Re: [RFC] support more qdisk types

["Roger Pau Monné" <roger.pau@citrix.com>]

El 3/2/16 a les 12:05, Ian Campbell ha escrit:
> On Wed, 2016-02-03 at 10:55 +0000, Wei Liu wrote:
>> On Wed, Feb 03, 2016 at 10:51:27AM +0000, Ian Campbell wrote:
>>> On Wed, 2016-02-03 at 10:35 +0000, Wei Liu wrote:
>>>>> Ok. So in your opinion, even if any new disk config is encoded in
>>>>> 'target=',
>>>>> libxlu should split that up into (new) members of
>>>>> libxl_device_disk, not just
>>>>> plop it into libxl_device_disk.pdev_path?
>>>>>
>>>>
>>>> No, not necessarily. I didn't look closely in the code yesterday when
>>>> replying, sorry.
>>>>
>>>> If  target= has always been shoveled into pdev_path, using that would
>>>> be
>>>> fine. We already have mechanism to parse target= outside of libxl in
>>>> hotplug script.
>>>>
>>>> Are you aware of all those hotplug scripts living under tools/hotplug
>>>> ?
>>>> Does using hotplug script sound plausible to you?
>>>>
>>>> Currently hotplug script for QEMU is broken and needs fixing though,
>>>> but
>>>> I'm sure we can figure it out.
>>>
>>> How do hotplug scripts factor into this?
>>>
>>
>> If supporting all such block devices  requires presenting a block device
>> to QEMU? If QEMU directly handles them then hotplug script is not in the
>> picture.
> 
> Perhaps I've misunderstood what this thread is about. I thought it was
> about exposing all the various backends which qdisk supports natively, like
> CEPH, sheepdog, iscsi, nbd etc.

AFAIK QEMU/Qdisk doesn't need a block device or regular file in order to
work, it can use as said above things like iSCSI (which we current
support using a script + blkback [0]), nbd, ceph...

There's been some discussion in the past about whether hotplug scripts
should also be supported by QEMU/Qdisk, or even whether the launch of
the Qdisk backend itself should be done inside of a hotplug script
(abstracting it away from libxl). I think George had some ideas/work on
this (or did look into similar issues in the past).

IMHO, I don't think we need hotplug scripts support for Qemu/Qdisk
handled backends.

Roger.

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http://xenbits.xen.org/gitweb/?p=xen.git;a=commit;h=bda856e1023868b1e9605e845bedbd8b7ed2944e