Re: [Qemu-devel] [PATCH v2 3/3] virtio: Make disable-legacy/disable-modern compat properties optional

[Eduardo Habkost]

On Thu, Jan 10, 2019 at 12:35:26PM +0400, Marc-André Lureau wrote:
> Hi
> 
> On Thu, Jan 10, 2019 at 6:05 AM Eduardo Habkost <address@hidden> wrote:
> >
> > The disable-legacy and disable-modern properties apply only to
> > some virtio-pci devices.  Make those properties optional.
> >
> > This fixes the crash introduced by commit f6e501a28ef9 ("virtio: Provide
> > version-specific variants of virtio PCI devices"):
> >
> >   $ qemu-system-x86_64 -machine pc-i440fx-2.6 \
> >     -device virtio-net-pci-non-transitional
> >   Unexpected error in object_property_find() at qom/object.c:1092:
> >   qemu-system-x86_64: -device virtio-net-pci-non-transitional: can't apply \
> >   global virtio-pci.disable-modern=on: Property '.disable-modern' not found
> >   Aborted (core dumped)
> >
> > Reported-by: Thomas Huth <address@hidden>
> > Fixes: f6e501a28ef9 ("virtio: Provide version-specific variants of virtio 
> > PCI devices")
> > Signed-off-by: Eduardo Habkost <address@hidden>
> > ---
> >  hw/core/machine.c | 5 +++--
> >  1 file changed, 3 insertions(+), 2 deletions(-)
> >
> > diff --git a/hw/core/machine.c b/hw/core/machine.c
> > index 5530b71981..a19143aa44 100644
> > --- a/hw/core/machine.c
> > +++ b/hw/core/machine.c
> > @@ -91,8 +91,9 @@ const size_t hw_compat_2_7_len = 
> > G_N_ELEMENTS(hw_compat_2_7);
> >
> >  GlobalProperty hw_compat_2_6[] = {
> >      { "virtio-mmio", "format_transport_address", "off" },
> > -    { "virtio-pci", "disable-modern", "on" },
> > -    { "virtio-pci", "disable-legacy", "off" },
> > +    /* Optional because not all virtio-pci devices support legacy mode */
> > +    { "virtio-pci", "disable-modern", "on",  .optional = true },
> > +    { "virtio-pci", "disable-legacy", "off", .optional = true },
> 
> Could the generic devices implement a specific interface instead?
> virtio-pci-generic?

This is the kind of complexity I wanted to avoid.  We already
have too many interface names for subsets of PCI and virtio
devices.

> 
> Adding "optional" handling looks like it may hide some other errors.

What if we just make "optional" mean "skip if the property
doesn't exist", as suggested by Cornelia and Dave?

-- 
Eduardo