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| author | Gao Xiang <gaoxiang25@huawei.com> | 2019-12-07 05:37:26 +0300 |
|---|---|---|
| committer | Gao Xiang <gaoxiang25@huawei.com> | 2019-12-08 16:37:01 +0300 |
| commit | ffafde478309af01b2a495ecaf203125abfb35bd (patch) | |
| tree | 4ec6d82bbd7d9c60dbcbadd3abbead92732fc8c7 /Documentation/filesystems/erofs.txt | |
| parent | 926d1650176448d7684b991fbe1a5b1a8289e97c (diff) | |
| download | linux-ffafde478309af01b2a495ecaf203125abfb35bd.tar.xz | |
erofs: update documentation
Some on-disk structures, fields have been renamed in v5.4,
the corresponding document should be updated as well.
Also fix misrespresentation of file time and words about
fixed-sized output compression, data inline, etc.
Link: https://lore.kernel.org/r/20191207025509.6614-1-hsiangkao@aol.com/
Signed-off-by: Gao Xiang <gaoxiang25@huawei.com>
Diffstat (limited to 'Documentation/filesystems/erofs.txt')
| -rw-r--r-- | Documentation/filesystems/erofs.txt | 27 |
1 files changed, 14 insertions, 13 deletions
diff --git a/Documentation/filesystems/erofs.txt b/Documentation/filesystems/erofs.txt index b0c085326e2e..db6d39c3ae71 100644 --- a/Documentation/filesystems/erofs.txt +++ b/Documentation/filesystems/erofs.txt @@ -24,11 +24,11 @@ Here is the main features of EROFS: - Metadata & data could be mixed by design; - 2 inode versions for different requirements: - v1 v2 + compact (v1) extended (v2) Inode metadata size: 32 bytes 64 bytes Max file size: 4 GB 16 EB (also limited by max. vol size) Max uids/gids: 65536 4294967296 - File creation time: no yes (64 + 32-bit timestamp) + File change time: no yes (64 + 32-bit timestamp) Max hardlinks: 65536 4294967296 Metadata reserved: 4 bytes 14 bytes @@ -39,7 +39,7 @@ Here is the main features of EROFS: - Support POSIX.1e ACLs by using xattrs; - Support transparent file compression as an option: - LZ4 algorithm with 4 KB fixed-output compression for high performance; + LZ4 algorithm with 4 KB fixed-sized output compression for high performance. The following git tree provides the file system user-space tools under development (ex, formatting tool mkfs.erofs): @@ -85,7 +85,7 @@ All data areas should be aligned with the block size, but metadata areas may not. All metadatas can be now observed in two different spaces (views): 1. Inode metadata space Each valid inode should be aligned with an inode slot, which is a fixed - value (32 bytes) and designed to be kept in line with v1 inode size. + value (32 bytes) and designed to be kept in line with compact inode size. Each inode can be directly found with the following formula: inode offset = meta_blkaddr * block_size + 32 * nid @@ -117,10 +117,10 @@ may not. All metadatas can be now observed in two different spaces (views): |-> aligned with 4B Inode could be 32 or 64 bytes, which can be distinguished from a common - field which all inode versions have -- i_advise: + field which all inode versions have -- i_format: __________________ __________________ - | i_advise | | i_advise | + | i_format | | i_format | |__________________| |__________________| | ... | | ... | | | | | @@ -129,12 +129,13 @@ may not. All metadatas can be now observed in two different spaces (views): |__________________| 64 bytes Xattrs, extents, data inline are followed by the corresponding inode with - proper alignes, and they could be optional for different data mappings, - _currently_ there are totally 3 valid data mappings supported: + proper alignment, and they could be optional for different data mappings. + _currently_ total 4 valid data mappings are supported: - 1) flat file data without data inline (no extent); - 2) fixed-output size data compression (must have extents); - 3) flat file data with tail-end data inline (no extent); + 0 flat file data without data inline (no extent); + 1 fixed-sized output data compression (with non-compacted indexes); + 2 flat file data with tail packing data inline (no extent); + 3 fixed-sized output data compression (with compacted indexes, v5.3+). The size of the optional xattrs is indicated by i_xattr_count in inode header. Large xattrs or xattrs shared by many different files can be @@ -182,8 +183,8 @@ introduce another on-disk field at all. Compression ----------- -Currently, EROFS supports 4KB fixed-output clustersize transparent file -compression, as illustrated below: +Currently, EROFS supports 4KB fixed-sized output transparent file compression, +as illustrated below: |---- Variant-Length Extent ----|-------- VLE --------|----- VLE ----- clusterofs clusterofs clusterofs |