Re: [PATCH] libs/light: pass some infos to qemu

[Manuel Bouyer <bouyer@xxxxxxxxxxxxxxx>]

On Mon, Jan 18, 2021 at 10:07:22AM +0100, Roger Pau Monné wrote:
> On Mon, Jan 18, 2021 at 09:52:14AM +0100, Manuel Bouyer wrote:
> > On Mon, Jan 18, 2021 at 09:36:42AM +0100, Roger Pau Monné wrote:
> > > I also wonder why NetBSD needs to add the tap interface to the bridge
> > > in the QEMU script instead of doing it from the hotplug script called
> > > by libxl, like Linux and FreeBSD do.
> > 
> > the tap interface is created by qemu itself, its name is not known outside
> > of qemu. Also, is there guarantee that qemu has created the tap before
> > the hotplug script is called ?
> 
> Yes, the toolstack will wait for QEMU to be initialized at which point
> the tap interface has been created.
> 
> I think I remember now why this didn't work on NetBSD. We ask QEMU to
> create the tap interface with a specific name (using the vifname=
> parameter), but NetBSD doesn't have the ioctl to rename network
> interfaces implemented, and thus cannot rename the interface from tapX
> to vifX.Y-emu, and hence you need to use the QEMU script from QEMU
> itself because it's the only entity that knows the name of the tap
> interface created.

Yes; at some point I proposed to support name aliases to interface
name in NetBSD but it got rejected ... so we have to use the
name the kernel did choose for us.

> 
> If you agree, can you add something along the lines to the commit
> message? So that we remember why NetBSD needs to use the QEMU scripts.

Will do.
thanks 

-- 
Manuel Bouyer <bouyer@xxxxxxxxxxxxxxx>
     NetBSD: 26 ans d'experience feront toujours la difference
--