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

[Greg Kurz]

On Thu, 23 Mar 2017 14:55:26 +0100
Juergen Gross <address@hidden> 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.
> 

Ok.

> 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?
> 

Not specifically, I was just feeling dubitative about that Xen header
being manually copied to the kernel tree and also to the QEMU tree.

> 
> Juergen
>

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