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

[George Dunlap <George.Dunlap@xxxxxxxxxxxxx>]

On Tue, Jun 16, 2015 at 12:12 PM, Ian Jackson <Ian.Jackson@xxxxxxxxxxxxx> wrote:
> George Dunlap writes ("Re: [Xen-devel] [PATCH V4 3/7] libxl: add pvusb API"):
>> The "busid" we're talking about here will identify a device at a
>> particular *port* in the USB topology; the busid will take whatever is
>> plugged into that particular port.  So in the example in my other
>> thread, the Yubikey "busid" is 2-3.1.2; but if I were to unplug the
>> yubikey and plud my mouse into that port, the mouse would then be at
>> 2-3.1.2.
>
> What you have just said contradicts Juergen's assertion that the busid
> is not stable across reboots.
>
> I think perhaps the difficulty is that the very first number, the usb
> controller number, may not be stable, because it depends on the order
> of device discovery.

I wasn't considering reboots when I made my statement.  According to a
comment on the libusb mailing list:

"The operating system does not guarantee that bus numbers will remain
fixed across reboots.  Usually they will (if the computer's hardware
hasn't been changed), but it isn't guaranteed." [1]

I just used "lsusb -v" to scan through all the devices I have
connected; some of them do have a field called "iSerial", but as most
of these are '0' and the ones that are non-zero are between 1 and 3, I
doubt that will be much use in most cases.  I don't immediately see
anything that might be a unique identifier.

 -George

[1] 
http://sourceforge.net/p/libusb/mailman/libusb-devel/thread/20080324215139.22289.qmail@xxxxxxx/

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