lib/zmap.c - platform/external/erofs-utils - Git at Google

 // SPDX-License-Identifier: GPL-2.0+
 /*
  * erofs-utils/lib/zmap.c
  *
  * (a large amount of code was adapted from Linux kernel. )
  *
  * Copyright (C) 2018-2019 HUAWEI, Inc.
  *             https://www.huawei.com/
  * Created by Gao Xiang <gaoxiang25@huawei.com>
  * Modified by Huang Jianan <huangjianan@oppo.com>
  */
 #include "erofs/io.h"
 #include "erofs/print.h"

 int z_erofs_fill_inode(struct erofs_inode *vi)
 {
 	if (vi->datalayout == EROFS_INODE_FLAT_COMPRESSION_LEGACY) {
 		vi->z_advise = 0;
 		vi->z_algorithmtype[0] = 0;
 		vi->z_algorithmtype[1] = 0;
 		vi->z_logical_clusterbits = LOG_BLOCK_SIZE;
 		vi->z_physical_clusterbits[0] = vi->z_logical_clusterbits;
 		vi->z_physical_clusterbits[1] = vi->z_logical_clusterbits;

 		vi->flags |= EROFS_I_Z_INITED;
 	}
 	return 0;
 }

 static int z_erofs_fill_inode_lazy(struct erofs_inode *vi)
 {
 	int ret;
 	erofs_off_t pos;
 	struct z_erofs_map_header *h;
 	char buf[sizeof(struct z_erofs_map_header)];

 	if (vi->flags & EROFS_I_Z_INITED)
 		return 0;

 	DBG_BUGON(vi->datalayout == EROFS_INODE_FLAT_COMPRESSION_LEGACY);
 	pos = round_up(iloc(vi->nid) + vi->inode_isize + vi->xattr_isize, 8);

 	ret = dev_read(buf, pos, sizeof(buf));
 	if (ret < 0)
 		return -EIO;

 	h = (struct z_erofs_map_header *)buf;
 	vi->z_advise = le16_to_cpu(h->h_advise);
 	vi->z_algorithmtype[0] = h->h_algorithmtype & 15;
 	vi->z_algorithmtype[1] = h->h_algorithmtype >> 4;

 	if (vi->z_algorithmtype[0] >= Z_EROFS_COMPRESSION_MAX) {
 		erofs_err("unknown compression format %u for nid %llu",
 			  vi->z_algorithmtype[0], (unsigned long long)vi->nid);
 		return -EOPNOTSUPP;
 	}

 	vi->z_logical_clusterbits = LOG_BLOCK_SIZE + (h->h_clusterbits & 7);
 	vi->z_physical_clusterbits[0] = vi->z_logical_clusterbits +
 					((h->h_clusterbits >> 3) & 3);

 	if (vi->z_physical_clusterbits[0] != LOG_BLOCK_SIZE) {
 		erofs_err("unsupported physical clusterbits %u for nid %llu",
 			  vi->z_physical_clusterbits[0], (unsigned long long)vi->nid);
 		return -EOPNOTSUPP;
 	}

 	vi->z_physical_clusterbits[1] = vi->z_logical_clusterbits +
 					((h->h_clusterbits >> 5) & 7);
 	vi->flags |= EROFS_I_Z_INITED;
 	return 0;
 }

 struct z_erofs_maprecorder {
 	struct erofs_inode *inode;
 	struct erofs_map_blocks *map;
 	void *kaddr;

 	unsigned long lcn;
 	/* compression extent information gathered */
 	u8  type;
 	u16 clusterofs;
 	u16 delta[2];
 	erofs_blk_t pblk;
 };

 static int z_erofs_reload_indexes(struct z_erofs_maprecorder *m,
 				  erofs_blk_t eblk)
 {
 	int ret;
 	struct erofs_map_blocks *const map = m->map;
 	char *mpage = map->mpage;

 	if (map->index == eblk)
 		return 0;

 	ret = blk_read(mpage, eblk, 1);
 	if (ret < 0)
 		return -EIO;

 	map->index = eblk;

 	return 0;
 }

 static int legacy_load_cluster_from_disk(struct z_erofs_maprecorder *m,
 					 unsigned long lcn)
 {
 	struct erofs_inode *const vi = m->inode;
 	const erofs_off_t ibase = iloc(vi->nid);
 	const erofs_off_t pos =
 		Z_EROFS_VLE_LEGACY_INDEX_ALIGN(ibase + vi->inode_isize +
 					       vi->xattr_isize) +
 		lcn * sizeof(struct z_erofs_vle_decompressed_index);
 	struct z_erofs_vle_decompressed_index *di;
 	unsigned int advise, type;
 	int err;

 	err = z_erofs_reload_indexes(m, erofs_blknr(pos));
 	if (err)
 		return err;

 	m->lcn = lcn;
 	di = m->kaddr + erofs_blkoff(pos);

 	advise = le16_to_cpu(di->di_advise);
 	type = (advise >> Z_EROFS_VLE_DI_CLUSTER_TYPE_BIT) &
 		((1 << Z_EROFS_VLE_DI_CLUSTER_TYPE_BITS) - 1);
 	switch (type) {
 	case Z_EROFS_VLE_CLUSTER_TYPE_NONHEAD:
 		m->clusterofs = 1 << vi->z_logical_clusterbits;
 		m->delta[0] = le16_to_cpu(di->di_u.delta[0]);
 		m->delta[1] = le16_to_cpu(di->di_u.delta[1]);
 		break;
 	case Z_EROFS_VLE_CLUSTER_TYPE_PLAIN:
 	case Z_EROFS_VLE_CLUSTER_TYPE_HEAD:
 		m->clusterofs = le16_to_cpu(di->di_clusterofs);
 		m->pblk = le32_to_cpu(di->di_u.blkaddr);
 		break;
 	default:
 		DBG_BUGON(1);
 		return -EOPNOTSUPP;
 	}
 	m->type = type;
 	return 0;
 }

 static unsigned int decode_compactedbits(unsigned int lobits,
 					 unsigned int lomask,
 					 u8 *in, unsigned int pos, u8 *type)
 {
 	const unsigned int v = get_unaligned_le32(in + pos / 8) >> (pos & 7);
 	const unsigned int lo = v & lomask;

 	*type = (v >> lobits) & 3;
 	return lo;
 }

 static int unpack_compacted_index(struct z_erofs_maprecorder *m,
 				  unsigned int amortizedshift,
 				  unsigned int eofs)
 {
 	struct erofs_inode *const vi = m->inode;
 	const unsigned int lclusterbits = vi->z_logical_clusterbits;
 	const unsigned int lomask = (1 << lclusterbits) - 1;
 	unsigned int vcnt, base, lo, encodebits, nblk;
 	int i;
 	u8 *in, type;

 	if (1 << amortizedshift == 4)
 		vcnt = 2;
 	else if (1 << amortizedshift == 2 && lclusterbits == 12)
 		vcnt = 16;
 	else
 		return -EOPNOTSUPP;

 	encodebits = ((vcnt << amortizedshift) - sizeof(__le32)) * 8 / vcnt;
 	base = round_down(eofs, vcnt << amortizedshift);
 	in = m->kaddr + base;

 	i = (eofs - base) >> amortizedshift;

 	lo = decode_compactedbits(lclusterbits, lomask,
 				  in, encodebits * i, &type);
 	m->type = type;
 	if (type == Z_EROFS_VLE_CLUSTER_TYPE_NONHEAD) {
 		m->clusterofs = 1 << lclusterbits;
 		if (i + 1 != (int)vcnt) {
 			m->delta[0] = lo;
 			return 0;
 		}
 		/*
 		 * since the last lcluster in the pack is special,
 		 * of which lo saves delta[1] rather than delta[0].
 		 * Hence, get delta[0] by the previous lcluster indirectly.
 		 */
 		lo = decode_compactedbits(lclusterbits, lomask,
 					  in, encodebits * (i - 1), &type);
 		if (type != Z_EROFS_VLE_CLUSTER_TYPE_NONHEAD)
 			lo = 0;
 		m->delta[0] = lo + 1;
 		return 0;
 	}
 	m->clusterofs = lo;
 	m->delta[0] = 0;
 	/* figout out blkaddr (pblk) for HEAD lclusters */
 	nblk = 1;
 	while (i > 0) {
 		--i;
 		lo = decode_compactedbits(lclusterbits, lomask,
 					  in, encodebits * i, &type);
 		if (type == Z_EROFS_VLE_CLUSTER_TYPE_NONHEAD)
 			i -= lo;

 		if (i >= 0)
 			++nblk;
 	}
 	in += (vcnt << amortizedshift) - sizeof(__le32);
 	m->pblk = le32_to_cpu(*(__le32 *)in) + nblk;
 	return 0;
 }

 static int compacted_load_cluster_from_disk(struct z_erofs_maprecorder *m,
 					    unsigned long lcn)
 {
 	struct erofs_inode *const vi = m->inode;
 	const unsigned int lclusterbits = vi->z_logical_clusterbits;
 	const erofs_off_t ebase = round_up(iloc(vi->nid) + vi->inode_isize +
 					   vi->xattr_isize, 8) +
 		sizeof(struct z_erofs_map_header);
 	const unsigned int totalidx = DIV_ROUND_UP(vi->i_size, EROFS_BLKSIZ);
 	unsigned int compacted_4b_initial, compacted_2b;
 	unsigned int amortizedshift;
 	erofs_off_t pos;
 	int err;

 	if (lclusterbits != 12)
 		return -EOPNOTSUPP;

 	if (lcn >= totalidx)
 		return -EINVAL;

 	m->lcn = lcn;
 	/* used to align to 32-byte (compacted_2b) alignment */
 	compacted_4b_initial = (32 - ebase % 32) / 4;
 	if (compacted_4b_initial == 32 / 4)
 		compacted_4b_initial = 0;

 	if (vi->z_advise & Z_EROFS_ADVISE_COMPACTED_2B)
 		compacted_2b = rounddown(totalidx - compacted_4b_initial, 16);
 	else
 		compacted_2b = 0;

 	pos = ebase;
 	if (lcn < compacted_4b_initial) {
 		amortizedshift = 2;
 		goto out;
 	}
 	pos += compacted_4b_initial * 4;
 	lcn -= compacted_4b_initial;

 	if (lcn < compacted_2b) {
 		amortizedshift = 1;
 		goto out;
 	}
 	pos += compacted_2b * 2;
 	lcn -= compacted_2b;
 	amortizedshift = 2;
 out:
 	pos += lcn * (1 << amortizedshift);
 	err = z_erofs_reload_indexes(m, erofs_blknr(pos));
 	if (err)
 		return err;
 	return unpack_compacted_index(m, amortizedshift, erofs_blkoff(pos));
 }

 static int z_erofs_load_cluster_from_disk(struct z_erofs_maprecorder *m,
 					  unsigned int lcn)
 {
 	const unsigned int datamode = m->inode->datalayout;

 	if (datamode == EROFS_INODE_FLAT_COMPRESSION_LEGACY)
 		return legacy_load_cluster_from_disk(m, lcn);

 	if (datamode == EROFS_INODE_FLAT_COMPRESSION)
 		return compacted_load_cluster_from_disk(m, lcn);

 	return -EINVAL;
 }

 static int z_erofs_extent_lookback(struct z_erofs_maprecorder *m,
 				   unsigned int lookback_distance)
 {
 	struct erofs_inode *const vi = m->inode;
 	struct erofs_map_blocks *const map = m->map;
 	const unsigned int lclusterbits = vi->z_logical_clusterbits;
 	unsigned long lcn = m->lcn;
 	int err;

 	if (lcn < lookback_distance) {
 		erofs_err("bogus lookback distance @ nid %llu",
 			  (unsigned long long)vi->nid);
 		DBG_BUGON(1);
 		return -EFSCORRUPTED;
 	}

 	/* load extent head logical cluster if needed */
 	lcn -= lookback_distance;
 	err = z_erofs_load_cluster_from_disk(m, lcn);
 	if (err)
 		return err;

 	switch (m->type) {
 	case Z_EROFS_VLE_CLUSTER_TYPE_NONHEAD:
 		if (!m->delta[0]) {
 			erofs_err("invalid lookback distance 0 @ nid %llu",
 				  (unsigned long long)vi->nid);
 			DBG_BUGON(1);
 			return -EFSCORRUPTED;
 		}
 		return z_erofs_extent_lookback(m, m->delta[0]);
 	case Z_EROFS_VLE_CLUSTER_TYPE_PLAIN:
 		map->m_flags &= ~EROFS_MAP_ZIPPED;
 	case Z_EROFS_VLE_CLUSTER_TYPE_HEAD:
 		map->m_la = (lcn << lclusterbits) | m->clusterofs;
 		break;
 	default:
 		erofs_err("unknown type %u @ lcn %lu of nid %llu",
 			  m->type, lcn, (unsigned long long)vi->nid);
 		DBG_BUGON(1);
 		return -EOPNOTSUPP;
 	}
 	return 0;
 }

 int z_erofs_map_blocks_iter(struct erofs_inode *vi,
 			    struct erofs_map_blocks *map)
 {
 	struct z_erofs_maprecorder m = {
 		.inode = vi,
 		.map = map,
 		.kaddr = map->mpage,
 	};
 	int err = 0;
 	unsigned int lclusterbits, endoff;
 	unsigned long long ofs, end;

 	/* when trying to read beyond EOF, leave it unmapped */
 	if (map->m_la >= vi->i_size) {
 		map->m_llen = map->m_la + 1 - vi->i_size;
 		map->m_la = vi->i_size;
 		map->m_flags = 0;
 		goto out;
 	}

 	err = z_erofs_fill_inode_lazy(vi);
 	if (err)
 		goto out;

 	lclusterbits = vi->z_logical_clusterbits;
 	ofs = map->m_la;
 	m.lcn = ofs >> lclusterbits;
 	endoff = ofs & ((1 << lclusterbits) - 1);

 	err = z_erofs_load_cluster_from_disk(&m, m.lcn);
 	if (err)
 		goto out;

 	map->m_flags = EROFS_MAP_ZIPPED;	/* by default, compressed */
 	end = (m.lcn + 1ULL) << lclusterbits;
 	switch (m.type) {
 	case Z_EROFS_VLE_CLUSTER_TYPE_PLAIN:
 		if (endoff >= m.clusterofs)
 			map->m_flags &= ~EROFS_MAP_ZIPPED;
 	case Z_EROFS_VLE_CLUSTER_TYPE_HEAD:
 		if (endoff >= m.clusterofs) {
 			map->m_la = (m.lcn << lclusterbits) | m.clusterofs;
 			break;
 		}
 		/* m.lcn should be >= 1 if endoff < m.clusterofs */
 		if (!m.lcn) {
 			erofs_err("invalid logical cluster 0 at nid %llu",
 				  (unsigned long long)vi->nid);
 			err = -EFSCORRUPTED;
 			goto out;
 		}
 		end = (m.lcn << lclusterbits) | m.clusterofs;
 		map->m_flags |= EROFS_MAP_FULL_MAPPED;
 		m.delta[0] = 1;
 	case Z_EROFS_VLE_CLUSTER_TYPE_NONHEAD:
 		/* get the correspoinding first chunk */
 		err = z_erofs_extent_lookback(&m, m.delta[0]);
 		if (err)
 			goto out;
 		break;
 	default:
 		erofs_err("unknown type %u @ offset %llu of nid %llu",
 			  m.type, ofs, (unsigned long long)vi->nid);
 		err = -EOPNOTSUPP;
 		goto out;
 	}

 	map->m_llen = end - map->m_la;
 	map->m_plen = 1 << lclusterbits;
 	map->m_pa = blknr_to_addr(m.pblk);
 	map->m_flags |= EROFS_MAP_MAPPED;

 out:
 	erofs_dbg("m_la %" PRIu64 " m_pa %" PRIu64 " m_llen %" PRIu64 " m_plen %" PRIu64 " m_flags 0%o",
 		  map->m_la, map->m_pa,
 		  map->m_llen, map->m_plen, map->m_flags);

 	DBG_BUGON(err < 0 && err != -ENOMEM);
 	return err;
 }
	// SPDX-License-Identifier: GPL-2.0+
	/*
	* erofs-utils/lib/zmap.c
	*
	* (a large amount of code was adapted from Linux kernel. )
	*
	* Copyright (C) 2018-2019 HUAWEI, Inc.
	* https://www.huawei.com/
	* Created by Gao Xiang <gaoxiang25@huawei.com>
	* Modified by Huang Jianan <huangjianan@oppo.com>
	*/
	#include "erofs/io.h"
	#include "erofs/print.h"

	int z_erofs_fill_inode(struct erofs_inode *vi)
	{
	if (vi->datalayout == EROFS_INODE_FLAT_COMPRESSION_LEGACY) {
	vi->z_advise = 0;
	vi->z_algorithmtype[0] = 0;
	vi->z_algorithmtype[1] = 0;
	vi->z_logical_clusterbits = LOG_BLOCK_SIZE;
	vi->z_physical_clusterbits[0] = vi->z_logical_clusterbits;
	vi->z_physical_clusterbits[1] = vi->z_logical_clusterbits;

	vi->flags \|= EROFS_I_Z_INITED;
	}
	return 0;
	}

	static int z_erofs_fill_inode_lazy(struct erofs_inode *vi)
	{
	int ret;
	erofs_off_t pos;
	struct z_erofs_map_header *h;
	char buf[sizeof(struct z_erofs_map_header)];

	if (vi->flags & EROFS_I_Z_INITED)
	return 0;

	DBG_BUGON(vi->datalayout == EROFS_INODE_FLAT_COMPRESSION_LEGACY);
	pos = round_up(iloc(vi->nid) + vi->inode_isize + vi->xattr_isize, 8);

	ret = dev_read(buf, pos, sizeof(buf));
	if (ret < 0)
	return -EIO;

	h = (struct z_erofs_map_header *)buf;
	vi->z_advise = le16_to_cpu(h->h_advise);
	vi->z_algorithmtype[0] = h->h_algorithmtype & 15;
	vi->z_algorithmtype[1] = h->h_algorithmtype >> 4;

	if (vi->z_algorithmtype[0] >= Z_EROFS_COMPRESSION_MAX) {
	erofs_err("unknown compression format %u for nid %llu",
	vi->z_algorithmtype[0], (unsigned long long)vi->nid);
	return -EOPNOTSUPP;
	}

	vi->z_logical_clusterbits = LOG_BLOCK_SIZE + (h->h_clusterbits & 7);
	vi->z_physical_clusterbits[0] = vi->z_logical_clusterbits +
	((h->h_clusterbits >> 3) & 3);

	if (vi->z_physical_clusterbits[0] != LOG_BLOCK_SIZE) {
	erofs_err("unsupported physical clusterbits %u for nid %llu",
	vi->z_physical_clusterbits[0], (unsigned long long)vi->nid);
	return -EOPNOTSUPP;
	}

	vi->z_physical_clusterbits[1] = vi->z_logical_clusterbits +
	((h->h_clusterbits >> 5) & 7);
	vi->flags \|= EROFS_I_Z_INITED;
	return 0;
	}

	struct z_erofs_maprecorder {
	struct erofs_inode *inode;
	struct erofs_map_blocks *map;
	void *kaddr;

	unsigned long lcn;
	/* compression extent information gathered */
	u8 type;
	u16 clusterofs;
	u16 delta[2];
	erofs_blk_t pblk;
	};

	static int z_erofs_reload_indexes(struct z_erofs_maprecorder *m,
	erofs_blk_t eblk)
	{
	int ret;
	struct erofs_map_blocks *const map = m->map;
	char *mpage = map->mpage;

	if (map->index == eblk)
	return 0;

	ret = blk_read(mpage, eblk, 1);
	if (ret < 0)
	return -EIO;

	map->index = eblk;

	return 0;
	}

	static int legacy_load_cluster_from_disk(struct z_erofs_maprecorder *m,
	unsigned long lcn)
	{
	struct erofs_inode *const vi = m->inode;
	const erofs_off_t ibase = iloc(vi->nid);
	const erofs_off_t pos =
	Z_EROFS_VLE_LEGACY_INDEX_ALIGN(ibase + vi->inode_isize +
	vi->xattr_isize) +
	lcn * sizeof(struct z_erofs_vle_decompressed_index);
	struct z_erofs_vle_decompressed_index *di;
	unsigned int advise, type;
	int err;

	err = z_erofs_reload_indexes(m, erofs_blknr(pos));
	if (err)
	return err;

	m->lcn = lcn;
	di = m->kaddr + erofs_blkoff(pos);

	advise = le16_to_cpu(di->di_advise);
	type = (advise >> Z_EROFS_VLE_DI_CLUSTER_TYPE_BIT) &
	((1 << Z_EROFS_VLE_DI_CLUSTER_TYPE_BITS) - 1);
	switch (type) {
	case Z_EROFS_VLE_CLUSTER_TYPE_NONHEAD:
	m->clusterofs = 1 << vi->z_logical_clusterbits;
	m->delta[0] = le16_to_cpu(di->di_u.delta[0]);
	m->delta[1] = le16_to_cpu(di->di_u.delta[1]);
	break;
	case Z_EROFS_VLE_CLUSTER_TYPE_PLAIN:
	case Z_EROFS_VLE_CLUSTER_TYPE_HEAD:
	m->clusterofs = le16_to_cpu(di->di_clusterofs);
	m->pblk = le32_to_cpu(di->di_u.blkaddr);
	break;
	default:
	DBG_BUGON(1);
	return -EOPNOTSUPP;
	}
	m->type = type;
	return 0;
	}

	static unsigned int decode_compactedbits(unsigned int lobits,
	unsigned int lomask,
	u8 in, unsigned int pos, u8 type)
	{
	const unsigned int v = get_unaligned_le32(in + pos / 8) >> (pos & 7);
	const unsigned int lo = v & lomask;

	*type = (v >> lobits) & 3;
	return lo;
	}

	static int unpack_compacted_index(struct z_erofs_maprecorder *m,
	unsigned int amortizedshift,
	unsigned int eofs)
	{
	struct erofs_inode *const vi = m->inode;
	const unsigned int lclusterbits = vi->z_logical_clusterbits;
	const unsigned int lomask = (1 << lclusterbits) - 1;
	unsigned int vcnt, base, lo, encodebits, nblk;
	int i;
	u8 *in, type;

	if (1 << amortizedshift == 4)
	vcnt = 2;
	else if (1 << amortizedshift == 2 && lclusterbits == 12)
	vcnt = 16;
	else
	return -EOPNOTSUPP;

	encodebits = ((vcnt << amortizedshift) - sizeof(__le32)) * 8 / vcnt;
	base = round_down(eofs, vcnt << amortizedshift);
	in = m->kaddr + base;

	i = (eofs - base) >> amortizedshift;

	lo = decode_compactedbits(lclusterbits, lomask,
	in, encodebits * i, &type);
	m->type = type;
	if (type == Z_EROFS_VLE_CLUSTER_TYPE_NONHEAD) {
	m->clusterofs = 1 << lclusterbits;
	if (i + 1 != (int)vcnt) {
	m->delta[0] = lo;
	return 0;
	}
	/*
	* since the last lcluster in the pack is special,
	* of which lo saves delta[1] rather than delta[0].
	* Hence, get delta[0] by the previous lcluster indirectly.
	*/
	lo = decode_compactedbits(lclusterbits, lomask,
	in, encodebits * (i - 1), &type);
	if (type != Z_EROFS_VLE_CLUSTER_TYPE_NONHEAD)
	lo = 0;
	m->delta[0] = lo + 1;
	return 0;
	}
	m->clusterofs = lo;
	m->delta[0] = 0;
	/* figout out blkaddr (pblk) for HEAD lclusters */
	nblk = 1;
	while (i > 0) {
	--i;
	lo = decode_compactedbits(lclusterbits, lomask,
	in, encodebits * i, &type);
	if (type == Z_EROFS_VLE_CLUSTER_TYPE_NONHEAD)
	i -= lo;

	if (i >= 0)
	++nblk;
	}
	in += (vcnt << amortizedshift) - sizeof(__le32);
	m->pblk = le32_to_cpu((__le32 )in) + nblk;
	return 0;
	}

	static int compacted_load_cluster_from_disk(struct z_erofs_maprecorder *m,
	unsigned long lcn)
	{
	struct erofs_inode *const vi = m->inode;
	const unsigned int lclusterbits = vi->z_logical_clusterbits;
	const erofs_off_t ebase = round_up(iloc(vi->nid) + vi->inode_isize +
	vi->xattr_isize, 8) +
	sizeof(struct z_erofs_map_header);
	const unsigned int totalidx = DIV_ROUND_UP(vi->i_size, EROFS_BLKSIZ);
	unsigned int compacted_4b_initial, compacted_2b;
	unsigned int amortizedshift;
	erofs_off_t pos;
	int err;

	if (lclusterbits != 12)
	return -EOPNOTSUPP;

	if (lcn >= totalidx)
	return -EINVAL;

	m->lcn = lcn;
	/* used to align to 32-byte (compacted_2b) alignment */
	compacted_4b_initial = (32 - ebase % 32) / 4;
	if (compacted_4b_initial == 32 / 4)
	compacted_4b_initial = 0;

	if (vi->z_advise & Z_EROFS_ADVISE_COMPACTED_2B)
	compacted_2b = rounddown(totalidx - compacted_4b_initial, 16);
	else
	compacted_2b = 0;

	pos = ebase;
	if (lcn < compacted_4b_initial) {
	amortizedshift = 2;
	goto out;
	}
	pos += compacted_4b_initial * 4;
	lcn -= compacted_4b_initial;

	if (lcn < compacted_2b) {
	amortizedshift = 1;
	goto out;
	}
	pos += compacted_2b * 2;
	lcn -= compacted_2b;
	amortizedshift = 2;
	out:
	pos += lcn * (1 << amortizedshift);
	err = z_erofs_reload_indexes(m, erofs_blknr(pos));
	if (err)
	return err;
	return unpack_compacted_index(m, amortizedshift, erofs_blkoff(pos));
	}

	static int z_erofs_load_cluster_from_disk(struct z_erofs_maprecorder *m,
	unsigned int lcn)
	{
	const unsigned int datamode = m->inode->datalayout;

	if (datamode == EROFS_INODE_FLAT_COMPRESSION_LEGACY)
	return legacy_load_cluster_from_disk(m, lcn);

	if (datamode == EROFS_INODE_FLAT_COMPRESSION)
	return compacted_load_cluster_from_disk(m, lcn);

	return -EINVAL;
	}

	static int z_erofs_extent_lookback(struct z_erofs_maprecorder *m,
	unsigned int lookback_distance)
	{
	struct erofs_inode *const vi = m->inode;
	struct erofs_map_blocks *const map = m->map;
	const unsigned int lclusterbits = vi->z_logical_clusterbits;
	unsigned long lcn = m->lcn;
	int err;

	if (lcn < lookback_distance) {
	erofs_err("bogus lookback distance @ nid %llu",
	(unsigned long long)vi->nid);
	DBG_BUGON(1);
	return -EFSCORRUPTED;
	}

	/* load extent head logical cluster if needed */
	lcn -= lookback_distance;
	err = z_erofs_load_cluster_from_disk(m, lcn);
	if (err)
	return err;

	switch (m->type) {
	case Z_EROFS_VLE_CLUSTER_TYPE_NONHEAD:
	if (!m->delta[0]) {
	erofs_err("invalid lookback distance 0 @ nid %llu",
	(unsigned long long)vi->nid);
	DBG_BUGON(1);
	return -EFSCORRUPTED;
	}
	return z_erofs_extent_lookback(m, m->delta[0]);
	case Z_EROFS_VLE_CLUSTER_TYPE_PLAIN:
	map->m_flags &= ~EROFS_MAP_ZIPPED;
	case Z_EROFS_VLE_CLUSTER_TYPE_HEAD:
	map->m_la = (lcn << lclusterbits) \| m->clusterofs;
	break;
	default:
	erofs_err("unknown type %u @ lcn %lu of nid %llu",
	m->type, lcn, (unsigned long long)vi->nid);
	DBG_BUGON(1);
	return -EOPNOTSUPP;
	}
	return 0;
	}

	int z_erofs_map_blocks_iter(struct erofs_inode *vi,
	struct erofs_map_blocks *map)
	{
	struct z_erofs_maprecorder m = {
	.inode = vi,
	.map = map,
	.kaddr = map->mpage,
	};
	int err = 0;
	unsigned int lclusterbits, endoff;
	unsigned long long ofs, end;

	/* when trying to read beyond EOF, leave it unmapped */
	if (map->m_la >= vi->i_size) {
	map->m_llen = map->m_la + 1 - vi->i_size;
	map->m_la = vi->i_size;
	map->m_flags = 0;
	goto out;
	}

	err = z_erofs_fill_inode_lazy(vi);
	if (err)
	goto out;

	lclusterbits = vi->z_logical_clusterbits;
	ofs = map->m_la;
	m.lcn = ofs >> lclusterbits;
	endoff = ofs & ((1 << lclusterbits) - 1);

	err = z_erofs_load_cluster_from_disk(&m, m.lcn);
	if (err)
	goto out;

	map->m_flags = EROFS_MAP_ZIPPED; /* by default, compressed */
	end = (m.lcn + 1ULL) << lclusterbits;
	switch (m.type) {
	case Z_EROFS_VLE_CLUSTER_TYPE_PLAIN:
	if (endoff >= m.clusterofs)
	map->m_flags &= ~EROFS_MAP_ZIPPED;
	case Z_EROFS_VLE_CLUSTER_TYPE_HEAD:
	if (endoff >= m.clusterofs) {
	map->m_la = (m.lcn << lclusterbits) \| m.clusterofs;
	break;
	}
	/* m.lcn should be >= 1 if endoff < m.clusterofs */
	if (!m.lcn) {
	erofs_err("invalid logical cluster 0 at nid %llu",
	(unsigned long long)vi->nid);
	err = -EFSCORRUPTED;
	goto out;
	}
	end = (m.lcn << lclusterbits) \| m.clusterofs;
	map->m_flags \|= EROFS_MAP_FULL_MAPPED;
	m.delta[0] = 1;
	case Z_EROFS_VLE_CLUSTER_TYPE_NONHEAD:
	/* get the correspoinding first chunk */
	err = z_erofs_extent_lookback(&m, m.delta[0]);
	if (err)
	goto out;
	break;
	default:
	erofs_err("unknown type %u @ offset %llu of nid %llu",
	m.type, ofs, (unsigned long long)vi->nid);
	err = -EOPNOTSUPP;
	goto out;
	}

	map->m_llen = end - map->m_la;
	map->m_plen = 1 << lclusterbits;
	map->m_pa = blknr_to_addr(m.pblk);
	map->m_flags \|= EROFS_MAP_MAPPED;

	out:
	erofs_dbg("m_la %" PRIu64 " m_pa %" PRIu64 " m_llen %" PRIu64 " m_plen %" PRIu64 " m_flags 0%o",
	map->m_la, map->m_pa,
	map->m_llen, map->m_plen, map->m_flags);

	DBG_BUGON(err < 0 && err != -ENOMEM);
	return err;
	}