Merge tag 'erofs-for-5.15-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/xiang/erofs

Pull erofs updates from Gao Xiang:
 "In this cycle, direct I/O and fsdax support for uncompressed files are
  now added in order to avoid double-caching for loop device and VM
  container use cases. All uncompressed cases are now turned into iomap
  infrastructure, which looks much simpler and cleaner.

  In addition, fiemap support is added for both (un)compressed files by
  using iomap infrastructure as well so end users can easily get file
  distribution. We've also added chunk-based uncompressed files support
  for data deduplication as the next step of VM container use cases.

  Summary:

   - support direct I/O for all uncompressed files

   - support fsdax for non-tailpacking regular files

   - use iomap infrastructure for all uncompressed cases

   - support fiemap for both (un)compressed files

   - introduce chunk-based files for chunk deduplication

   - some cleanups"

* tag 'erofs-for-5.15-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/xiang/erofs:
  erofs: fix double free of 'copied'
  erofs: support reading chunk-based uncompressed files
  erofs: introduce chunk-based file on-disk format
  erofs: add fiemap support with iomap
  erofs: add support for the full decompressed length
  erofs: remove the mapping parameter from erofs_try_to_free_cached_page()
  erofs: directly use wrapper erofs_page_is_managed() when shrinking
  erofs: convert all uncompressed cases to iomap
  erofs: dax support for non-tailpacking regular file
  erofs: iomap support for non-tailpacking DIO

1 files changed, 17 insertions, 2 deletions

diff --git a/Documentation/filesystems/erofs.rst b/Documentation/filesystems/erofs.rst
index 832839fcf4c3..b97579b7d8fb 100644
--- a/Documentation/filesystems/erofs.rst
+++ b/Documentation/filesystems/erofs.rst
@@ -84,6 +84,9 @@ cache_strategy=%s      Select a strategy for cached decompression from now on:
                                    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
@@ -153,13 +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
@@ -210,6 +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