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

[George Dunlap <george.dunlap@xxxxxxxxxx>]

On 07/10/15 15:47, Juergen Gross wrote:
> On 10/07/2015 04:35 PM, George Dunlap wrote:
>> On Wed, Oct 7, 2015 at 3:26 PM, Juergen Gross <jgross@xxxxxxxx> wrote:
>>> On 10/07/2015 04:05 PM, Ian Campbell wrote:
>>>>
>>>> On Wed, 2015-10-07 at 15:54 +0200, Juergen Gross wrote:
>>>>
>>>>> Hmm, technically all unassigned USB-devices are usable from Dom0.
>>>>> So why
>>>>> not list them there.
>>>>
>>>>
>>>> I think you'd at least want to distinguish USB devices available to
>>>> dom0
>>>> as
>>>> via a PCI host controller from those which are available via pvusb.
>>>
>>>
>>> Yeah, the non-pvusb devices should be listed as "assignable" if they
>>> are handled by a driver domain.
>>>
>>>> This also doesn't quite work when driver domains are in the picture.
>>>
>>>
>>> --host does?
>>>
>>> TBH: driver domains seem to be a reason to not support the --host
>>> option. So the options are --all or no special option. I'm still
>>> fine with both.
>>
>> I think the idea is that --host doesn't pretend to.  But yes, if we
>> made it clear which devices were *assigned* to dom0 from another VM,
>> and which were *available from* dom0 to be assigned, then actually
>> that could be extended at some point in the future to include devices
>> available *from* driver domains.
>>
>> Alternately, perhaps we should just have
>> # xl usb-available [domain]
> 
> Would work for me.
> 
> Wait, wasn't there a similar command suggested? Something like
> "xl usb-assignable-list"? ;-)

Indeed there was!  A very useful command with a very sensible name...
unfortunately one with a very *similar* name to another command but with
different functionality.  And this similarity even confused one of the
tools maintainers, so would almost certainly confuse our users. :-)

>> Which will tell you the usb devices available to be assigned from that
>> domain; or all available usb devices from all driver domains.  And of
>> course for the time being it only works on domain 0, but future
>> functionality could implement it for driver domains as well.
>>
>>> BTW: Do Xen concepts allow to assign a USB-device via pvUSB from a
>>> driver domain to Dom0?
>>
>> Sure, why not?
> 
> With driver domains the picture is becoming more complicated.
> 
> The main question now is: What is the real purpose of "xl usb-list"?
> Should it list the devices which are assigned to a domain, or should it
> list the devices which are usable by a domain (probably attributed
> whether the device is assignable to other domains)?

For *all* of our other -list commands relating to guest devices --
pci-list, disk-list, network-list, vtpm-list, channel-list, tmem-list --
the list command shows the virtual devices *actually assigned to the
VM*.   Based on that, the core information that any user will *expect*
from "usb-list" will be "what usb devices are assigned to this VM".

I'm not opposed to extending usb-list to include extra useful
information; but it should be made clear to the user which information
is the "core expected" information (i.e., what usb devices are assigned
to this VM) and what is "extra" information (i.e., what usb devices are
available to be assigned *from* this VM).

So I think we have 3 options that people don't find objectionable:

1. Add --all and --host options to usb-list. (Or perhaps, --available.)

2. Have usb-list also list "available" devices from driver domains,
clearly marked distinct from devices *assigned to* that driver domain
from another domain, and to begin with only working for dom0.

3. A new command, "usb-available" to list available devices from driver
domains, to begin with only working for dom0.

I think I'd go for #3, but mostly I think we need to decide *something*
so we can move forward.

 -George


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