Re: [Xen-devel] [PATCH] libxl: prefer qdisk over blktap when choosing disk backend

[Wei Liu <wei.liu2@xxxxxxxxxx>]

On Wed, Aug 28, 2013 at 02:35:56PM +0100, Wei Liu wrote:
> On Wed, Aug 28, 2013 at 03:16:23PM +0200, Fabio Fantoni wrote:
> > Il 28/08/2013 15:04, Ian Jackson ha scritto:
> > >Fabio Fantoni writes ("Re: [Xen-devel] [PATCH] libxl: prefer qdisk over 
> > >blktap when choosing disk backend"):
> > >>I think is good prefer qdisk also for significant performance increase
> > >>in comparison with blktap2.
> > >Thanks, that's useful information.  That, and what George said, have
> > >convinced me this is the right change.
> > >
> > >Acked-by: Ian Jackson <ian.jackson@xxxxxxxxxxxxx>
> > 
> > What about qemu traditional with this patch?
> > I haven't tested qdisk with qemu traditional but unfortunately
> > qemu-trad. is still widely used and therefore you have to be sure
> > that does not cause problems.
> 
> Ah, now I get your question.
> 
> > I asked about because devices parts seem the same with both qemu but
> > I not sure about it.
> 
> We've already switched to qemu-upstream in 4.3. And this patch is not
> backport material so old system would just work fine IMHO.
> 
> The only risk of breakage is: users have device_model_version set to
> qemu-trad and run blktap kernel with Xen pre-4.3, then upgrade to Xen
> post-4.3 (with this patch). I've tested that, and qemu-trad runs fine
> for me -- at least it boots and dd works well.
> 

I didn't have a VHD image (format commonly supported by blktap and qemu)
at hand so the test was not complete. But qemu-trad and qemu-xen are
both maintained so even if it breaks we are able to fix them -- which is
main point of this patch, to let users have better supported backend.

Wei.

> Wei.

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