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From: Juergen Gross <jgross@suse.com>
To: George Dunlap <george.dunlap@citrix.com>,
	George Dunlap <George.Dunlap@eu.citrix.com>
Cc: Wei Liu <wei.liu2@citrix.com>,
	"xen-devel@lists.xen.org" <xen-devel@lists.xen.org>,
	Ian Jackson <ian.jackson@eu.citrix.com>,
	Chunyan Liu <cyliu@suse.com>,
	Stefano Stabellini <stefano.stabellini@eu.citrix.com>
Subject: Re: [PATCH 2/3] libxl: add domain config parameter to force start of qemu
Date: Mon, 21 Mar 2016 15:44:57 +0100	[thread overview]
Message-ID: <56F008E9.7070205@suse.com> (raw)
In-Reply-To: <56F004F2.1070701@citrix.com>

On 21/03/16 15:28, George Dunlap wrote:
> 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.

Okay, let's see what can be arranged.

BTW: This patch is not strictly required for patch 3. Patch 3 is just
adding another case where no device model is available when needed.


Juergen

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  reply	other threads:[~2016-03-21 14:44 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
2016-03-21 14:44         ` Juergen Gross [this message]
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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