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Re: [libvirt PATCH] remove HAL node device driver

On Tue, Sep 08, 2020 at 03:42:58PM +0200, Pavel Hrdina wrote:
> On Tue, Sep 08, 2020 at 03:50:07PM +0400, Roman Bogorodskiy wrote:
> >   Pavel Hrdina wrote:
> > 
> > > There was one attempt a year ago done by me to drop HAL [1] but it was
> > > never resolved. There was another time when Dan suggested to drop HAL
> > > driver [2] but it was decided to keep it around in case device
> > > assignment will be implemented for FreeBSD and the fact that
> > > virt-manager uses node device driver [3].
> > > 
> > > I checked git history and code and it doesn't look like bhyve supports
> > > device assignment so from that POV it should not block removing HAL.
> > 
> > The bhyve driver currently does not support device assignment.
> > Bhyve it self does not support live device attach too.
> > 
> > What bhyve does support is passthru of some device types (I have tested
> > NIC passthrough and it works, and also it looks like GPU passthrough
> > also works in some configurations, and also there are some work going on
> > to make it better).
> > 
> > I'm wondering if the removal of HAL support will block adding support
> > for host device passthrough?
> So I checked qemu driver and we use node device driver only to implement
> these APIs:
> virNodeDeviceDettach
> virNodeDeviceDetachFlags
> virNodeDeviceReAttach
> virNodeDeviceReset
> which can be used by users or management applications to detach the PCI
> devices from host and prepare them to be used by VMs.  This can be done
> manually not using libvirt APIs as well.
> So it looks like HAL will not be required to support host device
> assignment.

That may be true from a strictly technical sense, but most existing mgmt
applications using libvirt expect the node device APIs to exist and won't
enable use of host device assignment without them.

> If the host device assignment will be implemented and these API required
> we can figure out how to use devd instead of HAL.
> Pavel

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