kernel: remove all local symbols from kernel modules at link time to reduce their...

[openwrt.git] / target / linux / generic / patches-2.6.37 / 209-overlayfs.patch

--- a/fs/open.c
+++ b/fs/open.c
@@ -651,19 +651,19 @@ 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)
 {
        struct inode *inode;
        int error;
 
+       path_get(path);
        f->f_mode = OPEN_FMODE(f->f_flags) | FMODE_LSEEK |
                                FMODE_PREAD | FMODE_PWRITE;
-       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))
@@ -671,8 +671,7 @@ 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;
        f->f_op = fops_get(inode->i_fop);
        file_sb_list_add(f, inode->i_sb);
@@ -718,7 +717,7 @@ cleanup_all:
                         * here, so just reset the state.
                         */
                        file_reset_write(f);
-                       mnt_drop_write(mnt);
+                       mnt_drop_write(path->mnt);
                }
        }
        file_sb_list_del(f);
@@ -726,8 +725,7 @@ cleanup_all:
        f->f_path.mnt = NULL;
 cleanup_file:
        put_filp(f);
-       dput(dentry);
-       mntput(mnt);
+       path_put(path);
        return ERR_PTR(error);
 }
 
@@ -753,14 +751,14 @@ cleanup_file:
 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;
@@ -787,10 +785,17 @@ struct file *nameidata_to_filp(struct na
        filp = nd->intent.open.file;
        /* 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;
 }
 
@@ -801,35 +806,45 @@ 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 path path = { .dentry = dentry, .mnt = mnt };
+       struct file *ret;
+
+       BUG_ON(!mnt);
+
+       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);
 
-       /*
-        * We must always pass in a valid mount pointer.   Historically
-        * callers got away with not passing it, but we must enforce this at
-        * the earliest possible point now to avoid strange problems deep in the
-        * filesystem stack.
-        */
-       if (!mnt) {
-               printk(KERN_WARNING "%s called with NULL vfsmount\n", __func__);
-               dump_stack();
-               return ERR_PTR(-EINVAL);
-       }
+       if (inode->i_op->open)
+               return inode->i_op->open(path->dentry, flags, cred);
 
-       error = -ENFILE;
        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)
 {
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -1574,6 +1574,7 @@ struct inode_operations {
                          loff_t len);
        int (*fiemap)(struct inode *, struct fiemap_extent_info *, u64 start,
                      u64 len);
+       struct file *(*open)(struct dentry *, int flags, const struct cred *);
 };
 
 struct seq_file;
@@ -1975,6 +1976,7 @@ extern int do_fallocate(struct file *fil
 extern long do_sys_open(int dfd, const char __user *filename, int flags,
                        int mode);
 extern struct file *filp_open(const char *, int, 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);
--- a/fs/splice.c
+++ b/fs/splice.c
@@ -1307,6 +1307,7 @@ 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,
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -1307,6 +1307,23 @@ 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)
 {
--- a/include/linux/mount.h
+++ b/include/linux/mount.h
@@ -121,6 +121,9 @@ static inline void mntput(struct vfsmoun
        }
 }
 
+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);
 
--- a/fs/Kconfig
+++ b/fs/Kconfig
@@ -64,6 +64,7 @@ source "fs/quota/Kconfig"
 
 source "fs/autofs4/Kconfig"
 source "fs/fuse/Kconfig"
+source "fs/overlayfs/Kconfig"
 
 config CUSE
        tristate "Character device in Userspace support"
--- a/fs/Makefile
+++ b/fs/Makefile
@@ -103,6 +103,7 @@ 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/
--- /dev/null
+++ b/fs/overlayfs/Kconfig
@@ -0,0 +1,4 @@
+config OVERLAYFS_FS
+       tristate "Overlay filesystem support"
+       help
+         Add support for overlay filesystem.
--- /dev/null
+++ b/fs/overlayfs/Makefile
@@ -0,0 +1,5 @@
+#
+# Makefile for the overlay filesystem.
+#
+
+obj-$(CONFIG_OVERLAYFS_FS) += overlayfs.o
--- /dev/null
+++ b/fs/overlayfs/overlayfs.c
@@ -0,0 +1,2358 @@
+#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,
+                                                  bool is_whiteout)
+{
+       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 = is_whiteout;
+       }
+
+       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, bool is_whiteout)
+{
+       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, is_whiteout);
+       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, false);
+               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;
+       bool is_whiteout = false;
+
+       rdd->count++;
+       if (d_type == DT_LNK) {
+               struct dentry *dentry;
+
+               dentry = lookup_one_len(name, rdd->dir, namelen);
+               if (IS_ERR(dentry)) {
+                       rdd->err = PTR_ERR(dentry);
+                       goto out;
+               }
+               is_whiteout = ovl_is_whiteout(dentry);
+               dput(dentry);
+       }
+
+       rdd->err = ovl_cache_entry_add_rb(rdd, name, namelen, ino, d_type,
+                                         is_whiteout);
+
+out:
+       return rdd->err;
+}
+
+static int ovl_dir_read(struct path *realpath, struct ovl_readdir_data *rdd,
+                         filldir_t filler)
+{
+       const struct cred *old_cred;
+       struct cred *override_cred;
+       struct file *realfile;
+       int err;
+
+       realfile = vfs_open(realpath, O_RDONLY | O_DIRECTORY, current_cred());
+       if (IS_ERR(realfile))
+               return PTR_ERR(realfile);
+
+       err = -ENOMEM;
+       override_cred = prepare_creds();
+       if (override_cred) {
+               /*
+                * CAP_SYS_ADMIN for getxattr
+                * CAP_DAC_OVERRIDE for lookup and unlink
+                */
+               cap_raise(override_cred->cap_effective, CAP_SYS_ADMIN);
+               cap_raise(override_cred->cap_effective, CAP_DAC_OVERRIDE);
+               old_cred = override_creds(override_cred);
+
+               do {
+                       rdd->count = 0;
+                       rdd->err = 0;
+                       err = vfs_readdir(realfile, filler, rdd);
+                       if (err >= 0)
+                               err = rdd->err;
+               } while (!err && rdd->count);
+
+               revert_creds(old_cred);
+               put_cred(override_cred);
+       }
+       fput(realfile);
+
+       if (err) {
+               if (rdd->list)
+                       ovl_cache_free(rdd->list);
+               return err;
+       }
+
+       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_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;
+       }
+       /*
+        * 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)
+                       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 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))
+                       return -EINTR;
+
+               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))
+                       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) {
+               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;
+       }
+
+       /* FIXME: recovery from failure to copy up */
+
+       if (S_ISREG(stat->mode)) {
+               err = ovl_copy_up_data(lowerpath, &newpath, stat->size);
+               if (err)
+                       return err;
+       }
+
+       err = ovl_copy_up_xattr(lowerpath->dentry, newpath.dentry);
+       if (err)
+               return err;
+
+       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)
+               return err;
+
+       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;
+}
+
+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)
+                       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_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);
+
+out_dput:
+       dput(newdentry);
+out_put_cred:
+       revert_creds(old_cred);
+       put_cred(override_cred);
+out:
+       return err;
+}
+
+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)
+{
+       int err;
+       struct path lowerpath;
+       struct path upperpath;
+       struct ovl_cache_entry *p;
+       LIST_HEAD(list);
+       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;
+       }
+
+       ovl_cache_free(&list);
+
+       return err;
+}
+
+static int ovl_unlink_whiteout(void *buf, const char *name, int namelen,
+                                loff_t offset, u64 ino, unsigned int d_type)
+{
+       struct ovl_readdir_data *rdd = buf;
+
+       rdd->count++;
+       /* check d_type to filter out "." and ".." */
+       if (d_type == DT_LNK) {
+               struct dentry *dentry;
+
+               dentry = lookup_one_len(name, rdd->dir, namelen);
+               if (IS_ERR(dentry)) {
+                       rdd->err = PTR_ERR(dentry);
+               } else {
+                       rdd->err = vfs_unlink(rdd->dir->d_inode, dentry);
+                       dput(dentry);
+               }
+       }
+
+       return rdd->err;
+}
+
+static int ovl_remove_whiteouts(struct dentry *dentry)
+{
+       struct path upperpath;
+       struct ovl_readdir_data rdd = { .list = NULL };
+
+       ovl_path_upper(dentry, &upperpath);
+       rdd.dir = upperpath.dentry;
+
+       return ovl_dir_read(&upperpath, &rdd, ovl_unlink_whiteout);
+}
+
+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_dir(dentry);
+               if (err)
+                       return err;
+
+               if (type == OVL_PATH_MERGE) {
+                       err = ovl_remove_whiteouts(dentry);
+                       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 {
+               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 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_dir(new);
+                       if (err)
+                               return err;
+
+                       if (new_type == OVL_PATH_MERGE) {
+                               err = ovl_remove_whiteouts(new);
+                               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;
+
+       err = vfs_rename(old_upperdir->d_inode, olddentry,
+                        new_upperdir->d_inode, newdentry);
+
+       if (!err) {
+               bool old_opaque = ovl_dentry_is_opaque(old);
+               bool new_opaque = ovl_dentry_is_opaque(new);
+
+               if (ovl_path_type(new) != OVL_PATH_UPPER)
+                       new_opaque = true;
+
+               if (old_type != OVL_PATH_UPPER || old_opaque)
+                       err = ovl_whiteout(old_upperdir, old);
+               if (!err && is_dir) {
+                       if (old_opaque && !new_opaque) {
+                               ovl_remove_opaque(olddentry);
+                               ovl_dentry_set_opaque(old, false);
+                       }
+                       if (!old_opaque && new_opaque) {
+                               err = ovl_set_opaque(olddentry);
+                               ovl_dentry_set_opaque(old, true);
+                       }
+               }
+               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);
+}
+
+/**
+ * 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 {
+       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 int ovl_get_sb(struct file_system_type *fs_type,
+                       int flags, const char *dev_name,
+                       void *raw_data, struct vfsmount *mnt)
+{
+       return get_sb_nodev(fs_type, flags, raw_data, ovl_fill_super, mnt);
+}
+
+static struct file_system_type ovl_fs_type = {
+       .owner          = THIS_MODULE,
+       .name           = "overlayfs",
+       .get_sb         = ovl_get_sb,
+       .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);
--- /dev/null
+++ b/Documentation/filesystems/overlayfs.txt
@@ -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
+case 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 for the overlay-filesystem,
+all non-directory objects will report an st_dev whichever of 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.