Re: [Xen-devel] [PATCH V4 3/7] libxl: add pvusb API

[George Dunlap <George.Dunlap@xxxxxxxxxxxxx>]

On Tue, Jun 16, 2015 at 12:19 PM, Juergen Gross <jgross@xxxxxxxx> wrote:
> On 06/16/2015 01:11 PM, George Dunlap wrote:
>>
>> On Tue, Jun 16, 2015 at 11:51 AM, Juergen Gross <jgross@xxxxxxxx> wrote:
>>>>
>>>> The "busid" interface that Chunyan is describing requires the caller
>>>> to find out that long name -- 2-3.1.2 -- rather than the traditional
>>>> short name (002:010).  Just accepting "2-3" is not sufficient.
>>>
>>>
>>>
>>> qemu with my patch will find the device only if the long name is used.
>>> So the "port" in qemu would be "3.1.2" in your example above.
>>
>>
>> Ah, right -- sorry, looking at the patch I saw that "port" was
>> converted using strtoul, but now I see that was "bus", and that "port"
>> is a string.  That's what I was missing.
>>
>>> BTW: be careful with the syntax: x:y is used by qemu to specify a device
>>> by vendorId:productId, you should write "002.010" to use the short name
>>> above.
>>
>>
>> Yes, thanks for the reminder.  I knew there was some way to
>> distinguish bus.addr and vendor:device, but I'd forgotten the exact
>> semantics.
>>
>> So as Juergen says, the typical way to write these would be:
>> - bus-port; e.g., 2-3.1.2  is bus=2, port=3.1.2.  Stable in topology,
>> not in device
>
>
> Nah, not stable in topology. At least on my laptop I've seen a memory
> stick plugged in at the same position as "3-3" or as "1-3".
>
> I'm pretty sure this is just a matter of timing during boot: the busses
> are all (or at least some of them) queried at the same time and the
> first answering gets number 1, the next 2, and so on. And timing seems
> to be different enough to result in unstable bus numbers.

Right -- I meant "stable in topology within one boot", but at least
two of you have now understood me to mean "across reboots" by default,
so that's obviously a detail that needs to be specified. :-)

 -George

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