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-rw-r--r--fs/overlayfs/super.c796
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);