Changes in Kconfig

c37460cd9b2fcb61ec66b7eb4fde737e65ec2a56 - erofs: remove fscache backend entirely

Mon, 22 Jun 2026 03:36:22 +0200

erofs: remove fscache backend entirelyEROFS over fscache was introduced to provide image lazy pullingfunctionality. After the feature landed, the fscache subsystem madenetfs a new hard dependency, which is unexpected for a local filesystemand has an kernel-defined caching hierarchy which could be inflexiblecompared to the fanotify pre-content hooks. Therefore, this feature hasbeen deprecated for almost two years.As EROFS file-backed mounts and fanotify pre-content hooks both upstreamfor a while and already providing equivalent functionality (erofs-utilshas supported fanotify pre-content hooks), let's remove the fscachebackend now.The main application of this feature is Nydus [1], and they plan to moveto use fanotify pre-content hooks in the near future too.I hope this patch can be merged into Linux 7.2, which is also motivatedby newly found implementation issues [2][3] that are not worthinvestigating given the deprecation and limited development resources.The associated fscache/cachefiles cleanup patch will follow separatelythrough the vfs tree (netfs) later: it seems fine since the codebase isisolated by CONFIG_CACHEFILES_ONDEMAND.[1] https://github.com/dragonflyoss/nydus/blob/v2.1.0/docs/nydus-fscache.md[2] https://github.com/dragonflyoss/nydus/pull/1824[3] https://lore.kernel.org/r/20260619135800.1594811-1-michael.bommarito@gmail.comAcked-by: Jingbo Xu Signed-off-by: Gao Xiang List of files: /linux/fs/erofs/Kconfig

938c418422c4b08523ae39aebbd828428dcfefd2 - erofs: update the Kconfig description

Mon, 23 Mar 2026 10:48:57 +0100

erofs: update the Kconfig descriptionRefine the description to better highlight its features and use cases.In addition, add instructions for building it as a module and clarifythe compression option.Reviewed-by: Chao Yu Signed-off-by: Gao Xiang List of files: /linux/fs/erofs/Kconfig

8f2fb72fd17eecd5a47c73ce7e228d157e613b80 - erofs: update compression algorithm status

Wed, 04 Feb 2026 10:37:31 +0100

erofs: update compression algorithm statusThe following changes are proposed in the upcoming Linux 7.0: - Enable LZMA support by default, as it's already in use by Fedora 42/43 and some Android vendors for minimal filesystem sizes; - Promote DEFLATE and Zstandard out of EXPERIMENTAL status, given that they have been landed and well-tested for over a year and are already ready for general use.Signed-off-by: Gao Xiang List of files: /linux/fs/erofs/Kconfig

e0bf7d1c074dc4252223ae897560345ccc24100d - erofs: support user-defined fingerprint name

Fri, 23 Jan 2026 02:31:25 +0100

erofs: support user-defined fingerprint nameWhen creating the EROFS image, users can specify the fingerprint name.This is to prepare for the upcoming inode page cache share.Signed-off-by: Hongzhen Luo Signed-off-by: Hongbo Li Reviewed-by: Gao Xiang Signed-off-by: Gao Xiang List of files: /linux/fs/erofs/Kconfig

74da24f0ac9b8aabfb8d7feeba6c32ddff3065e0 - erofs: Do not select tristate symbols from bool symbols

Wed, 30 Jul 2025 14:44:49 +0200

erofs: Do not select tristate symbols from bool symbolsThe EROFS filesystem has many configurable options, controlled throughboolean Kconfig symbols. When enabled, these options may need to enableadditional library functionality elsewhere. Currently this is done byselecting the symbol for the additional functionality. However, ifEROFS_FS itself is modular, and the target symbol is a tristate symbol,the additional functionality is always forced built-in.Selecting tristate symbols from a tristate symbol does keep modulartransitivity. Hence fix this by moving selects of tristate symbols tothe main EROFS_FS symbol.Signed-off-by: Geert Uytterhoeven Reviewed-by: Gao Xiang Link: https://lore.kernel.org/r/da1b899e511145dd43fd2d398f64b2e03c6a39e7.1753879351.git.geert+renesas@glider.beSigned-off-by: Gao Xiang List of files: /linux/fs/erofs/Kconfig

5e0bf36fd156b8d9b09f8481ee6daa6cdba1b064 - erofs: fix build error with CONFIG_EROFS_FS_ZIP_ACCEL=y

Fri, 18 Jul 2025 05:30:39 +0200

erofs: fix build error with CONFIG_EROFS_FS_ZIP_ACCEL=yfix build err: ld.lld: error: undefined symbol: crypto_req_done referenced by decompressor_crypto.c fs/erofs/decompressor_crypto.o:(z_erofs_crypto_decompress) in archive vmlinux.a referenced by decompressor_crypto.c fs/erofs/decompressor_crypto.o:(z_erofs_crypto_decompress) in archive vmlinux.a ld.lld: error: undefined symbol: crypto_acomp_decompress referenced by decompressor_crypto.c fs/erofs/decompressor_crypto.o:(z_erofs_crypto_decompress) in archive vmlinux.a ld.lld: error: undefined symbol: crypto_alloc_acomp referenced by decompressor_crypto.c fs/erofs/decompressor_crypto.o:(z_erofs_crypto_enable_engine) in archive vmlinux.aReported-by: kernel test robot Closes: https://lore.kernel.org/oe-kbuild-all/202507161032.QholMPtn-lkp@intel.com/Fixes: b4a29efc5146 ("erofs: support DEFLATE decompression by using Intel QAT")Signed-off-by: Bo Liu (OpenAnolis) Link: https://lore.kernel.org/r/20250718033039.3609-1-liubo03@inspur.comReviewed-by: Gao Xiang Signed-off-by: Gao Xiang List of files: /linux/fs/erofs/Kconfig

b4a29efc51461edf1a02e9da656d4480cabd24b0 - erofs: support DEFLATE decompression by using Intel QAT

Thu, 22 May 2025 11:49:31 +0200

erofs: support DEFLATE decompression by using Intel QATThis patch introduces the use of the Intel QAT to offload EROFS datadecompression, aiming to improve the decompression performance.A 285MiB dataset is used with the following command to create EROFSimages with different cluster sizes: $ mkfs.erofs -zdeflate,level=9 -C{4096,16384,65536,131072,262144}Fio is used to test the following read patterns: $ fio -filename=testfile -bs=4k -rw=read -name=job1 $ fio -filename=testfile -bs=4k -rw=randread -name=job1 $ fio -filename=testfile -bs=4k -rw=randread --io_size=14m -name=job1Here are some performance numbers for reference:Processors: Intel(R) Xeon(R) 6766E (144 cores)Memory: 512 GiB|-----------------------------------------------------------------------------|| | Cluster size | sequential read | randread | small randread(5%) ||-----------|--------------|-----------------|-----------|--------------------|| Intel QAT | 4096 | 538 MiB/s | 112 MiB/s | 20.76 MiB/s || Intel QAT | 16384 | 699 MiB/s | 158 MiB/s | 21.02 MiB/s || Intel QAT | 65536 | 917 MiB/s | 278 MiB/s | 20.90 MiB/s || Intel QAT | 131072 | 1056 MiB/s | 351 MiB/s | 23.36 MiB/s || Intel QAT | 262144 | 1145 MiB/s | 431 MiB/s | 26.66 MiB/s || deflate | 4096 | 499 MiB/s | 108 MiB/s | 21.50 MiB/s || deflate | 16384 | 422 MiB/s | 125 MiB/s | 18.94 MiB/s || deflate | 65536 | 452 MiB/s | 159 MiB/s | 13.02 MiB/s || deflate | 131072 | 452 MiB/s | 177 MiB/s | 11.44 MiB/s || deflate | 262144 | 466 MiB/s | 194 MiB/s | 10.60 MiB/s |Signed-off-by: Bo Liu Reviewed-by: Gao Xiang Link: https://lore.kernel.org/r/20250522094931.28956-1-liubo03@inspur.com[ Gao Xiang: refine the commit message. ]Signed-off-by: Gao Xiang List of files: /linux/fs/erofs/Kconfig

b261d2222063a9a8b9ec284244c285f2998ee01e - lib/crc: remove CONFIG_LIBCRC32C

Wed, 02 Apr 2025 00:16:00 +0200

lib/crc: remove CONFIG_LIBCRC32CNow that LIBCRC32C does nothing besides select CRC32, make every optionthat selects LIBCRC32C instead select CRC32 directly. Then removeLIBCRC32C.Reviewed-by: Christoph Hellwig Reviewed-by: "Martin K. Petersen" Acked-by: Ard Biesheuvel Link: https://lore.kernel.org/r/20250401221600.24878-8-ebiggers@kernel.orgSigned-off-by: Eric Biggers List of files: /linux/fs/erofs/Kconfig

0f24e3c05afeac905a9df557264cc48f3363ab47 - erofs: enable 48-bit layout support

Mon, 10 Mar 2025 10:56:25 +0100

erofs: enable 48-bit layout supportBoth 48-bit block addressing and encoded extents are implemented,let's enable them formally.Signed-off-by: Gao Xiang Acked-by: Chao Yu Link: https://lore.kernel.org/r/20250310095625.2623817-1-hsiangkao@linux.alibaba.com List of files: /linux/fs/erofs/Kconfig

0d442ce0b3027e99491520a3a8585e8c4ffd79dc - erofs: mark experimental fscache backend deprecated

Fri, 30 Aug 2024 05:28:40 +0200

erofs: mark experimental fscache backend deprecatedAlthough fscache is still described as "General Filesystem Caching" fornetwork filesystems and other things such as ISO9660 filesystems, it hasactually become a part of netfslib recently, which was unexpected at thetime when "EROFS over fscache" proposed (2021) since EROFS is entirely adisk filesystem and the dependency is redundant.Mark it deprecated and it will be removed after "fanotify pre-contenthooks" lands, which will provide the same functionality for EROFS.Reviewed-by: Sandeep Dhavale Reviewed-by: Chao Yu Signed-off-by: Gao Xiang Link: https://lore.kernel.org/r/20240830032840.3783206-4-hsiangkao@linux.alibaba.com List of files: /linux/fs/erofs/Kconfig

fb176750266a3d7f42ebdcf28e8ba40350b27847 - erofs: add file-backed mount support

Fri, 30 Aug 2024 05:28:37 +0200

erofs: add file-backed mount supportIt actually has been around for years: For containers and other sandboxuse cases, there will be thousands (and even more) of authenticated(sub)images running on the same host, unlike OS images.Of course, all scenarios can use the same EROFS on-disk format, butbdev-backed mounts just work well for OS images since golden data isdumped into real block devices. However, it's somewhat hard forcontainer runtimes to manage and isolate so many unnecessary virtualblock devices safely and efficiently [1]: they just look like a burdento orchestrators and file-backed mounts are preferred indeed. Therewere already enough attempts such as Incremental FS, the originalComposeFS and PuzzleFS acting in the same way for immutable fses. Asfor current EROFS users, ComposeFS, containerd and Android APEXs willbe directly benefited from it.On the other hand, previous experimental feature "erofs over fscache"was once also intended to provide a similar solution (inspired byIncremental FS discussion [2]), but the following facts show file-backedmounts will be a better approach: - Fscache infrastructure has recently been moved into new Netfslib which is an unexpected dependency to EROFS really, although it originally claims "it could be used for caching other things such as ISO9660 filesystems too." [3] - It takes an unexpectedly long time to upstream Fscache/Cachefiles enhancements. For example, the failover feature took more than one year, and the deamonless feature is still far behind now; - Ongoing HSM "fanotify pre-content hooks" [4] together with this will perfectly supersede "erofs over fscache" in a simpler way since developers (mainly containerd folks) could leverage their existing caching mechanism entirely in userspace instead of strictly following the predefined in-kernel caching tree hierarchy.After "fanotify pre-content hooks" lands upstream to provide the samefunctionality, "erofs over fscache" will be removed then (as an EROFSinternal improvement and EROFS will not have to bother with on-demandfetching and/or caching improvements anymore.)[1] https://github.com/containers/storage/pull/2039[2] https://lore.kernel.org/r/CAOQ4uxjbVxnubaPjVaGYiSwoGDTdpWbB=w_AeM6YM=zVixsUfQ@mail.gmail.com[3] https://docs.kernel.org/filesystems/caching/fscache.html[4] https://lore.kernel.org/r/cover.1723670362.git.josef@toxicpanda.comCloses: https://github.com/containers/composefs/issues/144Reviewed-by: Sandeep Dhavale Reviewed-by: Chao Yu Signed-off-by: Gao Xiang Link: https://lore.kernel.org/r/20240830032840.3783206-1-hsiangkao@linux.alibaba.com List of files: /linux/fs/erofs/Kconfig

7c35de4df1056a5a1fb4de042197b8f5b1033b61 - erofs: Zstandard compression support

Thu, 09 May 2024 01:44:53 +0200

erofs: Zstandard compression supportAdd Zstandard compression as the 4th supported algorithm since itbecomes more popular now and some end users have asked this forquite a while [1][2].Each EROFS physical cluster contains only one valid standardZstandard frame as described in [3] so that decompression can beperformed on a per-pcluster basis independently.Currently, it just leverages multi-call stream decompression APIs withinternal sliding window buffers. One-shot or bufferless decompressioncould be implemented later for even better performance if needed.[1] https://github.com/erofs/erofs-utils/issues/6[2] https://lore.kernel.org/r/Y08h+z6CZdnS1XBm@B-P7TQMD6M-0146.lan[3] https://www.rfc-editor.org/rfc/rfc8478.txtAcked-by: Chao Yu Signed-off-by: Gao Xiang Link: https://lore.kernel.org/r/20240508234453.17896-1-xiang@kernel.org List of files: /linux/fs/erofs/Kconfig

915cd30cdea8811cddd8f59e57dd9dd0a814b76c - netfs, fscache: Combine fscache with netfs

Mon, 20 Nov 2023 16:55:18 +0100

netfs, fscache: Combine fscache with netfsNow that the fscache code is moved to be colocated with the netfslib codeso that they combined into one module, do the combining.Signed-off-by: David Howells Reviewed-by: Jeff Layton cc: Christian Brauner cc: linux-fsdevel@vger.kernel.orgcc: linux-cachefs@redhat.comcc: linux-nfs@vger.kernel.org,cc: linux-erofs@lists.ozlabs.org List of files: /linux/fs/erofs/Kconfig

62b241efff99fc4d88a86f1c67c7516e31f432a3 - MAINTAINERS: erofs: add EROFS webpage

Fri, 17 Nov 2023 09:53:29 +0100

MAINTAINERS: erofs: add EROFS webpageAdd a new `W:` field of the EROFS entry points to the documentationsite at .In addition, update the in-tree documentation and Kconfig too.Signed-off-by: Gao Xiang Link: https://lore.kernel.org/r/20231117085329.1624223-1-hsiangkao@linux.alibaba.com List of files: /linux/fs/erofs/Kconfig

798eecaea0f0366306cbc76986a83041a7e8669f - erofs: don't warn MicroLZMA format anymore

Sat, 21 Oct 2023 04:01:37 +0200

erofs: don't warn MicroLZMA format anymoreThe LZMA algorithm support has been landed for more than one year sinceLinux 5.16. Besides, the new XZ Utils 5.4 has been available in mostLinux distributions.Reviewed-by: Chao Yu Signed-off-by: Gao Xiang Link: https://lore.kernel.org/r/20231021020137.1646959-1-hsiangkao@linux.alibaba.com List of files: /linux/fs/erofs/Kconfig

fd73a4395d477ae134f319f7368a9f8a6264fd8b - erofs: boost negative xattr lookup with bloom filter

Sat, 22 Jul 2023 11:45:38 +0200

erofs: boost negative xattr lookup with bloom filterOptimise the negative xattr lookup with bloom filter.The bit value for the bloom filter map has a reverse semantics forcompatibility. That is, the bit value of 0 indicates existence, whilethe bit value of 1 indicates the absence of corresponding xattr.The initial version is _only_ enabled when xattr_filter_reserved iszero. The filter map internals may change in the future, in which casethe reserved flag will be set non-zero and we don't need bothering thecompatible bits again at that time. For now disable the optimization ifthis reserved flag is non-zero.Signed-off-by: Jingbo Xu Reviewed-by: Gao Xiang Reviewed-by: Chao Yu Link: https://lore.kernel.org/r/20230722094538.11754-3-jefflexu@linux.alibaba.comSigned-off-by: Gao Xiang List of files: /linux/fs/erofs/Kconfig

ffa09b3bd02427ab631f0c1b64714ce6fc885f61 - erofs: DEFLATE compression support

Thu, 10 Aug 2023 17:48:59 +0200

erofs: DEFLATE compression supportAdd DEFLATE compression as the 3rd supported algorithm.DEFLATE is a popular generic-purpose compression algorithm for quitelong time (many advanced formats like gzip, zlib, zip, png are allbased on that) as Apple documentation written "If you requireinteroperability with non-Apple devices, use COMPRESSION_ZLIB. [1]".Due to its popularity, there are several hardware on-market DEFLATEaccelerators, such as (s390) DFLTCC, (Intel) IAA/QAT, (HiSilicon) ZIPaccelerator, etc. In addition, there are also several high-performenceIP cores and even open-source FPGA approches available for DEFLATE.Therefore, it's useful to support DEFLATE compression in order to finda way to utilize these accelerators for asynchronous I/Os and getbenefits from these later.Besides, it's a good choice to trade off between compression ratiosand performance compared to LZ4 and LZMA. The DEFLATE core format issimple as well as easy to understand, therefore the code size of itsdecompressor is small even for the bootloader use cases. The runtimememory consumption is quite limited too (e.g. 32K + ~7K for each zlibstream). As usual, EROFS ourperforms similar approaches too.Alternatively, DEFLATE could still be used for some specific filessince EROFS supports multiple compression algorithms in one image.[1] https://developer.apple.com/documentation/compression/compression_algorithmReviewed-by: Chao Yu Signed-off-by: Gao Xiang Link: https://lore.kernel.org/r/20230810154859.118330-1-hsiangkao@linux.alibaba.com List of files: /linux/fs/erofs/Kconfig

cf7f2732b4b83026842832e7e4e04bf862108ac2 - erofs: use HIPRI by default if per-cpu kthreads are enabled

Mon, 22 May 2023 11:21:41 +0200

erofs: use HIPRI by default if per-cpu kthreads are enabledAs Sandeep shown [1], high priority RT per-cpu kthreads aretypically helpful for Android scenarios to minimize the schedulinglatencies.Switch EROFS_FS_PCPU_KTHREAD_HIPRI on by default ifEROFS_FS_PCPU_KTHREAD is on since it's the typical use cases forEROFS_FS_PCPU_KTHREAD.Also clean up unneeded sched_set_normal().[1] https://lore.kernel.org/r/CAB=BE-SBtO6vcoyLNA9F-9VaN5R0t3o_Zn+FW8GbO6wyUqFneQ@mail.gmail.comReviewed-by: Yue Hu Reviewed-by: Sandeep Dhavale Reviewed-by: Chao Yu Signed-off-by: Gao Xiang Link: https://lore.kernel.org/r/20230522092141.124290-1-hsiangkao@linux.alibaba.com List of files: /linux/fs/erofs/Kconfig

3fffb589b9a6e331e39cb75373ee7691acd7b109 - erofs: add per-cpu threads for decompression as an option

Wed, 08 Feb 2023 10:33:22 +0100

erofs: add per-cpu threads for decompression as an optionUsing per-cpu thread pool we can reduce the scheduling latency comparedto workqueue implementation. With this patch scheduling latency andvariation is reduced as per-cpu threads are high priority kthread_workers.The results were evaluated on arm64 Android devices running 5.10 kernel.The table below shows resulting improvements of total scheduling latencyfor the same app launch benchmark runs with 50 iterations. Schedulinglatency is the latency between when the task (workqueue kworker vskthread_worker) became eligible to run to when it actually startedrunning.+-------------------------+-----------+----------------+---------+| | workqueue | kthread_worker | diff |+-------------------------+-----------+----------------+---------+| Average (us) | 15253 | 2914 | -80.89% || Median (us) | 14001 | 2912 | -79.20% || Minimum (us) | 3117 | 1027 | -67.05% || Maximum (us) | 30170 | 3805 | -87.39% || Standard deviation (us) | 7166 | 359 | |+-------------------------+-----------+----------------+---------+Background: Boot times and cold app launch benchmarks are veryimportant to the Android ecosystem as they directly translate toresponsiveness from user point of view. While EROFS providesa lot of important features like space savings, we saw someperformance penalty in cold app launch benchmarks in few scenarios.Analysis showed that the significant variance was coming from thescheduling cost while decompression cost was more or less the same.Having per-cpu thread pool we can see from the above table that thisvariation is reduced by ~80% on average. This problem was discussedat LPC 2022. Link to LPC 2022 slides and talk at [1][1] https://lpc.events/event/16/contributions/1338/[ Gao Xiang: At least, we have to add this until WQ_UNBOUND workqueue issue [2] on many arm64 devices is resolved. ][2] https://lore.kernel.org/r/CAJkfWY490-m6wNubkxiTPsW59sfsQs37Wey279LmiRxKt7aQYg@mail.gmail.comSigned-off-by: Sandeep Dhavale Signed-off-by: Gao Xiang Link: https://lore.kernel.org/r/20230208093322.75816-1-hsiangkao@linux.alibaba.com List of files: /linux/fs/erofs/Kconfig

c6be2bd0a5dd91f98d6b5d2df2c79bc32993352c - erofs: register fscache volume

Mon, 25 Apr 2022 14:21:33 +0200

erofs: register fscache volumeA new fscache based mode is going to be introduced for erofs, in whichcase on-demand read semantics is implemented through fscache.As the first step, register fscache volume for each erofs filesystem.That means, data blobs can not be shared among erofs filesystems. In thefollowing iteration, we are going to introduce the domain semantics, inwhich case several erofs filesystems can belong to one domain, and datablobs can be shared among these erofs filesystems of one domain.Signed-off-by: Jeffle Xu Reviewed-by: Gao Xiang Link: https://lore.kernel.org/r/20220425122143.56815-12-jefflexu@linux.alibaba.comAcked-by: Chao Yu Signed-off-by: Gao Xiang List of files: /linux/fs/erofs/Kconfig