[libvirt] [RFC PATCH] hostdev: add support for "managed='detach'"

[Gerd Hoffmann]

  Hi,

> For ad-hoc usage such as with desktop virt, then I think users would
> typically want to use have PCI devices re-assigned to host at shutdown
> for the most part.

Unfortunately that tends to not work very well for some kinds of
devices.

I have an explicit "managed=no" in my configs, otherwise I risk the igd
(intel gfx) hangs the system when assigning it back to the host.

> If apps change to use managed=detach then they will only work with
> new libvirt, where as if they change to use the virNodeDeviceDetach()
> API they'll work with all historic version of libvirt that support PCI
> assignment.

My "app" is "virsh edit" ;)

So, I have to do an explicit "virsh nodedev-detach" before I can start
the guest.  Yes, it's annonying.  But guest failing to start is better
than host crashing on guest shutdown in case I forget to do it.  And,
no, I don't want do that in the boot scripts somewhere because I might
want to use the igd on the host.

"managed=detach" would be a very nice solution to that problem.

cheers,
  Gerd