[libvirt] [PATCH 3/3] qemu: Forbid user aliases for USB controllers

[Peter Krempa]

On Fri, Mar 09, 2018 at 12:56:13 +0100, Michal Privoznik wrote:
> https://bugzilla.redhat.com/show_bug.cgi?id=1552127
> 
> These are bit different than other devices. Their alias also
> specify the name of the bus. For instance, if there are these
> 'joined' USB devices:
> 
>   <controller type='usb' index='0' model='ich9-ehci1'>
>     <alias name='ua-myUSB'/>
>     <address type='pci' domain='0x0000' bus='0x00' slot='0x04' function='0x7'/>
>   </controller>
>   <controller type='usb' index='0' model='ich9-uhci1'>
>     <master startport='0'/>
>     <address type='pci' domain='0x0000' bus='0x00' slot='0x04' function='0x0' multifunction='on'/>
>   </controller>
> 
> which translates to cmd line as:
> 
>   -device ich9-usb-ehci1,id=ua-myUSB,bus=pci.0,addr=0x4.0x7
>   -device ich9-usb-uhci1,masterbus=usb.0,firstport=0,bus=pci.0,multifunction=on,addr=0x4
> 
> The problem is that UHCI is still trying to serve 'usb.0' bus.
> Rather than trying to come up with some complicated algorithm to
> make everything work, lets forbid user aliases for USB
> controllers.

I'm not a fan of this. This creates situations where the user is not
able to know which devices support user aliases and which don't. If
there isn't a technical problem preventing this from working we should
not forbid it.
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