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

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@cosmos-ink.net>
---
 fs/squashfs/Config.in   | 26 ++++++++++++++++++++++++++
 fs/squashfs/squashfs.mk |  6 +++++-
 2 files changed, 31 insertions(+), 1 deletion(-)

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@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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