staging: erofs: add compacted compression indexes support (152a333a) · Commits · 戴 / test

drivers/staging/erofs/Makefile

+1 −1

Original line number	Diff line number	Diff line
		@@ -9,5 +9,5 @@ obj-$(CONFIG_EROFS_FS) += erofs.o
		ccflags-y += -I $(srctree)/$(src)/include
		erofs-objs := super.o inode.o data.o namei.o dir.o utils.o
		erofs-$(CONFIG_EROFS_FS_XATTR) += xattr.o
		erofs-$(CONFIG_EROFS_FS_ZIP) += unzip_vle.o unzip_vle_lz4.o
		erofs-$(CONFIG_EROFS_FS_ZIP) += unzip_vle.o unzip_vle_lz4.o zmap.o

drivers/staging/erofs/inode.c

+1 −6

Original line number	Diff line number	Diff line
		@@ -210,12 +210,7 @@ static int fill_inode(struct inode *inode, int isdir)
		}

		if (is_inode_layout_compression(inode)) {
		#ifdef CONFIG_EROFS_FS_ZIP
		inode->i_mapping->a_ops =
		&z_erofs_vle_normalaccess_aops;
		#else
		err = -ENOTSUPP;
		#endif
		err = z_erofs_fill_inode(inode);
		goto out_unlock;
		}

drivers/staging/erofs/internal.h

+16 −2

Original line number	Diff line number	Diff line
		@@ -339,9 +339,11 @@ static inline erofs_off_t iloc(struct erofs_sb_info *sbi, erofs_nid_t nid)

		/* atomic flag definitions */
		#define EROFS_V_EA_INITED_BIT 0
		#define EROFS_V_Z_INITED_BIT 1

		/* bitlock definitions (arranged in reverse order) */
		#define EROFS_V_BL_XATTR_BIT (BITS_PER_LONG - 1)
		#define EROFS_V_BL_Z_BIT (BITS_PER_LONG - 2)

		struct erofs_vnode {
		erofs_nid_t nid;
		@@ -356,8 +358,17 @@ struct erofs_vnode {
		unsigned xattr_shared_count;
		unsigned *xattr_shared_xattrs;

		union {
		erofs_blk_t raw_blkaddr;

		#ifdef CONFIG_EROFS_FS_ZIP
		struct {
		unsigned short z_advise;
		unsigned char z_algorithmtype[2];
		unsigned char z_logical_clusterbits;
		unsigned char z_physical_clusterbits[2];
		};
		#endif
		};
		/* the corresponding vfs inode */
		struct inode vfs_inode;
		};
		@@ -447,11 +458,14 @@ struct erofs_map_blocks {
		/* Flags used by erofs_map_blocks() */
		#define EROFS_GET_BLOCKS_RAW 0x0001

		/* zmap.c */
		#ifdef CONFIG_EROFS_FS_ZIP
		int z_erofs_fill_inode(struct inode *inode);
		int z_erofs_map_blocks_iter(struct inode *inode,
		struct erofs_map_blocks *map,
		int flags);
		#else
		static inline int z_erofs_fill_inode(struct inode *inode) { return -ENOTSUPP; }
		static inline int z_erofs_map_blocks_iter(struct inode *inode,
		struct erofs_map_blocks *map,
		int flags)

drivers/staging/erofs/unzip_vle.c

+0 −286

Original line number	Diff line number	Diff line
		@@ -1600,289 +1600,3 @@ const struct address_space_operations z_erofs_vle_normalaccess_aops = {
		.readpages = z_erofs_vle_normalaccess_readpages,
		};

		/*
		* Variable-sized Logical Extent (Fixed Physical Cluster) Compression Mode
		* ---
		* VLE compression mode attempts to compress a number of logical data into
		* a physical cluster with a fixed size.
		* VLE compression mode uses "struct z_erofs_vle_decompressed_index".
		*/
		#define __vle_cluster_advise(x, bit, bits) \
		((le16_to_cpu(x) >> (bit)) & ((1 << (bits)) - 1))

		#define __vle_cluster_type(advise) __vle_cluster_advise(advise, \
		Z_EROFS_VLE_DI_CLUSTER_TYPE_BIT, Z_EROFS_VLE_DI_CLUSTER_TYPE_BITS)

		#define vle_cluster_type(di) \
		__vle_cluster_type((di)->di_advise)

		static int
		vle_decompressed_index_clusterofs(unsigned int *clusterofs,
		unsigned int clustersize,
		struct z_erofs_vle_decompressed_index *di)
		{
		switch (vle_cluster_type(di)) {
		case Z_EROFS_VLE_CLUSTER_TYPE_NONHEAD:
		*clusterofs = clustersize;
		break;
		case Z_EROFS_VLE_CLUSTER_TYPE_PLAIN:
		case Z_EROFS_VLE_CLUSTER_TYPE_HEAD:
		*clusterofs = le16_to_cpu(di->di_clusterofs);
		break;
		default:
		DBG_BUGON(1);
		return -EIO;
		}
		return 0;
		}

		static inline erofs_blk_t
		vle_extent_blkaddr(struct inode *inode, pgoff_t index)
		{
		struct erofs_sb_info *sbi = EROFS_I_SB(inode);
		struct erofs_vnode *vi = EROFS_V(inode);

		unsigned int ofs = Z_EROFS_VLE_LEGACY_INDEX_ALIGN(vi->inode_isize +
		vi->xattr_isize) +
		index * sizeof(struct z_erofs_vle_decompressed_index);

		return erofs_blknr(iloc(sbi, vi->nid) + ofs);
		}

		static inline unsigned int
		vle_extent_blkoff(struct inode *inode, pgoff_t index)
		{
		struct erofs_sb_info *sbi = EROFS_I_SB(inode);
		struct erofs_vnode *vi = EROFS_V(inode);

		unsigned int ofs = Z_EROFS_VLE_LEGACY_INDEX_ALIGN(vi->inode_isize +
		vi->xattr_isize) +
		index * sizeof(struct z_erofs_vle_decompressed_index);

		return erofs_blkoff(iloc(sbi, vi->nid) + ofs);
		}

		struct vle_map_blocks_iter_ctx {
		struct inode *inode;
		struct super_block *sb;
		unsigned int clusterbits;

		struct page **mpage_ret;
		void **kaddr_ret;
		};

		static int
		vle_get_logical_extent_head(const struct vle_map_blocks_iter_ctx *ctx,
		unsigned int lcn, /* logical cluster number */
		unsigned long long *ofs,
		erofs_blk_t *pblk,
		unsigned int *flags)
		{
		const unsigned int clustersize = 1 << ctx->clusterbits;
		const erofs_blk_t mblk = vle_extent_blkaddr(ctx->inode, lcn);
		struct page mpage = ctx->mpage_ret; /* extent metapage */

		struct z_erofs_vle_decompressed_index *di;
		unsigned int cluster_type, delta0;

		if (mpage->index != mblk) {
		kunmap_atomic(*ctx->kaddr_ret);
		unlock_page(mpage);
		put_page(mpage);

		mpage = erofs_get_meta_page(ctx->sb, mblk, false);
		if (IS_ERR(mpage)) {
		*ctx->mpage_ret = NULL;
		return PTR_ERR(mpage);
		}
		*ctx->mpage_ret = mpage;
		*ctx->kaddr_ret = kmap_atomic(mpage);
		}

		di = *ctx->kaddr_ret + vle_extent_blkoff(ctx->inode, lcn);

		cluster_type = vle_cluster_type(di);
		switch (cluster_type) {
		case Z_EROFS_VLE_CLUSTER_TYPE_NONHEAD:
		delta0 = le16_to_cpu(di->di_u.delta[0]);
		if (unlikely(!delta0 \|\| delta0 > lcn)) {
		errln("invalid NONHEAD dl0 %u at lcn %u of nid %llu",
		delta0, lcn, EROFS_V(ctx->inode)->nid);
		DBG_BUGON(1);
		return -EIO;
		}
		return vle_get_logical_extent_head(ctx,
		lcn - delta0, ofs, pblk, flags);
		case Z_EROFS_VLE_CLUSTER_TYPE_PLAIN:
		*flags ^= EROFS_MAP_ZIPPED;
		/* fallthrough */
		case Z_EROFS_VLE_CLUSTER_TYPE_HEAD:
		/* clustersize should be a power of two */
		*ofs = ((u64)lcn << ctx->clusterbits) +
		(le16_to_cpu(di->di_clusterofs) & (clustersize - 1));
		*pblk = le32_to_cpu(di->di_u.blkaddr);
		break;
		default:
		errln("unknown cluster type %u at lcn %u of nid %llu",
		cluster_type, lcn, EROFS_V(ctx->inode)->nid);
		DBG_BUGON(1);
		return -EIO;
		}
		return 0;
		}

		int z_erofs_map_blocks_iter(struct inode *inode,
		struct erofs_map_blocks *map,
		int flags)
		{
		void *kaddr;
		const struct vle_map_blocks_iter_ctx ctx = {
		.inode = inode,
		.sb = inode->i_sb,
		.clusterbits = EROFS_I_SB(inode)->clusterbits,
		.mpage_ret = &map->mpage,
		.kaddr_ret = &kaddr
		};
		const unsigned int clustersize = 1 << ctx.clusterbits;
		/* if both m_(l,p)len are 0, regularize l_lblk, l_lofs, etc... */
		const bool initial = !map->m_llen;

		/* logicial extent (start, end) offset */
		unsigned long long ofs, end;
		unsigned int lcn;
		u32 ofs_rem;

		/* initialize `pblk' to keep gcc from printing foolish warnings */
		erofs_blk_t mblk, pblk = 0;
		struct page *mpage = map->mpage;
		struct z_erofs_vle_decompressed_index *di;
		unsigned int cluster_type, logical_cluster_ofs;
		int err = 0;

		trace_z_erofs_map_blocks_iter_enter(inode, map, flags);

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

		debugln("%s, m_la %llu m_llen %llu --- start", __func__,
		map->m_la, map->m_llen);

		ofs = map->m_la + map->m_llen;

		/* clustersize should be power of two */
		lcn = ofs >> ctx.clusterbits;
		ofs_rem = ofs & (clustersize - 1);

		mblk = vle_extent_blkaddr(inode, lcn);

		if (!mpage \|\| mpage->index != mblk) {
		if (mpage)
		put_page(mpage);

		mpage = erofs_get_meta_page(ctx.sb, mblk, false);
		if (IS_ERR(mpage)) {
		err = PTR_ERR(mpage);
		goto out;
		}
		map->mpage = mpage;
		} else {
		lock_page(mpage);
		DBG_BUGON(!PageUptodate(mpage));
		}

		kaddr = kmap_atomic(mpage);
		di = kaddr + vle_extent_blkoff(inode, lcn);

		debugln("%s, lcn %u mblk %u e_blkoff %u", __func__, lcn,
		mblk, vle_extent_blkoff(inode, lcn));

		err = vle_decompressed_index_clusterofs(&logical_cluster_ofs,
		clustersize, di);
		if (unlikely(err))
		goto unmap_out;

		if (!initial) {
		/* [walking mode] 'map' has been already initialized */
		map->m_llen += logical_cluster_ofs;
		goto unmap_out;
		}

		/* by default, compressed */
		map->m_flags \|= EROFS_MAP_ZIPPED;

		end = ((u64)lcn + 1) * clustersize;

		cluster_type = vle_cluster_type(di);

		switch (cluster_type) {
		case Z_EROFS_VLE_CLUSTER_TYPE_PLAIN:
		if (ofs_rem >= logical_cluster_ofs)
		map->m_flags ^= EROFS_MAP_ZIPPED;
		/* fallthrough */
		case Z_EROFS_VLE_CLUSTER_TYPE_HEAD:
		if (ofs_rem == logical_cluster_ofs) {
		pblk = le32_to_cpu(di->di_u.blkaddr);
		goto exact_hitted;
		}

		if (ofs_rem > logical_cluster_ofs) {
		ofs = (u64)lcn * clustersize \| logical_cluster_ofs;
		pblk = le32_to_cpu(di->di_u.blkaddr);
		break;
		}

		/* logical cluster number should be >= 1 */
		if (unlikely(!lcn)) {
		errln("invalid logical cluster 0 at nid %llu",
		EROFS_V(inode)->nid);
		err = -EIO;
		goto unmap_out;
		}
		end = ((u64)lcn-- * clustersize) \| logical_cluster_ofs;
		/* fallthrough */
		case Z_EROFS_VLE_CLUSTER_TYPE_NONHEAD:
		/* get the correspoinding first chunk */
		err = vle_get_logical_extent_head(&ctx, lcn, &ofs,
		&pblk, &map->m_flags);
		mpage = map->mpage;

		if (unlikely(err)) {
		if (mpage)
		goto unmap_out;
		goto out;
		}
		break;
		default:
		errln("unknown cluster type %u at offset %llu of nid %llu",
		cluster_type, ofs, EROFS_V(inode)->nid);
		err = -EIO;
		goto unmap_out;
		}

		map->m_la = ofs;
		exact_hitted:
		map->m_llen = end - ofs;
		map->m_plen = clustersize;
		map->m_pa = blknr_to_addr(pblk);
		map->m_flags \|= EROFS_MAP_MAPPED;
		unmap_out:
		kunmap_atomic(kaddr);
		unlock_page(mpage);
		out:
		debugln("%s, m_la %llu m_pa %llu m_llen %llu m_plen %llu m_flags 0%o",
		__func__, map->m_la, map->m_pa,
		map->m_llen, map->m_plen, map->m_flags);

		trace_z_erofs_map_blocks_iter_exit(inode, map, flags, err);

		/* aggressively BUG_ON iff CONFIG_EROFS_FS_DEBUG is on */
		DBG_BUGON(err < 0 && err != -ENOMEM);
		return err;
		}

drivers/staging/erofs/zmap.c

0 → 100644

+462 −0

Original line number	Diff line number	Diff line
		// SPDX-License-Identifier: GPL-2.0
		/*
		* linux/drivers/staging/erofs/zmap.c
		*
		* Copyright (C) 2018-2019 HUAWEI, Inc.
		* http://www.huawei.com/
		* Created by Gao Xiang <gaoxiang25@huawei.com>
		*/
		#include "internal.h"
		#include <asm/unaligned.h>
		#include <trace/events/erofs.h>

		int z_erofs_fill_inode(struct inode *inode)
		{
		struct erofs_vnode *const vi = EROFS_V(inode);
		struct super_block *const sb = inode->i_sb;

		if (vi->datamode == EROFS_INODE_FLAT_COMPRESSION_LEGACY) {
		vi->z_advise = 0;
		vi->z_algorithmtype[0] = 0;
		vi->z_algorithmtype[1] = 0;
		vi->z_logical_clusterbits = EROFS_SB(sb)->clusterbits;
		vi->z_physical_clusterbits[0] = vi->z_logical_clusterbits;
		vi->z_physical_clusterbits[1] = vi->z_logical_clusterbits;
		set_bit(EROFS_V_Z_INITED_BIT, &vi->flags);
		}

		inode->i_mapping->a_ops = &z_erofs_vle_normalaccess_aops;
		return 0;
		}

		static int fill_inode_lazy(struct inode *inode)
		{
		struct erofs_vnode *const vi = EROFS_V(inode);
		struct super_block *const sb = inode->i_sb;
		int err;
		erofs_off_t pos;
		struct page *page;
		void *kaddr;
		struct z_erofs_map_header *h;

		if (test_bit(EROFS_V_Z_INITED_BIT, &vi->flags))
		return 0;

		if (wait_on_bit_lock(&vi->flags, EROFS_V_BL_Z_BIT, TASK_KILLABLE))
		return -ERESTARTSYS;

		err = 0;
		if (test_bit(EROFS_V_Z_INITED_BIT, &vi->flags))
		goto out_unlock;

		DBG_BUGON(vi->datamode == EROFS_INODE_FLAT_COMPRESSION_LEGACY);

		pos = ALIGN(iloc(EROFS_SB(sb), vi->nid) + vi->inode_isize +
		vi->xattr_isize, 8);
		page = erofs_get_meta_page(sb, erofs_blknr(pos), false);
		if (IS_ERR(page)) {
		err = PTR_ERR(page);
		goto out_unlock;
		}

		kaddr = kmap_atomic(page);

		h = kaddr + erofs_blkoff(pos);
		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) {
		errln("unknown compression format %u for nid %llu, please upgrade kernel",
		vi->z_algorithmtype[0], vi->nid);
		err = -ENOTSUPP;
		goto unmap_done;
		}

		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) {
		errln("unsupported physical clusterbits %u for nid %llu, please upgrade kernel",
		vi->z_physical_clusterbits[0], vi->nid);
		err = -ENOTSUPP;
		goto unmap_done;
		}

		vi->z_physical_clusterbits[1] = vi->z_logical_clusterbits +
		((h->h_clusterbits >> 5) & 7);
		unmap_done:
		kunmap_atomic(kaddr);
		unlock_page(page);
		put_page(page);

		set_bit(EROFS_V_Z_INITED_BIT, &vi->flags);
		out_unlock:
		clear_and_wake_up_bit(EROFS_V_BL_Z_BIT, &vi->flags);
		return err;
		}

		struct z_erofs_maprecorder {
		struct 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)
		{
		struct super_block *const sb = m->inode->i_sb;
		struct erofs_map_blocks *const map = m->map;
		struct page *mpage = map->mpage;

		if (mpage) {
		if (mpage->index == eblk) {
		if (!m->kaddr)
		m->kaddr = kmap_atomic(mpage);
		return 0;
		}

		if (m->kaddr) {
		kunmap_atomic(m->kaddr);
		m->kaddr = NULL;
		}
		put_page(mpage);
		}

		mpage = erofs_get_meta_page(sb, eblk, false);
		if (IS_ERR(mpage)) {
		map->mpage = NULL;
		return PTR_ERR(mpage);
		}
		m->kaddr = kmap_atomic(mpage);
		unlock_page(mpage);
		map->mpage = mpage;
		return 0;
		}

		static int vle_legacy_load_cluster_from_disk(struct z_erofs_maprecorder *m,
		unsigned long lcn)
		{
		struct inode *const inode = m->inode;
		struct erofs_vnode *const vi = EROFS_V(inode);
		const erofs_off_t ibase = iloc(EROFS_I_SB(inode), 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 -EIO;
		}
		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_vnode *const vi = EROFS_V(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 -ENOTSUPP;

		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 != 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 inode *const inode = m->inode;
		struct erofs_vnode *const vi = EROFS_V(inode);
		const unsigned int lclusterbits = vi->z_logical_clusterbits;
		const erofs_off_t ebase = ALIGN(iloc(EROFS_I_SB(inode), vi->nid) +
		vi->inode_isize + vi->xattr_isize, 8) +
		sizeof(struct z_erofs_map_header);
		const unsigned int totalidx = DIV_ROUND_UP(inode->i_size, EROFS_BLKSIZ);
		unsigned int compacted_4b_initial, compacted_2b;
		unsigned int amortizedshift;
		erofs_off_t pos;
		int err;

		if (lclusterbits != 12)
		return -ENOTSUPP;

		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 vle_load_cluster_from_disk(struct z_erofs_maprecorder *m,
		unsigned int lcn)
		{
		const unsigned int datamode = EROFS_V(m->inode)->datamode;

		if (datamode == EROFS_INODE_FLAT_COMPRESSION_LEGACY)
		return vle_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 vle_extent_lookback(struct z_erofs_maprecorder *m,
		unsigned int lookback_distance)
		{
		struct erofs_vnode *const vi = EROFS_V(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) {
		DBG_BUGON(1);
		return -EIO;
		}

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

		switch (m->type) {
		case Z_EROFS_VLE_CLUSTER_TYPE_NONHEAD:
		return vle_extent_lookback(m, m->delta[0]);
		case Z_EROFS_VLE_CLUSTER_TYPE_PLAIN:
		map->m_flags &= ~EROFS_MAP_ZIPPED;
		/* fallthrough */
		case Z_EROFS_VLE_CLUSTER_TYPE_HEAD:
		map->m_la = (lcn << lclusterbits) \| m->clusterofs;
		break;
		default:
		errln("unknown type %u at lcn %lu of nid %llu",
		m->type, lcn, vi->nid);
		DBG_BUGON(1);
		return -EIO;
		}
		return 0;
		}

		int z_erofs_map_blocks_iter(struct inode *inode,
		struct erofs_map_blocks *map,
		int flags)
		{
		struct erofs_vnode *const vi = EROFS_V(inode);
		struct z_erofs_maprecorder m = {
		.inode = inode,
		.map = map,
		};
		int err = 0;
		unsigned int lclusterbits, endoff;
		unsigned long long ofs, end;

		trace_z_erofs_map_blocks_iter_enter(inode, map, flags);

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

		err = fill_inode_lazy(inode);
		if (err)
		goto out;

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

		err = vle_load_cluster_from_disk(&m, m.lcn);
		if (err)
		goto unmap_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;
		/* fallthrough */
		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 (unlikely(!m.lcn)) {
		errln("invalid logical cluster 0 at nid %llu",
		vi->nid);
		err = -EIO;
		goto unmap_out;
		}
		end = (m.lcn << lclusterbits) \| m.clusterofs;
		m.delta[0] = 1;
		/* fallthrough */
		case Z_EROFS_VLE_CLUSTER_TYPE_NONHEAD:
		/* get the correspoinding first chunk */
		err = vle_extent_lookback(&m, m.delta[0]);
		if (unlikely(err))
		goto unmap_out;
		break;
		default:
		errln("unknown type %u at offset %llu of nid %llu",
		m.type, ofs, vi->nid);
		err = -EIO;
		goto unmap_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;

		unmap_out:
		if (m.kaddr)
		kunmap_atomic(m.kaddr);

		out:
		debugln("%s, m_la %llu m_pa %llu m_llen %llu m_plen %llu m_flags 0%o",
		__func__, map->m_la, map->m_pa,
		map->m_llen, map->m_plen, map->m_flags);

		trace_z_erofs_map_blocks_iter_exit(inode, map, flags, err);

		/* aggressively BUG_ON iff CONFIG_EROFS_FS_DEBUG is on */
		DBG_BUGON(err < 0 && err != -ENOMEM);
		return err;
		}

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