overlay filesystem

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 overlayfs overlayfs -olowerdir=/lower,upperdir=/upper/upper,workdir=/upper/work /overlay

The following cotributions have been folded into this patch:

Neil Brown <neilb@suse.de>:
 - 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@openwrt.org>:
 - fix a deadlock in ovl_dir_read_merged
 - fix a deadlock in ovl_remove_whiteouts

Erez Zadok <ezk@fsl.cs.sunysb.edu>
 - fix cleanup after WARN_ON

Sedat Dilek <sedat.dilek@googlemail.com>
 - fix up permission to confirm to new API

Robin Dong <hao.bigrat@gmail.com>
 - fix possible leak in ovl_new_inode
 - create new inode in ovl_link

Andy Whitcroft <apw@canonical.com>
 - switch to __inode_permission()
 - copy up i_uid/i_gid from the underlying inode

AV:
 - ovl_copy_up_locked() - dput(ERR_PTR(...)) on two failure exits
 - ovl_clear_empty() - one failure exit forgetting to do unlock_rename(),
   lack of check for udir being the parent of upper, dropping and regaining
   the lock on udir (which would require _another_ check for parent being
   right).
 - bogus d_drop() in copyup and rename [fix from your mail]
 - copyup/remove and copyup/rename races [fix from your mail]
 - ovl_dir_fsync() leaving ERR_PTR() in ->realfile
 - ovl_entry_free() is pointless - it's just a kfree_rcu()
 - fold ovl_do_lookup() into ovl_lookup()
 - manually assigning ->d_op is wrong.  Just use ->s_d_op.
 [patches picked from Miklos]:
 * copyup/remove and copyup/rename races
 * bogus d_drop() in copyup and rename

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

  Jordi Pujol <jordipujolp@gmail.com>
  Andy Whitcroft <apw@canonical.com>
  Michal Suchanek <hramrach@centrum.cz>
  Felix Fietkau <nbd@openwrt.org>
  Erez Zadok <ezk@fsl.cs.sunysb.edu>
  Randy Dunlap <rdunlap@xenotime.net>

Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>

fs/Kconfig

@@ -67,6 +67,7 @@ source "fs/quota/Kconfig"
 
 source "fs/autofs4/Kconfig"
 source "fs/fuse/Kconfig"
+source "fs/overlayfs/Kconfig"
 
 menu "Caches"
 

fs/Makefile

@@ -104,6 +104,7 @@ obj-$(CONFIG_QNX6FS_FS)		+= qnx6/
 obj-$(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/

fs/overlayfs/Kconfig

@@ -0,0 +1,10 @@
+config OVERLAYFS_FS
+	tristate "Overlay filesystem support"
+	help
+	  An overlay filesystem combines two filesystems - an 'upper' filesystem
+	  and a 'lower' filesystem.  When a name exists in both filesystems, the
+	  object in the 'upper' filesystem is visible while the object in the
+	  'lower' filesystem is either hidden or, in the case of directories,
+	  merged with the 'upper' object.
+
+	  For more information see Documentation/filesystems/overlayfs.txt

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

fs/overlayfs/copy_up.c

@@ -0,0 +1,414 @@
+/*
+ *
+ * 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 <linux/sched.h>
+#include <linux/namei.h>
+#include "overlayfs.h"
+
+#define OVL_COPY_UP_CHUNK_SIZE (1 << 20)
+
+int ovl_copy_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;
+	loff_t old_pos = 0;
+	loff_t new_pos = 0;
+	int error = 0;
+
+	if (len == 0)
+		return 0;
+
+	old_file = ovl_path_open(old, O_RDONLY);
+	if (IS_ERR(old_file))
+		return PTR_ERR(old_file);
+
+	new_file = ovl_path_open(new, O_WRONLY);
+	if (IS_ERR(new_file)) {
+		error = PTR_ERR(new_file);
+		goto out_fput;
+	}
+
+	/* FIXME: copy up sparse files efficiently */
+	while (len) {
+		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, &old_pos,
+					 new_file, &new_pos,
+					 this_len, SPLICE_F_MOVE);
+		if (bytes <= 0) {
+			error = bytes;
+			break;
+		}
+		WARN_ON(old_pos != new_pos);
+
+		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, NULL);
+}
+
+int ovl_set_attr(struct dentry *upperdentry, struct kstat *stat)
+{
+	int err = 0;
+
+	if (!S_ISLNK(stat->mode)) {
+		struct iattr attr = {
+			.ia_valid = ATTR_MODE,
+			.ia_mode = stat->mode,
+		};
+		err = notify_change(upperdentry, &attr, NULL);
+	}
+	if (!err) {
+		struct iattr attr = {
+			.ia_valid = ATTR_UID | ATTR_GID,
+			.ia_uid = stat->uid,
+			.ia_gid = stat->gid,
+		};
+		err = notify_change(upperdentry, &attr, NULL);
+	}
+	if (!err)
+		ovl_set_timestamps(upperdentry, stat);
+
+	return err;
+
+}
+
+static int ovl_copy_up_locked(struct dentry *workdir, struct dentry *upperdir,
+			      struct dentry *dentry, struct path *lowerpath,
+			      struct kstat *stat, struct iattr *attr,
+			      const char *link)
+{
+	struct inode *wdir = workdir->d_inode;
+	struct inode *udir = upperdir->d_inode;
+	struct dentry *newdentry = NULL;
+	struct dentry *upper = NULL;
+	umode_t mode = stat->mode;
+	int err;
+
+	newdentry = ovl_lookup_temp(workdir, dentry);
+	err = PTR_ERR(newdentry);
+	if (IS_ERR(newdentry))
+		goto out;
+
+	upper = lookup_one_len(dentry->d_name.name, upperdir,
+			       dentry->d_name.len);
+	err = PTR_ERR(upper);
+	if (IS_ERR(upper))
+		goto out1;
+
+	/* Can't properly set mode on creation because of the umask */
+	stat->mode &= S_IFMT;
+	err = ovl_create_real(wdir, newdentry, stat, link, NULL, true);
+	stat->mode = mode;
+	if (err)
+		goto out2;
+
+	if (S_ISREG(stat->mode)) {
+		struct path upperpath;
+		ovl_path_upper(dentry, &upperpath);
+		BUG_ON(upperpath.dentry != NULL);
+		upperpath.dentry = newdentry;
+
+		err = ovl_copy_up_data(lowerpath, &upperpath, stat->size);
+		if (err)
+			goto out_cleanup;
+	}
+
+	err = ovl_copy_xattr(lowerpath->dentry, newdentry);
+	if (err)
+		goto out_cleanup;
+
+	mutex_lock(&newdentry->d_inode->i_mutex);
+	err = ovl_set_attr(newdentry, stat);
+	if (!err && attr)
+		err = notify_change(newdentry, attr, NULL);
+	mutex_unlock(&newdentry->d_inode->i_mutex);
+	if (err)
+		goto out_cleanup;
+
+	err = ovl_do_rename(wdir, newdentry, udir, upper, 0);
+	if (err)
+		goto out_cleanup;
+
+	ovl_dentry_update(dentry, newdentry);
+	newdentry = NULL;
+
+	/*
+	 * Non-directores become opaque when copied up.
+	 */
+	if (!S_ISDIR(stat->mode))
+		ovl_dentry_set_opaque(dentry, true);
+out2:
+	dput(upper);
+out1:
+	dput(newdentry);
+out:
+	return err;
+
+out_cleanup:
+	ovl_cleanup(wdir, newdentry);
+	goto out;
+}
+
+/*
+ * 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.
+ */
+int ovl_copy_up_one(struct dentry *parent, struct dentry *dentry,
+		    struct path *lowerpath, struct kstat *stat,
+		    struct iattr *attr)
+{
+	struct dentry *workdir = ovl_workdir(dentry);
+	int err;
+	struct kstat pstat;
+	struct path parentpath;
+	struct dentry *upperdir;
+	struct dentry *upperdentry;
+	const struct cred *old_cred;
+	struct cred *override_cred;
+	char *link = NULL;
+
+	ovl_path_upper(parent, &parentpath);
+	upperdir = parentpath.dentry;
+
+	err = vfs_getattr(&parentpath, &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_CHOWN for chown
+	 * 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_CHOWN);
+	cap_raise(override_cred->cap_effective, CAP_MKNOD);
+	old_cred = override_creds(override_cred);
+
+	err = -EIO;
+	if (lock_rename(workdir, upperdir) != NULL) {
+		pr_err("overlayfs: failed to lock workdir+upperdir\n");
+		goto out_unlock;
+	}
+	upperdentry = ovl_dentry_upper(dentry);
+	if (upperdentry) {
+		unlock_rename(workdir, upperdir);
+		err = 0;
+		/* Raced with another copy-up?  Do the setattr here */
+		if (attr) {
+			mutex_lock(&upperdentry->d_inode->i_mutex);
+			err = notify_change(upperdentry, attr, NULL);
+			mutex_unlock(&upperdentry->d_inode->i_mutex);
+		}
+		goto out_put_cred;
+	}
+
+	err = ovl_copy_up_locked(workdir, upperdir, dentry, lowerpath,
+				 stat, attr, link);
+	if (!err) {
+		/* Restore timestamps on parent (best effort) */
+		ovl_set_timestamps(upperdir, &pstat);
+	}
+out_unlock:
+	unlock_rename(workdir, upperdir);
+out_put_cred:
+	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, &stat);
+		if (!err)
+			err = ovl_copy_up_one(parent, next, &lowerpath, &stat, NULL);
+
+		dput(parent);
+		dput(next);
+	}
+
+	return err;
+}

fs/overlayfs/dir.c

@@ -0,0 +1,921 @@
+/*
+ *
+ * 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/cred.h>
+#include "overlayfs.h"
+
+void ovl_cleanup(struct inode *wdir, struct dentry *wdentry)
+{
+	int err;
+
+	dget(wdentry);
+	if (S_ISDIR(wdentry->d_inode->i_mode))
+		err = ovl_do_rmdir(wdir, wdentry);
+	else
+		err = ovl_do_unlink(wdir, wdentry);
+	dput(wdentry);
+
+	if (err) {
+		pr_err("overlayfs: cleanup of '%pd2' failed (%i)\n",
+		       wdentry, err);
+	}
+}
+
+struct dentry *ovl_lookup_temp(struct dentry *workdir, struct dentry *dentry)
+{
+	struct dentry *temp;
+	char name[20];
+
+	snprintf(name, sizeof(name), "#%lx", (unsigned long) dentry);
+
+	temp = lookup_one_len(name, workdir, strlen(name));
+	if (!IS_ERR(temp) && temp->d_inode) {
+		pr_err("overlayfs: workdir/%s already exists\n", name);
+		dput(temp);
+		temp = ERR_PTR(-EIO);
+	}
+
+	return temp;
+}
+
+/* caller holds i_mutex on workdir */
+static struct dentry *ovl_whiteout(struct dentry *workdir,
+				   struct dentry *dentry)
+{
+	int err;
+	struct dentry *whiteout;
+	struct inode *wdir = workdir->d_inode;
+
+	whiteout = ovl_lookup_temp(workdir, dentry);
+	if (IS_ERR(whiteout))
+		return whiteout;
+
+	err = ovl_do_whiteout(wdir, whiteout);
+	if (err) {
+		dput(whiteout);
+		whiteout = ERR_PTR(err);
+	}
+
+	return whiteout;
+}
+
+int ovl_create_real(struct inode *dir, struct dentry *newdentry,
+		    struct kstat *stat, const char *link,
+		    struct dentry *hardlink, bool debug)
+{
+	int err;
+
+	if (newdentry->d_inode)
+		return -ESTALE;
+
+	if (hardlink) {
+		err = ovl_do_link(hardlink, dir, newdentry, debug);
+	} else {
+		switch (stat->mode & S_IFMT) {
+		case S_IFREG:
+			err = ovl_do_create(dir, newdentry, stat->mode, debug);
+			break;
+
+		case S_IFDIR:
+			err = ovl_do_mkdir(dir, newdentry, stat->mode, debug);
+			break;
+
+		case S_IFCHR:
+		case S_IFBLK:
+		case S_IFIFO:
+		case S_IFSOCK:
+			err = ovl_do_mknod(dir, newdentry,
+					   stat->mode, stat->rdev, debug);
+			break;
+
+		case S_IFLNK:
+			err = ovl_do_symlink(dir, newdentry, link, debug);
+			break;
+
+		default:
+			err = -EPERM;
+		}
+	}
+	if (!err && 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.
+		 */
+		err = -ENOENT;
+	}
+	return err;
+}
+
+static int ovl_set_opaque(struct dentry *upperdentry)
+{
+	return ovl_do_setxattr(upperdentry, ovl_opaque_xattr, "y", 1, 0);
+}
+
+static void ovl_remove_opaque(struct dentry *upperdentry)
+{
+	int err;
+
+	err = ovl_do_removexattr(upperdentry, ovl_opaque_xattr);
+	if (err) {
+		pr_warn("overlayfs: failed to remove opaque from '%s' (%i)\n",
+			upperdentry->d_name.name, 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, 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_upper(struct dentry *dentry, struct inode *inode,
+			    struct kstat *stat, const char *link,
+			    struct dentry *hardlink)
+{
+	struct dentry *upperdir = ovl_dentry_upper(dentry->d_parent);
+	struct inode *udir = upperdir->d_inode;
+	struct dentry *newdentry;
+	int err;
+
+	mutex_lock_nested(&udir->i_mutex, I_MUTEX_PARENT);
+	newdentry = lookup_one_len(dentry->d_name.name, upperdir,
+				   dentry->d_name.len);
+	err = PTR_ERR(newdentry);
+	if (IS_ERR(newdentry))
+		goto out_unlock;
+	err = ovl_create_real(udir, newdentry, stat, link, hardlink, false);
+	if (err)
+		goto out_dput;
+
+	ovl_dentry_version_inc(dentry->d_parent);
+	ovl_dentry_update(dentry, newdentry);
+	ovl_copyattr(newdentry->d_inode, inode);
+	d_instantiate(dentry, inode);
+	newdentry = NULL;
+out_dput:
+	dput(newdentry);
+out_unlock:
+	mutex_unlock(&udir->i_mutex);
+	return err;
+}
+
+static int ovl_lock_rename_workdir(struct dentry *workdir,
+				   struct dentry *upperdir)
+{
+	/* Workdir should not be the same as upperdir */
+	if (workdir == upperdir)
+		goto err;
+
+	/* Workdir should not be subdir of upperdir and vice versa */
+	if (lock_rename(workdir, upperdir) != NULL)
+		goto err_unlock;
+
+	return 0;
+
+err_unlock:
+	unlock_rename(workdir, upperdir);
+err:
+	pr_err("overlayfs: failed to lock workdir+upperdir\n");
+	return -EIO;
+}
+
+static struct dentry *ovl_clear_empty(struct dentry *dentry,
+				      struct list_head *list)
+{
+	struct dentry *workdir = ovl_workdir(dentry);
+	struct inode *wdir = workdir->d_inode;
+	struct dentry *upperdir = ovl_dentry_upper(dentry->d_parent);
+	struct inode *udir = upperdir->d_inode;
+	struct path upperpath;
+	struct dentry *upper;
+	struct dentry *opaquedir;
+	struct kstat stat;
+	int err;
+
+	err = ovl_lock_rename_workdir(workdir, upperdir);
+	if (err)
+		goto out;
+
+	ovl_path_upper(dentry, &upperpath);
+	err = vfs_getattr(&upperpath, &stat);
+	if (err)
+		goto out_unlock;
+
+	err = -ESTALE;
+	if (!S_ISDIR(stat.mode))
+		goto out_unlock;
+	upper = upperpath.dentry;
+	if (upper->d_parent->d_inode != udir)
+		goto out_unlock;
+
+	opaquedir = ovl_lookup_temp(workdir, dentry);
+	err = PTR_ERR(opaquedir);
+	if (IS_ERR(opaquedir))
+		goto out_unlock;
+
+	err = ovl_create_real(wdir, opaquedir, &stat, NULL, NULL, true);
+	if (err)
+		goto out_dput;
+
+	err = ovl_copy_xattr(upper, opaquedir);
+	if (err)
+		goto out_cleanup;
+
+	err = ovl_set_opaque(opaquedir);
+	if (err)
+		goto out_cleanup;
+
+	mutex_lock(&opaquedir->d_inode->i_mutex);
+	err = ovl_set_attr(opaquedir, &stat);
+	mutex_unlock(&opaquedir->d_inode->i_mutex);
+	if (err)
+		goto out_cleanup;
+
+	err = ovl_do_rename(wdir, opaquedir, udir, upper, RENAME_EXCHANGE);
+	if (err)
+		goto out_cleanup;
+
+	ovl_cleanup_whiteouts(upper, list);
+	ovl_cleanup(wdir, upper);
+	unlock_rename(workdir, upperdir);
+
+	/* dentry's upper doesn't match now, get rid of it */
+	d_drop(dentry);
+
+	return opaquedir;
+
+out_cleanup:
+	ovl_cleanup(wdir, opaquedir);
+out_dput:
+	dput(opaquedir);
+out_unlock:
+	unlock_rename(workdir, upperdir);
+out:
+	return ERR_PTR(err);
+}
+
+static struct dentry *ovl_check_empty_and_clear(struct dentry *dentry,
+						enum ovl_path_type type)
+{
+	int err;
+	struct dentry *ret = NULL;
+	LIST_HEAD(list);
+
+	err = ovl_check_empty_dir(dentry, &list);
+	if (err)
+		ret = ERR_PTR(err);
+	else if (type == OVL_PATH_MERGE)
+		ret = ovl_clear_empty(dentry, &list);
+
+	ovl_cache_free(&list);
+
+	return ret;
+}
+
+static int ovl_create_over_whiteout(struct dentry *dentry, struct inode *inode,
+				    struct kstat *stat, const char *link,
+				    struct dentry *hardlink)
+{
+	struct dentry *workdir = ovl_workdir(dentry);
+	struct inode *wdir = workdir->d_inode;
+	struct dentry *upperdir = ovl_dentry_upper(dentry->d_parent);
+	struct inode *udir = upperdir->d_inode;
+	struct dentry *upper;
+	struct dentry *newdentry;
+	int err;
+
+	err = ovl_lock_rename_workdir(workdir, upperdir);
+	if (err)
+		goto out;
+
+	newdentry = ovl_lookup_temp(workdir, dentry);
+	err = PTR_ERR(newdentry);
+	if (IS_ERR(newdentry))
+		goto out_unlock;
+
+	upper = lookup_one_len(dentry->d_name.name, upperdir,
+			       dentry->d_name.len);
+	err = PTR_ERR(upper);
+	if (IS_ERR(upper))
+		goto out_dput;
+
+	err = ovl_create_real(wdir, newdentry, stat, link, hardlink, true);
+	if (err)
+		goto out_dput2;
+
+	if (S_ISDIR(stat->mode)) {
+		err = ovl_set_opaque(newdentry);
+		if (err)
+			goto out_cleanup;
+
+		err = ovl_do_rename(wdir, newdentry, udir, upper,
+				    RENAME_EXCHANGE);
+		if (err)
+			goto out_cleanup;
+
+		ovl_cleanup(wdir, upper);
+	} else {
+		err = ovl_do_rename(wdir, newdentry, udir, upper, 0);
+		if (err)
+			goto out_cleanup;
+	}
+	ovl_dentry_version_inc(dentry->d_parent);
+	ovl_dentry_update(dentry, newdentry);
+	ovl_copyattr(newdentry->d_inode, inode);
+	d_instantiate(dentry, inode);
+	newdentry = NULL;
+out_dput2:
+	dput(upper);
+out_dput:
+	dput(newdentry);
+out_unlock:
+	unlock_rename(workdir, upperdir);
+out:
+	return err;
+
+out_cleanup:
+	ovl_cleanup(wdir, newdentry);
+	goto out_dput2;
+}
+
+static int ovl_create_or_link(struct dentry *dentry, int mode, dev_t rdev,
+			      const char *link, struct dentry *hardlink)
+{
+	int err;
+	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;
+
+	if (!ovl_dentry_is_opaque(dentry)) {
+		err = ovl_create_upper(dentry, inode, &stat, link, hardlink);
+	} else {
+		const struct cred *old_cred;
+		struct cred *override_cred;
+
+		err = -ENOMEM;
+		override_cred = prepare_creds();
+		if (!override_cred)
+			goto out_iput;
+
+		/*
+		 * CAP_SYS_ADMIN for setting opaque xattr
+		 * CAP_DAC_OVERRIDE for create in workdir, rename
+		 * CAP_FOWNER for removing whiteout from sticky dir
+		 */
+		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);
+		old_cred = override_creds(override_cred);
+
+		err = ovl_create_over_whiteout(dentry, inode, &stat, link,
+					       hardlink);
+
+		revert_creds(old_cred);
+		put_cred(override_cred);
+	}
+
+	if (!err)
+		inode = NULL;
+out_iput:
+	iput(inode);
+out:
+	return err;
+}
+
+static int ovl_create_object(struct dentry *dentry, int mode, dev_t rdev,
+			     const char *link)
+{
+	int err;
+
+	err = ovl_want_write(dentry);
+	if (!err) {
+		err = ovl_create_or_link(dentry, mode, rdev, link, NULL);
+		ovl_drop_write(dentry);
+	}
+
+	return err;
+}
+
+static int ovl_create(struct inode *dir, struct dentry *dentry, umode_t mode,
+		      bool excl)
+{
+	return ovl_create_object(dentry, (mode & 07777) | S_IFREG, 0, NULL);
+}
+
+static int ovl_mkdir(struct inode *dir, struct dentry *dentry, umode_t mode)
+{
+	return ovl_create_object(dentry, (mode & 07777) | S_IFDIR, 0, NULL);
+}
+
+static int ovl_mknod(struct inode *dir, struct dentry *dentry, umode_t mode,
+		     dev_t rdev)
+{
+	/* Don't allow creation of "whiteout" on overlay */
+	if (S_ISCHR(mode) && rdev == WHITEOUT_DEV)
+		return -EPERM;
+
+	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_link(struct dentry *old, struct inode *newdir,
+		    struct dentry *new)
+{
+	int err;
+	struct dentry *upper;
+
+	err = ovl_want_write(old);
+	if (err)
+		goto out;
+
+	err = ovl_copy_up(old);
+	if (err)
+		goto out_drop_write;
+
+	upper = ovl_dentry_upper(old);
+	err = ovl_create_or_link(new, upper->d_inode->i_mode, 0, NULL, upper);
+
+out_drop_write:
+	ovl_drop_write(old);
+out:
+	return err;
+}
+
+static int ovl_remove_and_whiteout(struct dentry *dentry,
+				   enum ovl_path_type type, bool is_dir)
+{
+	struct dentry *workdir = ovl_workdir(dentry);
+	struct inode *wdir = workdir->d_inode;
+	struct dentry *upperdir = ovl_dentry_upper(dentry->d_parent);
+	struct inode *udir = upperdir->d_inode;
+	struct dentry *whiteout;
+	struct dentry *upper;
+	struct dentry *opaquedir = NULL;
+	int err;
+
+	if (is_dir) {
+		opaquedir = ovl_check_empty_and_clear(dentry, type);
+		err = PTR_ERR(opaquedir);
+		if (IS_ERR(opaquedir))
+			goto out;
+	}
+
+	err = ovl_lock_rename_workdir(workdir, upperdir);
+	if (err)
+		goto out_dput;
+
+	whiteout = ovl_whiteout(workdir, dentry);
+	err = PTR_ERR(whiteout);
+	if (IS_ERR(whiteout))
+		goto out_unlock;
+
+	if (type == OVL_PATH_LOWER) {
+		upper = lookup_one_len(dentry->d_name.name, upperdir,
+					   dentry->d_name.len);
+		err = PTR_ERR(upper);
+		if (IS_ERR(upper))
+			goto kill_whiteout;
+
+		err = ovl_do_rename(wdir, whiteout, udir, upper, 0);
+		dput(upper);
+		if (err)
+			goto kill_whiteout;
+	} else {
+		int flags = 0;
+
+		upper = ovl_dentry_upper(dentry);
+		if (opaquedir)
+			upper = opaquedir;
+		err = -ESTALE;
+		if (upper->d_parent != upperdir)
+			goto kill_whiteout;
+
+		if (is_dir)
+			flags |= RENAME_EXCHANGE;
+
+		err = ovl_do_rename(wdir, whiteout, udir, upper, flags);
+		if (err)
+			goto kill_whiteout;
+
+		if (is_dir)
+			ovl_cleanup(wdir, upper);
+	}
+	ovl_dentry_version_inc(dentry->d_parent);
+out_d_drop:
+	d_drop(dentry);
+	dput(whiteout);
+out_unlock:
+	unlock_rename(workdir, upperdir);
+out_dput:
+	dput(opaquedir);
+out:
+	return err;
+
+kill_whiteout:
+	ovl_cleanup(wdir, whiteout);
+	goto out_d_drop;
+}
+
+static int ovl_remove_upper(struct dentry *dentry, bool is_dir)
+{
+	struct dentry *upperdir = ovl_dentry_upper(dentry->d_parent);
+	struct inode *dir = upperdir->d_inode;
+	struct dentry *upper = ovl_dentry_upper(dentry);
+	int err;
+
+	mutex_lock_nested(&dir->i_mutex, I_MUTEX_PARENT);
+	err = -ESTALE;
+	if (upper->d_parent == upperdir) {
+		/* Don't let d_delete() think it can reset d_inode */
+		dget(upper);
+		if (is_dir)
+			err = vfs_rmdir(dir, upper);
+		else
+			err = vfs_unlink(dir, upper, NULL);
+		dput(upper);
+		ovl_dentry_version_inc(dentry->d_parent);
+	}
+
+	/*
+	 * 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.
+	 */
+	d_drop(dentry);
+	mutex_unlock(&dir->i_mutex);
+
+	return err;
+}
+
+static inline int ovl_check_sticky(struct dentry *dentry)
+{
+	struct inode *dir = ovl_dentry_real(dentry->d_parent)->d_inode;
+	struct inode *inode = ovl_dentry_real(dentry)->d_inode;
+
+	if (check_sticky(dir, inode))
+		return -EPERM;
+
+	return 0;
+}
+
+static int ovl_do_remove(struct dentry *dentry, bool is_dir)
+{
+	enum ovl_path_type type;
+	int err;
+
+	err = ovl_check_sticky(dentry);
+	if (err)
+		goto out;
+
+	err = ovl_want_write(dentry);
+	if (err)
+		goto out;
+
+	err = ovl_copy_up(dentry->d_parent);
+	if (err)
+		goto out_drop_write;
+
+	type = ovl_path_type(dentry);
+	if (type == OVL_PATH_PURE_UPPER) {
+		err = ovl_remove_upper(dentry, is_dir);
+	} else {
+		const struct cred *old_cred;
+		struct cred *override_cred;
+
+		err = -ENOMEM;
+		override_cred = prepare_creds();
+		if (!override_cred)
+			goto out_drop_write;
+
+		/*
+		 * CAP_SYS_ADMIN for setting xattr on whiteout, opaque dir
+		 * CAP_DAC_OVERRIDE for create in workdir, rename
+		 * CAP_FOWNER for removing whiteout from sticky dir
+		 * CAP_FSETID for chmod of opaque dir
+		 * CAP_CHOWN for chown of opaque dir
+		 */
+		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_CHOWN);
+		old_cred = override_creds(override_cred);
+
+		err = ovl_remove_and_whiteout(dentry, type, is_dir);
+
+		revert_creds(old_cred);
+		put_cred(override_cred);
+	}
+out_drop_write:
+	ovl_drop_write(dentry);
+out:
+	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)
+{
+	return ovl_do_remove(dentry, true);
+}
+
+static int ovl_rename2(struct inode *olddir, struct dentry *old,
+		       struct inode *newdir, struct dentry *new,
+		       unsigned int flags)
+{
+	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 cleanup_whiteout = false;
+	bool overwrite = !(flags & RENAME_EXCHANGE);
+	bool is_dir = S_ISDIR(old->d_inode->i_mode);
+	bool new_is_dir = false;
+	struct dentry *opaquedir = NULL;
+	const struct cred *old_cred = NULL;
+	struct cred *override_cred = NULL;
+
+	err = -EINVAL;
+	if (flags & ~(RENAME_EXCHANGE | RENAME_NOREPLACE))
+		goto out;
+
+	flags &= ~RENAME_NOREPLACE;
+
+	err = ovl_check_sticky(old);
+	if (err)
+		goto out;
+
+	/* Don't copy up directory trees */
+	old_type = ovl_path_type(old);
+	err = -EXDEV;
+	if ((old_type == OVL_PATH_LOWER || old_type == OVL_PATH_MERGE) && is_dir)
+		goto out;
+
+	if (new->d_inode) {
+		err = ovl_check_sticky(new);
+		if (err)
+			goto out;
+
+		if (S_ISDIR(new->d_inode->i_mode))
+			new_is_dir = true;
+
+		new_type = ovl_path_type(new);
+		err = -EXDEV;
+		if (!overwrite && (new_type == OVL_PATH_LOWER || new_type == OVL_PATH_MERGE) && new_is_dir)
+			goto out;
+
+		err = 0;
+		if (new_type == OVL_PATH_LOWER && old_type == OVL_PATH_LOWER) {
+			if (ovl_dentry_lower(old)->d_inode ==
+			    ovl_dentry_lower(new)->d_inode)
+				goto out;
+		}
+		if (new_type != OVL_PATH_LOWER && old_type != OVL_PATH_LOWER) {
+			if (ovl_dentry_upper(old)->d_inode ==
+			    ovl_dentry_upper(new)->d_inode)
+				goto out;
+		}
+	} else {
+		if (ovl_dentry_is_opaque(new))
+			new_type = OVL_PATH_UPPER;
+		else
+			new_type = OVL_PATH_PURE_UPPER;
+	}
+
+	err = ovl_want_write(old);
+	if (err)
+		goto out;
+
+	err = ovl_copy_up(old);
+	if (err)
+		goto out_drop_write;
+
+	err = ovl_copy_up(new->d_parent);
+	if (err)
+		goto out_drop_write;
+	if (!overwrite) {
+		err = ovl_copy_up(new);
+		if (err)
+			goto out_drop_write;
+	}
+
+	old_opaque = old_type != OVL_PATH_PURE_UPPER;
+	new_opaque = new_type != OVL_PATH_PURE_UPPER;
+
+	if (old_opaque || new_opaque) {
+		err = -ENOMEM;
+		override_cred = prepare_creds();
+		if (!override_cred)
+			goto out_drop_write;
+
+		/*
+		 * CAP_SYS_ADMIN for setting xattr on whiteout, opaque dir
+		 * CAP_DAC_OVERRIDE for create in workdir
+		 * CAP_FOWNER for removing whiteout from sticky dir
+		 * CAP_FSETID for chmod of opaque dir
+		 * CAP_CHOWN for chown of opaque dir
+		 */
+		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_CHOWN);
+		old_cred = override_creds(override_cred);
+	}
+
+	if (overwrite && (new_type == OVL_PATH_LOWER || new_type == OVL_PATH_MERGE) && new_is_dir) {
+		opaquedir = ovl_check_empty_and_clear(new, new_type);
+		err = PTR_ERR(opaquedir);
+		if (IS_ERR(opaquedir)) {
+			opaquedir = NULL;
+			goto out_revert_creds;
+		}
+	}
+
+	if (overwrite) {
+		if (old_opaque) {
+			if (new->d_inode || !new_opaque) {
+				/* Whiteout source */
+				flags |= RENAME_WHITEOUT;
+			} else {
+				/* Switch whiteouts */
+				flags |= RENAME_EXCHANGE;
+			}
+		} else if (is_dir && !new->d_inode && new_opaque) {
+			flags |= RENAME_EXCHANGE;
+			cleanup_whiteout = true;
+		}
+	}
+
+	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) {
+		if (opaquedir) {
+			newdentry = opaquedir;
+			opaquedir = NULL;
+		} else {
+			dget(newdentry);
+		}
+	} else {
+		new_create = true;
+		newdentry = lookup_one_len(new->d_name.name, new_upperdir,
+					   new->d_name.len);
+		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;
+
+	if (is_dir && !old_opaque && new_opaque) {
+		err = ovl_set_opaque(olddentry);
+		if (err)
+			goto out_dput;
+	}
+	if (!overwrite && new_is_dir && old_opaque && !new_opaque) {
+		err = ovl_set_opaque(newdentry);
+		if (err)
+			goto out_dput;
+	}
+
+	if (old_opaque || new_opaque) {
+		err = ovl_do_rename(old_upperdir->d_inode, olddentry,
+				    new_upperdir->d_inode, newdentry,
+				    flags);
+	} else {
+		/* No debug for the plain case */
+		BUG_ON(flags & ~RENAME_EXCHANGE);
+		err = vfs_rename(old_upperdir->d_inode, olddentry,
+				 new_upperdir->d_inode, newdentry,
+				 NULL, flags);
+	}
+
+	if (err) {
+		if (is_dir && !old_opaque && new_opaque)
+			ovl_remove_opaque(olddentry);
+		if (!overwrite && new_is_dir && old_opaque && !new_opaque)
+			ovl_remove_opaque(newdentry);
+		goto out_dput;
+	}
+
+	if (is_dir && old_opaque && !new_opaque)
+		ovl_remove_opaque(olddentry);
+	if (!overwrite && new_is_dir && !old_opaque && new_opaque)
+		ovl_remove_opaque(newdentry);
+
+	if (old_opaque != new_opaque) {
+		ovl_dentry_set_opaque(old, new_opaque);
+		if (!overwrite)
+			ovl_dentry_set_opaque(new, old_opaque);
+	}
+
+	if (cleanup_whiteout)
+		ovl_cleanup(old_upperdir->d_inode, newdentry);
+
+	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);
+out_revert_creds:
+	if (old_opaque || new_opaque) {
+		revert_creds(old_cred);
+		put_cred(override_cred);
+	}
+out_drop_write:
+	ovl_drop_write(old);
+out:
+	dput(opaquedir);
+	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,
+	.rename2	= ovl_rename2,
+	.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,
+};

fs/overlayfs/inode.c

@@ -0,0 +1,425 @@
+/*
+ *
+ * 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"
+
+static int ovl_copy_up_last(struct dentry *dentry, struct iattr *attr,
+			    bool no_data)
+{
+	int err;
+	struct dentry *parent;
+	struct kstat stat;
+	struct path lowerpath;
+
+	parent = dget_parent(dentry);
+	err = ovl_copy_up(parent);
+	if (err)
+		goto out_dput_parent;
+
+	ovl_path_lower(dentry, &lowerpath);
+	err = vfs_getattr(&lowerpath, &stat);
+	if (err)
+		goto out_dput_parent;
+
+	if (no_data)
+		stat.size = 0;
+
+	err = ovl_copy_up_one(parent, dentry, &lowerpath, &stat, attr);
+
+out_dput_parent:
+	dput(parent);
+	return err;
+}
+
+int ovl_setattr(struct dentry *dentry, struct iattr *attr)
+{
+	int err;
+	struct dentry *upperdentry;
+
+	err = ovl_want_write(dentry);
+	if (err)
+		goto out;
+
+	upperdentry = ovl_dentry_upper(dentry);
+	if (upperdentry) {
+		mutex_lock(&upperdentry->d_inode->i_mutex);
+		err = notify_change(upperdentry, attr, NULL);
+		mutex_unlock(&upperdentry->d_inode->i_mutex);
+	} else {
+		err = ovl_copy_up_last(dentry, attr, false);
+	}
+	ovl_drop_write(dentry);
+out:
+	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, stat);
+}
+
+int ovl_permission(struct inode *inode, int mask)
+{
+	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 (mask & MAY_NOT_BLOCK) {
+		return -ECHILD;
+	} else {
+		/*
+		 * For non-directories find an alias and get the info
+		 * from there.
+		 */
+		alias = d_find_any_alias(inode);
+		if (WARN_ON(!alias))
+			return -ENOENT;
+
+		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(!(mask & MAY_NOT_BLOCK));
+		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.
+		 *
+		 * If the overlay itself is read-only then proceed
+		 * with the permission check, don't return EROFS.
+		 * This will only happen if this is the lower layer of
+		 * another overlayfs.
+		 *
+		 * If upper fs becomes read-only after the overlay was
+		 * constructed return EROFS to prevent modification of
+		 * upper layer.
+		 */
+		err = -EROFS;
+		if (is_upper && !IS_RDONLY(inode) && IS_RDONLY(realinode) &&
+		    (S_ISREG(mode) || S_ISDIR(mode) || S_ISLNK(mode)))
+			goto out_dput;
+	}
+
+	err = __inode_permission(realinode, mask);
+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);
+
+	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;
+
+	err = ovl_want_write(dentry);
+	if (err)
+		goto out;
+
+	err = -EPERM;
+	if (ovl_is_private_xattr(name))
+		goto out_drop_write;
+
+	err = ovl_copy_up(dentry);
+	if (err)
+		goto out_drop_write;
+
+	upperdentry = ovl_dentry_upper(dentry);
+	err = vfs_setxattr(upperdentry, name, value, size, flags);
+
+out_drop_write:
+	ovl_drop_write(dentry);
+out:
+	return err;
+}
+
+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;
+
+	err = ovl_want_write(dentry);
+	if (err)
+		goto out;
+
+	if (ovl_path_type(dentry->d_parent) == OVL_PATH_MERGE &&
+	    ovl_is_private_xattr(name))
+		goto out_drop_write;
+
+	type = ovl_path_real(dentry, &realpath);
+	if (type == OVL_PATH_LOWER) {
+		err = vfs_getxattr(realpath.dentry, name, NULL, 0);
+		if (err < 0)
+			goto out_drop_write;
+
+		err = ovl_copy_up(dentry);
+		if (err)
+			goto out_drop_write;
+
+		ovl_path_upper(dentry, &realpath);
+	}
+
+	err = vfs_removexattr(realpath.dentry, name);
+out_drop_write:
+	ovl_drop_write(dentry);
+out:
+	return err;
+}
+
+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 int ovl_dentry_open(struct dentry *dentry, struct file *file,
+		    const struct cred *cred)
+{
+	int err;
+	struct path realpath;
+	enum ovl_path_type type;
+	bool want_write = false;
+
+	type = ovl_path_real(dentry, &realpath);
+	if (ovl_open_need_copy_up(file->f_flags, type, realpath.dentry)) {
+		want_write = true;
+		err = ovl_want_write(dentry);
+		if (err)
+			goto out;
+
+		if (file->f_flags & O_TRUNC)
+			err = ovl_copy_up_last(dentry, NULL, true);
+		else
+			err = ovl_copy_up(dentry);
+		if (err)
+			goto out_drop_write;
+
+		ovl_path_upper(dentry, &realpath);
+	}
+
+	err = vfs_open(&realpath, file, cred);
+out_drop_write:
+	if (want_write)
+		ovl_drop_write(dentry);
+out:
+	return err;
+}
+
+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,
+	.dentry_open	= ovl_dentry_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);
+		iput(inode);
+		inode = NULL;
+	}
+
+	return inode;
+
+}

fs/overlayfs/overlayfs.h

@@ -0,0 +1,191 @@
+/*
+ *
+ * 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/kernel.h>
+
+struct ovl_entry;
+
+enum ovl_path_type {
+	OVL_PATH_PURE_UPPER,
+	OVL_PATH_UPPER,
+	OVL_PATH_MERGE,
+	OVL_PATH_LOWER,
+};
+
+extern const char *ovl_opaque_xattr;
+
+static inline int ovl_do_rmdir(struct inode *dir, struct dentry *dentry)
+{
+	int err = vfs_rmdir(dir, dentry);
+	pr_debug("rmdir(%pd2) = %i\n", dentry, err);
+	return err;
+}
+
+static inline int ovl_do_unlink(struct inode *dir, struct dentry *dentry)
+{
+	int err = vfs_unlink(dir, dentry, NULL);
+	pr_debug("unlink(%pd2) = %i\n", dentry, err);
+	return err;
+}
+
+static inline int ovl_do_link(struct dentry *old_dentry, struct inode *dir,
+			      struct dentry *new_dentry, bool debug)
+{
+	int err = vfs_link(old_dentry, dir, new_dentry, NULL);
+	if (debug) {
+		pr_debug("link(%pd2, %pd2) = %i\n",
+			 old_dentry, new_dentry, err);
+	}
+	return err;
+}
+
+static inline int ovl_do_create(struct inode *dir, struct dentry *dentry,
+			     umode_t mode, bool debug)
+{
+	int err = vfs_create(dir, dentry, mode, true);
+	if (debug)
+		pr_debug("create(%pd2, 0%o) = %i\n", dentry, mode, err);
+	return err;
+}
+
+static inline int ovl_do_mkdir(struct inode *dir, struct dentry *dentry,
+			       umode_t mode, bool debug)
+{
+	int err = vfs_mkdir(dir, dentry, mode);
+	if (debug)
+		pr_debug("mkdir(%pd2, 0%o) = %i\n", dentry, mode, err);
+	return err;
+}
+
+static inline int ovl_do_mknod(struct inode *dir, struct dentry *dentry,
+			       umode_t mode, dev_t dev, bool debug)
+{
+	int err = vfs_mknod(dir, dentry, mode, dev);
+	if (debug) {
+		pr_debug("mknod(%pd2, 0%o, 0%o) = %i\n",
+			 dentry, mode, dev, err);
+	}
+	return err;
+}
+
+static inline int ovl_do_symlink(struct inode *dir, struct dentry *dentry,
+				 const char *oldname, bool debug)
+{
+	int err = vfs_symlink(dir, dentry, oldname);
+	if (debug)
+		pr_debug("symlink(\"%s\", %pd2) = %i\n", oldname, dentry, err);
+	return err;
+}
+
+static inline int ovl_do_setxattr(struct dentry *dentry, const char *name,
+				  const void *value, size_t size, int flags)
+{
+	int err = vfs_setxattr(dentry, name, value, size, flags);
+	pr_debug("setxattr(%pd2, \"%s\", \"%*s\", 0x%x) = %i\n",
+		 dentry, name, (int) size, (char *) value, flags, err);
+	return err;
+}
+
+static inline int ovl_do_removexattr(struct dentry *dentry, const char *name)
+{
+	int err = vfs_removexattr(dentry, name);
+	pr_debug("removexattr(%pd2, \"%s\") = %i\n", dentry, name, err);
+	return err;
+}
+
+static inline int ovl_do_rename(struct inode *olddir, struct dentry *olddentry,
+				struct inode *newdir, struct dentry *newdentry,
+				unsigned int flags)
+{
+	int err;
+
+	pr_debug("rename2(%pd2, %pd2, 0x%x)\n",
+		 olddentry, newdentry, flags);
+
+	err = vfs_rename(olddir, olddentry, newdir, newdentry, NULL, flags);
+
+	if (err) {
+		pr_debug("...rename2(%pd2, %pd2, ...) = %i\n",
+			 olddentry, newdentry, err);
+	}
+	return err;
+}
+
+static inline int ovl_do_whiteout(struct inode *dir, struct dentry *dentry)
+{
+	int err = vfs_whiteout(dir, dentry);
+	pr_debug("whiteout(%pd2) = %i\n", dentry, err);
+	return err;
+}
+
+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);
+struct ovl_dir_cache *ovl_dir_cache(struct dentry *dentry);
+void ovl_set_dir_cache(struct dentry *dentry, struct ovl_dir_cache *cache);
+struct dentry *ovl_workdir(struct dentry *dentry);
+int ovl_want_write(struct dentry *dentry);
+void ovl_drop_write(struct dentry *dentry);
+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);
+struct dentry *ovl_lookup(struct inode *dir, struct dentry *dentry,
+			  unsigned int flags);
+struct file *ovl_path_open(struct path *path, int flags);
+
+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_dir(struct dentry *dentry, struct list_head *list);
+void ovl_cleanup_whiteouts(struct dentry *upper, struct list_head *list);
+void ovl_cache_free(struct list_head *list);
+
+/* inode.c */
+int ovl_setattr(struct dentry *dentry, struct iattr *attr);
+int ovl_permission(struct inode *inode, int mask);
+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);
+static inline void ovl_copyattr(struct inode *from, struct inode *to)
+{
+	to->i_uid = from->i_uid;
+	to->i_gid = from->i_gid;
+}
+
+/* dir.c */
+extern const struct inode_operations ovl_dir_inode_operations;
+struct dentry *ovl_lookup_temp(struct dentry *workdir, struct dentry *dentry);
+int ovl_create_real(struct inode *dir, struct dentry *newdentry,
+		    struct kstat *stat, const char *link,
+		    struct dentry *hardlink, bool debug);
+void ovl_cleanup(struct inode *dir, struct dentry *dentry);
+
+/* copy_up.c */
+int ovl_copy_up(struct dentry *dentry);
+int ovl_copy_up_one(struct dentry *parent, struct dentry *dentry,
+		    struct path *lowerpath, struct kstat *stat,
+		    struct iattr *attr);
+int ovl_copy_xattr(struct dentry *old, struct dentry *new);
+int ovl_set_attr(struct dentry *upper, struct kstat *stat);

fs/overlayfs/readdir.c

@@ -0,0 +1,587 @@
+/*
+ *
+ * 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 <linux/cred.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_dir_cache {
+	long refcount;
+	u64 version;
+	struct list_head entries;
+};
+
+struct ovl_readdir_data {
+	struct dir_context ctx;
+	bool is_merge;
+	struct rb_root *root;
+	struct list_head *list;
+	struct list_head *middle;
+	int count;
+	int err;
+};
+
+struct ovl_dir_file {
+	bool is_real;
+	bool is_upper;
+	struct ovl_dir_cache *cache;
+	struct ovl_cache_entry cursor;
+	struct file *realfile;
+	struct file *upperfile;
+};
+
+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(struct ovl_readdir_data *rdd,
+			  const char *name, int namelen,
+			  loff_t offset, u64 ino, unsigned int d_type)
+{
+	struct ovl_cache_entry *p;
+
+	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;
+}
+
+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 void ovl_cache_put(struct ovl_dir_file *od, struct dentry *dentry)
+{
+	struct ovl_dir_cache *cache = od->cache;
+
+	list_del(&od->cursor.l_node);
+	WARN_ON(cache->refcount <= 0);
+	cache->refcount--;
+	if (!cache->refcount) {
+		if (ovl_dir_cache(dentry) == cache)
+			ovl_set_dir_cache(dentry, NULL);
+
+		ovl_cache_free(&cache->entries);
+		kfree(cache);
+	}
+}
+
+static int ovl_fill_merge(void *buf, const char *name, int namelen,
+			  loff_t offset, u64 ino, unsigned int d_type)
+{
+	struct ovl_readdir_data *rdd = buf;
+
+	rdd->count++;
+	if (!rdd->is_merge)
+		return ovl_cache_entry_add_rb(rdd, name, namelen, ino, d_type);
+	else
+		return ovl_fill_lower(rdd, name, namelen, offset, ino, d_type);
+}
+
+static inline int ovl_dir_read(struct path *realpath,
+			       struct ovl_readdir_data *rdd)
+{
+	struct file *realfile;
+	int err;
+
+	realfile = ovl_path_open(realpath, O_RDONLY | O_DIRECTORY);
+	if (IS_ERR(realfile))
+		return PTR_ERR(realfile);
+
+	rdd->ctx.pos = 0;
+	do {
+		rdd->count = 0;
+		rdd->err = 0;
+		err = iterate_dir(realfile, &rdd->ctx);
+		if (err >= 0)
+			err = rdd->err;
+	} while (!err && rdd->count);
+	fput(realfile);
+
+	return err;
+}
+
+static void ovl_dir_reset(struct file *file)
+{
+	struct ovl_dir_file *od = file->private_data;
+	struct ovl_dir_cache *cache = od->cache;
+	struct dentry *dentry = file->f_path.dentry;
+	enum ovl_path_type type = ovl_path_type(dentry);
+
+	if (cache && ovl_dentry_version_get(dentry) != cache->version) {
+		ovl_cache_put(od, dentry);
+		od->cache = NULL;
+	}
+	WARN_ON(!od->is_real && type != OVL_PATH_MERGE);
+	if (od->is_real && type == OVL_PATH_MERGE)
+		od->is_real = false;
+}
+
+static int ovl_dir_mark_whiteouts(struct dentry *dir,
+				  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_DAC_OVERRIDE for lookup
+	 */
+	cap_raise(override_cred->cap_effective, CAP_DAC_OVERRIDE);
+	old_cred = override_creds(override_cred);
+
+	mutex_lock(&dir->d_inode->i_mutex);
+	list_for_each_entry(p, rdd->list, l_node) {
+		if (!p->name)
+			continue;
+
+		if (p->type != DT_CHR)
+			continue;
+
+		dentry = lookup_one_len(p->name, dir, p->len);
+		if (IS_ERR(dentry))
+			continue;
+
+		p->is_whiteout = ovl_is_whiteout(dentry);
+		dput(dentry);
+	}
+	mutex_unlock(&dir->d_inode->i_mutex);
+
+	revert_creds(old_cred);
+	put_cred(override_cred);
+
+	return 0;
+}
+
+static inline int ovl_dir_read_merged(struct path *upperpath,
+				      struct path *lowerpath,
+				      struct list_head *list)
+{
+	int err;
+	struct rb_root root = RB_ROOT;
+	struct list_head middle;
+	struct ovl_readdir_data rdd = {
+		.ctx.actor = ovl_fill_merge,
+		.list = list,
+		.root = &root,
+		.is_merge = false,
+	};
+
+	if (upperpath->dentry) {
+		err = ovl_dir_read(upperpath, &rdd);
+		if (err)
+			goto out;
+
+		if (lowerpath->dentry) {
+			err = ovl_dir_mark_whiteouts(upperpath->dentry, &rdd);
+			if (err)
+				goto out;
+		}
+	}
+	if (lowerpath->dentry) {
+		/*
+		 * Insert lowerpath entries before upperpath ones, this allows
+		 * offsets to be reasonably constant
+		 */
+		list_add(&middle, rdd.list);
+		rdd.middle = &middle;
+		rdd.is_merge = true;
+		err = ovl_dir_read(lowerpath, &rdd);
+		list_del(&middle);
+	}
+out:
+	return err;
+
+}
+
+static void ovl_seek_cursor(struct ovl_dir_file *od, loff_t pos)
+{
+	struct ovl_cache_entry *p;
+	loff_t off = 0;
+
+	list_for_each_entry(p, &od->cache->entries, l_node) {
+		if (!p->name)
+			continue;
+		if (off >= pos)
+			break;
+		off++;
+	}
+	list_move_tail(&od->cursor.l_node, &p->l_node);
+}
+
+static struct ovl_dir_cache *ovl_cache_get(struct dentry *dentry)
+{
+	int res;
+	struct path lowerpath;
+	struct path upperpath;
+	struct ovl_dir_cache *cache;
+
+	cache = ovl_dir_cache(dentry);
+	if (cache && ovl_dentry_version_get(dentry) == cache->version) {
+		cache->refcount++;
+		return cache;
+	}
+	ovl_set_dir_cache(dentry, NULL);
+
+	cache = kzalloc(sizeof(struct ovl_dir_cache), GFP_KERNEL);
+	if (!cache)
+		return ERR_PTR(-ENOMEM);
+
+	cache->refcount = 1;
+	INIT_LIST_HEAD(&cache->entries);
+
+	ovl_path_lower(dentry, &lowerpath);
+	ovl_path_upper(dentry, &upperpath);
+
+	res = ovl_dir_read_merged(&upperpath, &lowerpath, &cache->entries);
+	if (res) {
+		ovl_cache_free(&cache->entries);
+		kfree(cache);
+		return ERR_PTR(res);
+	}
+
+	cache->version = ovl_dentry_version_get(dentry);
+	ovl_set_dir_cache(dentry, cache);
+
+	return cache;
+}
+
+static int ovl_iterate(struct file *file, struct dir_context *ctx)
+{
+	struct ovl_dir_file *od = file->private_data;
+	struct dentry *dentry = file->f_path.dentry;
+
+	if (!ctx->pos)
+		ovl_dir_reset(file);
+
+	if (od->is_real)
+		return iterate_dir(od->realfile, ctx);
+
+	if (!od->cache) {
+		struct ovl_dir_cache *cache;
+
+		cache = ovl_cache_get(dentry);
+		if (IS_ERR(cache))
+			return PTR_ERR(cache);
+
+		od->cache = cache;
+		ovl_seek_cursor(od, ctx->pos);
+	}
+
+	while (od->cursor.l_node.next != &od->cache->entries) {
+		struct ovl_cache_entry *p;
+
+		p = list_entry(od->cursor.l_node.next, struct ovl_cache_entry, l_node);
+		/* Skip cursors */
+		if (p->name) {
+			if (!p->is_whiteout) {
+				if (!dir_emit(ctx, p->name, p->len, p->ino, p->type))
+					break;
+			}
+			ctx->pos++;
+		}
+		list_move(&od->cursor.l_node, &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_inode(file)->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->cache)
+				ovl_seek_cursor(od, offset);
+		}
+		res = offset;
+	}
+out_unlock:
+	mutex_unlock(&file_inode(file)->i_mutex);
+
+	return res;
+}
+
+static int ovl_dir_fsync(struct file *file, loff_t start, loff_t end,
+			 int datasync)
+{
+	struct ovl_dir_file *od = file->private_data;
+	struct dentry *dentry = file->f_path.dentry;
+	struct file *realfile = od->realfile;
+
+	/*
+	 * Need to check if we started out being a lower dir, but got copied up
+	 */
+	if (!od->is_upper && ovl_path_type(dentry) == OVL_PATH_MERGE) {
+		struct inode *inode = file_inode(file);
+
+		mutex_lock(&inode->i_mutex);
+		realfile = od->upperfile;
+		if (!realfile) {
+			struct path upperpath;
+
+			ovl_path_upper(dentry, &upperpath);
+			realfile = ovl_path_open(&upperpath, O_RDONLY);
+			if (IS_ERR(realfile)) {
+				mutex_unlock(&inode->i_mutex);
+				return PTR_ERR(realfile);
+			}
+			od->upperfile = realfile;
+		}
+		mutex_unlock(&inode->i_mutex);
+	}
+
+	return vfs_fsync_range(realfile, start, end, datasync);
+}
+
+static int ovl_dir_release(struct inode *inode, struct file *file)
+{
+	struct ovl_dir_file *od = file->private_data;
+
+	if (od->cache) {
+		mutex_lock(&inode->i_mutex);
+		ovl_cache_put(od, file->f_path.dentry);
+		mutex_unlock(&inode->i_mutex);
+	}
+	fput(od->realfile);
+	if (od->upperfile)
+		fput(od->upperfile);
+	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 = ovl_path_open(&realpath, file->f_flags);
+	if (IS_ERR(realfile)) {
+		kfree(od);
+		return PTR_ERR(realfile);
+	}
+	INIT_LIST_HEAD(&od->cursor.l_node);
+	od->realfile = realfile;
+	od->is_real = (type != OVL_PATH_MERGE);
+	od->is_upper = (type != OVL_PATH_LOWER);
+	file->private_data = od;
+
+	return 0;
+}
+
+const struct file_operations ovl_dir_operations = {
+	.read		= generic_read_dir,
+	.open		= ovl_dir_open,
+	.iterate	= ovl_iterate,
+	.llseek		= ovl_dir_llseek,
+	.fsync		= ovl_dir_fsync,
+	.release	= ovl_dir_release,
+};
+
+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;
+
+	ovl_path_upper(dentry, &upperpath);
+	ovl_path_lower(dentry, &lowerpath);
+
+	err = ovl_dir_read_merged(&upperpath, &lowerpath, list);
+	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;
+}
+
+void ovl_cleanup_whiteouts(struct dentry *upper, struct list_head *list)
+{
+	struct ovl_cache_entry *p;
+
+	mutex_lock_nested(&upper->d_inode->i_mutex, I_MUTEX_PARENT);
+	list_for_each_entry(p, list, l_node) {
+		struct dentry *dentry;
+
+		if (!p->is_whiteout)
+			continue;
+
+		dentry = lookup_one_len(p->name, upper, p->len);
+		if (IS_ERR(dentry)) {
+			pr_err("overlayfs: lookup '%s/%.*s' failed (%i)\n",
+			       upper->d_name.name, p->len, p->name,
+			       (int) PTR_ERR(dentry));
+			continue;
+		}
+		ovl_cleanup(upper->d_inode, dentry);
+		dput(dentry);
+	}
+	mutex_unlock(&upper->d_inode->i_mutex);
+}

fs/overlayfs/super.c

@@ -0,0 +1,727 @@
+/*
+ *
+ * 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 "overlayfs.h"
+
+MODULE_AUTHOR("Miklos Szeredi <miklos@szeredi.hu>");
+MODULE_DESCRIPTION("Overlay filesystem");
+MODULE_LICENSE("GPL");
+
+/* private information held for overlayfs's superblock */
+struct ovl_fs {
+	struct vfsmount *upper_mnt;
+	struct vfsmount *lower_mnt;
+	struct dentry *workdir;
+};
+
+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);
+}
+
+static const struct super_operations ovl_super_operations = {
+	.put_super	= ovl_put_super,
+};
+
+struct ovl_config {
+	char *lowerdir;
+	char *upperdir;
+	char *workdir;
+};
+
+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;
+
+	config->upperdir = NULL;
+	config->lowerdir = NULL;
+	config->workdir = 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;
+
+		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 ovl_config config;
+	int err;
+
+	err = ovl_parse_opt((char *) data, &config);
+	if (err)
+		goto out;
+
+	/* FIXME: workdir is not needed for a R/O mount */
+	err = -EINVAL;
+	if (!config.upperdir || !config.lowerdir || !config.workdir) {
+		pr_err("overlayfs: missing upperdir or lowerdir or workdir\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;
+
+	err = ovl_mount_dir(config.upperdir, &upperpath);
+	if (err)
+		goto out_free_oe;
+
+	err = ovl_mount_dir(config.lowerdir, &lowerpath);
+	if (err)
+		goto out_put_upperpath;
+
+	err = ovl_mount_dir(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;
+	}
+
+	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",
+		       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_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_ufs:
+	kfree(ufs);
+out_free_config:
+	kfree(config.lowerdir);
+	kfree(config.upperdir);
+	kfree(config.workdir);
+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,
+};
+MODULE_ALIAS_FS("overlayfs");
+
+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);