Re: [PATCH RFC v1] libxl: Introduce a template for devices with a controller

[Juergen Gross <jgross@suse.com>]

On 05/27/2015 03:57 PM, George Dunlap wrote:
> On 05/27/2015 11:09 AM, Juergen Gross wrote:
>> George,
>>
>> I'm on vacation this and the next week with only limited email access.
>> So please don't expect fast reaction on any further questions during
>> this time. :-)
>
> Then quit reading your work e-mail and get back to the important stuff! :-)
>
>>> OK, so I looked it up[1] and the full address seems to be:
>>> * adapter number / host
>>> * channel number / bus
>>> * id number / target
>>> * LUN
>>>
>>> In which case, "controller" would correspond to "adapter / host", right?
>>>
>>> In the vscsi world, what levels of what can you make?  I know you
>>> mentioned before that some devices have multiple LUNs, and those need
>>> to be grouped together, with the same LUNs as they do on real
>>> hardware, to work properly -- is that right?
>>
>> Not all of the devices have this requirement, but some.
>>
>>> The USB case actually has something somewhat similar:
>>> * USB controller
>>> * USB bus
>>> * USB device
>>> * USB function
>>>
>>> So far, there's not really a controller/bus distinction: each
>>> controller has exactly one bus.  When we assign a USB device to a bus,
>>> we automatically go through and assign each function fo that device
>>> individually.
>>>
>>> Would it make sense to treat vscsi the same way -- i.e., to make a
>>> "bus", and then attach "targets"s to it, and have the LUNs for any
>>> given target automatically assigned when the target is assigned?
>>
>> As long as it is still possible to assign individual LUNs as well.
>> If dom0 is controlling e.g. a RAID system you might want to assign
>> one LUN of a target to domU A and one LUN of the same target to domU B.
>
> OK, so it sounds like in the vscsi case, it would be useful to assign
> either an entire target, or an individual LUN.
>
> In the case of assigning a target, you'll want to assign all the LUNs as
> well, such that the virtual LUNs mirror the real LUNs.
>
> In the case of assigning a LUN, I assume you'll still need a virtual
> target.  Will you be wanting an interface for creating virtual targets,
> so that you can assign several real LUNs to the same target?  Or will
> you just want one virtual target per LUN if you're not assigning an
> entire target?

Nearly missed this question.

Hmm, I think the first option would be better. Otherwise it could be
difficult to assign a just created LUN of a target to the same virtual
target while the system is running.


Juergen