linux-kernel - Re: [PATCH v2] f2fs: compress: Allow modular (de)compression algorithms

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Date:   Fri, 26 Feb 2021 20:09:12 +0900
From:   Masahiro Yamada <masahiroy@...nel.org>
To:     Geert Uytterhoeven <geert@...ux-m68k.org>
Cc:     Jaegeuk Kim <jaegeuk@...nel.org>, Chao Yu <chao@...nel.org>,
        linux-f2fs-devel@...ts.sourceforge.net,
        Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] f2fs: compress: Allow modular (de)compression algorithms

On Fri, Feb 26, 2021 at 7:10 PM Geert Uytterhoeven <geert@...ux-m68k.org> wrote:
>
> If F2FS_FS is modular, enabling the compressions options
> F2FS_FS_{LZ4,LZ4HZ,LZO,LZORLE,ZSTD} will make the (de)compression
> algorithms {LZ4,LZ4HC,LZO,ZSTD}_{,DE}COMPRESS builtin instead of
> modular, as the former depend on an intermediate boolean
> F2FS_FS_COMPRESSION, which in-turn depends on tristate F2FS_FS.
>
> Indeed, if a boolean symbol A depends directly on a tristate symbol B
> and selects another tristate symbol C:
>
>     tristate B
>
>     tristate C
>
>     bool A
>       depends on B
>       select C
>
> and B is modular, then C will also be modular.
>
> However, if there is an intermediate boolean D in the dependency chain
> between A and B:
>
>     tristate B
>
>     tristate C
>
>     bool D
>       depends on B
>
>     bool A
>       depends on D
>       select C
>
> then the modular state won't propagate from B to C, and C will be
> builtin instead of modular.
>
> As modular dependency propagation through intermediate symbols is
> obscure, fix this in a robust way by moving the selection of tristate
> (de)compression algorithms from the boolean compression options to the
> tristate main F2FS_FS option.
>
> Signed-off-by: Geert Uytterhoeven <geert@...ux-m68k.org>
> ---
> v2:
>   - Move the selects to F2FS_FS instead of adding direct dependencies
>     on F2FS_FS.
> ---
>  fs/f2fs/Kconfig | 18 +++++++++---------
>  1 file changed, 9 insertions(+), 9 deletions(-)
>
> diff --git a/fs/f2fs/Kconfig b/fs/f2fs/Kconfig
> index 62e638a49bbf089a..cca79029a577151c 100644
> --- a/fs/f2fs/Kconfig
> +++ b/fs/f2fs/Kconfig
> @@ -7,6 +7,15 @@ config F2FS_FS
>         select CRYPTO_CRC32
>         select F2FS_FS_XATTR if FS_ENCRYPTION
>         select FS_ENCRYPTION_ALGS if FS_ENCRYPTION
> +       select LZ4_COMPRESS if F2FS_FS_LZ4
> +       select LZ4_DECOMPRESS if F2FS_FS_LZ4
> +       select LZ4HC_COMPRESS if F2FS_FS_LZ4HC
> +       select LZO_COMPRESS if F2FS_FS_LZO
> +       select LZO_COMPRESS if F2FS_FS_LZORLE

This line is redundant because
F2FS_FS_LZORLE depends on F2FS_FS_LZO.


> +       select LZO_DECOMPRESS if F2FS_FS_LZO
> +       select LZO_DECOMPRESS if F2FS_FS_LZORLE

Ditto.


> +       select ZSTD_COMPRESS if F2FS_FS_ZSTD
> +       select ZSTD_DECOMPRESS if F2FS_FS_ZSTD
>         help
>           F2FS is based on Log-structured File System (LFS), which supports
>           versatile "flash-friendly" features. The design has been focused on


-- 
Best Regards
Masahiro Yamada