[PATCH 1/2] erofs-utils: README: trivial updates

[PATCH 1/2] erofs-utils: README: trivial updates

[Gao Xiang]

- update erofs naming to EROFS;
- add some words about compression levels;
- add more description about legacy EROFS images.

Signed-off-by: Gao Xiang <xiang@kernel.org>
---
 README | 29 ++++++++++++++++++-----------
 1 file changed, 18 insertions(+), 11 deletions(-)

diff --git a/README b/README
index b57550b2a09e..bcf30e11aa52 100644
--- a/README
+++ b/README
@@ -1,7 +1,7 @@
 erofs-utils
 ===========
 
-erofs-utils includes user-space tools for erofs filesystem.
+erofs-utils includes user-space tools for EROFS filesystem.
 Currently mkfs.erofs and erofsfuse (experimental) are available.
 
 Dependencies & build
@@ -50,7 +50,7 @@ as well.
 mkfs.erofs
 ----------
 
-two main kinds of erofs images can be generated: (un)compressed.
+two main kinds of EROFS images can be generated: (un)compressed.
 
  - For uncompressed images, there will be none of compression
    files in these images. However, it can decide whether the tail
@@ -61,8 +61,8 @@ two main kinds of erofs images can be generated: (un)compressed.
    saved with compression. If not, fallback to an uncompressed
    file.
 
-How to generate erofs images
-~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+How to generate EROFS images (Linux 5.3+)
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
 Currently lz4 and lz4hc are available for compression, e.g.
  $ mkfs.erofs -zlz4hc foo.erofs.img foo/
@@ -70,17 +70,24 @@ Currently lz4 and lz4hc are available for compression, e.g.
 Or leave all files uncompressed as an option:
  $ mkfs.erofs foo.erofs.img foo/
 
-How to generate legacy erofs images
-~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+In addition, you could specify a higher compression level to get a
+(slightly) better compression ratio than the default level, e.g.
+ $ mkfs.erofs -zlz4hc,12 foo.erofs.img foo/
+
+How to generate legacy EROFS images (Linux 4.19+)
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
 Decompression inplace and compacted indexes have been introduced in
 linux-5.3, which are not forward-compatible with older kernels.
 
-In order to generate _legacy_ erofs images for old kernels,
+In order to generate _legacy_ EROFS images for old kernels,
 consider adding "-E legacy-compress" to the command line, e.g.
 
  $ mkfs.erofs -E legacy-compress -zlz4hc foo.erofs.img foo/
 
+For Linux kernel >= 5.3, legacy EROFS images are _NOT recommended_
+due to runtime performance loss compared with non-legacy images.
+
 Obsoleted erofs.mkfs
 ~~~~~~~~~~~~~~~~~~~~
 
@@ -94,7 +101,7 @@ PLEASE NOTE: This version is highly _NOT recommended_ now.
 erofsfuse (experimental, unstable)
 ----------------------------------
 
-erofsfuse is introduced to support erofs format for various platforms
+erofsfuse is introduced to support EROFS format for various platforms
 (including older linux kernels) and new on-disk features iteration.
 It can also be used as an unpacking tool for unprivileged users.
 
@@ -120,7 +127,7 @@ and build it manually:
 
 erofsfuse binary will be generated under fuse folder.
 
-How to mount an erofs image with erofsfuse
+How to mount an EROFS image with erofsfuse
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
 As the other FUSE implementations, it's quite simple to mount with
@@ -139,7 +146,7 @@ To unmount an erofsfuse mountpoint as a non-root user:
 Contribution
 ------------
 
-erofs-utils is under GPLv2+ as a part of erofs project,
+erofs-utils is under GPLv2+ as a part of EROFS filesystem project,
 feel free to send patches or feedback to us.
 
 To:
@@ -155,7 +162,7 @@ Cc:
 Comments
 --------
 
-[1] According to the erofs on-disk format, the tail block of files
+[1] According to the EROFS on-disk format, the tail block of files
     could be inlined aggressively with its metadata in order to reduce
     the I/O overhead and save the storage space (called tail-packing).
 
-- 
2.20.1

[PATCH 2/2] erofs-utils: README: big pcluster feature update

[Gao Xiang]

Add some description for end users to know its usage.

Signed-off-by: Gao Xiang <xiang@kernel.org>
---
 README | 18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

diff --git a/README b/README
index bcf30e11aa52..567192c8c497 100644
--- a/README
+++ b/README
@@ -74,6 +74,24 @@ In addition, you could specify a higher compression level to get a
 (slightly) better compression ratio than the default level, e.g.
  $ mkfs.erofs -zlz4hc,12 foo.erofs.img foo/
 
+How to generate EROFS big pcluster images (Linux 5.13+)
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+In order to get much better compression ratios (thus better sequential
+read performance for common storage devices), big pluster feature has
+been introduced since linux-5.13, which is not forward-compatible with
+old kernels.
+
+In details, -C is used to specify the maximum size of each big pcluster
+in bytes, e.g.
+ $ mkfs.erofs -zlz4hc -C65536 foo.erofs.img foo/
+
+So in that case, pcluster size can be 64KiB at most.
+
+Note that large big pcluster size can cause bad random performance, so
+please evaluate carefully in advance. Or make your own per-(sub)file
+compression strategies according to file access patterns if needed.
+
 How to generate legacy EROFS images (Linux 4.19+)
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
-- 
2.20.1