[Buildroot] [PATCH 2/2] fs/squashfs: Add option to compress with extreme options

[Yann E. MORIN]

Linus, All,

On 2022-05-17 03:24 +0000, Linus Kaschulla via buildroot spake thusly:
> mksquashfs allows to tweak many compressions parameters. Currently they
> can't be changed from kmenu. Leaving out potential space savings.
> 
> This adds the option to enable a set of predetermined compression
> options. This option is enabled by default for lz4 since lz4 currently
> implicitly added the extreme to it in the makefile. So this aids in
> keeping backward compatibility.
> 
> Signed-off-by: Linus Kaschulla <linus at cosmos-ink.net>
> ---
>  fs/squashfs/Config.in   | 26 ++++++++++++++++++++++++++
>  fs/squashfs/squashfs.mk |  6 +++++-
>  2 files changed, 31 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/squashfs/Config.in b/fs/squashfs/Config.in
> index 341e50a08c..41c782105d 100644
> --- a/fs/squashfs/Config.in
> +++ b/fs/squashfs/Config.in
> @@ -89,4 +89,30 @@ config BR2_TARGET_ROOTFS_SQUASHFS4_ZSTD
>  
>  endchoice
>  
> +config BR2_TARGET_ROOTFS_SQUASHFS_EXTREME_COMP
> +	bool "extreme compression if possible"
> +	default BR2_TARGET_ROOTFS_SQUASHFS4_LZ4

This is technically correct, but we are not using that code style
anywhere else (that I am aware of), so I tweaked it to the more
tracitional form we use everywhere else. I also added a comment to
explain why it is:
    default y if BR2_TARGET_ROOTFS_SQUASHFS4_LZ4  # legacy

> +	help
> +	  Use options to increase compression ration as much as
> +	  possible, like using architecture-specific options, at
> +	  the cost of time when assembling the filesystem image.
> +
> +	  For example:
> +	   - with gzip and lzo, use -Xcompression-level 9
> +	   - with xz use a architecture specific bjc (branch-call-jump) filter
> +	   - with zstd use -Xcompression-level 22
> +	   - and more

    $ make check-package
    WARNING: fs/squashfs/Config.in:102: help text: <tab><2 spaces><62 chars> (http://nightly.buildroot.org/#writing-rules-config-in)

> +config BR2_TARGET_ROOTFS_SQUASHFS_COMP_OPTS
> +	string
> +	depends on BR2_TARGET_ROOTFS_SQUASHFS_EXTREME_COMP
> +	default "-Xcompression-level 9" if BR2_TARGET_ROOTFS_SQUASHFS4_GZIP
> +	default "-Xcompression-level 9" if BR2_TARGET_ROOTFS_SQUASHFS4_LZO
> +	default "-Xhc" if BR2_TARGET_ROOTFS_SQUASHFS4_LZ4
> +	default "-Xbcj arm,armthumb" if BR2_TARGET_ROOTFS_SQUASHFS4_XZ && (BR2_arm || BR_aarch64)
> +	default "-Xbcj powerpc" if BR2_TARGET_ROOTFS_SQUASHFS4_XZ && (BR2_powerpc || BR2_powerpc64)
> +	default "-Xbcj sparc" if BR2_TARGET_ROOTFS_SQUASHFS4_XZ && (BR2_sparc || BR2_sparc64)
> +	default "-Xbcj x86" if BR2_TARGET_ROOTFS_SQUASHFS4_XZ && (BR2_i386 || BR2_x86_64)
> +	default "-Xcompression-level 22" if BR2_TARGET_ROOTFS_SQUASHFS4_ZSTD

    $ make check-package
    WARNING: fs/squashfs/Config.in:109: attributes order: type, default, depends on, select, help (http://nightly.buildroot.org/#_config_files)

So I fixed that too.

>  endif
> diff --git a/fs/squashfs/squashfs.mk b/fs/squashfs/squashfs.mk
> index 1790773f7e..51f8d0d7c9 100644
> --- a/fs/squashfs/squashfs.mk
> +++ b/fs/squashfs/squashfs.mk
> @@ -25,7 +25,7 @@ ROOTFS_SQUASHFS_ARGS += -nopad
>  endif
>  
>  ifeq ($(BR2_TARGET_ROOTFS_SQUASHFS4_LZ4),y)
> -ROOTFS_SQUASHFS_ARGS += -comp lz4 -Xhc
> +ROOTFS_SQUASHFS_ARGS += -comp lz4
>  else ifeq ($(BR2_TARGET_ROOTFS_SQUASHFS4_LZO),y)
>  ROOTFS_SQUASHFS_ARGS += -comp lzo
>  else ifeq ($(BR2_TARGET_ROOTFS_SQUASHFS4_LZMA),y)
> @@ -38,6 +38,10 @@ else
>  ROOTFS_SQUASHFS_ARGS += -comp gzip
>  endif
>  
> +ifeq ($(BR2_TARGET_ROOTFS_SQUASHFS_EXTREME_COMP),y)
> +ROOTFS_SQUASHFS_ARGS += $(call qstrip,$(BR2_TARGET_ROOTFS_SQUASHFS_COMP_OPTS))
> +endif

If BR2_TARGET_ROOTFS_SQUASHFS_EXTREME_COMP is not set, or if no
condition match, then BR2_TARGET_ROOTFS_SQUASHFS_COMP_OPTS will be an
empty string, so we can just always expand it unconditionally.

Applied to master with the abov e fixed;
  - fix check-package
  - change the default code-style, add the legacy comment
  - always add the qstriped string, as it's empty when not used

Thanks!

Ditto, a test-case would be awesome!

Regards,
Yann E. MORIN.

>  define ROOTFS_SQUASHFS_CMD
>  	$(HOST_DIR)/bin/mksquashfs $(TARGET_DIR) $@ $(ROOTFS_SQUASHFS_ARGS)
>  endef
> -- 
> 2.35.1
> 
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