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

[Greg Kurz]

On Thu, 23 Mar 2017 15:19:28 +0100
Paolo Bonzini <address@hidden> wrote:

> 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
> 

If the header (or at least the parts that are relevant to QEMU) are stable
then my questioning can be ignored :)

Thanks.

--
Greg

> > 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
> >

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