Re: [Qemu-devel] [PATCH 1/2 v16] fsdev: add IO throttle support to fsdev devices

[Greg Kurz <groug@kaod.org>]

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Eric,

I fully understand your concern about the missing QMP bits, but given the other
comments people made on this series, I'd like to move forward and merge it for
2.9, without the 'x-' prefixed options. Is it okay with you ?

Cheers.

--
Greg

On Tue, 14 Feb 2017 13:21:22 +0000
Stefan Hajnoczi <stefanha@redhat.com> wrote:

> On Tue, Feb 07, 2017 at 05:29:33PM +0100, Greg Kurz wrote:
> > Cc'ing Stefan who reviewed patch 2/2.
> > 
> > On Tue, 7 Feb 2017 09:56:08 -0600
> > Eric Blake <eblake@redhat.com> wrote:
> >   
> > > On 02/07/2017 04:32 AM, Greg Kurz wrote:  
> > > >>
> > > >> I'm not aware of anything related to fsdev in QMP... and libvirt seems to
> > > >> only parse the output of -help to guess fsdev capabilities.    
> > > > 
> > > > Oops, reading some more libvirt code I now see that libvirt doesn't parse
> > > > -help anymore with QEMU >= 1.2.0... sorry for the noise :)
> > > >     
> > > >> And indeed,
> > > >> qemu-options.hx doesn't expose this new feature.
> > > >>    
> > > >>> Please make sure we don't reach 2.9 with only a half-baked feature;
> > > >>> whether that means finishing the QMP work or temporarily disabling the
> > > >>> cli additions until a later release can finish the work.
> > > >>>       
> > > >>
> > > >> Would this be ok to add the missing bits in qemu-options.hx or do you
> > > >> expect more ?    
> > > 
> > > If it cannot be probed via QMP, then libvirt will most likely assume
> > > that it does not exist.  I guess we're okay having command line only in
> > > 2.9 if you can't get QMP working, because libvirt will just never drive
> > > the feature until 2.10 when QMP is available; but then we risk the
> > > command line subtly changing and breaking someone else that was using
> > > the command line without QMP.  Maybe the safest approach is to just use
> > > the 'x-' prefix to the command line portion, until the feature is complete.
> > >   
> > 
> > The semantics here are exactly the same as for block devices. The
> > command line options added to -fsdev are the very same already used
> > by -drive for years.
> > 
> > Patch 2/2 in this series even factors them out to a common header file
> > to be used by fsdev and blockdev. I really don't expect any modification
> > at all on the command line (nor the other people who reviewed that patch
> > obviously)... are you suggesting that we should put 2/2 on hold and
> > use the 'x-' prefix anyway ?  
> 
> I see these parameter names as stable.  There is little risk that they
> would change.
> 
> Stefan

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