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From 46bf8f6d30d6ddf2446c110f122482b5e5e16933 Mon Sep 17 00:00:00 2001
From: Sean Purcell <me@seanp.xyz>
Date: Mon, 17 Jul 2017 17:08:59 -0700
Subject: [PATCH v5 4/5] squashfs: Add zstd support

Add zstd compression and decompression support to SquashFS. zstd is a
great fit for SquashFS because it can compress at ratios approaching xz,
while decompressing twice as fast as zlib. For SquashFS in particular,
it can decompress as fast as lzo and lz4. It also has the flexibility
to turn down the compression ratio for faster compression times.

The compression benchmark is run on the file tree from the SquashFS archive
found in ubuntu-16.10-desktop-amd64.iso [1]. It uses `mksquashfs` with the
default block size (128 KB) and and various compression algorithms/levels.
xz and zstd are also benchmarked with 256 KB blocks. The decompression
benchmark times how long it takes to `tar` the file tree into `/dev/null`.
See the benchmark file in the upstream zstd source repository located under
`contrib/linux-kernel/squashfs-benchmark.sh` [2] for details.

I ran the benchmarks on a Ubuntu 14.04 VM with 2 cores and 4 GiB of RAM.
The VM is running on a MacBook Pro with a 3.1 GHz Intel Core i7 processor,
16 GB of RAM, and a SSD.

| Method         | Ratio | Compression MB/s | Decompression MB/s |
|----------------|-------|------------------|--------------------|
| gzip           |  2.92 |               15 |                128 |
| lzo            |  2.64 |              9.5 |                217 |
| lz4            |  2.12 |               94 |                218 |
| xz             |  3.43 |              5.5 |                 35 |
| xz 256 KB      |  3.53 |              5.4 |                 40 |
| zstd 1         |  2.71 |               96 |                210 |
| zstd 5         |  2.93 |               69 |                198 |
| zstd 10        |  3.01 |               41 |                225 |
| zstd 15        |  3.13 |             11.4 |                224 |
| zstd 16 256 KB |  3.24 |              8.1 |                210 |

This patch was written by Sean Purcell <me@seanp.xyz>, but I will be
taking over the submission process.

[1] http://releases.ubuntu.com/16.10/
[2] https://github.com/facebook/zstd/blob/dev/contrib/linux-kernel/squashfs-benchmark.sh

zstd source repository: https://github.com/facebook/zstd

Signed-off-by: Sean Purcell <me@seanp.xyz>
Signed-off-by: Nick Terrell <terrelln@fb.com>
---
v3 -> v4:
- Fix minor linter warnings

v4 -> v5:
- Fix ZSTD_DStream initialization code in squashfs
- Fix patch documentation to reflect that Sean Purcell is the author

 fs/squashfs/Kconfig        |  14 +++++
 fs/squashfs/Makefile       |   1 +
 fs/squashfs/decompressor.c |   7 +++
 fs/squashfs/decompressor.h |   4 ++
 fs/squashfs/squashfs_fs.h  |   1 +
 fs/squashfs/zstd_wrapper.c | 151 +++++++++++++++++++++++++++++++++++++++++++++
 6 files changed, 178 insertions(+)
 create mode 100644 fs/squashfs/zstd_wrapper.c

diff --git a/fs/squashfs/Kconfig b/fs/squashfs/Kconfig
index ffb093e..1adb334 100644
--- a/fs/squashfs/Kconfig
+++ b/fs/squashfs/Kconfig
@@ -165,6 +165,20 @@ config SQUASHFS_XZ

 	  If unsure, say N.

+config SQUASHFS_ZSTD
+	bool "Include support for ZSTD compressed file systems"