Re: [Xen-devel] [PATCH 2/2] tools/libxl: Switch Arm guest type to PVH

[Roger Pau Monné <roger.pau@xxxxxxxxxx>]

On Mon, Sep 03, 2018 at 12:15:16PM +0100, Julien Grall wrote:
> On 03/09/18 12:09, Julien Grall wrote:
> > 
> > 
> > On 23/08/18 08:58, Roger Pau Monné wrote:
> > > On Wed, Aug 22, 2018 at 06:48:05PM +0100, Julien Grall wrote:
> > > > > 
> > > > > > +
> > > > > > +    b_info->type = LIBXL_DOMAIN_TYPE_PVH;
> > > > > > +
> > > > > > +    /*
> > > > > > +     * They only field in u.pv that matters on Arm are:
> > > > > > kernel, cmdline,
> > > > > > +     * ramdisk.
> > > > > > +     */
> > > > > > +
> > > > > > +    if (!b_info->kernel && b_info->u.pv.kernel)
> > > > > > +            b_info->kernel = b_info->u.pv.kernel;
> > > > > > +
> > > > > > +    if (!b_info->ramdisk && b_info->u.pv.ramdisk)
> > > > > > +        b_info->ramdisk = b_info->u.pv.ramdisk;
> > > > > > +
> > > > > > +    if (!b_info->cmdline && b_info->u.pv.cmdline)
> > > > > > +        b_info->cmdline = b_info->u.pv.cmdline;
> > > > > > +
> > > > > > +    /* Reset b_info->u.pvh to default values */
> > > > > > +    memset(&b_info->u.pvh, 0, sizeof(b_info->u.pvh));
> > > > > 
> > > > > I'm afraid that's not correct. The default values for u.pvh are set
> > > > > by libxl__domain_build_info_setdefault.
> > > > 
> > > > I thought that this should be covered by the switch right after
> > > > the call of
> > > > libxl__arch_domain_build_info_setdefault. Did I miss anything?
> > > 
> > > Oh right, libxl__arch_domain_build_info_setdefault is called by
> > > libxl__domain_build_info_setdefault.
> > > 
> > > > What I wanted to do here is resetting the union to 0 so you
> > > > don't get data
> > > > mangled by the pv fields.
> > > 
> > > Another possible option I think would be to mark those fields as
> > > deprecated in the IDL, and libxl__domain_build_info_copy_deprecated
> > > will take care of copying them to the new place. In fact I think all
> > > guest types should be using the top level kernel, ramdisk and cmdline
> > > fields.
> > 
> > I will have a look at it.
> > 
> > > 
> > > I'm not specially comfortable with changing the guest type in the
> > > middle of libxl__domain_build_info_setdefault, but I also don't have a
> > > much better suggestion apart from using the deprecation helper.
> 
> I forgot to answer to this bit. I don't think the deprecation helper will do
> all the jobs. There are still PV specific parameters: slack_memkb, features,
> e820_host.

Those can be left inside the PV sub-struct and shouldn't be marked as
deprecated.

> Those are not necessary for Arm, if you don't zero them then you will not
> initialize the PVH structure with default values. How do you suggest to
> handle them?

But I guess ARM doesn't use any of those fields (or else they should
be moved to the pvh sub-struct anyway)?

In which case allowing the user to set them in the first place seems
like an error to me.

Roger.

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