Re: [Xen-devel] [PATCH v6 2/2] kconfig: add xenconfig defconfig helper

[Masahiro Yamada <yamada.masahiro@xxxxxxxxxxxxx>]

Hi Luis,

2015-05-22 3:47 GMT+09:00 Luis R. Rodriguez <mcgrof@xxxxxxxx>:
> On Thu, May 21, 2015 at 11:49:17PM +0900, Masahiro Yamada wrote:
>> Hi,
>>
>> I am not familiar with xen at all, just some comments
>> from the build system side.
>>
>>
>>
>> 2015-05-21 3:53 GMT+09:00 Luis R. Rodriguez <mcgrof@xxxxxxxxxxxxxxxx>:
>> > From: "Luis R. Rodriguez" <mcgrof@xxxxxxxx>
>> >
>> > This lets you build a kernel which can support xen dom0
>> > or xen guests on i386, x86-64 and arm64 by just using:
>> >
>> >    make xenconfig
>> >
>> > You can start from an allnoconfig and then switch to xenconfig.
>> > This also splits out the options which are available currently
>> > to be built with x86 and 'make ARCH=arm64' under a shared config.
>> >
>> > Technically xen supports a dom0 kernel and also a guest
>> > kernel configuration but upon review with the xen team
>> > since we don't have many dom0 options its best to just
>> > combine these two into one.
>> >
>> > A few generic notes: we enable both of these:
>> >
>> > CONFIG_INET=y
>> > CONFIG_BINFMT_ELF=y
>> >
>> > although technically not required given you likely will
>> > end up with a pretty useless system otherwise.
>> >
>> > A few architectural differences worth noting:
>> >
>> > $ make allnoconfig; make xenconfig > /dev/null ; \
>> >         grep XEN .config > 64-bit-config
>> > $ make ARCH=i386 allnoconfig; make ARCH=i386 xenconfig > /dev/null; \
>> >         grep XEN .config > 32-bit-config
>> > $ make ARCH=arm64 allnoconfig; make ARCH=arm64 xenconfig > /dev/null; \
>> >         grep XEN .config > arm64-config
>> >
>> > Since the options are already split up with a generic config and
>> > architecture specific configs you anything on the x86 configs
>> > are known to only work right now on x86. For instance arm64 doesn't
>> > support MEMORY_HOTPLUG yet as such although we try to enabe it
>> > generically arm64 doesn't have it yet, so we leave the xen
>> > specific kconfig option XEN_BALLOON_MEMORY_HOTPLUG on x86's config
>> > file to set expecations correctly.
>> >
>> > Then on x86 we have differences between i386 and x86-64. The difference
>> > between 64-bit-config and 32-bit-config is you don't get XEN_MCE_LOG as
>> > this is only supported on 64-bit. You also do not get on i386
>> > XEN_BALLOON_MEMORY_HOTPLUG, there does not seem to be any technical
>> > reasons to not allow this but I gave up after a few attempts.
>> >
>> > Cc: Josh Triplett <josh@xxxxxxxxxxxxxxxx>
>> > Cc: Borislav Petkov <bp@xxxxxxx>
>> > Cc: Pekka Enberg <penberg@xxxxxxxxxx>
>> > Cc: David Rientjes <rientjes@xxxxxxxxxx>
>> > Cc: Michal Marek <mmarek@xxxxxxx>
>> > Cc: Randy Dunlap <rdunlap@xxxxxxxxxxxxx>
>> > Cc: penberg@xxxxxxxxxx
>> > Cc: levinsasha928@xxxxxxxxx
>> > Cc: mtosatti@xxxxxxxxxx
>> > Cc: fengguang.wu@xxxxxxxxx
>> > Cc: David Vrabel <david.vrabel@xxxxxxxxxx>
>> > Cc: Ian Campbell <Ian.Campbell@xxxxxxxxxx>
>> > Cc: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
>> > Cc: xen-devel@xxxxxxxxxxxxxxxxxxxx
>> > Acked-by: Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>
>> > Acked-by: Julien Grall <julien.grall@xxxxxxxxxx>
>> > Acked-by: Michal Marek <mmarek@xxxxxxx>
>> > Acked-by: David Rientjes <rientjes@xxxxxxxxxx>
>> > Reviewed-by: Josh Triplett <josh@xxxxxxxxxxxxxxxx>
>> > Signed-off-by: Luis R. Rodriguez <mcgrof@xxxxxxxx>
>> > ---
>>
>> > diff --git a/scripts/kconfig/Makefile b/scripts/kconfig/Makefile
>> > index 6950032..f52abae 100644
>> > --- a/scripts/kconfig/Makefile
>> > +++ b/scripts/kconfig/Makefile
>> > @@ -115,6 +115,10 @@ PHONY += kvmconfig
>> >  kvmconfig: kvm_guest.config
>> >         @:
>> >
>> > +PHONY += xenconfig
>> > +xenconfig: xen.config
>> > +       @:
>> > +
>> >  PHONY += tinyconfig
>> >  tinyconfig:
>> >         $(Q)$(MAKE) -f $(srctree)/Makefile allnoconfig tiny.config
>>
>>
>> "make xenconfig" is equivalent to "make xen.config"
>> and only saves one character.
>>
>> Now we have only three targets for mergeconfig (tiny, kvm, xen),
>> so it is OK to add this as an alias.
>> But if we have more such targets, we might have
>> to consider to use generic targets (*.config) at some point.
>
> I'm frankly terrified of all these config target options growing more and
> the possible large collateral of patches to Kconfig files in the future. Since
> this is a small specialized group now, I think we should treat it as such but
> I think what you say has good merit long run.
>
> For now I'm more of a fan we limit what we stuff in here and if this explodes
> then only have new options use the subject.config target. Thoughts?


Sounds good to me.






>> I do not intend to block this.
>> Just take my comment with a grain of salt..
>>
>>
>> > @@ -140,6 +144,7 @@ help:
>> >         @echo  '  listnewconfig   - List new options'
>> >         @echo  '  olddefconfig    - Same as silentoldconfig but sets new 
>> > symbols to their default value'
>> >         @echo  '  kvmconfig       - Enable additional options for kvm 
>> > guest kernel support'
>> > +       @echo  '  xenconfig       - Enable additional options for xen dom0 
>> > and guest kernel support'
>> >         @echo  '  tinyconfig      - Configure the tiniest possible kernel'
>> >
>> >  # lxdialog stuff
>>
>>
>> If kvmconfig and xenconfig are only available for x86,
>> is it better to enclose those helps with
>> ifeq ($(ARCH),x86)
>>  ...
>> endif
>
> That's true if kvm was only for x86 but it is not, and likewise for xen.
>

OK, then.  Thanks for explaining this.




-- 
Best Regards
Masahiro Yamada

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