It still does in-place I/O decompression
for the rest compressed physical clusters.
========== =============================================
+dax={always,never} Use direct access (no page cache). See
+ Documentation/filesystems/dax.rst.
+dax A legacy option which is an alias for ``dax=always``.
=================== =========================================================
On-disk details
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
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