[1/1] Handle generated kernel defconfigs

As of commit ea4d1a8 "powerpc/configs: Replace pseries_le_defconfig
with a Makefile target using merge_config" some kernel defconfigs (one
so far: "pseries_le_defconfig") can be generated using "make <defconfig>"
and they do not exist on disk as a single kconfig file.

This causes buildroot's build to fail for those configs with:
'/home/samb/projects/buildroot/scratch/output-guest-le/build/linux-custom/arch/powerpc/configs/pseries_le_defconfig' for 'linux' does not exist

To handle this case and keep the makefile steps as simple as possible,
have the linux.mk fragment set the defconfig name into a new variable
(LINUX_KCONFIG_DEFCONFIG) and leave the kconfig file
name (LINUX_KCONFIG_FILE) empty. Leaving the file name empty prevents
the file existance rule (in pkg-kconfig.mk) from failing on the
missing file, without having to add special cases.

Then have the rule that generates the .config file use this new value
so that it's first step is to either copy the input kconfig file to
.config or run "make <defconfig>" (which writes to .config). Then
merge_config.sh can be run the same way in either case, using .config
as both input and output.

Note that merge_config.sh is now modifying .config in-place but this
is safe because it uses a temporary copy while making changes.

Signed-off-by: Sam Bobroff <sam.bobroff@au1.ibm.com>
---
This patch is somewhat of an RFC, as there are several different
approaches that could be taken to resolve the issue. I ended up with
this one as the least invasive, but I'm happy to persue other options.

 linux/linux.mk         |  3 ++-
 package/pkg-kconfig.mk | 20 ++++++++++++++++----
 2 files changed, 18 insertions(+), 5 deletions(-)

On 07/02/15 06:19, Sam Bobroff wrote:
> As of commit ea4d1a8 "powerpc/configs: Replace pseries_le_defconfig
> with a Makefile target using merge_config" some kernel defconfigs (one
> so far: "pseries_le_defconfig") can be generated using "make <defconfig>"
> and they do not exist on disk as a single kconfig file.
> 
> This causes buildroot's build to fail for those configs with:
> '/home/samb/projects/buildroot/scratch/output-guest-le/build/linux-custom/arch/powerpc/configs/pseries_le_defconfig' for 'linux' does not exist
> 
> To handle this case and keep the makefile steps as simple as possible,
> have the linux.mk fragment set the defconfig name into a new variable
> (LINUX_KCONFIG_DEFCONFIG) and leave the kconfig file
> name (LINUX_KCONFIG_FILE) empty. Leaving the file name empty prevents
> the file existance rule (in pkg-kconfig.mk) from failing on the
> missing file, without having to add special cases.
> 
> Then have the rule that generates the .config file use this new value
> so that it's first step is to either copy the input kconfig file to
> .config or run "make <defconfig>" (which writes to .config). Then
> merge_config.sh can be run the same way in either case, using .config
> as both input and output.
> 
> Note that merge_config.sh is now modifying .config in-place but this
> is safe because it uses a temporary copy while making changes.
> 
> Signed-off-by: Sam Bobroff <sam.bobroff@au1.ibm.com>

Reviewed-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>

 I have looked at this patch from several sides and I can only conclude that I
like it :). I was a bit worried that there might have been a reason why we copy
the in-tree defconfig instead of just running make foo_defconfig, but it turns
out that that was just a simplification to make it fit in the pkg-generic
infrastructure (commit 9af0ee86).

 I especially like the splitting of in-package and out-of-package defconfigs,
because I think that could be useful for keeping the infra simple when more
features are added to it. For example, the infrastructure could automatically
determine the defconfig to use from the BR2_ symbol:

$(2)_KCONFIG_FILE ?=  \
	$$(call qstrip,$$($$($(2)_KCONFIG_VAR)_CUSTOM_CONFIG_FILE))
$(2)_KCONFIG_DEFCONFIG ?= \
	$$(call qstrip,$$($$($(2)_KCONFIG_VAR)_DEFCONFIG))

(and then append _defconfig where it's used). Note BTW that _KCONFIG_VAR is
defined for all packages in pkg-generic.mk - it's a bit confusing.

 Also, this fixes a shortcoming in the original kconfig infra. Quoting dff25ea2b9:

    - the targets linux-update-(def)config are now always saving the config
      file, even for a defconfig bundled in the linux sources. This is done
      to keep the kconfig infrastructure simple.



 I do have a few remarks still (which could be in follow-up patches if this one
is already applied), but more importantly, I have a couple of additional feature
requests (like the one above).

 If you would respin this patch, please split it into one patch that updates the
infrastructure, and a second patch that updates linux.mk.

 It would be nice if you could do the same for the other packages with in-tree
defconfigs: at91bootstrap3 and barebox (and uboot if that patch ever gets applied).


> ---
> This patch is somewhat of an RFC, as there are several different
> approaches that could be taken to resolve the issue. I ended up with
> this one as the least invasive, but I'm happy to persue other options.
> 
>  linux/linux.mk         |  3 ++-
>  package/pkg-kconfig.mk | 20 ++++++++++++++++----
>  2 files changed, 18 insertions(+), 5 deletions(-)
> 
> diff --git a/linux/linux.mk b/linux/linux.mk
> index eca1450..f988d5a 100644
> --- a/linux/linux.mk
> +++ b/linux/linux.mk
> @@ -176,12 +176,13 @@ endef
>  LINUX_POST_PATCH_HOOKS += LINUX_APPLY_LOCAL_PATCHES
>  
>  ifeq ($(BR2_LINUX_KERNEL_USE_DEFCONFIG),y)
> -KERNEL_SOURCE_CONFIG = $(KERNEL_ARCH_PATH)/configs/$(call qstrip,$(BR2_LINUX_KERNEL_DEFCONFIG))_defconfig
> +KERNEL_SOURCE_DEFCONFIG = $(call qstrip,$(BR2_LINUX_KERNEL_DEFCONFIG))_defconfig

 Why not assign to LINUX_KCONFIG_DEFCONFIG right away? I think the only reason
why Yann and Thomas didn't replace KERNEL_SOURCE_CONFIG with LINUX_KCONFIG_FILE
in the original series is because they overlooked it, or maybe because they
wanted to keep changes minimal.

>  else ifeq ($(BR2_LINUX_KERNEL_USE_CUSTOM_CONFIG),y)
>  KERNEL_SOURCE_CONFIG = $(call qstrip,$(BR2_LINUX_KERNEL_CUSTOM_CONFIG_FILE))
>  endif
>  
>  LINUX_KCONFIG_FILE = $(KERNEL_SOURCE_CONFIG)
> +LINUX_KCONFIG_DEFCONFIG = $(KERNEL_SOURCE_DEFCONFIG)
>  LINUX_KCONFIG_FRAGMENT_FILES = $(call qstrip,$(BR2_LINUX_KERNEL_CONFIG_FRAGMENT_FILES))

 Look, here there is no additional variable.

>  LINUX_KCONFIG_EDITORS = menuconfig xconfig gconfig nconfig
>  LINUX_KCONFIG_OPTS = $(LINUX_MAKE_FLAGS)
> diff --git a/package/pkg-kconfig.mk b/package/pkg-kconfig.mk
> index c86c340..7685509 100644
> --- a/package/pkg-kconfig.mk
> +++ b/package/pkg-kconfig.mk
> @@ -35,6 +35,8 @@ $(call inner-generic-package,$(1),$(2),$(3),$(4))
>  $(2)_KCONFIG_EDITORS ?= menuconfig
>  $(2)_KCONFIG_OPTS ?=
>  $(2)_KCONFIG_FIXUP_CMDS ?=
> +$(2)_KCONFIG_KCONFIG_FILE ?=
> +$(2)_KCONFIG_KCONFIG_DEFCONFIG ?=

 I don't really like these empty assignments - it just adds overhead. And in
this case it is especially bad IMHO, because only one of them should be defined
to begin with...

>  $(2)_KCONFIG_FRAGMENT_FILES ?=
>  
>  # The config file as well as the fragments could be in-tree, so before
> @@ -63,8 +65,14 @@ $$($(2)_KCONFIG_FILE) $$($(2)_KCONFIG_FRAGMENT_FILES): | $(1)-patch

 Since _KCONFIG_FILE is no longer in-tree (at least, after at91bootstrap and
barebox have been converted as well), this dependency is only needed for the
fragments (but then it should be conditional on it being non-empty, otherwise
there's a no-target rule).

>  # full .config first. We use 'make oldconfig' because this can be safely
>  # done even when the package does not support defconfigs.
>  $$($(2)_DIR)/.config: $$($(2)_KCONFIG_FILE) $$($(2)_KCONFIG_FRAGMENT_FILES)
> +	if [ ! -z "$$($(2)_KCONFIG_DEFCONFIG)" ] ; then \
> +		$$($(2)_MAKE_ENV) $$(MAKE) -C $$($(2)_DIR) \
> +			$$($(2)_KCONFIG_OPTS) $$($(2)_KCONFIG_DEFCONFIG) ; \
> +	else \
> +		cp $$($(2)_KCONFIG_FILE) $$(@) ; \
> +	fi
>  	support/kconfig/merge_config.sh -m -O $$(@D) \
> -		$$($(2)_KCONFIG_FILE) $$($(2)_KCONFIG_FRAGMENT_FILES)
> +		$$(@) $$($(2)_KCONFIG_FRAGMENT_FILES)
>  	@yes "" | $$($(2)_MAKE_ENV) $$(MAKE) -C $$($(2)_DIR) \
>  		$$($(2)_KCONFIG_OPTS) oldconfig
>  
> @@ -89,9 +97,9 @@ $$($(2)_TARGET_CONFIGURE): $$($(2)_DIR)/.stamp_kconfig_fixup_done
>  # already called above, so we can effectively use this variable.
>  ifeq ($$($$($(2)_KCONFIG_VAR)),y)
>  
> -# FOO_KCONFIG_FILE is required
> -ifeq ($$($(2)_KCONFIG_FILE),)
> -$$(error Internal error: no value specified for $(2)_KCONFIG_FILE)
> +# Either FOO_KCONFIG_FILE or FOO_KCONFIG_DEFCONFIG is required
> +ifeq ($$($(2)_KCONFIG_FILE)$$($(2)_KCONFIG_DEFCONFIG),)
> +$$(error Internal error: no value specified for $(2)_KCONFIG_FILE or $(2)_KCONFIG_DEFCONFIG)

 There could also be a check that only one of them is defined, not both.

ifneq ($$(and $$($(2)_KCONFIG_FILE),$$($(2)_KCONFIG_DEFCONFIG)),)
$$(error ...)
endif

 Not very readable, though, so if you can find something better...


>  endif
>  
>  # Configuration editors (menuconfig, ...)
> @@ -147,6 +155,8 @@ $(1)-savedefconfig: $(1)-check-configuration-done
>  $(1)-update-config: $(1)-check-configuration-done
>  	@$$(if $$($(2)_KCONFIG_FRAGMENT_FILES), \
>  		echo "Unable to perform $(1)-update-config when fragment files are set"; exit 1)
> +	@$$(if $$($(2)_KCONFIG_DEFCONFIG), \
> +		echo "Unable to perform $(1)-update-config when using an in-tree defconfig"; exit 1)

 It's OK the way it is (because that is how it's done for the fragment files),
but in fact it's also possible to do this with $$(error) instead of a shell
command, because the $$(error) will only be expanded when the rule is executed.


 Regards,
 Arnout

>  	cp -f $$($(2)_DIR)/.config $$($(2)_KCONFIG_FILE)
>  	touch --reference $$($(2)_DIR)/.config $$($(2)_KCONFIG_FILE)
>  
> @@ -157,6 +167,8 @@ $(1)-update-config: $(1)-check-configuration-done
>  $(1)-update-defconfig: $(1)-savedefconfig
>  	@$$(if $$($(2)_KCONFIG_FRAGMENT_FILES), \
>  		echo "Unable to perform $(1)-update-defconfig when fragment files are set"; exit 1)
> +	@$$(if $$($(2)_KCONFIG_DEFCONFIG), \
> +		echo "Unable to perform $(1)-update-defconfig when using an in-tree defconfig"; exit 1)
>  	cp -f $$($(2)_DIR)/defconfig $$($(2)_KCONFIG_FILE)
>  	touch --reference $$($(2)_DIR)/.config $$($(2)_KCONFIG_FILE)
>  
>