1 files changed, 796 insertions, 0 deletions

diff --git a/fs/overlayfs/super.c b/fs/overlayfs/super.c
new file mode 100644
index 000000000000..08b704cebfc4
--- /dev/null
+++ b/fs/overlayfs/super.c
@@ -0,0 +1,796 @@
+/*
+ *
+ * Copyright (C) 2011 Novell Inc.
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 as published by
+ * the Free Software Foundation.
+ */
+
+#include <linux/fs.h>
+#include <linux/namei.h>
+#include <linux/xattr.h>
+#include <linux/security.h>
+#include <linux/mount.h>
+#include <linux/slab.h>
+#include <linux/parser.h>
+#include <linux/module.h>
+#include <linux/sched.h>
+#include <linux/statfs.h>
+#include <linux/seq_file.h>
+#include "overlayfs.h"
+
+MODULE_AUTHOR("Miklos Szeredi <miklos@szeredi.hu>");
+MODULE_DESCRIPTION("Overlay filesystem");
+MODULE_LICENSE("GPL");
+
+#define OVERLAYFS_SUPER_MAGIC 0x794c764f
+
+struct ovl_config {
+        char *lowerdir;
+        char *upperdir;
+        char *workdir;
+};
+
+/* private information held for overlayfs's superblock */
+struct ovl_fs {
+        struct vfsmount *upper_mnt;
+        struct vfsmount *lower_mnt;
+        struct dentry *workdir;
+        long lower_namelen;
+        /* pathnames of lower and upper dirs, for show_options */
+        struct ovl_config config;
+};
+
+struct ovl_dir_cache;
+
+/* private information held for every overlayfs dentry */
+struct ovl_entry {
+        struct dentry *__upperdentry;
+        struct dentry *lowerdentry;
+        struct ovl_dir_cache *cache;
+        union {
+                struct {
+                        u64 version;
+                        bool opaque;
+                };
+                struct rcu_head rcu;
+        };
+};
+
+const char *ovl_opaque_xattr = "trusted.overlay.opaque";
+
+
+enum ovl_path_type ovl_path_type(struct dentry *dentry)
+{
+        struct ovl_entry *oe = dentry->d_fsdata;
+
+        if (oe->__upperdentry) {
+                if (oe->lowerdentry) {
+                        if (S_ISDIR(dentry->d_inode->i_mode))
+                                return OVL_PATH_MERGE;
+                        else
+                                return OVL_PATH_UPPER;
+                } else {
+                        if (oe->opaque)
+                                return OVL_PATH_UPPER;
+                        else
+                                return OVL_PATH_PURE_UPPER;
+                }
+        } else {
+                return OVL_PATH_LOWER;
+        }
+}
+
+static struct dentry *ovl_upperdentry_dereference(struct ovl_entry *oe)
+{
+        struct dentry *upperdentry = ACCESS_ONCE(oe->__upperdentry);
+        /*
+         * Make sure to order reads to upperdentry wrt ovl_dentry_update()
+         */
+        smp_read_barrier_depends();
+        return upperdentry;
+}
+
+void ovl_path_upper(struct dentry *dentry, struct path *path)
+{
+        struct ovl_fs *ofs = dentry->d_sb->s_fs_info;
+        struct ovl_entry *oe = dentry->d_fsdata;
+
+        path->mnt = ofs->upper_mnt;
+        path->dentry = ovl_upperdentry_dereference(oe);
+}
+
+enum ovl_path_type ovl_path_real(struct dentry *dentry, struct path *path)
+{
+
+        enum ovl_path_type type = ovl_path_type(dentry);
+
+        if (type == OVL_PATH_LOWER)
+                ovl_path_lower(dentry, path);
+        else
+                ovl_path_upper(dentry, path);
+
+        return type;
+}
+
+struct dentry *ovl_dentry_upper(struct dentry *dentry)
+{
+        struct ovl_entry *oe = dentry->d_fsdata;
+
+        return ovl_upperdentry_dereference(oe);
+}
+
+struct dentry *ovl_dentry_lower(struct dentry *dentry)
+{
+        struct ovl_entry *oe = dentry->d_fsdata;
+
+        return oe->lowerdentry;
+}
+
+struct dentry *ovl_dentry_real(struct dentry *dentry)
+{
+        struct ovl_entry *oe = dentry->d_fsdata;
+        struct dentry *realdentry;
+
+        realdentry = ovl_upperdentry_dereference(oe);
+        if (!realdentry)
+                realdentry = oe->lowerdentry;
+
+        return realdentry;
+}
+
+struct dentry *ovl_entry_real(struct ovl_entry *oe, bool *is_upper)
+{
+        struct dentry *realdentry;
+
+        realdentry = ovl_upperdentry_dereference(oe);
+        if (realdentry) {
+                *is_upper = true;
+        } else {
+                realdentry = oe->lowerdentry;
+                *is_upper = false;
+        }
+        return realdentry;
+}
+
+struct ovl_dir_cache *ovl_dir_cache(struct dentry *dentry)
+{
+        struct ovl_entry *oe = dentry->d_fsdata;
+
+        return oe->cache;
+}
+
+void ovl_set_dir_cache(struct dentry *dentry, struct ovl_dir_cache *cache)
+{
+        struct ovl_entry *oe = dentry->d_fsdata;
+
+        oe->cache = cache;
+}
+
+void ovl_path_lower(struct dentry *dentry, struct path *path)
+{
+        struct ovl_fs *ofs = dentry->d_sb->s_fs_info;
+        struct ovl_entry *oe = dentry->d_fsdata;
+
+        path->mnt = ofs->lower_mnt;
+        path->dentry = oe->lowerdentry;
+}
+
+int ovl_want_write(struct dentry *dentry)
+{
+        struct ovl_fs *ofs = dentry->d_sb->s_fs_info;
+        return mnt_want_write(ofs->upper_mnt);
+}
+
+void ovl_drop_write(struct dentry *dentry)
+{
+        struct ovl_fs *ofs = dentry->d_sb->s_fs_info;
+        mnt_drop_write(ofs->upper_mnt);
+}
+
+struct dentry *ovl_workdir(struct dentry *dentry)
+{
+        struct ovl_fs *ofs = dentry->d_sb->s_fs_info;
+        return ofs->workdir;
+}
+
+bool ovl_dentry_is_opaque(struct dentry *dentry)
+{
+        struct ovl_entry *oe = dentry->d_fsdata;
+        return oe->opaque;
+}
+
+void ovl_dentry_set_opaque(struct dentry *dentry, bool opaque)
+{
+        struct ovl_entry *oe = dentry->d_fsdata;
+        oe->opaque = opaque;
+}
+
+void ovl_dentry_update(struct dentry *dentry, struct dentry *upperdentry)
+{
+        struct ovl_entry *oe = dentry->d_fsdata;
+
+        WARN_ON(!mutex_is_locked(&upperdentry->d_parent->d_inode->i_mutex));
+        WARN_ON(oe->__upperdentry);
+        BUG_ON(!upperdentry->d_inode);
+        /*
+         * Make sure upperdentry is consistent before making it visible to
+         * ovl_upperdentry_dereference().
+         */
+        smp_wmb();
+        oe->__upperdentry = upperdentry;
+}
+
+void ovl_dentry_version_inc(struct dentry *dentry)
+{
+        struct ovl_entry *oe = dentry->d_fsdata;
+
+        WARN_ON(!mutex_is_locked(&dentry->d_inode->i_mutex));
+        oe->version++;
+}
+
+u64 ovl_dentry_version_get(struct dentry *dentry)
+{
+        struct ovl_entry *oe = dentry->d_fsdata;
+
+        WARN_ON(!mutex_is_locked(&dentry->d_inode->i_mutex));
+        return oe->version;
+}
+
+bool ovl_is_whiteout(struct dentry *dentry)
+{
+        struct inode *inode = dentry->d_inode;
+
+        return inode && IS_WHITEOUT(inode);
+}
+
+static bool ovl_is_opaquedir(struct dentry *dentry)
+{
+        int res;
+        char val;
+        struct inode *inode = dentry->d_inode;
+
+        if (!S_ISDIR(inode->i_mode) || !inode->i_op->getxattr)
+                return false;
+
+        res = inode->i_op->getxattr(dentry, ovl_opaque_xattr, &val, 1);
+        if (res == 1 && val == 'y')
+                return true;
+
+        return false;
+}
+
+static void ovl_dentry_release(struct dentry *dentry)
+{
+        struct ovl_entry *oe = dentry->d_fsdata;
+
+        if (oe) {
+                dput(oe->__upperdentry);
+                dput(oe->lowerdentry);
+                kfree_rcu(oe, rcu);
+        }
+}
+
+static const struct dentry_operations ovl_dentry_operations = {
+        .d_release = ovl_dentry_release,
+};
+
+static struct ovl_entry *ovl_alloc_entry(void)
+{
+        return kzalloc(sizeof(struct ovl_entry), GFP_KERNEL);
+}
+
+static inline struct dentry *ovl_lookup_real(struct dentry *dir,
+                                             struct qstr *name)
+{
+        struct dentry *dentry;
+
+        mutex_lock(&dir->d_inode->i_mutex);
+        dentry = lookup_one_len(name->name, dir, name->len);
+        mutex_unlock(&dir->d_inode->i_mutex);
+
+        if (IS_ERR(dentry)) {
+                if (PTR_ERR(dentry) == -ENOENT)
+                        dentry = NULL;
+        } else if (!dentry->d_inode) {
+                dput(dentry);
+                dentry = NULL;
+        }
+        return dentry;
+}
+
+struct dentry *ovl_lookup(struct inode *dir, struct dentry *dentry,
+                          unsigned int flags)
+{
+        struct ovl_entry *oe;
+        struct dentry *upperdir;
+        struct dentry *lowerdir;
+        struct dentry *upperdentry = NULL;
+        struct dentry *lowerdentry = NULL;
+        struct inode *inode = NULL;
+        int err;
+
+        err = -ENOMEM;
+        oe = ovl_alloc_entry();
+        if (!oe)
+                goto out;
+
+        upperdir = ovl_dentry_upper(dentry->d_parent);
+        lowerdir = ovl_dentry_lower(dentry->d_parent);
+
+        if (upperdir) {
+                upperdentry = ovl_lookup_real(upperdir, &dentry->d_name);
+                err = PTR_ERR(upperdentry);
+                if (IS_ERR(upperdentry))
+                        goto out_put_dir;
+
+                if (lowerdir && upperdentry) {
+                        if (ovl_is_whiteout(upperdentry)) {
+                                dput(upperdentry);
+                                upperdentry = NULL;
+                                oe->opaque = true;
+                        } else if (ovl_is_opaquedir(upperdentry)) {
+                                oe->opaque = true;
+                        }
+                }
+        }
+        if (lowerdir && !oe->opaque) {
+                lowerdentry = ovl_lookup_real(lowerdir, &dentry->d_name);
+                err = PTR_ERR(lowerdentry);
+                if (IS_ERR(lowerdentry))
+                        goto out_dput_upper;
+        }
+
+        if (lowerdentry && upperdentry &&
+            (!S_ISDIR(upperdentry->d_inode->i_mode) ||
+             !S_ISDIR(lowerdentry->d_inode->i_mode))) {
+                dput(lowerdentry);
+                lowerdentry = NULL;
+                oe->opaque = true;
+        }
+
+        if (lowerdentry || upperdentry) {
+                struct dentry *realdentry;
+
+                realdentry = upperdentry ? upperdentry : lowerdentry;
+                err = -ENOMEM;
+                inode = ovl_new_inode(dentry->d_sb, realdentry->d_inode->i_mode,
+                                      oe);
+                if (!inode)
+                        goto out_dput;
+                ovl_copyattr(realdentry->d_inode, inode);
+        }
+
+        oe->__upperdentry = upperdentry;
+        oe->lowerdentry = lowerdentry;
+
+        dentry->d_fsdata = oe;
+        d_add(dentry, inode);
+
+        return NULL;
+
+out_dput:
+        dput(lowerdentry);
+out_dput_upper:
+        dput(upperdentry);
+out_put_dir:
+        kfree(oe);
+out:
+        return ERR_PTR(err);
+}
+
+struct file *ovl_path_open(struct path *path, int flags)
+{
+        return dentry_open(path, flags, current_cred());
+}
+
+static void ovl_put_super(struct super_block *sb)
+{
+        struct ovl_fs *ufs = sb->s_fs_info;
+
+        dput(ufs->workdir);
+        mntput(ufs->upper_mnt);
+        mntput(ufs->lower_mnt);
+
+        kfree(ufs->config.lowerdir);
+        kfree(ufs->config.upperdir);
+        kfree(ufs->config.workdir);
+        kfree(ufs);
+}
+
+/**
+ * ovl_statfs
+ * @sb: The overlayfs super block
+ * @buf: The struct kstatfs to fill in with stats
+ *
+ * Get the filesystem statistics.  As writes always target the upper layer
+ * filesystem pass the statfs to the same filesystem.
+ */
+static int ovl_statfs(struct dentry *dentry, struct kstatfs *buf)
+{
+        struct ovl_fs *ofs = dentry->d_sb->s_fs_info;
+        struct dentry *root_dentry = dentry->d_sb->s_root;
+        struct path path;
+        int err;
+
+        ovl_path_upper(root_dentry, &path);
+
+        err = vfs_statfs(&path, buf);
+        if (!err) {
+                buf->f_namelen = max(buf->f_namelen, ofs->lower_namelen);
+                buf->f_type = OVERLAYFS_SUPER_MAGIC;
+        }
+
+        return err;
+}
+
+/**
+ * ovl_show_options
+ *
+ * Prints the mount options for a given superblock.
+ * Returns zero; does not fail.
+ */
+static int ovl_show_options(struct seq_file *m, struct dentry *dentry)
+{
+        struct super_block *sb = dentry->d_sb;
+        struct ovl_fs *ufs = sb->s_fs_info;
+
+        seq_printf(m, ",lowerdir=%s", ufs->config.lowerdir);
+        seq_printf(m, ",upperdir=%s", ufs->config.upperdir);
+        seq_printf(m, ",workdir=%s", ufs->config.workdir);
+        return 0;
+}
+
+static const struct super_operations ovl_super_operations = {
+        .put_super      = ovl_put_super,
+        .statfs         = ovl_statfs,
+        .show_options   = ovl_show_options,
+};
+
+enum {
+        OPT_LOWERDIR,
+        OPT_UPPERDIR,
+        OPT_WORKDIR,
+        OPT_ERR,
+};
+
+static const match_table_t ovl_tokens = {
+        {OPT_LOWERDIR,                  "lowerdir=%s"},
+        {OPT_UPPERDIR,                  "upperdir=%s"},
+        {OPT_WORKDIR,                   "workdir=%s"},
+        {OPT_ERR,                       NULL}
+};
+
+static int ovl_parse_opt(char *opt, struct ovl_config *config)
+{
+        char *p;
+
+        while ((p = strsep(&opt, ",")) != NULL) {
+                int token;
+                substring_t args[MAX_OPT_ARGS];
+
+                if (!*p)
+                        continue;
+
+                token = match_token(p, ovl_tokens, args);
+                switch (token) {
+                case OPT_UPPERDIR:
+                        kfree(config->upperdir);
+                        config->upperdir = match_strdup(&args[0]);
+                        if (!config->upperdir)
+                                return -ENOMEM;
+                        break;
+
+                case OPT_LOWERDIR:
+                        kfree(config->lowerdir);
+                        config->lowerdir = match_strdup(&args[0]);
+                        if (!config->lowerdir)
+                                return -ENOMEM;
+                        break;
+
+                case OPT_WORKDIR:
+                        kfree(config->workdir);
+                        config->workdir = match_strdup(&args[0]);
+                        if (!config->workdir)
+                                return -ENOMEM;
+                        break;
+
+                default:
+                        return -EINVAL;
+                }
+        }
+        return 0;
+}
+
+#define OVL_WORKDIR_NAME "work"
+
+static struct dentry *ovl_workdir_create(struct vfsmount *mnt,
+                                         struct dentry *dentry)
+{
+        struct inode *dir = dentry->d_inode;
+        struct dentry *work;
+        int err;
+        bool retried = false;
+
+        err = mnt_want_write(mnt);
+        if (err)
+                return ERR_PTR(err);
+
+        mutex_lock_nested(&dir->i_mutex, I_MUTEX_PARENT);
+retry:
+        work = lookup_one_len(OVL_WORKDIR_NAME, dentry,
+                              strlen(OVL_WORKDIR_NAME));
+
+        if (!IS_ERR(work)) {
+                struct kstat stat = {
+                        .mode = S_IFDIR | 0,
+                };
+
+                if (work->d_inode) {
+                        err = -EEXIST;
+                        if (retried)
+                                goto out_dput;
+
+                        retried = true;
+                        ovl_cleanup(dir, work);
+                        dput(work);
+                        goto retry;
+                }
+
+                err = ovl_create_real(dir, work, &stat, NULL, NULL, true);
+                if (err)
+                        goto out_dput;
+        }
+out_unlock:
+        mutex_unlock(&dir->i_mutex);
+        mnt_drop_write(mnt);
+
+        return work;
+
+out_dput:
+        dput(work);
+        work = ERR_PTR(err);
+        goto out_unlock;
+}
+
+static int ovl_mount_dir(const char *name, struct path *path)
+{
+        int err;
+
+        err = kern_path(name, LOOKUP_FOLLOW, path);
+        if (err) {
+                pr_err("overlayfs: failed to resolve '%s': %i\n", name, err);
+                err = -EINVAL;
+        }
+        return err;
+}
+
+static bool ovl_is_allowed_fs_type(struct dentry *root)
+{
+        const struct dentry_operations *dop = root->d_op;
+
+        /*
+         * We don't support:
+         *  - automount filesystems
+         *  - filesystems with revalidate (FIXME for lower layer)
+         *  - filesystems with case insensitive names
+         */
+        if (dop &&
+            (dop->d_manage || dop->d_automount ||
+             dop->d_revalidate || dop->d_weak_revalidate ||
+             dop->d_compare || dop->d_hash)) {
+                return false;
+        }
+        return true;
+}
+
+/* Workdir should not be subdir of upperdir and vice versa */
+static bool ovl_workdir_ok(struct dentry *workdir, struct dentry *upperdir)
+{
+        bool ok = false;
+
+        if (workdir != upperdir) {
+                ok = (lock_rename(workdir, upperdir) == NULL);
+                unlock_rename(workdir, upperdir);
+        }
+        return ok;
+}
+
+static int ovl_fill_super(struct super_block *sb, void *data, int silent)
+{
+        struct path lowerpath;
+        struct path upperpath;
+        struct path workpath;
+        struct inode *root_inode;
+        struct dentry *root_dentry;
+        struct ovl_entry *oe;
+        struct ovl_fs *ufs;
+        struct kstatfs statfs;
+        int err;
+
+        err = -ENOMEM;
+        ufs = kzalloc(sizeof(struct ovl_fs), GFP_KERNEL);
+        if (!ufs)
+                goto out;
+
+        err = ovl_parse_opt((char *) data, &ufs->config);
+        if (err)
+                goto out_free_config;
+
+        /* FIXME: workdir is not needed for a R/O mount */
+        err = -EINVAL;
+        if (!ufs->config.upperdir || !ufs->config.lowerdir ||
+            !ufs->config.workdir) {
+                pr_err("overlayfs: missing upperdir or lowerdir or workdir\n");
+                goto out_free_config;
+        }
+
+        err = -ENOMEM;
+        oe = ovl_alloc_entry();
+        if (oe == NULL)
+                goto out_free_config;
+
+        err = ovl_mount_dir(ufs->config.upperdir, &upperpath);
+        if (err)
+                goto out_free_oe;
+
+        err = ovl_mount_dir(ufs->config.lowerdir, &lowerpath);
+        if (err)
+                goto out_put_upperpath;
+
+        err = ovl_mount_dir(ufs->config.workdir, &workpath);
+        if (err)
+                goto out_put_lowerpath;
+
+        err = -EINVAL;
+        if (!S_ISDIR(upperpath.dentry->d_inode->i_mode) ||
+            !S_ISDIR(lowerpath.dentry->d_inode->i_mode) ||
+            !S_ISDIR(workpath.dentry->d_inode->i_mode)) {
+                pr_err("overlayfs: upperdir or lowerdir or workdir not a directory\n");
+                goto out_put_workpath;
+        }
+
+        if (upperpath.mnt != workpath.mnt) {
+                pr_err("overlayfs: workdir and upperdir must reside under the same mount\n");
+                goto out_put_workpath;
+        }
+        if (!ovl_workdir_ok(workpath.dentry, upperpath.dentry)) {
+                pr_err("overlayfs: workdir and upperdir must be separate subtrees\n");
+                goto out_put_workpath;
+        }
+
+        if (!ovl_is_allowed_fs_type(upperpath.dentry)) {
+                pr_err("overlayfs: filesystem of upperdir is not supported\n");
+                goto out_put_workpath;
+        }
+
+        if (!ovl_is_allowed_fs_type(lowerpath.dentry)) {
+                pr_err("overlayfs: filesystem of lowerdir is not supported\n");
+                goto out_put_workpath;
+        }
+
+        err = vfs_statfs(&lowerpath, &statfs);
+        if (err) {
+                pr_err("overlayfs: statfs failed on lowerpath\n");
+                goto out_put_workpath;
+        }
+        ufs->lower_namelen = statfs.f_namelen;
+
+        sb->s_stack_depth = max(upperpath.mnt->mnt_sb->s_stack_depth,
+                                lowerpath.mnt->mnt_sb->s_stack_depth) + 1;
+
+        err = -EINVAL;
+        if (sb->s_stack_depth > FILESYSTEM_MAX_STACK_DEPTH) {
+                pr_err("overlayfs: maximum fs stacking depth exceeded\n");
+                goto out_put_workpath;
+        }
+
+        ufs->upper_mnt = clone_private_mount(&upperpath);
+        err = PTR_ERR(ufs->upper_mnt);
+        if (IS_ERR(ufs->upper_mnt)) {
+                pr_err("overlayfs: failed to clone upperpath\n");
+                goto out_put_workpath;
+        }
+
+        ufs->lower_mnt = clone_private_mount(&lowerpath);
+        err = PTR_ERR(ufs->lower_mnt);
+        if (IS_ERR(ufs->lower_mnt)) {
+                pr_err("overlayfs: failed to clone lowerpath\n");
+                goto out_put_upper_mnt;
+        }
+
+        ufs->workdir = ovl_workdir_create(ufs->upper_mnt, workpath.dentry);
+        err = PTR_ERR(ufs->workdir);
+        if (IS_ERR(ufs->workdir)) {
+                pr_err("overlayfs: failed to create directory %s/%s\n",
+                       ufs->config.workdir, OVL_WORKDIR_NAME);
+                goto out_put_lower_mnt;
+        }
+
+        /*
+         * Make lower_mnt R/O.  That way fchmod/fchown on lower file
+         * will fail instead of modifying lower fs.
+         */
+        ufs->lower_mnt->mnt_flags |= MNT_READONLY;
+
+        /* If the upper fs is r/o, we mark overlayfs r/o too */
+        if (ufs->upper_mnt->mnt_sb->s_flags & MS_RDONLY)
+                sb->s_flags |= MS_RDONLY;
+
+        sb->s_d_op = &ovl_dentry_operations;
+
+        err = -ENOMEM;
+        root_inode = ovl_new_inode(sb, S_IFDIR, oe);
+        if (!root_inode)
+                goto out_put_workdir;
+
+        root_dentry = d_make_root(root_inode);
+        if (!root_dentry)
+                goto out_put_workdir;
+
+        mntput(upperpath.mnt);
+        mntput(lowerpath.mnt);
+        path_put(&workpath);
+
+        oe->__upperdentry = upperpath.dentry;
+        oe->lowerdentry = lowerpath.dentry;
+
+        root_dentry->d_fsdata = oe;
+
+        sb->s_magic = OVERLAYFS_SUPER_MAGIC;
+        sb->s_op = &ovl_super_operations;
+        sb->s_root = root_dentry;
+        sb->s_fs_info = ufs;
+
+        return 0;
+
+out_put_workdir:
+        dput(ufs->workdir);
+out_put_lower_mnt:
+        mntput(ufs->lower_mnt);
+out_put_upper_mnt:
+        mntput(ufs->upper_mnt);
+out_put_workpath:
+        path_put(&workpath);
+out_put_lowerpath:
+        path_put(&lowerpath);
+out_put_upperpath:
+        path_put(&upperpath);
+out_free_oe:
+        kfree(oe);
+out_free_config:
+        kfree(ufs->config.lowerdir);
+        kfree(ufs->config.upperdir);
+        kfree(ufs->config.workdir);
+        kfree(ufs);
+out:
+        return err;
+}
+
+static struct dentry *ovl_mount(struct file_system_type *fs_type, int flags,
+                                const char *dev_name, void *raw_data)
+{
+        return mount_nodev(fs_type, flags, raw_data, ovl_fill_super);
+}
+
+static struct file_system_type ovl_fs_type = {
+        .owner          = THIS_MODULE,
+        .name           = "overlayfs",
+        .mount          = ovl_mount,
+        .kill_sb        = kill_anon_super,
+};
+MODULE_ALIAS_FS("overlayfs");
+
+static int __init ovl_init(void)
+{
+        return register_filesystem(&ovl_fs_type);
+}
+
+static void __exit ovl_exit(void)
+{
+        unregister_filesystem(&ovl_fs_type);
+}
+
+module_init(ovl_init);
+module_exit(ovl_exit);