Re: [Xen-devel] [PATCH V7 6/7] xl: add usb-assignable-list command

[George Dunlap <george.dunlap@xxxxxxxxxx>]

On 07/10/15 13:05, Juergen Gross wrote:
> On 10/07/2015 01:55 PM, Ian Campbell wrote:
>> On Wed, 2015-10-07 at 13:49 +0200, Juergen Gross wrote:
>>> On 10/07/2015 01:39 PM, Ian Campbell wrote:
>>>> On Wed, 2015-10-07 at 13:25 +0200, Juergen Gross wrote:
>>>>>> The "usb-assignable-list" that Chunyan has submitted will give you
>>>>>> a
>>>>>> list of all dom0 USB devices that have not yet been assigned to a
>>>>>> guest.
>>>>>>     It should be basically equivalent to "lsusb", except that it
>>>>>> filters
>>>>>> out devices which have already been assigned to VMs.
>>>>
>>>> Right, that does sound like useful enough functionality to justify not
>>>> just
>>>> using lsusb.
>>>>
>>>>>> In the e-mail you respond to, I was suggesting that
>>>>>>
>>>>>> # xl usb-list --all
>>>>>>
>>>>>> would show you usb devices attached to every VM, and also USB
>>>>>> devices
>>>>>> attached to no VM, and that
>>>>
>>>> And would "xl usb-list" list all domain attached to every VM but not
>>>> the
>>>> unattached ones?
>>>>
>>>>>> # xl usb-list --host
>>>>>>
>>>>>> would show you only host usb devices not attached to any VM.
>>>>>>
>>>>>> I think it's the second bit if functionality which Juergen is keen
>>>>>> be
>>>>>> available in some form or other.
>>>>>
>>>>> Exactly.
>>>>
>>>> I'm happy with this proposal too.
>>>>
>>>> Is the distinction between --host and --all important to you? Assuming
>>>> unassigned devices are clearly indicated in the --all output (as they
>>>> should be).
>>>
>>> Depends on how the output would look like.
>>>
>>> In case it either isn't containing VMs without any attached USB device
>>> or the unassigned devices are listed at the end this would be okay. I
>>> just wouldn't want to have to scroll a lot in case of a host with 1000
>>> domains.
>>
>> Makes sense.
>>
>>> BTW: In case you don't have the --host option it would be nice to omit
>>> --all as well and just assume --all when no domain was specified (like
>>> xl list).
>>
>> I think "xl usb-list" should list the devices attached to all domains,
>> for
>> sure. I'm ambivalent about whether it also lists unattached devices (in
>> which case --all is unnecessary) or if --all is required to get those.
> 
> I'd go for nuking the --all option. I suppose xl usb-list without
> specifying a domain will nearly always be used to see the unassigned
> devices and not "uuh, to which domain did I assign device x?".

I don't know -- if you've assigned a device to one particular domain,
then it seems pretty likely that at some point in the future you might
want to say, "Wait, what devices do I have assigned where again?"

I think
* people will expect "xl usb-list" to show all VMs but *not* all
unassigned host devices
* In this sort of a case, doing what people expect is probably more
important than doing what we think is probably more convenient for them.

I'd go for "--all" and "--host", but I think it's not terribly important.

Chunyan, do you have any input / opinions?

 -George

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