diff --git a/fs/erofs/internal.h b/fs/erofs/internal.h
new file mode 100644
index 0000000..2a3cd45
--- /dev/null
+++ b/fs/erofs/internal.h
@@ -0,0 +1,300 @@
+/* SPDX-License-Identifier: GPL-2.0
+ *
+ * linux/fs/erofs/internal.h
+ *
+ * Copyright (C) 2017-2018 HUAWEI, Inc.
+ *             http://www.huawei.com/
+ * Created by Gao Xiang <gaoxiang25@huawei.com>
+ *
+ * This file is subject to the terms and conditions of the GNU General Public
+ * License.  See the file COPYING in the main directory of the Linux
+ * distribution for more details.
+ */
+#ifndef __INTERNAL_H
+#define __INTERNAL_H
+
+#include <linux/fs.h>
+#include <linux/dcache.h>
+#include <linux/mm.h>
+#include <linux/pagemap.h>
+#include <linux/bio.h>
+#include <linux/buffer_head.h>
+#include <linux/cleancache.h>
+#include <linux/vmalloc.h>
+#include "erofs_fs.h"
+
+#include "staging.h"
+
+/* redefine pr_fmt "erofs: " */
+#undef pr_fmt
+#define pr_fmt(fmt) "erofs: " fmt
+
+#define errln(x, ...)   pr_err(x "\n", ##__VA_ARGS__)
+#define infoln(x, ...)  pr_info(x "\n", ##__VA_ARGS__)
+#ifdef CONFIG_EROFS_FS_DEBUG
+#define debugln(x, ...) pr_debug(x "\n", ##__VA_ARGS__)
+
+#define erofs_dbg_might_sleep   might_sleep
+#define DBG_BUGON       BUG_ON
+#else
+#define debugln(x, ...) ((void)0)
+#define erofs_dbg_might_sleep() ((void)0)
+#define DBG_BUGON(...)  ((void)0)
+#endif
+
+/* EROFS_SUPER_MAGIC_V1 to represent the whole file system */
+#define EROFS_SUPER_MAGIC   EROFS_SUPER_MAGIC_V1
+
+typedef u64 erofs_nid_t;
+
+struct erofs_sb_info {
+	u32 blocks;
+	u32 meta_blkaddr;
+
+	/* inode slot unit size in bit shift */
+	unsigned char islotbits;
+
+	u32 build_time_nsec;
+	u64 build_time;
+
+	/* what we really care is nid, rather than ino.. */
+	erofs_nid_t root_nid;
+	/* used for statfs, f_files - f_favail */
+	u64 inos;
+
+	u8 uuid[16];                    /* 128-bit uuid for volume */
+	u8 volume_name[16];             /* volume name */
+	char *dev_name;
+
+	unsigned int mount_opt;
+};
+
+#define EROFS_SB(sb) ((struct erofs_sb_info *)(sb)->s_fs_info)
+#define EROFS_I_SB(inode) ((struct erofs_sb_info *)(inode)->i_sb->s_fs_info)
+
+#define clear_opt(sbi, option)	((sbi)->mount_opt &= ~EROFS_MOUNT_##option)
+#define set_opt(sbi, option)	((sbi)->mount_opt |= EROFS_MOUNT_##option)
+#define test_opt(sbi, option)	((sbi)->mount_opt & EROFS_MOUNT_##option)
+
+/* we strictly follow PAGE_SIZE and no buffer head */
+#define LOG_BLOCK_SIZE		PAGE_SHIFT
+
+#undef LOG_SECTORS_PER_BLOCK
+#define LOG_SECTORS_PER_BLOCK	(PAGE_SHIFT - 9)
+
+#undef SECTORS_PER_BLOCK
+#define SECTORS_PER_BLOCK	(1 << SECTORS_PER_BLOCK)
+
+#define EROFS_BLKSIZ		(1 << LOG_BLOCK_SIZE)
+
+#if (EROFS_BLKSIZ % 4096 || !EROFS_BLKSIZ)
+#error erofs cannot be used in this platform
+#endif
+
+#define ROOT_NID(sb)		((sb)->root_nid)
+
+typedef u64 erofs_off_t;
+
+/* data type for filesystem-wide blocks number */
+typedef u32 erofs_blk_t;
+
+static inline erofs_off_t iloc(struct erofs_sb_info *sbi, erofs_nid_t nid)
+{
+	return sbi->meta_blkaddr * EROFS_BLKSIZ + (nid << sbi->islotbits);
+}
+
+#define erofs_blknr(addr)       ((addr) / EROFS_BLKSIZ)
+#define erofs_blkoff(addr)      ((addr) % EROFS_BLKSIZ)
+#define blknr_to_addr(nr)       ((nr) * EROFS_BLKSIZ)
+
+#define inode_set_inited_xattr(inode)   (EROFS_V(inode)->flags |= 1)
+#define inode_has_inited_xattr(inode)   (EROFS_V(inode)->flags & 1)
+
+struct erofs_vnode {
+	erofs_nid_t nid;
+	unsigned int flags;
+
+	unsigned char data_mapping_mode;
+	/* inline size in bytes */
+	unsigned char inode_isize;
+	unsigned short xattr_isize;
+
+#if (LINUX_VERSION_CODE < KERNEL_VERSION(4, 2, 0))
+	char *i_link;
+#endif
+	unsigned xattr_shared_count;
+	unsigned *xattr_shared_xattrs;
+
+	erofs_blk_t raw_blkaddr;
+
+	/* the corresponding vfs inode */
+	struct inode vfs_inode;
+};
+
+#define EROFS_V(ptr)	\
+	container_of(ptr, struct erofs_vnode, vfs_inode)
+
+#define __inode_advise(x, bit, bits) \
+	(((x) >> (bit)) & ((1 << (bits)) - 1))
+
+#define __inode_version(advise)	\
+	__inode_advise(advise, EROFS_I_VERSION_BIT,	\
+		EROFS_I_VERSION_BITS)
+
+#define __inode_data_mapping(advise)	\
+	__inode_advise(advise, EROFS_I_DATA_MAPPING_BIT,\
+		EROFS_I_DATA_MAPPING_BITS)
+
+static inline unsigned long inode_datablocks(struct inode *inode)
+{
+	/* since i_size cannot be changed */
+	return DIV_ROUND_UP(inode->i_size, EROFS_BLKSIZ);
+}
+
+static inline bool is_inode_layout_plain(struct inode *inode)
+{
+	return EROFS_V(inode)->data_mapping_mode == EROFS_INODE_LAYOUT_PLAIN;
+}
+
+static inline bool is_inode_layout_compression(struct inode *inode)
+{
+	return EROFS_V(inode)->data_mapping_mode ==
+					EROFS_INODE_LAYOUT_COMPRESSION;
+}
+
+static inline bool is_inode_layout_inline(struct inode *inode)
+{
+	return EROFS_V(inode)->data_mapping_mode == EROFS_INODE_LAYOUT_INLINE;
+}
+
+extern const struct super_operations erofs_sops;
+extern const struct inode_operations erofs_dir_iops;
+extern const struct file_operations erofs_dir_fops;
+
+extern const struct file_operations erofs_unaligned_compressed_fops;
+
+extern const struct address_space_operations erofs_raw_access_aops;
+
+/*
+ * Logical to physical block mapping, used by erofs_map_blocks()
+ *
+ * Different with other file systems, it is used for 2 access modes:
+ *
+ * 1) RAW access mode:
+ *
+ * Users pass a valid (m_lblk, m_lofs -- usually 0) pair,
+ * and get the valid m_pblk, m_pofs and the longest m_len(in bytes).
+ *
+ * Note that m_lblk in the RAW access mode refers to the number of
+ * the compressed ondisk block rather than the uncompressed
+ * in-memory block for the compressed file.
+ *
+ * m_pofs equals to m_lofs except for the inline data page.
+ *
+ * 2) Normal access mode:
+ *
+ * If the inode is not compressed, it has no difference with
+ * the RAW access mode. However, if the inode is compressed,
+ * users should pass a valid (m_lblk, m_lofs) pair, and get
+ * the needed m_pblk, m_pofs, m_len to get the compressed data
+ * and the updated m_lblk, m_lofs which indicates the start
+ * of the corresponding uncompressed data in the file.
+ */
+enum {
+	BH_Zipped = BH_PrivateStart,
+};
+
+/* Has a disk mapping */
+#define EROFS_MAP_MAPPED	(1 << BH_Mapped)
+/* Located in metadata (could be copied from bd_inode) */
+#define EROFS_MAP_META		(1 << BH_Meta)
+/* The extent has been compressed */
+#define EROFS_MAP_ZIPPED	(1 << BH_Zipped)
+
+struct erofs_map_blocks {
+	erofs_off_t m_pa, m_la;
+	u64 m_plen, m_llen;
+
+	unsigned int m_flags;
+};
+
+/* Flags used by erofs_map_blocks() */
+#define EROFS_GET_BLOCKS_RAW    0x0001
+
+/* data.c */
+extern struct page *erofs_get_meta_page(struct super_block *sb,
+	erofs_blk_t blkaddr, bool prio);
+extern int erofs_map_blocks(struct inode *, struct erofs_map_blocks *, int);
+extern int erofs_map_blocks_iter(struct inode *, struct erofs_map_blocks *,
+	struct page **, int);
+
+struct erofs_map_blocks_iter {
+	struct erofs_map_blocks map;
+	struct page *mpage;
+};
+
+
+static inline struct page *erofs_get_inline_page(struct inode *inode,
+	erofs_blk_t blkaddr)
+{
+	return erofs_get_meta_page(inode->i_sb,
+		blkaddr, S_ISDIR(inode->i_mode));
+}
+
+/* inode.c */
+extern struct inode *erofs_iget(struct super_block *sb,
+	erofs_nid_t nid, bool dir);
+
+/* dir.c */
+int erofs_namei(struct inode *dir, struct qstr *name,
+	erofs_nid_t *nid, unsigned *d_type);
+
+/* xattr.c */
+extern const struct xattr_handler *erofs_xattr_handlers[];
+
+extern void test_meta_ops(struct super_block *sb);
+
+/* symlink */
+#if (LINUX_VERSION_CODE < KERNEL_VERSION(4, 2, 0))
+extern const struct inode_operations simple_symlink_inode_operations;
+#endif
+
+static inline void set_inode_fast_symlink(struct inode *inode)
+{
+	inode->i_op = &simple_symlink_inode_operations;
+}
+
+static inline bool is_inode_fast_symlink(struct inode *inode)
+{
+	return inode->i_op == &simple_symlink_inode_operations;
+}
+
+static inline void *erofs_vmap(struct page **pages, unsigned int count)
+{
+#ifdef CONFIG_EROFS_FS_USE_VM_MAP_RAM
+	int i = 0;
+
+	while (1) {
+		void *addr = vm_map_ram(pages, count, -1, PAGE_KERNEL);
+		/* retry two more times (totally 3 times) */
+		if (addr != NULL || ++i >= 3)
+			return addr;
+		vm_unmap_aliases();
+	}
+	return NULL;
+#else
+	return vmap(pages, count, VM_MAP, PAGE_KERNEL);
+#endif
+}
+
+static inline void erofs_vunmap(const void *mem, unsigned int count)
+{
+#ifdef CONFIG_EROFS_FS_USE_VM_MAP_RAM
+	vm_unmap_ram(mem, count);
+#else
+	vunmap(mem);
+#endif
+}
+
+#endif
+
