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

[Jürgen Groß <jgross@xxxxxxxx>]

On 06/16/2015 06:51 PM, Ross Philipson wrote:
> On 06/16/2015 12:39 PM, George Dunlap wrote:
> > On 06/16/2015 05:32 PM, Ian Jackson wrote:
> > > I have just discovered that the value used in /dev/disk/by-path is not
> > > from sysfs, or at least, not directly.
> > >
> > > udev cobbles it together with a bunch of string mangling, from
> > > information mostly from sysfs.  There is no corresponding thing for
> > > usb devices.
> > >
> > > So Linux, the kernel, does not actually provide a stable device name
> > > string.  This is obviously absurd, but I think fixing it is out of
> > > scope.
> > >
> > > I suggest we provide a facility to allow a user to specify a fnmatch
> > > glob pattern to be applied to the sysfs path.  That way when they see
> > > their device is
> > >    /devices/pci0000:00/0000:00:1d.7/usb1/1-1
> > > they can write
> > >    /devices/pci0000:00/0000:00:1d.7/usb*/*-1
> > > which will match exactly and only the right thing.
> > What about Juergen's system that has two usbN directories in a single
> > pci node?
> >
> > Quoting:
> > ---
> > Hmm, perhaps. On my system I've got:
> >
> > /sys/devices/pci0000:00/0000:00:14.0/usb3/
> > /sys/devices/pci0000:00/0000:00:14.0/usb4/
> >
> > So two busses on one pci bus address. Are usb3 and usb4 always in this
> > order or are they sometimes just numbered the other way round?
> > ---
> >
> > Assuming that usb3 and usb4 are actually distinct busses, and they might
> > both have something plugged into port; in which case a glob like this:
> >
> > devices/pci0000:00/0000:00:14.0/usb*/*-1
> >
> > Might match both of the following:
> >
> > /sys/devices/pci0000:00/0000:00:14.0/usb3/3-1
> > /sys/devices/pci0000:00/0000:00:14.0/usb4/4-1
> Is that an xHCI host controller? If so that might be how the system
> represents the 2 logical (USB2/USB3) root hubs - each as its own
> separate bus.
See my other reply: this is the case. So Ian's suggestion would still
work.


Juergen


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