->lower_mnt)) {
+		printk(KERN_ERR "overlayfs: failed to clone lowerpath\n");
+		goto out_put_upper_mnt;
+	}
+
+	if (!(sb->s_flags & MS_RDONLY)) {
+		err = mnt_want_write(ufs->upper_mnt);
+		if (err)
+			goto out_put_lower_mnt;
+	}
+
+	err = -ENOMEM;
+	root_dentry = d_alloc_root(root_inode);
+	if (!root_dentry)
+		goto out_drop_write;
+
+	mntput(upperpath.mnt);
+	mntput(lowerpath.mnt);
+
+	oe->__upperdentry = dget(upperpath.dentry);
+	oe->lowerdentry = lowerpath.dentry;
+
+	root_dentry->d_fsdata = oe;
+	root_dentry->d_op = &ovl_dentry_operations;
+
+	sb->s_op = &ovl_super_operations;
+	sb->s_root = root_dentry;
+	sb->s_fs_info = ufs;
+
+	return 0;
+
+out_drop_write:
+	if (!(sb->s_flags & MS_RDONLY))
+		mnt_drop_write(ufs->upper_mnt);
+out_put_lower_mnt:
+	mntput(ufs->lower_mnt);
+out_put_upper_mnt:
+	mntput(ufs->upper_mnt);
+out_put_lowerpath:
+	path_put(&lowerpath);
+out_put_upperpath:
+	path_put(&upperpath);
+out_put_root:
+	iput(root_inode);
+out_free_oe:
+	kfree(oe);
+out_free_ufs:
+	kfree(ufs);
+out_free_config:
+	kfree(config.lowerdir);
+	kfree(config.upperdir);
+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		= "overlayfs",
+	.mount		= ovl_mount,
+	.kill_sb	= kill_anon_super,
+};
+
+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);
-- 
1.7.3.4

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