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>

diff --git a/Documentation/filesystems/erofs.txt b/Documentation/filesystems/erofs.txt
index b0c085326e2e68f4ead9063af48beeda0b48dcf9..db6d39c3ae715ee90b876c4660346581f3b67171 100644 (file)
--- 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