linux-kernel - Re: [PATCH v2] Makefile: Fix lying comment re. silentoldconfig

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Message-ID: <CAK7LNAT+FDWeg5MSjx0wNE6vpCN-ZZZ7fSA6L-hND2Jxgefn6g@mail.gmail.com>
Date:   Mon, 19 Feb 2018 08:37:33 +0900
From:   Masahiro Yamada <yamada.masahiro@...ionext.com>
To:     Ulf Magnusson <ulfalizer@...il.com>
Cc:     Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Michal Marek <michal.lkml@...kovi.net>
Subject: Re: [PATCH v2] Makefile: Fix lying comment re. silentoldconfig

2018-02-13 16:58 GMT+09:00 Ulf Magnusson <ulfalizer@...il.com>:
> The comment above the silentoldconfig invocation is outdated.
> 'make oldconfig' updates just .config and doesn't touch the
> include/config/ tree.
>
> This came up in https://lkml.org/lkml/2018/2/12/415.
>
> While fixing the comment, make it more informative by explaining the
> purpose of the unfortunately named silentoldconfig.
>
> I can't make sense of the comment re. auto.conf.cmd and a cleaned tree.
> include/config/auto.conf and include/config/auto.conf.cmd are both
> created simultaneously by silentoldconfig (in
> scripts/kconfig/confdata.c, by conf_write_autoconf()), and nothing seems
> to remove auto.conf.cmd that wouldn't remove auto.conf. Remove that part
> of the comment rather than blindly copying it. It might be a leftover
> from an older way of doing things.
>
> The include/config/auto.conf.cmd prerequisite might be there to ensure
> that silentoldconfig gets rerun if conf_write_autoconf() fails between
> writing out auto.conf.cmd and auto.conf (a comment in the function
> indicates that auto.conf is deliberately written out last to mark
> completion of the operation). It seems the Makefile dependency between
> include/config/auto.conf and .config would already take care of that
> though, since include/config/auto.conf would still be out of date re.
> .config if the operation fails.
>
> Cop out and leave the prerequisite in for now.
>
> Signed-off-by: Ulf Magnusson <ulfalizer@...il.com>
> ---
> Changes in v2:
> include/config/auto.conf depends on .config, not the other way around, so swap
> them in some places in the commit message to make it less confusing.
>
>  Makefile | 11 +++++++----
>  1 file changed, 7 insertions(+), 4 deletions(-)
>
> diff --git a/Makefile b/Makefile
> index 79ad2bfa24b6..61ed99ad4b1b 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -579,10 +579,13 @@ ifeq ($(KBUILD_EXTMOD),)
>  # To avoid any implicit rule to kick in, define an empty command
>  $(KCONFIG_CONFIG) include/config/auto.conf.cmd: ;
>
> -# If .config is newer than include/config/auto.conf, someone tinkered
> -# with it and forgot to run make oldconfig.
> -# if auto.conf.cmd is missing then we are probably in a cleaned tree so
> -# we execute the config step to be sure to catch updated Kconfig files
> +# The actual configuration files used during the build are stored in
> +# include/generated/ and include/config/. Update them if .config is newer than
> +# include/config/auto.conf (which mirrors .config).


Yes, the first paragraph perfectly explains the code.


> +# The include/config/ tree manages dependencies between source files and
> +# Kconfig symbols and lets us avoid doing a full rebuild whenever the
> +# configuration is changed. See scripts/basic/fixdep.c

Do you insist on this paragraph?

I know silentoldconfig touches include/config/* for extra cleverness,
but, to me, this looks unnecessary information to
understand the following code.

>  include/config/%.conf: $(KCONFIG_CONFIG) include/config/auto.conf.cmd
>         $(Q)$(MAKE) -f $(srctree)/Makefile silentoldconfig
>  else




-- 
Best Regards
Masahiro Yamada