Re: [PATCH v5 01/11] xen/arm: xc_domain_ioport_permission(..) not supported on ARM.

[Bertrand Marquis <Bertrand.Marquis@xxxxxxx>]

Hi Ian,

> On 12 Oct 2021, at 15:53, Ian Jackson <iwj@xxxxxxxxxxxxxx> wrote:
> 
> Bertrand Marquis writes ("Re: [PATCH v5 01/11] xen/arm: 
> xc_domain_ioport_permission(..) not supported on ARM."):
>> So there is no comment remaining on this patch ?
> 
> I have been following this thread.  I think I have a notion of why
> this is needed but I'm not 100% clear on it.  The commit message says
> this:
> 
>> ARM architecture does not implement I/O ports. Ignore this call on ARM
>> to avoid the overhead of making a hypercall just for Xen to return
>> -ENOSYS.
> 
> which implies it's a performance improvement.  But the change also
> suppresses an error return, so this commit message is false.  I think
> that the thread has concluded something different, but it should be
> explained in the commit message.  The purpose of a commit message is
> precisely to capture the kind of considerations and discussion that
> occurred in this thread.

I can add something in the commit message about the fact that we improve
performance and prevent to do a call that is and will not be supported in Xen.

> 
> If the overall outcome implied by this patch is correct (as I *think*
> the thread has concluded) then I don't think the #ifdefery is
> appropriate.  This should be done with a new arch-specific function in
> libxl_x86.c and libxl_arm.c.  I'm not sure precisely what that
> function should be called, but maybe something like
>  libxl_ioports_supported
> ?
> 
> I see that the fact that we avoid #ifdefs wasn't documented in
> CODING_STYLE, so I have sent a patch to add that.  Sorry about that.

I saw your change in CODING_STYLE and I understand the request.
I will try to see if we can handle this change before the feature freeze.

Regards
Bertrand

> 
> Thanks,
> Ian.