[Buildroot] [PATCH] infra/pkg-virtual: validate only one provider provides an implementation

[Arnout Vandecappelle <arnout@mind.be>]

On 13/05/14 23:47, Yann E. MORIN wrote:
> From: "Yann E. MORIN" <yann.morin.1998@free.fr>
> 
> BIG FAT NOTICE:
>     This is *not* tested.
>     This is only a track I'd like to further explore to fix the issue.
> 
> Currently, it is possible that more than one provider of a virtual package
> is selected in the menuconfig.
> 
> This leads to autobuild failures, and we do not protect the user from
> making a mistake in the configuration. The failure is then hard to
> troubleshoot in any case.
> 
> We can't use kconfig constructs to prevent this, sicne kconfig does not
> tell how many options did a select on another option.
> 
> This patch adds a new function that providers *must* call in their .mk
> to ensure at most one provider is selected.

 I like it!

 It's really simple, it's easy to understand. And since it has to be called
explicitly, it doesn't block the possibility for virtual packages with multiple
providers that _don't_ conflict (although admittedly those would still have a
reproducibility problem, but anyway we're not looking at that issue now).

 It's also really easy to check for in review.

> 
> This works by taking advantage that when more than one provider is
> selected, only one of them will 'win' in setting the _PROVIDES_FOO
> option. Thus any provider just have to check they are indeed the declared
> provider. If not, it means that one or more other provider is selected.
> 
> This gives the opportunity to the user to change its configuration, and
> we can match the error message in the autobuilders to skip those failures
> (we can skip them instead of reporting them, since they are obviously
> configuration errors that should not happen in the first place.)
> 
> NOT Signed-off-by on purpose.
> Cc: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
> Cc: Peter Korsgaard <jacmet@uclibc.org>
> Cc: Thomas De Schampheleire <patrickdepinguin@gmail.com>
> Cc: Arnout Vandecappelle <arnout@mind.be>
> Cc: Samuel Martin <s.martin49@gmail.com>
> ---
>  package/pkg-virtual.mk               | 9 +++++++++
>  package/rpi-userland/rpi-userland.mk | 3 +++
>  2 files changed, 12 insertions(+)
> 
> diff --git a/package/pkg-virtual.mk b/package/pkg-virtual.mk
> index 617e5f2..66537bf 100644
> --- a/package/pkg-virtual.mk
> +++ b/package/pkg-virtual.mk
> @@ -13,6 +13,15 @@
>  #
>  ################################################################################
>  
> +# Providers shall call this function with all the FEATURES they provide
> +# 	$(eval $(call virt-provides,FEATURE[ FEATURE ...]))
> +# where FEATURE has a corresponding BR2_PACKAGE_HAS_FEATURE
> +define virt-provides

 Even better would be to make this part of generic-package, and add a
PKG_PROVIDES = ... variable

> +$(foreach p,$(1),\
> +ifneq ($$(BR2_PACKAGE_PROVIDES_$(p)),$(pkgname))$(sep)\

 We could throw in an UPPERCASE here so the caller can put it in lowercase.

> +$$(error $(pkgname is trying to override $$(BR2_PACKAGE_PROVIDES_$(p)) to provide $(p)))$(sep)\
> +endif$(sep))
> +endef

 How about (assuming the PKG_PROVIDES path):

Before inner-generic-package:

--------------------------------
# virt-provides-single <virt-pkg> <VIRT_PKG> <provider-pkg>
define virt-provides-single
ifneq ($$(BR2_PACKAGE_PROVIDES_$(2)),$(3))
$$(error Configuration error: $(3) and $$(BR2_PACKAGE_PROVIDES_$(2))$(sep)\
	are both selected as providers for virtual package $(1).$(sep)\
	Only one of them should be selected. Please adapt your configuration.)
endif
endef
--------------------------------


Within inner-generic-package:

--------------------------------
ifneq ($$($(2)_PROVIDES),)
$$(foreach pkg,$$($(2)_PROVIDES),\
	$$(call virt-provides-single,$$(pkg),$$(call UPPERCASE,$$(pkg)),$(1)))
endif
--------------------------------

>  
>  ################################################################################
>  # inner-virtual-package -- defines the dependency rules of the virtual
> diff --git a/package/rpi-userland/rpi-userland.mk b/package/rpi-userland/rpi-userland.mk
> index f6e4443..86125f2 100644
> --- a/package/rpi-userland/rpi-userland.mk
> +++ b/package/rpi-userland/rpi-userland.mk
> @@ -16,4 +16,7 @@ define RPI_USERLAND_POST_TARGET_CLEANUP
>  endef
>  RPI_USERLAND_POST_INSTALL_TARGET_HOOKS += RPI_USERLAND_POST_TARGET_CLEANUP
>  
> +# rpi-userland is a provider for those features:
> +$(eval $(call virt-provides,LIBEGL LIBGLES OPENVG OPENMAX))

 So this would become

RPI_USERLAND_PROVIDES = libegl libegles openvg openmax



 I'm thinking, with this approach, it may even be possible to remove the
Config.in part of the providers. Ah, no it's not possible, because then you have
the ordering problem that Yann already mentioned in another mail. Maybe it would
be possible somehow to force the virtual packages to be evaluated only at the
end, but I think that that's just going to complicate stuff unnecessarily.


 Again, I'm pretty happy with what we have here.


 Regards,
 Arnout

> +
>  $(eval $(cmake-package))
> 


-- 
Arnout Vandecappelle                          arnout at mind be
Senior Embedded Software Architect            +32-16-286500
Essensium/Mind                                http://www.mind.be
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