Re: [Xen-devel] Any plan to support disk driver domain?

[George Dunlap <George.Dunlap@xxxxxxxxxxxxx>]

On Thu, Jul 25, 2013 at 9:31 AM, Roger Pau Monné <roger.pau@xxxxxxxxxx> wrote:
> On 24/07/13 18:17, G.R. wrote:
>>>
>>>> In your example, the driver is setup using zvol. I wonder if there are
>>>> any constraint prohibiting using a file based backend?
>>>
>>> I have not tried it, but FreeBSD blkback should be able to handle raw
>>> files also.
>>>
>>>> Finally, I saw this limitation in the wiki:
>>>>>> It is not possible to use driver domains with pygrub or HVM guests yet, 
>>>>>> so it will only work with PV guests that have the kernel in Dom0.
>>>> While I can imagine why pygrub does not work, I don't understand the
>>>> reason HVM is affected here. Could you explain a little bit?
>>>> And what about a HVM with PV driver? (e.g. those windows guests)
>>>
>>> If you use HVM, Qemu needs to access the block/file used as disk, so if
>>> the disk is on another domain Qemu has no way to access it (unless you
>>> plug the disk to the Dom0 and then pass the created block device
>>> /dev/xvd* to Qemu).
>>>
>>
>> I just upgrade to xen 4.3 and here is my quick report.
>>
>> With some preliminary test, I can confirm that freebsd 8.3 is able to
>> serve as disk backend, exporting file as a disk.
>> I was able to block-attach it and mount it in dom0.
>> However, there are some issues with the xl block-list / block-detach command.
>> The attached disk cannot be listed. And block-detach will report fail
>> when I try to get it removed.
>
> This is probably due to block-list/attach commands making assumptions
> about the backend domain always being Dom0. I will take a look, thanks
> for the report.

Yes, I also discovered this recently when using a network driver
domain -- the *-list commands only look in dom0 for stuff.   That will
have to be sorted out for 4.4.

 -George

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