EROFS

EROFS (Enhanced Read-Only File System) is a lightweight read-only file system initially developed by Huawei for the Linux kernel.

EROFS
Developer(s)Huawei
Full nameEnhanced Read-Only File System
IntroducedNovember 24, 2019 (2019-11-24) with Linux 5.4
Limits
Max. file size
Max. number of filesDepends on volume size
Max. filename length255 bytes
Features
Dates recordedFile change time (extended only)[1]
Date resolution1 ns
AttributesPOSIX, xattr
File system permissionsPOSIX, ACL
Transparent compressionYes (LZ4)[1]
Other
Supported operating systemsLinux

EROFS aims to provide a solution to save storage space by using transparent compression for scenarios which need high-performance read-only requirements on their devices with limited hardware resources, e.g. smartphones like Android.[2][3] All of Huawei's new products shipped with EMUI 9.0.1 or later used EROFS,[4] and it was promoted as one of the key features of EMUI 9.1.[5]

The file system was formally merged into the mainline kernel with Linux kernel v5.4.[6]

Features

The file system has two different inode on-disk layouts. One is compacted, and the other is extended.[1]

  • Little-endian on-disk design[1]
  • 4KB block size and 32-bit block address, which limits the total possible capacity of a EROFS filesystem to 16 TB.[1]
  • Metadata and data could be mixed by tail-packing inline data technology[1]
  • Support POSIX attributes and permissions, xattr and ACL[1]
  • Fixed-output transparent compression with LZ4 for relative higher compression ratio[1]
  • In-place decompression for higher sequential read [7][8]

See also

References
  1. Gao Xiang. "erofs.txt". git.kernel.org. Retrieved 2020-12-03.
  2. Michael Larabel (2018-11-19). "There Is Finally A User-Space Utility To Make EROFS Linux File-Systems". Phoronix. Phoronix. Retrieved 2018-12-13.
  3. Xiang, Gao (2018-05-31). "erofs: introduce erofs file system". Linux kernel (Mailing list). Retrieved 2018-12-13.
  4. Xiang, Gao (2019-07-04). "erofs: promote erofs from staging". Linux kernel (Mailing list). Retrieved 2019-09-03.
  5. "EMUI 9.1, the Intelligent Android OS". HUAWEI Global. Huawei Technologies. Retrieved 2019-09-03.
  6. corbet (2019-11-25). "The 5.4 kernel has been released". LWN.net. Retrieved 2019-12-01.
  7. "staging: erofs: introduce LZ4 decompression inplace". Retrieved 2020-12-03.
  8. "staging: erofs: integrate decompression inplace". Retrieved 2020-12-03.
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