linux-kernel - Re: [f2fs-dev] [PATCH v3] f2fs: compress: Allow modular (de)compression algorithms

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Message-ID: <c77e72ad-fa15-db64-7348-7b1a34b6153f@huawei.com>
Date:   Sat, 27 Feb 2021 09:12:40 +0800
From:   Chao Yu <yuchao0@...wei.com>
To:     Geert Uytterhoeven <geert@...ux-m68k.org>
CC:     Jaegeuk Kim <jaegeuk@...nel.org>, Chao Yu <chao@...nel.org>,
        "Masahiro Yamada" <masahiroy@...nel.org>,
        Randy Dunlap <rdunlap@...radead.org>,
        <linux-kbuild@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <linux-f2fs-devel@...ts.sourceforge.net>
Subject: Re: [f2fs-dev] [PATCH v3] f2fs: compress: Allow modular
 (de)compression algorithms

On 2021/2/26 23:51, Geert Uytterhoeven 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>

Reviewed-by: Chao Yu <yuchao0@...wei.com>

Thanks,