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From: George Dunlap <george.dunlap@citrix.com>
To: Juergen Gross <jgross@suse.com>,
	George Dunlap <George.Dunlap@eu.citrix.com>
Cc: Ian Jackson <ian.jackson@eu.citrix.com>,
	Stefano Stabellini <stefano.stabellini@eu.citrix.com>,
	Wei Liu <wei.liu2@citrix.com>, Chunyan Liu <cyliu@suse.com>,
	"xen-devel@lists.xen.org" <xen-devel@lists.xen.org>
Subject: Re: [PATCH 2/3] libxl: add domain config parameter to force start of qemu
Date: Mon, 21 Mar 2016 14:28:02 +0000	[thread overview]
Message-ID: <56F004F2.1070701@citrix.com> (raw)
In-Reply-To: <56EBB83F.7040008@suse.com>

On 18/03/16 08:11, Juergen Gross wrote:
> On 17/03/16 17:06, George Dunlap wrote:
>> On Thu, Mar 10, 2016 at 3:00 PM, Juergen Gross <jgross@suse.com> wrote:
>>> Today the device model (qemu) is started for a pv domain only in case
>>> a device requiring qemu is specified in the domain configuration
>>> (qdisk, vfb, channel). If there is no such device the device model
>>> isn't started and hence it is possible to add such a device to the
>>> domain later.
>>>
>>> Add a domain configuration parameter to specify the device model is
>>> to be started in any case. This will enable adding devices with a
>>> qemu based backend later.
>>>
>>> While the optimal solution would be to start the device model
>>> automatically when needed this would require some major rework of
>>> libxl at multiple places.
>>>
>>> Signed-off-by: Juergen Gross <jgross@suse.com>
>>
>> So wait -- what happens now if you try to attach a disk with a qdisk
>> backend to a PV guest that didn't start with qemu running?
> 
> It won't work (that was my test case for the patch).
> 
>> I'd really like to see patch 3 get in, but I'm not really in favor of
>> this sort of a user-visible hack, particularly as we have to support
>> it in libxl more or less indefinitely.
> 
> Hmm, really? We can add a smarter variant later which will start the
> device model in case it isn't started yet. Then the new config parameter
> could be just ignored.

Sure; but it will (probably) only actually be useful for one release
cycle (now 6 months), and then it will sit around cluttering up the
interface for years to come.  The situation wrt hotplug has been this
way for years now, and nobody has complained; I don't think an extra 6
months will be a big deal.

Ultimately it's the tools maintainers' call; I wouldn't argue against it
if one of them think it's a good idea.

> I didn't do the smart variant as I'm not sure I could set it up in time
> for 4.7. I'd be happy to do it with some assistance regarding the async
> framework of libxl I'm not at all familiar with.

I'm sure help could be arranged; but it might be difficult to do by 4.7.

 -George


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  reply	other threads:[~2016-03-21 14:28 UTC|newest]

Thread overview: 19+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-03-10 15:00 [PATCH 0/3] libxl: add support for qemu base pvusb backend Juergen Gross
2016-03-10 15:00 ` [PATCH 1/3] libxl: make libxl__need_xenpv_qemu() operate on domain config Juergen Gross
2016-03-17 16:53   ` George Dunlap
2016-03-18  8:23     ` Juergen Gross
2016-03-10 15:00 ` [PATCH 2/3] libxl: add domain config parameter to force start of qemu Juergen Gross
2016-03-17 16:06   ` George Dunlap
2016-03-18  8:11     ` Juergen Gross
2016-03-21 14:28       ` George Dunlap [this message]
2016-03-21 14:44         ` Juergen Gross
2016-03-10 15:00 ` [PATCH 3/3] libxl: add new pvusb backend "qusb" provided by qemu Juergen Gross
2016-03-17 16:39   ` George Dunlap
2016-03-18  8:22     ` Juergen Gross
2016-03-17 16:55   ` George Dunlap
2016-03-18  8:24     ` Juergen Gross
2016-03-24 20:07       ` Wei Liu
2016-03-25  6:09         ` Juergen Gross
2016-03-29  9:45           ` George Dunlap
2016-03-29 10:35             ` Juergen Gross
2016-03-30  4:43               ` Juergen Gross

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