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Re: [Xen-devel] [PVUSB] usbbusname is changing after rebooting

To: Neobiker <neo-ml-efw-1106@xxxxxxxxxxx>
Subject: Re: [Xen-devel] [PVUSB] usbbusname is changing after rebooting
From: Sergey Tovpeko <tsv.devel@xxxxxxxxx>
Date: Mon, 07 Sep 2009 13:20:30 +0400
Cc: xen-devel@xxxxxxxxxxxxxxxxxxx
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Hi, Neobiker!

Usbbusnumber is the combination of 'usb host controller' number and 'hub port' number. I'm not USB expert, but as i understood, 'USB host controller' number is assigned during computer booting by 'usb core driver'. And on my machine I see that the same USB host controller may get different number on rebooting. I suppose here is a race between controllers on device probing process. But i don't have any technical referencies of this. It's my notion only. And, perhaps it's the question of PCI devices detection process, because USB host controller is part of a PCI device.

And, in your case, you have to different usb host controllers and they have got different numbers. UHCI is the USB 1.0 standard with low data throughput, this enough for printers. USB stick requires more speed for data transfer, and USB 2.0 (EHCI controller) is granted for it. I suppose, you're lucky and you have the stable numbers for each controllers.

Sergey.
Hi Sergey,

i thought i had trouble with that too, until i figured out that the USB-Bus
only seemed to have changed, when i changed the connected Device e.g. from
USB-Printer to USB-Stick. The Printer uses the UHCI Controller (3-1), versus
the USB-Stick connected to the EHCI Controller (5-1). Besides this the USB
ports are stable on my Debian Lenny System.
So in my summary, the USB-Bus don't changes if you don't switch from UHCI to
EHCI according to the connected device.

regards Neobiker

Sergey-53 wrote:
Hello, all!
Hello, Noboru!

Hotplug rule for PVUSB consists of
<usbbusname>:<domid>:<vusb number>:<port number>

I noticed that usbbusname sometimes changes from time to time after host rebooting.
For example, yesterday i had it as "6-1", today it is "2-1".

I saw the topic about usbbusname on replugging.
http://lists.xensource.com/archives/html/xen-devel/2009-04/msg00400.html
Replugging doesn't change the usbbusname, but what about host rebooting?

I suppose, usb bus number is assigned during booting and may vary each time. To identify usb device correctly i have to see dmesg after rebooting. It's quite inconvinient, imho.

What do you think about another method of USB naming like VendorId:ProductId of usb devices to be grabbed by domU? It seems that HVM guests use this method by means of the parameter 'usbdevice'.

Thank you.

Sergey.


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