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

[Manuel Bouyer <bouyer@antioche.eu.org>]

On Sat, Jan 16, 2021 at 11:16:06AM +0100, Roger Pau Monné wrote:
> On Tue, Jan 12, 2021 at 07:12:37PM +0100, Manuel Bouyer wrote:
> > From: Manuel Bouyer <bouyer@netbsd.org>
> > 
> > Pass bridge name to qemu as command line option
> > When starting qemu, set an environnement variable XEN_DOMAIN_ID,
> > to be used by qemu helper scripts
> > 
> > Signed-off-by: Manuel Bouyer <bouyer@netbsd.org>
> > ---
> >  tools/libs/light/libxl_dm.c | 6 ++++++
> >  1 file changed, 6 insertions(+)
> > 
> > diff --git a/tools/libs/light/libxl_dm.c b/tools/libs/light/libxl_dm.c
> > index 3da83259c0..8866c3f5ad 100644
> > --- a/tools/libs/light/libxl_dm.c
> > +++ b/tools/libs/light/libxl_dm.c
> > @@ -761,6 +761,8 @@ static int libxl__build_device_model_args_old(libxl__gc *gc,
> >          int nr_set_cpus = 0;
> >          char *s;
> >  
> > +        flexarray_append_pair(dm_envs, "XEN_DOMAIN_ID", GCSPRINTF("%d", domid));
> > +
> >          if (b_info->kernel) {
> >              LOGD(ERROR, domid, "HVM direct kernel boot is not supported by "
> >                   "qemu-xen-traditional");
> > @@ -1547,8 +1549,10 @@ static int libxl__build_device_model_args_new(libxl__gc *gc,
> >                  flexarray_append(dm_args, "-netdev");
> >                  flexarray_append(dm_args,
> >                                   GCSPRINTF("type=tap,id=net%d,ifname=%s,"
> > +					   "br=%s,"
> >                                             "script=%s,downscript=%s",
> >                                             nics[i].devid, ifname,
> > +					   nics[i].bridge,
> 
> You have some hard tabs in there.

Yes. What's the problem ?

> 
> Also looking at the manual the br= option seems to only be available
> for the bridge networking mode, while here Xen is using tap instead?

Unless I missed something, the bridge networking mode is using the
tap interface, to connect qemu to the bridge. And indeed, the qemu-ifup
script is doing
exec /sbin/brconfig $2 add $1

(the script is called with: qemu-ifup <tap if> <bridge if>)

This is a problem that hit me when I converted NetBSD to qemu-xen:
qemu-traditional does call the qemu-ifup script with the 2 parameters,
while qemu-xen calls it only with the tap if. So the qemu-ifup script can't
know to which bridge the tap interface should be attached to.

-- 
Manuel Bouyer <bouyer@antioche.eu.org>
     NetBSD: 26 ans d'experience feront toujours la difference
--