Re: [Xen-devel] [PATCH] [RFC] qemu-upstream: add discard support for xen_disk

[Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>]

On Fri, 17 Jan 2014, Olaf Hering wrote:
> On Fri, Jan 17, Stefano Stabellini wrote:
> 
> > On Thu, 9 Jan 2014, Olaf Hering wrote:
> > > The discard support is enabled unconditionally. But it would be worth to
> > > have a knob to disable it in case the backing file was intentionally
> > > created non-sparse to avoid fragmentation.
> > > How could this be knob be passed from domU.cfg:disk=[] to the actual
> > > qemu process?
> > 
> > It would need to be on xenstore, because that is the only per-disk
> > interface xen_disk is listening to.
> 
> I figured that out. There are already script=, backend= and other knobs.
> I will see how to add a discard=on|off to libxl and write that to the
> xenstore backend node so qemu can get it from there.
> What property name do you suggest? I have something like
> "toolstack-option-discard" in mind.

discard_enabled?


> > > blkfront_setup_discard should check for "qdisk" instead of (, or in
> > > addition to?) "file" to actually make use of this new feature.
> > 
> > Why? I don't think that would be correct: if the feature is advertised
> > on xenstore by the backend (feature-discard) then blkfront can/should
> > use it. If it is not present then it is not going to use it.
> > Let's not complicate things further.
> 
> blockfront is broken:
> http://lists.xenproject.org/archives/html/xen-devel/2014-01/msg00988.html

blkfront should be fixed then :-)


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