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

From: Greg Kurz <groug@kaod.org>
To: Eric Blake <eblake@redhat.com>
Cc: Stefan Hajnoczi <stefanha@redhat.com>,
	Pradeep Jagadeesh <pradeepkiruvale@gmail.com>,
	"Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>,
	Alberto Garcia <berto@igalia.com>,
	Pradeep Jagadeesh <pradeep.jagadeesh@huawei.com>,
	qemu-devel@nongnu.org, Fam Zheng <famz@redhat.com>
Subject: Re: [Qemu-devel] [PATCH 1/2 v16] fsdev: add IO throttle support to fsdev devices
Date: Wed, 22 Feb 2017 17:59:17 +0100	[thread overview]
Message-ID: <20170222175917.53c27906@bahia.lan> (raw)
In-Reply-To: <18735c6a-e21e-6aaf-4283-53f980afae3f@redhat.com>

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On Wed, 22 Feb 2017 10:01:09 -0600
Eric Blake <eblake@redhat.com> wrote:

> On 02/22/2017 07:41 AM, Greg Kurz wrote:
> > 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 ?  
> 
> Yes, I think we'll be okay. Libvirt will just be unable to recognize the
> feature until the QMP bits are in place.
> 

Ok. I'll work this out with Pradeep for 2.10.

> 
> >>>> 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.  
> 
> We just need to be sure that when we do add QMP, that it doesn't use
> names that differ from the command line (blockdev is an example where we
> weren't careful in 2.8, and had to rename things in 2.9 to be
> consistent, and I want to avoid repeating that mistake).
> 

Can you provide some pointers on what had to be fixed in blockdev ?

Thanks.

--
Greg

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