Re: [Qemu-devel] [PATCH 05/17] kvm: add kvm stub for arch specific stuff

[Jan Kiszka <jan.kiszka@siemens.com>]

On 2011-05-04 07:19, Alexander Graf wrote:
> 
> On 03.05.2011, at 16:57, Jan Kiszka wrote:
> 
>> On 2011-05-03 16:17, Alexander Graf wrote:
>>>
>>> On 18.04.2011, at 20:34, Aurelien Jarno wrote:
>>>
>>>> On Fri, Apr 15, 2011 at 05:32:46PM +0200, Alexander Graf wrote:
>>>>> We have a generic stub architecture for kvm calls, but some architectures
>>>>> are different from others. So we do want to be able to have stubs for
>>>>> architecture specific functionality as well.
>>>>>
>>>>> This patch adds kvm stubs for all architectures.
>>>>>
>>>>> Signed-off-by: Alexander Graf <agraf@suse.de>
>>>>> ---
>>>>> Makefile.target                   |    2 +-
>>>>> target-alpha/kvm-arch-stub.c      |   26 +++++++++++++++++++++++++
>>>>> target-arm/kvm-arch-stub.c        |   26 +++++++++++++++++++++++++
>>>>> target-cris/kvm-arch-stub.c       |   26 +++++++++++++++++++++++++
>>>>> target-i386/kvm-arch-stub.c       |   26 +++++++++++++++++++++++++
>>>>> target-lm32/kvm-arch-stub.c       |   26 +++++++++++++++++++++++++
>>>>> target-m68k/kvm-arch-stub.c       |   26 +++++++++++++++++++++++++
>>>>> target-microblaze/kvm-arch-stub.c |   26 +++++++++++++++++++++++++
>>>>> target-mips/kvm-arch-stub.c       |   26 +++++++++++++++++++++++++
>>>>> target-ppc/kvm-arch-stub.c        |   26 +++++++++++++++++++++++++
>>>>> target-s390x/kvm-arch-stub.c      |   38 +++++++++++++++++++++++++++++++++++++
>>>>> target-sh4/kvm-arch-stub.c        |   26 +++++++++++++++++++++++++
>>>>> target-sparc/kvm-arch-stub.c      |   26 +++++++++++++++++++++++++
>>>>> target-unicore32/kvm-arch-stub.c  |   26 +++++++++++++++++++++++++
>>>>> 14 files changed, 351 insertions(+), 1 deletions(-)
>>>>> create mode 100644 target-alpha/kvm-arch-stub.c
>>>>> create mode 100644 target-arm/kvm-arch-stub.c
>>>>> create mode 100644 target-cris/kvm-arch-stub.c
>>>>> create mode 100644 target-i386/kvm-arch-stub.c
>>>>> create mode 100644 target-lm32/kvm-arch-stub.c
>>>>> create mode 100644 target-m68k/kvm-arch-stub.c
>>>>> create mode 100644 target-microblaze/kvm-arch-stub.c
>>>>> create mode 100644 target-mips/kvm-arch-stub.c
>>>>> create mode 100644 target-ppc/kvm-arch-stub.c
>>>>> create mode 100644 target-s390x/kvm-arch-stub.c
>>>>> create mode 100644 target-sh4/kvm-arch-stub.c
>>>>> create mode 100644 target-sparc/kvm-arch-stub.c
>>>>> create mode 100644 target-unicore32/kvm-arch-stub.c
>>>>
>>>> Do we really want to create so much files on architectures we will never
>>>> see KVM support? Actually I know very few things about KVM, so it would
>>>> be better to have this patch reviewed by someone else. Avi or Anthony
>>>> maybe?
>>>
>>> Well, the main idea is to be able to have a unified place to put stub functions into. And as it stands with most generalizations, we either make it generic or not :).
>>> Maybe there's some Makefile magic to only compile the stub if the file exists? I certainly don't know of any.
>>
>> This approach looks wrong.
>>
>> The point of kvm stubs is to allow generic components to be built
>> independently of kvm enabled/disabled. But target-specific callbacks
>> can't be part of generic components anyway. So there is no need for a
>> stub, those bits will be built per-target anyway.
>>
>> The examples you provided with this patch underline it:
>> s390-virtio-bus.c should be built for s390 but nothing else.
> 
> And it is, yes. The point is to not require #ifdefs in device emulation code :).

But that's not the purpose of the stubs. They shall avoid building
components target specific when just the kvm on/off dependency would
force them to. Moreover, I do not see any need for such in
infrastructure beyond s390 when considering that case valid.

Why not simply define those few functions as static inline in the
already s390-specific header depending on #ifdef CONFIG_KVM?

Jan

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