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Re: [Xen-devel] [PATCH V3 4/6] xl: add pvusb commands

On 05/20/2015 04:41 PM, George Dunlap wrote:
On Wed, May 20, 2015 at 3:33 PM, Juergen Gross <jgross@xxxxxxxx> wrote:
On 05/20/2015 04:20 PM, George Dunlap wrote:

On Mon, Apr 20, 2015 at 9:12 AM, Juergen Gross <jgross@xxxxxxxx> wrote:

On 04/19/2015 05:50 AM, Chunyan Liu wrote:

Add pvusb commands: usb-ctrl-attach, usb-ctrl-detach, usb-list,
usb-attach and usb-detach.

To attach a usb device to guest through pvusb, one could follow
following example:

    #xl usb-ctrl-attach test_vm version=1 num_ports=8

    #xl usb-list test_vm
    will show the usb controllers and port usage under the domain.

    #xl usb-attach test_vm 1.6
    will find the first usable controller:port, and attach usb
    device whose bus address is 1.6 (busnum is 1, devnum is 6)
    to it. One could also specify which <controller> and which <port>.

    #xl usb-detach test_vm 1.6

    #xl usb-ctrl-detach test_vm dev_id
    will destroy the controller with specified dev_id. Dev_id
    can be traced in usb-list info.

Signed-off-by: Chunyan Liu <cyliu@xxxxxxxx>
Signed-off-by: Simon Cao <caobosimon@xxxxxxxxx>
Changes to v2:
     * use bus.addr as user interface instead of busid in
     * remove usb-assignable-list interface

Why? While lsusb in combination with xl usb-list for each domain will
give the same information, having to iterate through all domains can be
quite annoying.

An alternative would be to accept omitting the domain for xl usb-list
and list all domains with assigned usb devices in this case.

I don't understand what information it is that you want.  Do you want
a list of devices *not already assigned* to domains?


...and why do you need that, instead of just remembering what you'd
assigned to whom?

We don't really have the equivalent for pci either.  That is, if a
device shows up in "lspci" but not in "pci-assignable-list", that may
be either because 1) I hasn't yet been assigned to pciback (and this
is available to be assigned to a domain), or 2) because it's already
been assigned to a domain.  Someone new coming to the system would
need to check all VMs to see which devices hadn't yet been assigned.

So this is a problem of pci-assignable-list, which isn't present for
USB devices. Any USB device not already assigned to a VM would be listed
as before with "xm usb-assignable-list".

Additionally all systems support hotplug of USB devices - the list of
available USB-devices can change rather often. If you unplug e.g. a
memory stick which has been assigned to a VM and stick it in again it
might show up under a different address and has to be reassigned.
Remembering having it already assigned won't help in this case as much
as a simple command to list the devices ready for assignment.


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