[Buildroot] [PATCH v4 3/3] core/pkg-kconfig: Use oldnoconfig when possible

[Yann E. MORIN]

Romain, All,

On 2016-04-18 11:23 +0200, Romain Izard spake thusly:
> Using 'yes "" | make oldconfig' to regenerate a .config file from an
> existing defconfig does not work reliably in all cases. Specifically, it
> does not work well with tristate choice entries.
> 
> The correct way to do it is to use 'make olddefconfig', but this target
> is not supported in projects that use an old version of kconfig. As
> most projects do not use tristate entries, there is no need for them to
> upgrade.
> 
> 'oldnoconfig' is an alias for 'olddefconfig', but it also is the only
> name for this target between Linux versions 2.6.36 and 3.6.
> 
> Try to use 'oldnoconfig' by default, using 'oldconfig' as a fallback
> 
> Reviewed-by: Arnout Vandecappelle (Essensium/Mind) <arnout at mind.be>
> Signed-off-by: Romain Izard <romain.izard.pro at gmail.com>

Usually, reviewd-by tags are staged after the signed-off-by tag, as in a
temporal mark: first signed-off-by, then reviewed.

> ---
> Changelog:
> v1: New patch
> v2: Use oldnoconfig instead of olddefconfig
>     Fix silent mode
>     Change the pattern in both places where it is used
>     Use a macro to avoid redundancy
> v3: Do not use $(call ...)
>     Use the $(2)_KCONFIG_MAKE variable
> v4: No change
> 
>  package/pkg-kconfig.mk | 18 ++++++++++++++----
>  1 file changed, 14 insertions(+), 4 deletions(-)
> 
> diff --git a/package/pkg-kconfig.mk b/package/pkg-kconfig.mk
> index 4033915..e04cfd5 100644
> --- a/package/pkg-kconfig.mk
> +++ b/package/pkg-kconfig.mk
> @@ -60,18 +60,28 @@ $$($(2)_KCONFIG_FILE) $$($(2)_KCONFIG_FRAGMENT_FILES): | $(1)-patch
>  $(2)_KCONFIG_MAKE = \
>  	$$($(2)_MAKE_ENV) $$(MAKE) -C $$($(2)_DIR) $$($(2)_KCONFIG_OPTS)
>  
> +# The correct way to regenerate a .config file is to use 'make olddefconfig'.
> +# For historical reasons, the target name is 'oldnoconfig' between Linux kernel
> +# versions 2.6.36 and 3.6, and remains as an alias in later versions.
> +# In older versions, and in some other projects that use kconfig, the target is
> +# not supported at all, and we use 'yes "" | make oldconfig' as a fallback
> +# only, as this can fail in complex cases.
> +define $(2)_REGEN_DOT_CONFIG
> +	$$(Q)$$($(2)_KCONFIG_MAKE) oldnoconfig || \
> +		(yes "" | $$($(2)_KCONFIG_MAKE) oldconfig)

What I don't much like here, is that we conflate two things:
  - a non-zero return code because of a missing oldnoconfig,
  - a non-zero return code because of an error found by olnoconfig.

What I would have loved however, would be a way to detect whether
oldnoconfig (better, olddefconfig) was supported before calling it.
Maybe something along the lines of:

    if [ -n "`$$($(2)_KCONFIG_MAKE) -pqn .DEFAULT 2>/dev/null |grep -E '^olddefconfig'`" ]; then \
        $$($(2)_KCONFIG_MAKE) olddefconfig || exit 1; \
    elif [ -n "`$$($(2)_KCONFIG_MAKE) -pqn .DEFAULT |grep -E '^oldnoconfig'`" ]; then \
        $$($(2)_KCONFIG_MAKE) oldnoconfig || exit 1; \
    else
        (yes "" | $$($(2)_KCONFIG_MAKE) oldconfig) || exit 1; \
    fi
        
Yes, this is more code, less compact, but it is more systematic. At the
very least, it would not fallback to the yes|oldconfig trick in case
old{def,no}config do exist but fail, which we do want to catch.

BTW, the make trick above is highly (as in: almost identical) from the
bash-autocompletion package.

Regards,
Yann E. MORIN.

> +endef
> +
>  # The specified source configuration file and any additional configuration file
>  # fragments are merged together to .config, after the package has been patched.
>  # Since the file could be a defconfig file it needs to be expanded to a
> -# full .config first. We use 'make oldconfig' because this can be safely
> -# done even when the package does not support defconfigs.
> +# full .config first.
>  $$($(2)_DIR)/.config: $$($(2)_KCONFIG_FILE) $$($(2)_KCONFIG_FRAGMENT_FILES)
>  	$$(Q)$$(if $$($(2)_KCONFIG_DEFCONFIG), \
>  		$$($(2)_KCONFIG_MAKE) $$($(2)_KCONFIG_DEFCONFIG), \
>  		cp $$($(2)_KCONFIG_FILE) $$(@))
>  	$$(Q)support/kconfig/merge_config.sh -m -O $$(@D) \
>  		$$(@) $$($(2)_KCONFIG_FRAGMENT_FILES)
> -	$$(Q)yes "" | $$($(2)_KCONFIG_MAKE) oldconfig
> +	$$($(2)_REGEN_DOT_CONFIG)
>  
>  # If _KCONFIG_FILE or _KCONFIG_FRAGMENT_FILES exists, this dependency is
>  # already implied, but if we only have a _KCONFIG_DEFCONFIG we have to add
> @@ -82,7 +92,7 @@ $$($(2)_DIR)/.config: | $(1)-patch
>  # The exact rules are specified by the package .mk file.
>  define $(2)_FIXUP_DOT_CONFIG
>  	$$($(2)_KCONFIG_FIXUP_CMDS)
> -	$$(Q)yes "" | $$($(2)_KCONFIG_MAKE) oldconfig
> +	$$($(2)_REGEN_DOT_CONFIG)
>  	$$(Q)touch $$($(2)_DIR)/.stamp_kconfig_fixup_done
>  endef
>  
> -- 
> 2.5.0
> 

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