[PATCH 0/6 v7] overlay filesystem - request for inclusion

[PATCH 0/6 v7] overlay filesystem - request for inclusion

[Miklos Szeredi]

Here's an updated version of the overlay filesystem.  I'd like to
propose it for inclusion into mainline.

Executive summary:

  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.

For more information see the excellent documentation written by Neil
Brown at the end of the series.

Al, can you please review the VFS parts (patches 1-3)?

Git tree is here:

  git://git.kernel.org/pub/scm/linux/kernel/git/mszeredi/vfs.git overlayfs.v7

Thanks,
Miklos

---
Andy Whitcroft (1):
      overlayfs: add statfs support

Miklos Szeredi (4):
      vfs: add i_op->open()
      vfs: export do_splice_direct() to modules
      vfs: introduce clone_private_mount()
      overlay filesystem prototype

Neil Brown (1):
      overlay: overlay filesystem documentation

---
 Documentation/filesystems/overlayfs.txt |  163 +++
 fs/Kconfig                              |    1 +
 fs/Makefile                             |    1 +
 fs/namespace.c                          |   17 +
 fs/open.c                               |   76 +-
 fs/overlayfs/Kconfig                    |    4 +
 fs/overlayfs/Makefile                   |    5 +
 fs/overlayfs/overlayfs.c                | 2414 +++++++++++++++++++++++++++++++
 fs/splice.c                             |    1 +
 include/linux/fs.h                      |    2 +
 include/linux/mount.h                   |    3 +
 11 files changed, 2661 insertions(+), 26 deletions(-)
 create mode 100644 Documentation/filesystems/overlayfs.txt
 create mode 100644 fs/overlayfs/Kconfig
 create mode 100644 fs/overlayfs/Makefile
 create mode 100644 fs/overlayfs/overlayfs.c

------------------------------------------------------------------------------
Changes from v6 to v7

- added patches from Felix Fietkau to fix deadlocks on jffs2

- optimized directory removal

- properly clean up after copy-up and other failures

------------------------------------------------------------------------------
Changes from v5 to v6

- optimize directory merging

  o use rbtree for weeding out duplicates

  o use a cursor for current position within the stream

- instead of f_op->open_other(), implement i_op->open()

- don't share inodes for non-directory dentries - for now.  I hope
  this can come back once RCU lookup code has settled.

- misc bug fixes

------------------------------------------------------------------------------
Changes from v4 to v5

- fix copying up if fs doesn't support xattrs (Andy Whitcroft)

- clone mounts to be used internally to access the underlying
  filesystems

------------------------------------------------------------------------------
Changes from v3 to v4

- export security_inode_permission to allow overlayfs to be modular
  (Andy Whitcroft)

- add statfs support (Andy Whitcroft)

- change BUG_ON to WARN_ON

- Revert "vfs: add flag to allow rename to same inode", instead
  introduce s_op->is_same_inode()

- overlayfs: fix rename to self

- fix whiteout after rename

------------------------------------------------------------------------------
Changes from v2 to v3

 - Minimal remount support.  As overlayfs reflects the 'readonly'
   mount status in write-access to the upper filesystem, we must
   handle remount and either drop or take write access when the ro
   status changes. (NeilBrown)

 - Use correct seek function for directories.  It is incorrect to call
   generic_llseek_file on a file from a different filesystem.  For
   that we must use the seek function that the filesystem defines,
   which is called by vfs_llseek.  Also, we only want to seek the
   realfile when is_real is true.  Otherwise we just want to update
   our own f_pos pointer, so use generic_llseek_file for
   that. (NeilBrown)

 - Initialise is_real before use.  The previous patch can use
   od->is_real before it is properly initialised is llseek is called
   before readdir.  So factor out the initialisation of is_real and
   call it from both readdir and llseek when f_pos is 0. (NeilBrown)

 - Rename ovl_fill_cache to ovl_dir_read (NeilBrown)

 - Tiny optimisation in open_other handling (NeilBrown)

 - Assorted updates to Documentation/filesystems/overlayfs.txt (NeilBrown)

 - Make copy-up work for >=4G files, make it killable during copy-up.
   Need to fix recovery after a failed/interrupted copy-up.

 - Store and reference upper/lower dentries in overlay dentries.
   Store and reference upper/lower vfsmounts in overlay superblock.

 - Add necessary barriers for setting upper dentry in copyup and for
   retrieving upper dentry locklessly.

 - Make sure the right file is used for directory fsync() after
   copy-up.

 - Add locking to ovl_dir_llseek() to prevent concurrent call of
   ovl_dir_reset() with ovl_dir_read().

 - Get rid of ovl_dentry_iput().  The VFS doesn't provide enough
   locking for this function that the contents of ->d_fsdata could be
   safely updated.

 - After copying up a non-directory unhash the dentry.  This way the
   lower dentry ref, which is no longer necessary, can go away.  This
   revealed a use-after-free bug in truncate handling in
   fs/namei.c:finish_open().

 - Fix if a copy-up happens between the follow_linka the put_link
   calls.

 - Replace some WARN_ONs with BUG_ON.  Some things just _really_
   shouldn't happen.

 - Extract common code from ovl_unlink and ovl_rmdir to a helper
   function.

 - After unlink and rmdir unhash the dentry.  This will get rid of the
   lower and upper dentry references after there are no more users of
   the deleted dentry.  This is a safe replacement for the removed
   ->d_iput() functionality.

 - Added checks to unlink, rmdir and rename to verify that the
   parent-child relationship in the upper filesystem matches that of
   the overlay.  This is necessary to prevent crash and/or corruption
   if the upper filesystem topology is being modified while part of
   the overlay.

 - Optimize checking whiteout and opaque attributes.

 - Optimize copy-up on truncate: don't copy up whole file before
   truncating

 - Misc bug fixes

------------------------------------------------------------------------------
Changes from v1 to v2

 - rename "hybrid union filesystem" to "overlay filesystem" or overlayfs

 - added documentation written by Neil

 - correct st_dev for directories (reported by Neil)

 - use getattr() to get attributes from the underlying filesystems,
   this means that now an overlay filesystem itself can be the lower,
   read-only layer of another overlay

 - listxattr filters out private extended attributes

 - get write ref on the upper layer on mount unless the overlay
   itself is mounted read-only

 - raise capabilities for copy up, dealing with whiteouts and opaque
   directories.  Now the overlay works for non-root users as well

 - "rm -rf" didn't work correctly in all cases if the directory was
   copied up between opendir and the first readdir, this is now fixed
   (and the directory operations consolidated)

 - simplified copy up, this broke optimization for truncate and
   open(O_TRUNC) (now file is copied up to be immediately truncated,
   will fix)

 - st_nlink for merged directories set to 1, this is an "illegal"
   value that normal filesystems never have but some use it to
   indicate that the number of subdirectories is unknown.  Utilities
   (find, ...) seem to tolerate this well.

 - misc fixes I forgot about

[PATCH 1/6 v7] vfs: add i_op->open()

[Miklos Szeredi]

[-- Attachment #1: vfs-add-i_op-open.patch --]
[-- Type: text/plain, Size: 5768 bytes --]

From: Miklos Szeredi <mszeredi@suse.cz>

Add a new inode operation i_op->open().  This is for stacked
filesystems that want to return a struct file from a different
filesystem.

Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
---
 fs/open.c          |   76 ++++++++++++++++++++++++++++++++++-------------------
 include/linux/fs.h |    2 +
 2 files changed, 52 insertions(+), 26 deletions(-)

Index: linux-2.6/include/linux/fs.h
===================================================================
--- linux-2.6.orig/include/linux/fs.h	2011-03-22 15:11:27.000000000 +0100
+++ linux-2.6/include/linux/fs.h	2011-03-22 15:11:30.000000000 +0100
@@ -1597,6 +1597,7 @@ struct inode_operations {
 	void (*truncate_range)(struct inode *, loff_t, loff_t);
 	int (*fiemap)(struct inode *, struct fiemap_extent_info *, u64 start,
 		      u64 len);
+	struct file *(*open)(struct dentry *, int flags, const struct cred *);
 } ____cacheline_aligned;
 
 struct seq_file;
@@ -1991,6 +1992,7 @@ extern long do_sys_open(int dfd, const c
 extern struct file *filp_open(const char *, int, int);
 extern struct file *file_open_root(struct dentry *, struct vfsmount *,
 				   const char *, int);
+extern struct file *vfs_open(struct path *, int flags, const struct cred *);
 extern struct file * dentry_open(struct dentry *, struct vfsmount *, int,
 				 const struct cred *);
 extern int filp_close(struct file *, fl_owner_t id);
Index: linux-2.6/fs/open.c
===================================================================
--- linux-2.6.orig/fs/open.c	2011-03-22 15:11:27.000000000 +0100
+++ linux-2.6/fs/open.c	2011-03-22 15:11:30.000000000 +0100
@@ -666,8 +666,7 @@ static inline int __get_file_write_acces
 	return error;
 }
 
-static struct file *__dentry_open(struct dentry *dentry, struct vfsmount *mnt,
-					struct file *f,
+static struct file *__dentry_open(struct path *path, struct file *f,
 					int (*open)(struct inode *, struct file *),
 					const struct cred *cred)
 {
@@ -675,15 +674,16 @@ static struct file *__dentry_open(struct
 	struct inode *inode;
 	int error;
 
+	path_get(path);
 	f->f_mode = OPEN_FMODE(f->f_flags) | FMODE_LSEEK |
 				FMODE_PREAD | FMODE_PWRITE;
 
 	if (unlikely(f->f_flags & O_PATH))
 		f->f_mode = FMODE_PATH;
 
-	inode = dentry->d_inode;
+	inode = path->dentry->d_inode;
 	if (f->f_mode & FMODE_WRITE) {
-		error = __get_file_write_access(inode, mnt);
+		error = __get_file_write_access(inode, path->mnt);
 		if (error)
 			goto cleanup_file;
 		if (!special_file(inode->i_mode))
@@ -691,8 +691,7 @@ static struct file *__dentry_open(struct
 	}
 
 	f->f_mapping = inode->i_mapping;
-	f->f_path.dentry = dentry;
-	f->f_path.mnt = mnt;
+	f->f_path = *path;
 	f->f_pos = 0;
 	file_sb_list_add(f, inode->i_sb);
 
@@ -745,7 +744,7 @@ static struct file *__dentry_open(struct
 			 * here, so just reset the state.
 			 */
 			file_reset_write(f);
-			mnt_drop_write(mnt);
+			mnt_drop_write(path->mnt);
 		}
 	}
 	file_sb_list_del(f);
@@ -753,8 +752,7 @@ static struct file *__dentry_open(struct
 	f->f_path.mnt = NULL;
 cleanup_file:
 	put_filp(f);
-	dput(dentry);
-	mntput(mnt);
+	path_put(path);
 	return ERR_PTR(error);
 }
 
@@ -780,14 +778,14 @@ static struct file *__dentry_open(struct
 struct file *lookup_instantiate_filp(struct nameidata *nd, struct dentry *dentry,
 		int (*open)(struct inode *, struct file *))
 {
+	struct path path = { .dentry = dentry, .mnt = nd->path.mnt };
 	const struct cred *cred = current_cred();
 
 	if (IS_ERR(nd->intent.open.file))
 		goto out;
 	if (IS_ERR(dentry))
 		goto out_err;
-	nd->intent.open.file = __dentry_open(dget(dentry), mntget(nd->path.mnt),
-					     nd->intent.open.file,
+	nd->intent.open.file = __dentry_open(&path, nd->intent.open.file,
 					     open, cred);
 out:
 	return nd->intent.open.file;
@@ -816,10 +814,17 @@ struct file *nameidata_to_filp(struct na
 
 	/* Has the filesystem initialised the file for us? */
 	if (filp->f_path.dentry == NULL) {
-		path_get(&nd->path);
-		filp = __dentry_open(nd->path.dentry, nd->path.mnt, filp,
-				     NULL, cred);
+		struct inode *inode = nd->path.dentry->d_inode;
+
+		if (inode->i_op->open) {
+			int flags = filp->f_flags;
+			put_filp(filp);
+			filp = inode->i_op->open(nd->path.dentry, flags, cred);
+		} else {
+			filp = __dentry_open(&nd->path, filp, NULL, cred);
+		}
 	}
+
 	return filp;
 }
 
@@ -830,26 +835,45 @@ struct file *nameidata_to_filp(struct na
 struct file *dentry_open(struct dentry *dentry, struct vfsmount *mnt, int flags,
 			 const struct cred *cred)
 {
-	int error;
-	struct file *f;
-
-	validate_creds(cred);
+	struct path path = { .dentry = dentry, .mnt = mnt };
+	struct file *ret;
 
 	/* We must always pass in a valid mount pointer. */
 	BUG_ON(!mnt);
 
-	error = -ENFILE;
+	ret = vfs_open(&path, flags, cred);
+	path_put(&path);
+
+	return ret;
+}
+EXPORT_SYMBOL(dentry_open);
+
+/**
+ * vfs_open - open the file at the given path
+ * @path: path to open
+ * @flags: open flags
+ * @cred: credentials to use
+ *
+ * Open the file.  If successful, the returned file will have acquired
+ * an additional reference for path.
+ */
+struct file *vfs_open(struct path *path, int flags, const struct cred *cred)
+{
+	struct file *f;
+	struct inode *inode = path->dentry->d_inode;
+
+	validate_creds(cred);
+
+	if (inode->i_op->open)
+		return inode->i_op->open(path->dentry, flags, cred);
 	f = get_empty_filp();
-	if (f == NULL) {
-		dput(dentry);
-		mntput(mnt);
-		return ERR_PTR(error);
-	}
+	if (f == NULL)
+		return ERR_PTR(-ENFILE);
 
 	f->f_flags = flags;
-	return __dentry_open(dentry, mnt, f, NULL, cred);
+	return __dentry_open(path, f, NULL, cred);
 }
-EXPORT_SYMBOL(dentry_open);
+EXPORT_SYMBOL(vfs_open);
 
 static void __put_unused_fd(struct files_struct *files, unsigned int fd)
 {

-- 

Re: [PATCH 1/6 v7] vfs: add i_op->open()

[Linus Torvalds]

On Tue, Mar 22, 2011 at 8:26 AM, Miklos Szeredi <miklos@szeredi.hu> wrote:
>
> Add a new inode operation i_op->open().  This is for stacked
> filesystems that want to return a struct file from a different
> filesystem.

Hmm..

> +               struct inode *inode = nd->path.dentry->d_inode;
> +
> +               if (inode->i_op->open) {
> +                       int flags = filp->f_flags;
> +                       put_filp(filp);
> +                       filp = inode->i_op->open(nd->path.dentry, flags, cred);
> +               } else {
> +                       filp = __dentry_open(&nd->path, filp, NULL, cred);
> +               }

This seems broken.

Why don't you just pass in the filp to the ->open routine, and drop
that "flags" argument. Maybe other filesystems want to use ->open, but
don't want to put_filp() on the filp we already allocated, only to
allocate a new one?

It seems like you made that unnecessarily hard on purpose, with no
advantage to the interface.

                        Linus

Re: [PATCH 1/6 v7] vfs: add i_op->open()

[Miklos Szeredi]

On Tue, 22 Mar 2011, Linus Torvalds wrote:
> > +               struct inode *inode = nd->path.dentry->d_inode;
> > +
> > +               if (inode->i_op->open) {
> > +                       int flags = filp->f_flags;
> > +                       put_filp(filp);
> > +                       filp = inode->i_op->open(nd->path.dentry, flags, cred);
> > +               } else {
> > +                       filp = __dentry_open(&nd->path, filp, NULL, cred);
> > +               }
> 
> This seems broken.
> 
> Why don't you just pass in the filp to the ->open routine, and drop
> that "flags" argument. Maybe other filesystems want to use ->open, but
> don't want to put_filp() on the filp we already allocated, only to
> allocate a new one?

Maybe, although I don't see the reason to do that.  Why keep the
original one?  It doesn't contain any information besides the flags
and the dentry/vfsmount.

Thanks,
Miklos
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Re: [PATCH 1/6 v7] vfs: add i_op->open()

[Linus Torvalds]

On Tue, Mar 22, 2011 at 11:12 AM, Miklos Szeredi <miklos@szeredi.hu> wrote:
>>
>> Why don't you just pass in the filp to the ->open routine, and drop
>> that "flags" argument. Maybe other filesystems want to use ->open, but
>> don't want to put_filp() on the filp we already allocated, only to
>> allocate a new one?
>
> Maybe, although I don't see the reason to do that.  Why keep the
> original one?  It doesn't contain any information besides the flags
> and the dentry/vfsmount.

Umm? Because that way you can avoid allocating a new one?

So let's turn your questions on its head: why do you insist on
free'ing the old one, WHEN YOU KNOW THAT THE ->open ROUTINE NEEDS TO
ALLOCATE A NEW ONE?

Sure, in _your_ case, you'll get a new filp because you're going to do
a whole new open of a lower-level filesystem, but if the ->open
routine is all about just your case, then I don't want it as a VFS
layer operation. So for your filesystem, you will always discard the
old one as useless. But that's purely an implementation detail for
you. It has nothing to do with the VFS interfaces.

So why do that idiotic free, only to force the callee to then
re-allocate a new "struct file"?

                           Linus
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[PATCH 2/6 v7] vfs: export do_splice_direct() to modules

[Miklos Szeredi]

[-- Attachment #1: vfs-export-do_splice_direct.patch --]
[-- Type: text/plain, Size: 673 bytes --]

From: Miklos Szeredi <mszeredi@suse.cz>

Export do_splice_direct() to modules.  Needed by overlay filesystem.

Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
---
 fs/splice.c |    1 +
 1 file changed, 1 insertion(+)

Index: linux-2.6/fs/splice.c
===================================================================
--- linux-2.6.orig/fs/splice.c	2011-03-22 15:11:27.000000000 +0100
+++ linux-2.6/fs/splice.c	2011-03-22 15:11:32.000000000 +0100
@@ -1296,6 +1296,7 @@ long do_splice_direct(struct file *in, l
 
 	return ret;
 }
+EXPORT_SYMBOL(do_splice_direct);
 
 static int splice_pipe_to_pipe(struct pipe_inode_info *ipipe,
 			       struct pipe_inode_info *opipe,

-- 

[PATCH 3/6 v7] vfs: introduce clone_private_mount()

[Miklos Szeredi]

[-- Attachment #1: vfs-export-clone_mnt.patch --]
[-- Type: text/plain, Size: 1732 bytes --]

From: Miklos Szeredi <mszeredi@suse.cz>

Overlayfs needs a private clone of the mount, so create a function for
this and export to modules.

Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
---
 fs/namespace.c        |   17 +++++++++++++++++
 include/linux/mount.h |    3 +++
 2 files changed, 20 insertions(+)

Index: linux-2.6/fs/namespace.c
===================================================================
--- linux-2.6.orig/fs/namespace.c	2011-03-22 15:11:27.000000000 +0100
+++ linux-2.6/fs/namespace.c	2011-03-22 15:11:34.000000000 +0100
@@ -1510,6 +1510,23 @@ void drop_collected_mounts(struct vfsmou
 	release_mounts(&umount_list);
 }
 
+struct vfsmount *clone_private_mount(struct path *path)
+{
+	struct vfsmount *mnt;
+
+	if (IS_MNT_UNBINDABLE(path->mnt))
+		return ERR_PTR(-EINVAL);
+
+	down_read(&namespace_sem);
+	mnt = clone_mnt(path->mnt, path->dentry, CL_PRIVATE);
+	up_read(&namespace_sem);
+	if (!mnt)
+		return ERR_PTR(-ENOMEM);
+
+	return mnt;
+}
+EXPORT_SYMBOL_GPL(clone_private_mount);
+
 int iterate_mounts(int (*f)(struct vfsmount *, void *), void *arg,
 		   struct vfsmount *root)
 {
Index: linux-2.6/include/linux/mount.h
===================================================================
--- linux-2.6.orig/include/linux/mount.h	2011-03-22 15:11:27.000000000 +0100
+++ linux-2.6/include/linux/mount.h	2011-03-22 15:11:34.000000000 +0100
@@ -100,6 +100,9 @@ extern void mnt_pin(struct vfsmount *mnt
 extern void mnt_unpin(struct vfsmount *mnt);
 extern int __mnt_is_readonly(struct vfsmount *mnt);
 
+struct path;
+extern struct vfsmount *clone_private_mount(struct path *path);
+
 extern struct vfsmount *do_kern_mount(const char *fstype, int flags,
 				      const char *name, void *data);
 

-- 

[PATCH 4/6 v7] overlay filesystem prototype

[Miklos Szeredi]

[-- Attachment #1: overlayfs.patch --]
[-- Type: text/plain, Size: 57913 bytes --]

From: Miklos Szeredi <mszeredi@suse.cz>

This overlay filesystem is a hybrid of entirely filesystem based
(unionfs, aufs) and entierly VFS based (union mounts) solutions.

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

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

Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
---
 fs/Kconfig               |    1 
 fs/Makefile              |    1 
 fs/overlayfs/Kconfig     |    4 
 fs/overlayfs/Makefile    |    5 
 fs/overlayfs/overlayfs.c | 2394 +++++++++++++++++++++++++++++++++++++++++++++++
 5 files changed, 2405 insertions(+)

Index: linux-2.6/fs/overlayfs/overlayfs.c
===================================================================
--- /dev/null	1970-01-01 00:00:00.000000000 +0000
+++ linux-2.6/fs/overlayfs/overlayfs.c	2011-03-22 15:12:13.000000000 +0100
@@ -0,0 +1,2394 @@
+#include <linux/fs.h>
+#include <linux/namei.h>
+#include <linux/sched.h>
+#include <linux/fs_struct.h>
+#include <linux/file.h>
+#include <linux/xattr.h>
+#include <linux/security.h>
+#include <linux/device_cgroup.h>
+#include <linux/mount.h>
+#include <linux/splice.h>
+#include <linux/slab.h>
+#include <linux/parser.h>
+#include <linux/module.h>
+#include <linux/uaccess.h>
+#include <linux/rbtree.h>
+
+MODULE_AUTHOR("Miklos Szeredi <miklos@szeredi.hu>");
+MODULE_DESCRIPTION("Overlay filesystem");
+MODULE_LICENSE("GPL");
+
+#define OVL_COPY_UP_CHUNK_SIZE (1 << 20)
+
+struct ovl_fs {
+	struct vfsmount *upper_mnt;
+	struct vfsmount *lower_mnt;
+};
+
+struct ovl_entry {
+	struct dentry *__upperdentry;
+	struct dentry *lowerdentry;
+	union {
+		struct {
+			u64 version;
+			bool opaque;
+		};
+		struct rcu_head rcu;
+	};
+};
+
+static const char *ovl_whiteout_xattr = "trusted.overlay.whiteout";
+static const char *ovl_opaque_xattr = "trusted.overlay.opaque";
+static const char *ovl_whiteout_symlink = "(overlay-whiteout)";
+
+enum ovl_path_type {
+	OVL_PATH_UPPER,
+	OVL_PATH_MERGE,
+	OVL_PATH_LOWER,
+};
+
+static 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;
+}
+
+static 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);
+}
+
+static 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;
+}
+
+static 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;
+}
+
+static struct dentry *ovl_dentry_upper(struct dentry *dentry)
+{
+	struct ovl_entry *oe = dentry->d_fsdata;
+
+	return ovl_upperdentry_dereference(oe);
+}
+
+static struct dentry *ovl_dentry_lower(struct dentry *dentry)
+{
+	struct ovl_entry *oe = dentry->d_fsdata;
+
+	return oe->lowerdentry;
+}
+
+static 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;
+}
+
+static bool ovl_dentry_is_opaque(struct dentry *dentry)
+{
+	struct ovl_entry *oe = dentry->d_fsdata;
+	return oe->opaque;
+}
+
+static void ovl_dentry_set_opaque(struct dentry *dentry, bool opaque)
+{
+	struct ovl_entry *oe = dentry->d_fsdata;
+	oe->opaque = opaque;
+}
+
+static 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);
+	smp_wmb();
+	oe->__upperdentry = upperdentry;
+}
+
+static 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++;
+}
+
+static 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;
+}
+
+static 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;
+}
+
+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;
+		file->f_pos++;
+		list_move(&od->cursor, &p->l_node);
+
+		if (p->is_whiteout)
+			continue;
+
+		over = filler(buf, p->name, p->len, off, p->ino, p->type);
+		if (over)
+			break;
+	}
+
+	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;
+}
+
+static 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 const struct inode_operations ovl_dir_inode_operations;
+
+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->lowerdentry);
+		call_rcu(&oe->rcu, ovl_entry_free);
+	}
+}
+
+static const struct dentry_operations ovl_dentry_operations = {
+	.d_release = ovl_dentry_release,
+};
+
+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;
+}
+
+static struct ovl_entry *ovl_alloc_entry(void)
+{
+	return kzalloc(sizeof(struct ovl_entry), GFP_KERNEL);
+}
+
+static struct inode *ovl_new_inode(struct super_block *sb, umode_t mode,
+				   struct ovl_entry *oe);
+
+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_raise(override_cred->cap_effective, CAP_SYS_ADMIN);
+	cap_raise(override_cred->cap_effective, CAP_DAC_OVERRIDE);
+	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(struct inode *dir, struct dentry *dentry,
+				   struct nameidata *nd)
+{
+	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(dir->i_sb, realdentry->d_inode->i_mode, oe);
+		if (!inode)
+			goto out_dput;
+	}
+
+	if (upperdentry)
+		oe->__upperdentry = upperdentry;
+
+	if (lowerdentry)
+		oe->lowerdentry = lowerdentry;
+
+	dentry->d_fsdata = oe;
+	dentry->d_op = &ovl_dentry_operations;
+	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);
+}
+
+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 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);
+}
+
+static 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);
+	}
+
+out:
+	return newdentry;
+
+}
+
+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_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_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;
+	struct ovl_fs *ofs = dentry->d_sb->s_fs_info;
+
+	/* Can't properly set mode on creation because of the umask */
+	stat->mode &= S_IFMT;
+
+	newpath.mnt = ofs->upper_mnt;
+	newpath.dentry = ovl_upper_create(upperdir, dentry, stat, link);
+	if (IS_ERR(newpath.dentry)) {
+		err = PTR_ERR(newpath.dentry);
+
+		/* Already copied up? */
+		if (err == -EEXIST && ovl_path_type(dentry) != OVL_PATH_LOWER)
+			return 0;
+
+		return err;
+	}
+
+	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;
+}
+
+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);
+	/*
+	 * Using upper filesystem locking to protect against copy up
+	 * racing with rename (rename means the copy up was already
+	 * successful).
+	 */
+	if (dentry->d_parent != parent) {
+		WARN_ON((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;
+}
+
+static 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 */
+static 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;
+}
+
+static 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);
+}
+
+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_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_upperdentry_dereference(oe);
+	is_upper = true;
+	if (!realdentry) {
+		realdentry = oe->lowerdentry;
+		is_upper = false;
+	}
+
+	/* Careful in RCU walk mode */
+	realinode = ACCESS_ONCE(realdentry->d_inode);
+	if (!realinode) {
+		WARN_ON(!(flags & IPERM_FLAG_RCU));
+		return -ENOENT;
+	}
+
+	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;
+}
+
+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);
+}
+
+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 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;
+
+		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_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 ret = 0;
+
+	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_raise(override_cred->cap_effective, CAP_DAC_OVERRIDE);
+	old_cred = override_creds(override_cred);
+
+	mutex_lock(&upperdir->d_inode->i_mutex);
+	list_for_each_entry(p, list, l_node) {
+		if (p->is_whiteout) {
+			struct dentry *dentry;
+
+			dentry = lookup_one_len(p->name, upperdir, p->len);
+			if (IS_ERR(dentry)) {
+				ret = PTR_ERR(dentry);
+				break;
+			}
+			ret = vfs_unlink(upperdir->d_inode, dentry);
+			dput(dentry);
+			if (ret)
+				break;
+		}
+	}
+	mutex_unlock(&upperdir->d_inode->i_mutex);
+
+	revert_creds(old_cred);
+	put_cred(override_cred);
+
+	return ret;
+}
+
+static 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;
+}
+
+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) {
+		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;
+	struct dentry *old_upperdir;
+	struct dentry *new_upperdir;
+	struct dentry *olddentry;
+	struct dentry *newdentry;
+	struct dentry *trap;
+	bool old_opaque;
+	bool new_opaque;
+	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) {
+		enum ovl_path_type new_type;
+
+		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;
+		}
+	}
+
+	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 {
+		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) ||
+		ovl_path_type(new) != 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 (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;
+}
+
+static bool ovl_is_private_xattr(const char *name)
+{
+	return strncmp(name, "trusted.overlay.", 14) == 0;
+}
+
+static 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);
+}
+
+static 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);
+}
+
+static 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;
+}
+
+static 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_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,
+};
+
+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,
+};
+
+static 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;
+
+}
+
+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 = 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);
Index: linux-2.6/fs/Kconfig
===================================================================
--- linux-2.6.orig/fs/Kconfig	2011-03-22 15:11:27.000000000 +0100
+++ linux-2.6/fs/Kconfig	2011-03-22 15:11:36.000000000 +0100
@@ -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"
Index: linux-2.6/fs/Makefile
===================================================================
--- linux-2.6.orig/fs/Makefile	2011-03-22 15:11:27.000000000 +0100
+++ linux-2.6/fs/Makefile	2011-03-22 15:11:36.000000000 +0100
@@ -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/
Index: linux-2.6/fs/overlayfs/Kconfig
===================================================================
--- /dev/null	1970-01-01 00:00:00.000000000 +0000
+++ linux-2.6/fs/overlayfs/Kconfig	2011-03-22 15:11:36.000000000 +0100
@@ -0,0 +1,4 @@
+config OVERLAYFS_FS
+	tristate "Overlay filesystem support"
+	help
+	  Add support for overlay filesystem.
Index: linux-2.6/fs/overlayfs/Makefile
===================================================================
--- /dev/null	1970-01-01 00:00:00.000000000 +0000
+++ linux-2.6/fs/overlayfs/Makefile	2011-03-22 15:11:36.000000000 +0100
@@ -0,0 +1,5 @@
+#
+# Makefile for the overlay filesystem.
+#
+
+obj-$(CONFIG_OVERLAYFS_FS) += overlayfs.o

-- 

Re: [PATCH 4/6 v7] overlay filesystem prototype

[Linus Torvalds]

On Tue, Mar 22, 2011 at 8:26 AM, Miklos Szeredi <miklos@szeredi.hu> wrote:
>
>  fs/Kconfig               |    1
>  fs/Makefile              |    1
>  fs/overlayfs/Kconfig     |    4
>  fs/overlayfs/Makefile    |    5
>  fs/overlayfs/overlayfs.c | 2394 +++++++++++++++++++++++++++++++++++++++++++++++
>  5 files changed, 2405 insertions(+)

Just one single C file? Is there no structure to the code at all? No
separate issues for directory lookup vs file operations, no helper
libraries vs core ops? No "mount time" vs "runtime" structure to the
code?

So 2400 lines isn't all that much, but things have a tendency to grow.
So when I see one single file that tries to do everything, I go "hmm".
Normal filesystems tend to have super.c for handling the mount itself,
and dir.c vs file.c for directory ops vs file ops. Maybe this doesn't
have a file.c because that's all delegated to the lower filesystems,
but still.. Just one file?

Yeah, yeah, we have those horrible drivers that have 10k+ files, and
there are certainly filesystems with much bigger files, but I'd still
wish for more structure.  You've got a whole subdirectory of your own.

                          Linus

Re: [PATCH 4/6 v7] overlay filesystem prototype

[Miklos Szeredi]

On Tue, 22 Mar 2011, Linus Torvalds wrote:
> Just one single C file? Is there no structure to the code at all? No
> separate issues for directory lookup vs file operations, no helper
> libraries vs core ops? No "mount time" vs "runtime" structure to the
> code?
> 
> So 2400 lines isn't all that much, but things have a tendency to grow.
> So when I see one single file that tries to do everything, I go "hmm".
> Normal filesystems tend to have super.c for handling the mount itself,
> and dir.c vs file.c for directory ops vs file ops. Maybe this doesn't
> have a file.c because that's all delegated to the lower filesystems,
> but still.. Just one file?
> 
> Yeah, yeah, we have those horrible drivers that have 10k+ files, and
> there are certainly filesystems with much bigger files, but I'd still
> wish for more structure.  You've got a whole subdirectory of your own.

Sure, good comment.

I'll split this for the actual pull request, if the overall approach
gets an ACK.

Thanks,
Miklos

[PATCH 5/6 v7] overlayfs: add statfs support

[Miklos Szeredi]

[-- Attachment #1: ovl-add-statfs-support.patch --]
[-- Type: text/plain, Size: 1782 bytes --]

From: Andy Whitcroft <apw@canonical.com>

Add support for statfs to the overlayfs filesystem.  As the upper layer
is the target of all write operations assume that the space in that
filesystem is the space in the overlayfs.  There will be some inaccuracy as
overwriting a file will copy it up and consume space we were not expecting,
but it is better than nothing.

Use the upper layer dentry and mount from the overlayfs root inode,
passing the statfs call to that filesystem.

Signed-off-by: Andy Whitcroft <apw@canonical.com>
Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
---
 fs/overlayfs/overlayfs.c |   20 ++++++++++++++++++++
 1 file changed, 20 insertions(+)

Index: linux-2.6/fs/overlayfs/overlayfs.c
===================================================================
--- linux-2.6.orig/fs/overlayfs/overlayfs.c	2011-03-22 15:12:13.000000000 +0100
+++ linux-2.6/fs/overlayfs/overlayfs.c	2011-03-22 15:12:25.000000000 +0100
@@ -2197,9 +2197,29 @@ static int ovl_remount_fs(struct super_b
 		return mnt_want_write(ufs->upper_mnt);
 }
 
+/**
+ * ovl_statfs
+ * @sb: The overlayfs super block
+ * @buf: The struct kstatfs to fill in with stats
+ *
+ * Get the filesystem statistics.  As writes always target the upper layer
+ * filesystem pass the statfs to the same filesystem.
+ */
+static int ovl_statfs(struct dentry *dentry, struct kstatfs *buf)
+{
+	struct dentry *root_dentry = dentry->d_sb->s_root;
+	struct path path;
+	ovl_path_upper(root_dentry, &path);
+
+	if (!path.dentry->d_sb->s_op->statfs)
+		return -ENOSYS;
+	return path.dentry->d_sb->s_op->statfs(path.dentry, buf);
+}
+
 static const struct super_operations ovl_super_operations = {
 	.put_super	= ovl_put_super,
 	.remount_fs	= ovl_remount_fs,
+	.statfs		= ovl_statfs,
 };
 
 struct ovl_config {

-- 

[PATCH 6/6 v7] overlay: overlay filesystem documentation

[Miklos Szeredi]

[-- Attachment #1: overlayfs-documentation.patch --]
[-- Type: text/plain, Size: 7719 bytes --]

From: Neil Brown <neilb@suse.de>

Document the overlay filesystem.

Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
---
 Documentation/filesystems/overlayfs.txt |  163 ++++++++++++++++++++++++++++++++
 1 file changed, 163 insertions(+)

Index: linux-2.6/Documentation/filesystems/overlayfs.txt
===================================================================
--- /dev/null	1970-01-01 00:00:00.000000000 +0000
+++ linux-2.6/Documentation/filesystems/overlayfs.txt	2011-03-22 15:11:40.000000000 +0100
@@ -0,0 +1,163 @@
+Written by: Neil Brown <neilb@suse.de>
+
+Overlay Filesystem
+==================
+
+This document describes a prototype for a new approach to providing
+overlay-filesystem functionality in Linux (sometimes referred to as
+union-filesystems).  An overlay-filesystem tries to present a
+filesystem which is the result over overlaying one filesystem on top
+of the other.
+
+The result will inevitably fail to look exactly like a normal
+filesystem for various technical reasons.  The expectation is that
+many use cases will be able to ignore these differences.
+
+This approach is 'hybrid' because the objects that appear in the
+filesystem do not all appear to belong to that filesystem.  In many
+cases an object accessed in the union will be indistinguishable
+from accessing the corresponding object from the original filesystem.
+This is most obvious from the 'st_dev' field returned by stat(2).
+
+While directories will report an st_dev from the overlay-filesystem,
+all non-directory objects will report an st_dev from the lower or
+upper filesystem that is providing the object.  Similarly st_ino will
+only be unique when combined with st_dev, and both of these can change
+over the lifetime of a non-directory object.  Many applications and
+tools ignore these values and will not be affected.
+
+Upper and Lower
+---------------
+
+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.
+
+It would be more correct to refer to an upper and lower 'directory
+tree' rather than 'filesystem' as it is quite possible for both
+directory trees to be in the same filesystem and there is no
+requirement that the root of a filesystem be given for either upper or
+lower.
+
+The lower filesystem can be any filesystem supported by Linux and does
+not need to be writable.  The lower filesystem can even be another
+overlayfs.  The upper filesystem will normally be writable and if it
+is it must support the creation of trusted.* extended attributes, and
+must provide valid d_type in readdir responses, at least for symbolic
+links - so NFS is not suitable.
+
+A read-only overlay of two read-only filesystems may use any
+filesystem type.
+
+Directories
+-----------
+
+Overlaying mainly involved directories.  If a given name appears in both
+upper and lower filesystems and refers to a non-directory in either,
+then the lower object is hidden - the name refers only to the upper
+object.
+
+Where both upper and lower objects are directories, a merged directory
+is formed.
+
+At mount time, the two directories given as mount options are combined
+into a merged directory.  Then whenever a lookup is requested in such
+a merged directory, the lookup is performed in each actual directory
+and the combined result is cached in the dentry belonging to the overlay
+filesystem.  If both actual lookups find directories, both are stored
+and a merged directory is created, otherwise only one is stored: the
+upper if it exists, else the lower.
+
+Only the lists of names from directories are merged.  Other content
+such as metadata and extended attributes are reported for the upper
+directory only.  These attributes of the lower directory are hidden.
+
+whiteouts and opaque directories
+--------------------------------
+
+In order to support rm and rmdir without changing the lower
+filesystem, an overlay filesystem needs to record in the upper filesystem
+that files have been removed.  This is done using whiteouts and opaque
+directories (non-directories are always opaque).
+
+The overlay filesystem uses extended attributes with a
+"trusted.overlay."  prefix to record these details.
+
+A whiteout is created as a symbolic link with target
+"(overlay-whiteout)" and with xattr "trusted.overlay.whiteout" set to "y".
+When a whiteout is found in the upper level of a merged directory, any
+matching name in the lower level is ignored, and the whiteout itself
+is also hidden.
+
+A directory is made opaque by setting the xattr "trusted.overlay.opaque"
+to "y".  Where the upper filesystem contains an opaque directory, any
+directory in the lower filesystem with the same name is ignored.
+
+readdir
+-------
+
+When a 'readdir' request is made on a merged directory, the upper and
+lower directories are each read and the name lists merged in the
+obvious way (upper is read first, then lower - entries that already
+exist are not re-added).  This merged name list is cached in the
+'struct file' and so remains as long as the file is kept open.  If the
+directory is opened and read by two processes at the same time, they
+will each have separate caches.  A seekdir to the start of the
+directory (offset 0) followed by a readdir will cause the cache to be
+discarded and rebuilt.
+
+This means that changes to the merged directory do not appear while a
+directory is being read.  This is unlikely to be noticed by many
+programs.
+
+seek offsets are assigned sequentially when the directories are read.
+Thus if
+  - read part of a directory
+  - remember an offset, and close the directory
+  - re-open the directory some time later
+  - seek to the remembered offset
+
+there may be little correlation between the old and new locations in
+the list of filenames, particularly if anything has changed in the
+directory.
+
+Readdir on directories that are not merged is simply handled by the
+underlying directory (upper or lower).
+
+
+Non-directories
+---------------
+
+Objects that are not directories (files, symlinks, device-special
+files etc.) are presented either from the upper or lower filesystem as
+appropriate.  When a file in the lower filesystem is accessed in a way
+the requires write-access, such as opening for write access, changing
+some metadata etc., the file is first copied from the lower filesystem
+to the upper filesystem (copy_up).  Note that creating a hard-link
+also requires copy_up, though of course creation of a symlink does
+not.
+
+The copy_up process first makes sure that the containing directory
+exists in the upper filesystem - creating it and any parents as
+necessary.  It then creates the object with the same metadata (owner,
+mode, mtime, symlink-target etc.) and then if the object is a file, the
+data is copied from the lower to the upper filesystem.  Finally any
+extended attributes are copied up.
+
+Once the copy_up is complete, the overlay filesystem simply
+provides direct access to the newly created file in the upper
+filesystem - future operations on the file are barely noticed by the
+overlay filesystem (though an operation on the name of the file such as
+rename or unlink will of course be noticed and handled).
+
+Changes to underlying filesystems
+---------------------------------
+
+Offline changes, when the overlay is not mounted, are allowed to either
+the upper or the lower trees.
+
+Changes to the underlying filesystems while part of a mounted overlay
+filesystem are not allowed.  This is not yet enforced, but will be in
+the future.

-- 

Re: [PATCH 0/6 v7] overlay filesystem - request for inclusion

[Linus Torvalds]

On Tue, Mar 22, 2011 at 8:26 AM, Miklos Szeredi <miklos@szeredi.hu> wrote:
> Here's an updated version of the overlay filesystem.  I'd like to
> propose it for inclusion into mainline.

So on the whole it looked pretty small and simple. And most of the VFS
level changes looked fine and I just reacted to the odd calling
convention for open (I really think you should aim for ->open to have
the basically same arguments as you made __dentry_open have: 'struct
path', 'struct filp' and 'struct cred').

But I'd want Al's ack on the series. And also hear who uses it and how
it's been tested?

                                Linus

Re: [PATCH 0/6 v7] overlay filesystem - request for inclusion

[Felix Fietkau]

On 2011-03-22 6:36 PM, Linus Torvalds wrote:
> On Tue, Mar 22, 2011 at 8:26 AM, Miklos Szeredi <miklos@szeredi.hu> wrote:
>> Here's an updated version of the overlay filesystem.  I'd like to
>> propose it for inclusion into mainline.
> 
> So on the whole it looked pretty small and simple. And most of the VFS
> level changes looked fine and I just reacted to the odd calling
> convention for open (I really think you should aim for ->open to have
> the basically same arguments as you made __dentry_open have: 'struct
> path', 'struct filp' and 'struct cred').
> 
> But I'd want Al's ack on the series. And also hear who uses it and how
> it's been tested?
We're using it in OpenWrt (an Embedded Linux distribution) for devices
with tiny amounts of flash for the entire system (e.g. 4 MB).
We're using it to provide a writable on-flash root filesystem with
squashfs for the read-only part and jffs2 for the writable overlay. This
saves some precious flash space compared to using only jffs2, and it
makes it easy for users to reset their device to defaults without having
to reflash.
With a backport of v6 of this series + my fixes that went into v7 this
is working quite well on 2.6.37 and 2.6.38 - I'm using it on a few
wireless access points at home.

- Felix

Re: [PATCH 0/6 v7] overlay filesystem - request for inclusion

[Linus Torvalds]

On Tue, Mar 22, 2011 at 11:22 AM, Felix Fietkau <nbd@openwrt.org> wrote:
>
> We're using it in OpenWrt (an Embedded Linux distribution) for devices
> with tiny amounts of flash for the entire system (e.g. 4 MB).
> We're using it to provide a writable on-flash root filesystem with
> squashfs for the read-only part and jffs2 for the writable overlay. This
> saves some precious flash space compared to using only jffs2, and it
> makes it easy for users to reset their device to defaults without having
> to reflash.
> With a backport of v6 of this series + my fixes that went into v7 this
> is working quite well on 2.6.37 and 2.6.38 - I'm using it on a few
> wireless access points at home.

Ok - sounds like an eminently sane and reasonable usage scenario.

Al?

                        Linus

Re: [PATCH 0/6 v7] overlay filesystem - request for inclusion

[Al Viro]

On Tue, Mar 22, 2011 at 10:36:09AM -0700, Linus Torvalds wrote:
> On Tue, Mar 22, 2011 at 8:26 AM, Miklos Szeredi <miklos@szeredi.hu> wrote:
> > Here's an updated version of the overlay filesystem. ?I'd like to
> > propose it for inclusion into mainline.
> 
> So on the whole it looked pretty small and simple. And most of the VFS
> level changes looked fine and I just reacted to the odd calling
> convention for open (I really think you should aim for ->open to have
> the basically same arguments as you made __dentry_open have: 'struct
> path', 'struct filp' and 'struct cred').
> 
> But I'd want Al's ack on the series. And also hear who uses it and how
> it's been tested?

To be honest, I *really* don't like to touch that before ->atomic_open()
is finished.  We are nearly there (the only remaining prereq is to sort out
revalidate vs. mountpoint crossing issues), so with any luck the neighborhood
of open() will be finished in for-next circa -rc3 or so.

As for the rest of it... I'll need to review that in details, but the first
impression from that code is that I don't like the way copyup is done.
Locking analysis would be really nice; AFAICS, it violates locking order
when called from e.g. ->setattr() and its protection against renames is
nowhere near enough.  I might be missing something subtle, but...

Re: [PATCH 0/6 v7] overlay filesystem - request for inclusion

[Linus Torvalds]

On Tue, Mar 22, 2011 at 11:39 AM, Al Viro <viro@zeniv.linux.org.uk> wrote:
>
> Locking analysis would be really nice; AFAICS, it violates locking order
> when called from e.g. ->setattr() and its protection against renames is
> nowhere near enough.  I might be missing something subtle, but...

Miklos - have you tried using this with lockdep (together with the
same filesystems mounted natively too)? I'd expect that that should
show any bad lock usage..

                   Linus

Re: [PATCH 0/6 v7] overlay filesystem - request for inclusion

[Miklos Szeredi]

On Tue, 22 Mar 2011, Linus Torvalds wrote:
> On Tue, Mar 22, 2011 at 11:39 AM, Al Viro <viro@zeniv.linux.org.uk> wrote:
> >
> > Locking analysis would be really nice; AFAICS, it violates locking order
> > when called from e.g. ->setattr()

Locking order is always:

-> overlayfs locks
   -> upper fs locks
   -> lower fs locks

So it's really pretty simple and easy to validate.

> >  and its protection against renames is
> > nowhere near enough.  I might be missing something subtle, but...

Protection is exactly as for userspace callers.  AFAICT.

> Miklos - have you tried using this with lockdep (together with the
> same filesystems mounted natively too)? I'd expect that that should
> show any bad lock usage..

Ah, lockdep.  I have tried, but there seems to be always something
that triggers it at boot time on my laptop, which makes it useless.  I
could find some other machine to test this on, though.

Thanks,
Miklos
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Re: [PATCH 0/6 v7] overlay filesystem - request for inclusion

[Al Viro]

On Tue, Mar 22, 2011 at 07:58:17PM +0100, Miklos Szeredi wrote:
> On Tue, 22 Mar 2011, Linus Torvalds wrote:
> > On Tue, Mar 22, 2011 at 11:39 AM, Al Viro <viro@zeniv.linux.org.uk> wrote:
> > >
> > > Locking analysis would be really nice; AFAICS, it violates locking order
> > > when called from e.g. ->setattr()
> 
> Locking order is always:
> 
> -> overlayfs locks
>    -> upper fs locks
>    -> lower fs locks
> 
> So it's really pretty simple and easy to validate.

In which *order* on the upper fs?

> Protection is exactly as for userspace callers.  AFAICT.

Pardon?  You traverse the chain of ancestors; fine, but who says it stays
anywhere near being relevant as you go?

Re: [PATCH 0/6 v7] overlay filesystem - request for inclusion

[Miklos Szeredi]

On Tue, 22 Mar 2011, Al Viro wrote:
> On Tue, Mar 22, 2011 at 07:58:17PM +0100, Miklos Szeredi wrote:
> > On Tue, 22 Mar 2011, Linus Torvalds wrote:
> > > On Tue, Mar 22, 2011 at 11:39 AM, Al Viro <viro@zeniv.linux.org.uk> wrote:
> > > >
> > > > Locking analysis would be really nice; AFAICS, it violates locking order
> > > > when called from e.g. ->setattr()
> > 
> > Locking order is always:
> > 
> > -> overlayfs locks
> >    -> upper fs locks
> >    -> lower fs locks
> > 
> > So it's really pretty simple and easy to validate.
> 
> In which *order* on the upper fs?

In copy up it does:

-> lock parent on upper
  -> lock child on upper

So a setattr with copy up would go like this:

-> lock child on overlayfs
  -> lock parent on upper
     ->lock child on upper
  -> lock child on upper

> > Protection is exactly as for userspace callers.  AFAICT.
> 
> Pardon?  You traverse the chain of ancestors; fine, but who says it stays
> anywhere near being relevant as you go?

Not quite sure I understand.

There are no assumptions about locks in overlayfs keeping anything
relevant in upper/lower fs.  Everything is re-checked and re-locked on
the upper layer before proceeding with the rename.

Thanks,
Miklos

Re: [PATCH 0/6 v7] overlay filesystem - request for inclusion

[Al Viro]

On Tue, Mar 22, 2011 at 08:43:17PM +0100, Miklos Szeredi wrote:
> In copy up it does:
> 
> -> lock parent on upper
>   -> lock child on upper
> 
> So a setattr with copy up would go like this:
> 
> -> lock child on overlayfs
>   -> lock parent on upper
>      ->lock child on upper
>   -> lock child on upper
> 
> > > Protection is exactly as for userspace callers.  AFAICT.
> > 
> > Pardon?  You traverse the chain of ancestors; fine, but who says it stays
> > anywhere near being relevant as you go?
> 
> Not quite sure I understand.
> 
> There are no assumptions about locks in overlayfs keeping anything
> relevant in upper/lower fs.  Everything is re-checked and re-locked on
> the upper layer before proceeding with the rename.

Proceeding with rename is not interesting; proceeding with copyup is.

Who said that by the time we get to copy_up_locked you will still have
dentry (and upper) match lowerpath?  Or that ->d_parent on overlay and
on upper will change in sync, for that matter - there are two d_move()
calls involved...

Re: [PATCH 0/6 v7] overlay filesystem - request for inclusion

[Miklos Szeredi]

On Tue, 22 Mar 2011, Al Viro wrote:
> Proceeding with rename is not interesting; proceeding with copyup is.
> 
> Who said that by the time we get to copy_up_locked you will still have
> dentry (and upper) match lowerpath?  Or that ->d_parent on overlay and
> on upper will change in sync, for that matter - there are two d_move()
> calls involved...

If rename is involved, than rename itself already did the copy up.
And that's checked before proceeding with the actual copy up.  If
there was no rename, then that guarantees that things are in sync, at
least for the duration of the copy up.

Is that not enough?

Thanks,
Miklos

Re: [PATCH 0/6 v7] overlay filesystem - request for inclusion

[Al Viro]

On Tue, Mar 22, 2011 at 09:06:38PM +0100, Miklos Szeredi wrote:
> On Tue, 22 Mar 2011, Al Viro wrote:
> > Proceeding with rename is not interesting; proceeding with copyup is.
> > 
> > Who said that by the time we get to copy_up_locked you will still have
> > dentry (and upper) match lowerpath?  Or that ->d_parent on overlay and
> > on upper will change in sync, for that matter - there are two d_move()
> > calls involved...
> 
> If rename is involved, than rename itself already did the copy up.
> And that's checked before proceeding with the actual copy up.  If
> there was no rename, then that guarantees that things are in sync, at
> least for the duration of the copy up.

What do you mean, before?  It's not atomic...  What happens if e.g.
you get

A: decided to do copy_up_locked
   blocked on i_mutex

B: did copy_up
   did rename(), complete with d_move()
   did unlink() in new place

A: got CPU back, got i_mutex
   proceeded to copy lower into new location
   set dentry to very odd (upper,lower) pair

Re: [PATCH 0/6 v7] overlay filesystem - request for inclusion

[Miklos Szeredi]

On Tue, 22 Mar 2011, Al Viro wrote:
> On Tue, Mar 22, 2011 at 09:06:38PM +0100, Miklos Szeredi wrote:
> > On Tue, 22 Mar 2011, Al Viro wrote:
> > > Proceeding with rename is not interesting; proceeding with copyup is.
> > > 
> > > Who said that by the time we get to copy_up_locked you will still have
> > > dentry (and upper) match lowerpath?  Or that ->d_parent on overlay and
> > > on upper will change in sync, for that matter - there are two d_move()
> > > calls involved...
> > 
> > If rename is involved, than rename itself already did the copy up.
> > And that's checked before proceeding with the actual copy up.  If
> > there was no rename, then that guarantees that things are in sync, at
> > least for the duration of the copy up.
> 
> What do you mean, before?  It's not atomic...  What happens if e.g.
> you get
> 
> A: decided to do copy_up_locked
>    blocked on i_mutex
> 
> B: did copy_up
>    did rename(), complete with d_move()
>    did unlink() in new place
> 
> A: got CPU back, got i_mutex

Here it can check if the file was copied up or not.  OK, I see the
code doesn't quite get that right.

Patch below would fix it, I think.

Thanks,
Miklos

diff --git a/fs/overlayfs/overlayfs.c b/fs/overlayfs/overlayfs.c
index e7fcbde..0a1137b 100644
--- a/fs/overlayfs/overlayfs.c
+++ b/fs/overlayfs/overlayfs.c
@@ -1269,8 +1269,7 @@ static int ovl_copy_up_one(struct dentry *parent, struct dentry *dentry,
 	 * racing with rename (rename means the copy up was already
 	 * successful).
 	 */
-	if (dentry->d_parent != parent) {
-		WARN_ON((ovl_path_type(dentry) == OVL_PATH_LOWER));
+	if (ovl_path_type(dentry) != OVL_PATH_LOWER) {
 		err = 0;
 	} else {
 		err = ovl_copy_up_locked(upperdir, dentry, lowerpath,

Re: [PATCH 0/6 v7] overlay filesystem - request for inclusion

[Miklos Szeredi]

On Tue, 22 Mar 2011, Miklos Szeredi wrote:
> On Tue, 22 Mar 2011, Al Viro wrote:
> > On Tue, Mar 22, 2011 at 09:06:38PM +0100, Miklos Szeredi wrote:
> > > On Tue, 22 Mar 2011, Al Viro wrote:
> > > > Proceeding with rename is not interesting; proceeding with copyup is.
> > > > 
> > > > Who said that by the time we get to copy_up_locked you will still have
> > > > dentry (and upper) match lowerpath?  Or that ->d_parent on overlay and
> > > > on upper will change in sync, for that matter - there are two d_move()
> > > > calls involved...
> > > 
> > > If rename is involved, than rename itself already did the copy up.
> > > And that's checked before proceeding with the actual copy up.  If
> > > there was no rename, then that guarantees that things are in sync, at
> > > least for the duration of the copy up.
> > 
> > What do you mean, before?  It's not atomic...  What happens if e.g.
> > you get
> > 
> > A: decided to do copy_up_locked
> >    blocked on i_mutex
> > 
> > B: did copy_up
> >    did rename(), complete with d_move()
> >    did unlink() in new place
> > 
> > A: got CPU back, got i_mutex
> 
> Here it can check if the file was copied up or not.  OK, I see the
> code doesn't quite get that right.
> 
> Patch below would fix it, I think.

Scratch that, d_move() on overlayfs would also have to be under
i_mutex of upper.  But that should be doable as well.  I'll fix that
tomorrow when my brain is a little fresher.

Thanks,
Miklos

Re: [PATCH 0/6 v7] overlay filesystem - request for inclusion

[Miklos Szeredi]

On Tue, 22 Mar 2011, Miklos Szeredi wrote:
> > What do you mean, before?  It's not atomic...  What happens if e.g.
> > you get
> > 
> > A: decided to do copy_up_locked
> >    blocked on i_mutex
> > 
> > B: did copy_up
> >    did rename(), complete with d_move()
> >    did unlink() in new place
> > 
> > A: got CPU back, got i_mutex
> 
> Here it can check if the file was copied up or not.  OK, I see the
> code doesn't quite get that right.
> 
> Patch below would fix it, I think.

Patch is correct, after all.  More cleanups in that area below, as
well as analysis of rename vs. copy up race.

Thanks for taking a look.

Miklos



diff --git a/fs/overlayfs/overlayfs.c b/fs/overlayfs/overlayfs.c
index e7fcbde..b97a481 100644
--- a/fs/overlayfs/overlayfs.c
+++ b/fs/overlayfs/overlayfs.c
@@ -1166,15 +1166,8 @@ static int ovl_copy_up_locked(struct dentry *upperdir, struct dentry *dentry,
 
 	newpath.mnt = ofs->upper_mnt;
 	newpath.dentry = ovl_upper_create(upperdir, dentry, stat, link);
-	if (IS_ERR(newpath.dentry)) {
-		err = PTR_ERR(newpath.dentry);
-
-		/* Already copied up? */
-		if (err == -EEXIST && ovl_path_type(dentry) != OVL_PATH_LOWER)
-			return 0;
-
-		return err;
-	}
+	if (IS_ERR(newpath.dentry))
+		return PTR_ERR(newpath.dentry);
 
 	if (S_ISREG(stat->mode)) {
 		err = ovl_copy_up_data(lowerpath, &newpath, stat->size);
@@ -1218,6 +1211,21 @@ err_remove:
 	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)
 {
@@ -1264,13 +1272,7 @@ static int ovl_copy_up_one(struct dentry *parent, struct dentry *dentry,
 	old_cred = override_creds(override_cred);
 
 	mutex_lock_nested(&upperdir->d_inode->i_mutex, I_MUTEX_PARENT);
-	/*
-	 * Using upper filesystem locking to protect against copy up
-	 * racing with rename (rename means the copy up was already
-	 * successful).
-	 */
-	if (dentry->d_parent != parent) {
-		WARN_ON((ovl_path_type(dentry) == OVL_PATH_LOWER));
+	if (ovl_path_type(dentry) != OVL_PATH_LOWER) {
 		err = 0;
 	} else {
 		err = ovl_copy_up_locked(upperdir, dentry, lowerpath,

Re: [PATCH 0/6 v7] overlay filesystem - request for inclusion

[Al Viro]

On Tue, Mar 22, 2011 at 07:58:17PM +0100, Miklos Szeredi wrote:

> > >  and its protection against renames is
> > > nowhere near enough. ??I might be missing something subtle, but...
> 
> Protection is exactly as for userspace callers.  AFAICT.

BTW, what filesystems can act as upper layers and how are you going to
prevent modifications of upper layer in normal way?  It is mounted,
after all, or you would be unable to find it when mounting overlayfs.
And it might be mounted in any number of places, not all even visible to
you...  I realize that you have it listed as a problem, but do you have
any ideas on how to deal with that?

If you allow NFS as upper layer, you really have a problem; with this
approach you probably want to prevent that very forcibly.  Not that
your open() handling would work correctly with NFS, even with no modifications
from other clients or from server...

Re: [PATCH 0/6 v7] overlay filesystem - request for inclusion

[Miklos Szeredi]

On Tue, 22 Mar 2011, Al Viro wrote:
> On Tue, Mar 22, 2011 at 07:58:17PM +0100, Miklos Szeredi wrote:
> 
> > > >  and its protection against renames is
> > > > nowhere near enough. ??I might be missing something subtle, but...
> > 
> > Protection is exactly as for userspace callers.  AFAICT.
> 
> BTW, what filesystems can act as upper layers and how are you going to
> prevent modifications of upper layer in normal way?  It is mounted,
> after all, or you would be unable to find it when mounting overlayfs.
> And it might be mounted in any number of places, not all even visible to
> you...  I realize that you have it listed as a problem, but do you have
> any ideas on how to deal with that?

Yes, I have some patches, but decided that that should be a separate
set, once the basics are ironed out.

Since the locking guarantees are separated on the upper/lower fs from
the overlayfs, allowing modification is not a huge problem.  The worst
that can happen is that an attacker who has access to both the overlay
and the upper or lower fs then can "build" an arbitrarily deep
directory tree on the overlayfs.  Not a big issue.  There won't be
deadlocks or filesystem corruption.

> If you allow NFS as upper layer, you really have a problem; with this
> approach you probably want to prevent that very forcibly.  Not that
> your open() handling would work correctly with NFS, even with no modifications
> from other clients or from server...

Upper layer doesn't work on NFS for multiple reasons.

Thanks,
Miklos