erofs: fix up compacted indexes for block size < 4096

[ Upstream commit 8d2517aaeea3ab8651bb517bca8f3c8664d318ea ]

Previously, the block size always equaled to PAGE_SIZE, therefore
`lclusterbits` c

erofs: fix up compacted indexes for block size < 4096

[ Upstream commit 8d2517aaeea3ab8651bb517bca8f3c8664d318ea ]

Previously, the block size always equaled to PAGE_SIZE, therefore
`lclusterbits` couldn't be less than 12.

Since sub-page compressed blocks are now considered, `lobits` for
a lcluster in each pack cannot always be `lclusterbits` as before.
Otherwise, there is no enough room for the special value
`Z_EROFS_LI_D0_CBLKCNT`.

To support smaller block sizes, `lobits` for each compacted lcluster is
now calculated as:
lobits = max(lclusterbits, ilog2(Z_EROFS_LI_D0_CBLKCNT) + 1)

Reviewed-by: Yue Hu <huyue2@coolpad.com>
Reviewed-by: Chao Yu <chao@kernel.org>
Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>
Link: https://lore.kernel.org/r/20231206091057.87027-4-hsiangkao@linux.alibaba.com
Signed-off-by: Sasha Levin <sashal@kernel.org>

show more ...

erofs: fix inconsistent per-file compression format

[ Upstream commit 118a8cf504d7dfa519562d000f423ee3ca75d2c4 ]

EROFS can select compression algorithms on a per-file basis, and each
per-file compr

erofs: fix inconsistent per-file compression format

[ Upstream commit 118a8cf504d7dfa519562d000f423ee3ca75d2c4 ]

EROFS can select compression algorithms on a per-file basis, and each
per-file compression algorithm needs to be marked in the on-disk
superblock for initialization.

However, syzkaller can generate inconsistent crafted images that use
an unsupported algorithmtype for specific inodes, e.g. use MicroLZMA
algorithmtype even it's not set in `sbi->available_compr_algs`. This
can lead to an unexpected "BUG: kernel NULL pointer dereference" if
the corresponding decompressor isn't built-in.

Fix this by checking against `sbi->available_compr_algs` for each
m_algorithmformat request. Incorrect !erofs_sb_has_compr_cfgs preset
bitmap is now fixed together since it was harmless previously.

Reported-by: <bugreport@ubisectech.com>
Fixes: 8f89926290c4 ("erofs: get compression algorithms directly on mapping")
Fixes: 622ceaddb764 ("erofs: lzma compression support")
Reviewed-by: Yue Hu <huyue2@coolpad.com>
Link: https://lore.kernel.org/r/20240113150602.1471050-1-hsiangkao@linux.alibaba.com
Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>

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erofs: DEFLATE compression support

Add DEFLATE compression as the 3rd supported algorithm.

DEFLATE is a popular generic-purpose compression algorithm for quite
long time (many advanced formats like

erofs: DEFLATE compression support

Add DEFLATE compression as the 3rd supported algorithm.

DEFLATE is a popular generic-purpose compression algorithm for quite
long time (many advanced formats like gzip, zlib, zip, png are all
based on that) as Apple documentation written "If you require
interoperability with non-Apple devices, use COMPRESSION_ZLIB. [1]".

Due to its popularity, there are several hardware on-market DEFLATE
accelerators, such as (s390) DFLTCC, (Intel) IAA/QAT, (HiSilicon) ZIP
accelerator, etc. In addition, there are also several high-performence
IP cores and even open-source FPGA approches available for DEFLATE.
Therefore, it's useful to support DEFLATE compression in order to find
a way to utilize these accelerators for asynchronous I/Os and get
benefits from these later.

Besides, it's a good choice to trade off between compression ratios
and performance compared to LZ4 and LZMA. The DEFLATE core format is
simple as well as easy to understand, therefore the code size of its
decompressor is small even for the bootloader use cases. The runtime
memory consumption is quite limited too (e.g. 32K + ~7K for each zlib
stream). As usual, EROFS ourperforms similar approaches too.

Alternatively, DEFLATE could still be used for some specific files
since EROFS supports multiple compression algorithms in one image.

[1] https://developer.apple.com/documentation/compression/compression_algorithm
Reviewed-by: Chao Yu <chao@kernel.org>
Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>
Link: https://lore.kernel.org/r/20230810154859.118330-1-hsiangkao@linux.alibaba.com

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erofs: clean up zmap.c

Several trivial cleanups which aren't quite necessary to split:

- Rename lcluster load functions as well as justify full indexes
since they are typically used for global

erofs: clean up zmap.c

Several trivial cleanups which aren't quite necessary to split:

- Rename lcluster load functions as well as justify full indexes
since they are typically used for global deduplication for
compressed data;

- Avoid unnecessary lines, comments for simplicity.

No logic changes.

Reviewed-by: Guo Xuenan <guoxuenan@huaweicloud.com>
Reviewed-by: Yue Hu <huyue2@coolpad.com>
Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>
Link: https://lore.kernel.org/r/20230615064421.103178-1-hsiangkao@linux.alibaba.com

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erofs: fix compact 4B support for 16k block size

In compact 4B, two adjacent lclusters are packed together as a unit to
form on-disk indexes for effective random access, as below:

(amortized = 4, v

erofs: fix compact 4B support for 16k block size

In compact 4B, two adjacent lclusters are packed together as a unit to
form on-disk indexes for effective random access, as below:

(amortized = 4, vcnt = 2)
_____________________________________________
|___@_____ encoded bits __________|_ blkaddr _|
0 . amortized * vcnt = 8
. .
. . amortized * vcnt - 4 = 4
. .
.____________________________.
|_type (2 bits)_|_clusterofs_|

Therefore, encoded bits for each pack are 32 bits (4 bytes). IOWs,
since each lcluster can get 16 bits for its type and clusterofs, the
maximum supported lclustersize for compact 4B format is 16k (14 bits).

Fix this to enable compact 4B format for 16k lclusters (blocks), which
is tested on an arm64 server with 16k page size.

Fixes: 152a333a5895 ("staging: erofs: add compacted compression indexes support")
Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>
Link: https://lore.kernel.org/r/20230601112341.56960-1-hsiangkao@linux.alibaba.com

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erofs: sunset erofs_dbg()

Such debug messages are rarely used now. Let's get rid of these,
and revert locally if they are needed for debugging.

Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.co

erofs: sunset erofs_dbg()

Such debug messages are rarely used now. Let's get rid of these,
and revert locally if they are needed for debugging.

Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>
Reviewed-by: Chao Yu <chao@kernel.org>
Link: https://lore.kernel.org/r/20230414083027.12307-1-hsiangkao@linux.alibaba.com

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erofs: get rid of z_erofs_fill_inode()

Prior to big pclusters, non-compact compression indexes could have
empty headers.

Let's just avoid the legacy path since it can be handled properly
as a speci

erofs: get rid of z_erofs_fill_inode()

Prior to big pclusters, non-compact compression indexes could have
empty headers.

Let's just avoid the legacy path since it can be handled properly
as a specific compression header with z_erofs_fill_inode_lazy() too.

Tested with erofs-utils exist versions.

Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>
Reviewed-by: Yue Hu <huyue2@coolpad.com>
Reviewed-by: Chao Yu <chao@kernel.org>
Link: https://lore.kernel.org/r/20230413092241.73829-1-hsiangkao@linux.alibaba.com

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erofs: stop parsing non-compact HEAD index if clusterofs is invalid

Syzbot generated a crafted image [1] with a non-compact HEAD index of
clusterofs 33024 while valid numbers should be 0 ~ lclusters

erofs: stop parsing non-compact HEAD index if clusterofs is invalid

Syzbot generated a crafted image [1] with a non-compact HEAD index of
clusterofs 33024 while valid numbers should be 0 ~ lclustersize-1,
which causes the following unexpected behavior as below:

BUG: unable to handle page fault for address: fffff52101a3fff9
#PF: supervisor read access in kernel mode
#PF: error_code(0x0000) - not-present page
PGD 23ffed067 P4D 23ffed067 PUD 0
Oops: 0000 [#1] PREEMPT SMP KASAN
CPU: 1 PID: 4398 Comm: kworker/u5:1 Not tainted 6.3.0-rc6-syzkaller-g09a9639e56c0 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 03/30/2023
Workqueue: erofs_worker z_erofs_decompressqueue_work
RIP: 0010:z_erofs_decompress_queue+0xb7e/0x2b40
...
Call Trace:
<TASK>
z_erofs_decompressqueue_work+0x99/0xe0
process_one_work+0x8f6/0x1170
worker_thread+0xa63/0x1210
kthread+0x270/0x300
ret_from_fork+0x1f/0x30

Note that normal images or images using compact indexes are not
impacted. Let's fix this now.

[1] https://lore.kernel.org/r/000000000000ec75b005ee97fbaa@google.com

Reported-and-tested-by: syzbot+aafb3f37cfeb6534c4ac@syzkaller.appspotmail.com
Fixes: 02827e1796b3 ("staging: erofs: add erofs_map_blocks_iter")
Fixes: 152a333a5895 ("staging: erofs: add compacted compression indexes support")
Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>
Reviewed-by: Chao Yu <chao@kernel.org>
Link: https://lore.kernel.org/r/20230410173714.104604-1-hsiangkao@linux.alibaba.com

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erofs: tidy up EROFS on-disk naming

- Get rid of all "vle" (variable-length extents) expressions
since they only expand overall name lengths unnecessarily;
- Rename COMPRESSION_LEGACY to COMPRE

erofs: tidy up EROFS on-disk naming

- Get rid of all "vle" (variable-length extents) expressions
since they only expand overall name lengths unnecessarily;
- Rename COMPRESSION_LEGACY to COMPRESSED_FULL;
- Move on-disk directory definitions ahead of compression;
- Drop unused extended attribute definitions;
- Move inode ondisk union `i_u` out as `union erofs_inode_i_u`.

No actual logical change.

Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>
Reviewed-by: Yue Hu <huyue2@coolpad.com>
Reviewed-by: Chao Yu <chao@kernel.org>
Link: https://lore.kernel.org/r/20230331063149.25611-1-hsiangkao@linux.alibaba.com

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erofs: avoid hardcoded blocksize for subpage block support

As the first step of converting hardcoded blocksize to that specified in
on-disk superblock, convert all call sites of hardcoded blocksize

erofs: avoid hardcoded blocksize for subpage block support

As the first step of converting hardcoded blocksize to that specified in
on-disk superblock, convert all call sites of hardcoded blocksize to
sb->s_blocksize except for:

1) use sbi->blkszbits instead of sb->s_blocksize in
erofs_superblock_csum_verify() since sb->s_blocksize has not been
updated with the on-disk blocksize yet when the function is called.

2) use inode->i_blkbits instead of sb->s_blocksize in erofs_bread(),
since the inode operated on may be an anonymous inode in fscache mode.
Currently the anonymous inode is allocated from an anonymous mount
maintained in erofs, while in the near future we may allocate anonymous
inodes from a generic API directly and thus have no access to the
anonymous inode's i_sb. Thus we keep the block size in i_blkbits for
anonymous inodes in fscache mode.

Be noted that this patch only gets rid of the hardcoded blocksize, in
preparation for actually setting the on-disk block size in the following
patch. The hard limit of constraining the block size to PAGE_SIZE still
exists until the next patch.

Signed-off-by: Jingbo Xu <jefflexu@linux.alibaba.com>
Reviewed-by: Gao Xiang <hsiangkao@linux.alibaba.com>
Reviewed-by: Yue Hu <huyue2@coolpad.com>
Reviewed-by: Chao Yu <chao@kernel.org>
Link: https://lore.kernel.org/r/20230313135309.75269-2-jefflexu@linux.alibaba.com
[ Gao Xiang: fold a patch to fix incorrect truncated offsets. ]
Link: https://lore.kernel.org/r/20230413035734.15457-1-zhujia.zj@bytedance.com
Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>

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erofs: get rid of a useless DBG_BUGON

`err` could be -EINTR and it should not be the case. Actually such
DBG_BUGON is useless.

Reviewed-by: Chao Yu <chao@kernel.org>
Link: https://lore.kernel.org/

erofs: get rid of a useless DBG_BUGON

`err` could be -EINTR and it should not be the case. Actually such
DBG_BUGON is useless.

Reviewed-by: Chao Yu <chao@kernel.org>
Link: https://lore.kernel.org/r/20230309053148.9223-2-hsiangkao@linux.alibaba.com
Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>

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erofs: get rid of z_erofs_do_map_blocks() forward declaration

The code can be neater without forward declarations. Let's
get rid of z_erofs_do_map_blocks() forward declaration.

Reviewed-by: Yue Hu

erofs: get rid of z_erofs_do_map_blocks() forward declaration

The code can be neater without forward declarations. Let's
get rid of z_erofs_do_map_blocks() forward declaration.

Reviewed-by: Yue Hu <huyue2@coolpad.com>
Reviewed-by: Chao Yu <chao@kernel.org>
Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>
Link: https://lore.kernel.org/r/20230204093040.97967-5-hsiangkao@linux.alibaba.com

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erofs: simplify iloc()

Actually we could pass in inodes directly to clean up all callers.
Also rename iloc() as erofs_iloc().

Link: https://lore.kernel.org/r/20230114150823.432069-1-xiang@kernel.or

erofs: simplify iloc()

Actually we could pass in inodes directly to clean up all callers.
Also rename iloc() as erofs_iloc().

Link: https://lore.kernel.org/r/20230114150823.432069-1-xiang@kernel.org
Reviewed-by: Yue Hu <huyue2@coolpad.com>
Reviewed-by: Jingbo Xu <jefflexu@linux.alibaba.com>
Reviewed-by: Chao Yu <chao@kernel.org>
Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>

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erofs/zmap.c: Fix incorrect offset calculation

Effective offset to add to length was being incorrectly calculated,
which resulted in iomap->length being set to 0, triggering a WARN_ON
in iomap_iter_

erofs/zmap.c: Fix incorrect offset calculation

Effective offset to add to length was being incorrectly calculated,
which resulted in iomap->length being set to 0, triggering a WARN_ON
in iomap_iter_done().

Fix that, and describe it in comments.

This was reported as a crash by syzbot under an issue about a warning
encountered in iomap_iter_done(), but unrelated to erofs.

C reproducer: https://syzkaller.appspot.com/text?tag=ReproC&x=1037a6b2880000
Kernel config: https://syzkaller.appspot.com/text?tag=KernelConfig&x=e2021a61197ebe02
Dashboard link: https://syzkaller.appspot.com/bug?extid=a8e049cd3abd342936b6

Reported-by: syzbot+a8e049cd3abd342936b6@syzkaller.appspotmail.com
Suggested-by: Gao Xiang <hsiangkao@linux.alibaba.com>
Signed-off-by: Siddh Raman Pant <code@siddh.me>
Reviewed-by: Gao Xiang <hsiangkao@linux.alibaba.com>
Reviewed-by: Chao Yu <chao@kernel.org>
Link: https://lore.kernel.org/r/20221209102151.311049-1-code@siddh.me
Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>

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erofs: validate the extent length for uncompressed pclusters

syzkaller reported a KASAN use-after-free:
https://syzkaller.appspot.com/bug?extid=2ae90e873e97f1faf6f2

The referenced fuzzed image actu

erofs: validate the extent length for uncompressed pclusters

syzkaller reported a KASAN use-after-free:
https://syzkaller.appspot.com/bug?extid=2ae90e873e97f1faf6f2

The referenced fuzzed image actually has two issues:
- m_pa == 0 as a non-inlined pcluster;
- The logical length is longer than its physical length.

The first issue has already been addressed. This patch addresses
the second issue by checking the extent length validity.

Reported-by: syzbot+2ae90e873e97f1faf6f2@syzkaller.appspotmail.com
Fixes: 02827e1796b3 ("staging: erofs: add erofs_map_blocks_iter")
Reviewed-by: Chao Yu <chao@kernel.org>
Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>
Link: https://lore.kernel.org/r/20221205150050.47784-2-hsiangkao@linux.alibaba.com

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erofs: fix missing unmap if z_erofs_get_extent_compressedlen() fails

Otherwise, meta buffers could be leaked.

Fixes: cec6e93beadf ("erofs: support parsing big pcluster compress indexes")
Reviewed-b

erofs: fix missing unmap if z_erofs_get_extent_compressedlen() fails

Otherwise, meta buffers could be leaked.

Fixes: cec6e93beadf ("erofs: support parsing big pcluster compress indexes")
Reviewed-by: Yue Hu <huyue2@coolpad.com>
Reviewed-by: Chao Yu <chao@kernel.org>
Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>
Link: https://lore.kernel.org/r/20221205150050.47784-1-hsiangkao@linux.alibaba.com

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erofs: use kmap_local_page() only for erofs_bread()

Convert all mapped erofs_bread() users to use kmap_local_page()
instead of kmap() or kmap_atomic().

Signed-off-by: Gao Xiang <hsiangkao@linux.ali

erofs: use kmap_local_page() only for erofs_bread()

Convert all mapped erofs_bread() users to use kmap_local_page()
instead of kmap() or kmap_atomic().

Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>
Reviewed-and-tested-by: Jingbo Xu <jefflexu@linux.alibaba.com>
Reviewed-by: Chao Yu <chao@kernel.org>
Link: https://lore.kernel.org/r/20221018105313.4940-1-hsiangkao@linux.alibaba.com
Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>

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erofs: fix illegal unmapped accesses in z_erofs_fill_inode_lazy()

Note that we are still accessing 'h_idata_size' and 'h_fragmentoff'
after calling erofs_put_metabuf(), that is not correct. Fix it.

erofs: fix illegal unmapped accesses in z_erofs_fill_inode_lazy()

Note that we are still accessing 'h_idata_size' and 'h_fragmentoff'
after calling erofs_put_metabuf(), that is not correct. Fix it.

Fixes: ab92184ff8f1 ("erofs: add on-disk compressed tail-packing inline support")
Fixes: b15b2e307c3a ("erofs: support on-disk compressed fragments data")
Signed-off-by: Yue Hu <huyue2@coolpad.com>
Reviewed-by: Gao Xiang <hsiangkao@linux.alibaba.com>
Reviewed-by: Chao Yu <chao@kernel.org>
Link: https://lore.kernel.org/r/20221005013528.62977-1-zbestahu@163.com
Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>

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erofs: clean up unnecessary code and comments

Some conditional macros and comments are useless.

Link: https://lore.kernel.org/r/20220927063607.54832-1-hsiangkao@linux.alibaba.com
Reviewed-by: Yue H

erofs: clean up unnecessary code and comments

Some conditional macros and comments are useless.

Link: https://lore.kernel.org/r/20220927063607.54832-1-hsiangkao@linux.alibaba.com
Reviewed-by: Yue Hu <huyue2@coolpad.com>
Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>

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erofs: fold in z_erofs_reload_indexes()

The name of this function looks not very accurate compared to it's
implementation and it's only a wrapper to erofs_read_metabuf(). So,
let's fold it directly

erofs: fold in z_erofs_reload_indexes()

The name of this function looks not very accurate compared to it's
implementation and it's only a wrapper to erofs_read_metabuf(). So,
let's fold it directly instead.

Signed-off-by: Yue Hu <huyue2@coolpad.com>
Reviewed-by: Gao Xiang <hsiangkao@linux.alibaba.com>
Link: https://lore.kernel.org/r/20220927032518.25266-1-zbestahu@gmail.com
Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>

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erofs: introduce partial-referenced pclusters

Due to deduplication for compressed data, pclusters can be partially
referenced with their prefixes.

Together with the user-space implementation, it en

erofs: introduce partial-referenced pclusters

Due to deduplication for compressed data, pclusters can be partially
referenced with their prefixes.

Together with the user-space implementation, it enables EROFS
variable-length global compressed data deduplication with rolling
hash.

Link: https://lore.kernel.org/r/20220923014915.4362-1-hsiangkao@linux.alibaba.com
Reviewed-by: Yue Hu <huyue2@coolpad.com>
Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>

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erofs: support on-disk compressed fragments data

Introduce on-disk compressed fragments data feature.

This approach adds a new field called `h_fragmentoff' in the per-file
compression header to ind

erofs: support on-disk compressed fragments data

Introduce on-disk compressed fragments data feature.

This approach adds a new field called `h_fragmentoff' in the per-file
compression header to indicate the fragment offset of each tail pcluster
or the whole file in the special packed inode.

Similar to ztailpacking, it will also find and record the 'headlcn'
of the tail pcluster when initializing per-inode zmap for making
follow-on requests more easy.

Signed-off-by: Yue Hu <huyue2@coolpad.com>
Reviewed-by: Gao Xiang <hsiangkao@linux.alibaba.com>
Link: https://lore.kernel.org/r/YzHKxcFTlHGgXeH9@B-P7TQMD6M-0146.local
Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>

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erofs: support interlaced uncompressed data for compressed files

Currently, uncompressed data is all handled in the shifted way, which
means we have to shift the whole on-disk plain pcluster to get

erofs: support interlaced uncompressed data for compressed files

Currently, uncompressed data is all handled in the shifted way, which
means we have to shift the whole on-disk plain pcluster to get the
logical data. However, since we are also using in-place I/O for
uncompressed data, data copy will be reduced a lot if pcluster is
recorded in the interlaced way as illustrated below:
_______________________________________________________________
| | | |_ tail part |_ head part _|
|<- blk0 ->| .. |<- blkn-2 ->|<- blkn-1 ->|

The logical data then becomes:
________________________________________________________
|_ head part _|_ blk0 _| .. |_ blkn-2 _|_ tail part _|

In addition, non-4k plain pclusters are also survived by the
interlaced way, which can be used for non-4k lclusters as well.

However, it's almost impossible to de-duplicate uncompressed data
in the interlaced way, therefore shifted uncompressed data is still
useful.

Signed-off-by: Yue Hu <huyue2@coolpad.com>
Reviewed-by: Gao Xiang <hsiangkao@linux.alibaba.com>
Link: https://lore.kernel.org/r/8369112678604fdf4ef796626d59b1fdd0745a53.1663898962.git.huyue2@coolpad.com
Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>

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erofs: avoid the potentially wrong m_plen for big pcluster

Actually, 'compressedlcs' stores compressed block count rather than
lcluster count. Therefore, the number of bits for shifting the count
sh

erofs: avoid the potentially wrong m_plen for big pcluster

Actually, 'compressedlcs' stores compressed block count rather than
lcluster count. Therefore, the number of bits for shifting the count
should be 'LOG_BLOCK_SIZE' rather than 'lclusterbits' although current
lcluster size is 4K.

The value of 'm_plen' will be wrong once we enable the non 4K-sized
lcluster.

Signed-off-by: Yue Hu <huyue2@coolpad.com>
Reviewed-by: Gao Xiang <hsiangkao@linux.alibaba.com>
Reviewed-by: Chao Yu <chao@kernel.org>
Link: https://lore.kernel.org/r/20220812060150.8510-1-huyue2@coolpad.com
Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>

show more ...

erofs: clean up z_erofs_extent_lookback

Avoid the unnecessary tail recursion since it can be converted into
a loop directly in order to prevent potential stack overflow.

It's a pretty straightforwa

erofs: clean up z_erofs_extent_lookback

Avoid the unnecessary tail recursion since it can be converted into
a loop directly in order to prevent potential stack overflow.

It's a pretty straightforward conversion.

Link: https://lore.kernel.org/r/20220310182743.102365-1-hsiangkao@linux.alibaba.com
Reviewed-by: Yue Hu <huyue2@coolpad.com>
Reviewed-by: Chao Yu <chao@kernel.org>
Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>

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