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

[Alexander Graf]

On 04.05.2011, at 10:31, Jan Kiszka wrote:

> 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 <address@hidden>
>>>>>> ---
>>>>>> 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?

Which already-s390-specific header depending on #ifdef CONFIG_KVM? The current 
definitions are in cpu.h which is included in code that doesn't include CONFIG*.


Alex