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| author |   Gao Xiang <hsiangkao@linux.alibaba.com> | 2021-08-20 18:00:18 +0800 |
|---|---|---|
| committer | Gao Xiang <hsiangkao@linux.alibaba.com> | 2021-08-20 22:38:01 +0800 |
| commit | 2a9dc7a8fec6ca287e2c038f9441e24269e10b5f (patch) | |
| tree | 69cc5664ddef0dd151f1c9fb3d573cb36640a42b /Documentation/filesystems | |
| parent | erofs: add fiemap support with iomap (diff) | |
| download | linux-dev-2a9dc7a8fec6ca287e2c038f9441e24269e10b5f.tar.xz linux-dev-2a9dc7a8fec6ca287e2c038f9441e24269e10b5f.zip | |
erofs: introduce chunk-based file on-disk format
Currently, uncompressed data except for tail-packing inline is
consecutive on disk.
In order to support chunk-based data deduplication, add a new
corresponding inode data layout.
In the future, the data source of chunks can be either (un)compressed.
Link: https://lore.kernel.org/r/20210820100019.208490-1-hsiangkao@linux.alibaba.com
Reviewed-by: Liu Bo <bo.liu@linux.alibaba.com>
Reviewed-by: Chao Yu <chao@kernel.org>
Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>
Diffstat (limited to 'Documentation/filesystems')
| -rw-r--r-- | Documentation/filesystems/erofs.rst | 16 |
1 files changed, 14 insertions, 2 deletions
diff --git a/Documentation/filesystems/erofs.rst b/Documentation/filesystems/erofs.rst index 868e3972227f..b97579b7d8fb 100644 --- a/Documentation/filesystems/erofs.rst +++ b/Documentation/filesystems/erofs.rst @@ -156,13 +156,14 @@ may not. All metadatas can be now observed in two different spaces (views): Xattrs, extents, data inline are followed by the corresponding inode with proper alignment, and they could be optional for different data mappings. - _currently_ total 4 valid data mappings are supported: + _currently_ total 5 data layouts are supported: == ==================================================================== 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+). + 3 fixed-sized output data compression (with compacted indexes, v5.3+); + 4 chunk-based file (v5.15+). == ==================================================================== The size of the optional xattrs is indicated by i_xattr_count in inode @@ -213,6 +214,17 @@ Note that apart from the offset of the first filename, nameoff0 also indicates the total number of directory entries in this block since it is no need to introduce another on-disk field at all. +Chunk-based file +---------------- +In order to support chunk-based data deduplication, a new inode data layout has +been supported since Linux v5.15: Files are split in equal-sized data chunks +with ``extents`` area of the inode metadata indicating how to get the chunk +data: these can be simply as a 4-byte block address array or in the 8-byte +chunk index form (see struct erofs_inode_chunk_index in erofs_fs.h for more +details.) + +By the way, chunk-based files are all uncompressed for now. + Data compression ---------------- EROFS implements LZ4 fixed-sized output compression which generates fixed-sized |