Re: [PATCH v5 14/21] libxl: require qemu in dom0 even if stubdomain is in use

[Marek Marczykowski-Górecki <marmarek@xxxxxxxxxxxxxxxxxxxxxx>]

On Thu, May 14, 2020 at 05:42:36PM +0100, Ian Jackson wrote:
> Jason Andryuk writes ("[PATCH v5 14/21] libxl: require qemu in dom0 even if 
> stubdomain is in use"):
> > From: Marek Marczykowski-Górecki <marmarek@xxxxxxxxxxxxxxxxxxxxxx>
> > 
> > Until xenconsoled learns how to handle multiple consoles, this is needed
> > for save/restore support (qemu state is transferred over secondary
> > consoles).
> > Additionally, Linux-based stubdomain waits for all the backends to
> > initialize during boot. Lack of some console backends results in
> > stubdomain startup timeout.
> > 
> > This is a temporary patch until xenconsoled will be improved.
> > 
> > Signed-off-by: Marek Marczykowski-Górecki <marmarek@xxxxxxxxxxxxxxxxxxxxxx>
> > Signed-off-by: Jason Andryuk <jandryuk@xxxxxxxxx>
> > ---
> >  tools/libxl/libxl_dm.c | 12 ++++++++++--
> >  1 file changed, 10 insertions(+), 2 deletions(-)
> > 
> > diff --git a/tools/libxl/libxl_dm.c b/tools/libxl/libxl_dm.c
> > index e420c3fc7b..5e5e7a27b3 100644
> > --- a/tools/libxl/libxl_dm.c
> > +++ b/tools/libxl/libxl_dm.c
> > @@ -2484,7 +2484,11 @@ static void spawn_stub_launch_dm(libxl__egc *egc,
> >          }
> >      }
> >  
> > -    need_qemu = libxl__need_xenpv_qemu(gc, dm_config);
> > +    /*
> > +     * Until xenconsoled learns how to handle multiple consoles, require 
> > qemu
> > +     * in dom0 to serve consoles for a stubdomain - it require at least 3 
> > of them.
> > +     */
> > +    need_qemu = 1 || libxl__need_xenpv_qemu(gc, &sdss->dm_config);
> 
> But I don't think this is true for a trad non-linux stubdm ?
> So I think this ought to be conditional.

For qemu-trad is true too. Stubdomain (mini-os + qemu-trad and linux +
qemu-xen) is always started with at least 3 consoles: log, save,
restore. Which currently requires qemu in dom0. So, yes, technically it
is a bug in the current libxl for qemu-trad. In practice, it works in
most cases because there is something else that triggers qemu in dom0
too: vfb/vkb added if vnc/sdl/spice is enabled.

-- 
Best Regards,
Marek Marczykowski-Górecki
Invisible Things Lab
A: Because it messes up the order in which people normally read text.
Q: Why is top-posting such a bad thing?

Attachment: signature.asc
Description: PGP signature