Re: [PATCH 6/7] xen/guest_access: Consolidate guest access helpers in xen/guest_access.h

[Jan Beulich <jbeulich@xxxxxxxx>]

On 29.04.2020 16:04, Julien Grall wrote:
> Gentle ping. Any comments on the direction to take?

Just to avoid misunderstanding - while the mail was sent with me as
the only one on the To list, I don't think I've been meant, as I've
voiced my opinion. I assume you rather meant to ping others to chime
in?

Jan

> On 09/04/2020 10:28, Julien Grall wrote:
>>
>>
>> On 09/04/2020 09:06, Jan Beulich wrote:
>>> On 09.04.2020 10:01, Julien Grall wrote:
>>>> Hi,
>>>>
>>>> On 09/04/2020 07:30, Jan Beulich wrote:
>>>>> On 09.04.2020 00:05, Julien Grall wrote:
>>>>> I don't see why a new port may not also want
>>>>> to go that route instead of the x86/Arm one.
>>>> I could accept that someone would want to reinvent a new ABI
>>>> from scratch for just an hypothetical new arch. However it would
>>>> be quite an effort to reinvent XEN_GUEST_HANDLE(). The chance is
>>>> RISC-V is only going to re-use what Arm did as Arm already did
>>>> with x86.
>>>>
>>>> I would like to avoid to introduce a new directory asm-generic
>>>> with just one header in it. Maybe you have some other headers in
>>>> mind?
>>>
>>> I recall having wondered a few times whether we shouldn't use this
>>> concept elsewhere. One case iirc was bitops stuff. Looking over
>>> the Linux ones, some atomic and barrier fallback implementations
>>> may also sensibly live there, and there are likely more.
>>
>> In theory it makes sense but, in the current state of Xen, 'asm-generic' 
>> means they are common to Arm and x86. This is basically the same definition 
>> as for the directory 'xen'. So how do you draw a line which files go where?
>>
>> To be honest, I don't think we can draw a line without a 3rd architecture. 
>> So I would recommend to wait until then to create an asm-generic directory.
>>
>> Meanwhile, I still think the consolidation in xen/ is useful as it makes 
>> easier to maintain. It is also going to make easier for RISCv (or a new 
>> arch) as they don't have to worry about duplication (if any).
>>
>> In the event they decide to purse their own route, then it is not going to 
>> be a massive pain to move part of xen/guest_access.h in 
>> asm-generic/guest_access.h and include the latter from {xen, asm} 
>> /guest_access.h.
> 
> Cheers,
>