Re: [Qemu-devel] [PATCH v4 1/8] xen: import ring.h from xen

[Paolo Bonzini]

On 23/03/2017 14:55, Juergen Gross wrote:
> On 23/03/17 14:00, Greg Kurz wrote:
>> On Mon, 20 Mar 2017 11:19:05 -0700
>> Stefano Stabellini <address@hidden> wrote:
>>
>>> Do not use the ring.h header installed on the system. Instead, import
>>> the header into the QEMU codebase. This avoids problems when QEMU is
>>> built against a Xen version too old to provide all the ring macros.
>>>
>>> Signed-off-by: Stefano Stabellini <address@hidden>
>>> Reviewed-by: Greg Kurz <address@hidden>
>>> CC: address@hidden
>>> CC: address@hidden
>>> ---
>>> NB: The new macros have not been committed to Xen yet. Do not apply this
>>> patch until they do.
>>> ---
>>
>> Looking at your other series for the kernel part of this feature:
>>
>> https://lkml.org/lkml/2017/3/22/761
>>
>> I realize that the ring.h header from Xen also exists in the kernel tree... 
>>
>> Shouldn't all the code that can be used in both kernel and userspace go to a
>> header file under include/uapi in the kernel tree ? And then we would import
>> it under include/standard-headers/linux in the QEMU tree and we could keep it
>> in sync using scripts/update-linux-headers.sh.
>>
>> Cc'ing Paolo for insights.
> 
> As Xen isn't part of the kernel we don't want that. You can use and/or
> build qemu with xen-9pfs backend support on an old Linux kernel without
> the related frontend.

As long as the header changes rarely, I guess it's fine not to go
through update-linux-headers.sh.

Paolo

> OTOH I don't see the advantage of not using the headers from Xen. This
> is working for qdisk and pvusb backends and for all the Xen libraries.
> Do you expect the 9pfs backend to be used for a qemu version built
> against a Xen version not supporting that backend?
> 
> 
> Juergen
>