On Sun, 2014-02-23 at 20:32 -0500, Bandan Das wrote: > "Michael S. Tsirkin" <m...@redhat.com> writes: > > > On Sun, Feb 23, 2014 at 07:18:07AM -0700, Alex Williamson wrote: > >> On Sun, 2014-02-23 at 08:32 +0200, Michael S. Tsirkin wrote: > >> > On Sat, Feb 22, 2014 at 04:28:26PM -0700, Alex Williamson wrote: > >> > > On Thu, 2014-02-20 at 10:12 +0200, Michael S. Tsirkin wrote: > >> > > > On Wed, Feb 19, 2014 at 03:20:54PM -0500, Bandan Das wrote: > >> > > > > The following patch depends on the value of rom_bar to > >> > > > > determine rom blacklist behavior. Existing code shouldn't > >> > > > > be affected by changing the default value of rom_bar since > >> > > > > all relevant decisions only rely on whether rom_bar is zero > >> > > > > or non-zero. > >> > > > > > >> > > > > Signed-off-by: Bandan Das <b...@redhat.com> > >> > > > > --- > >> > > > > hw/pci/pci.c | 7 ++++++- > >> > > > > 1 file changed, 6 insertions(+), 1 deletion(-) > >> > > > > > >> > > > > diff --git a/hw/pci/pci.c b/hw/pci/pci.c > >> > > > > index 4e0701d..12c3e27 100644 > >> > > > > --- a/hw/pci/pci.c > >> > > > > +++ b/hw/pci/pci.c > >> > > > > @@ -53,7 +53,12 @@ static void pci_bus_finalize(Object *obj); > >> > > > > static Property pci_props[] = { > >> > > > > DEFINE_PROP_PCI_DEVFN("addr", PCIDevice, devfn, -1), > >> > > > > DEFINE_PROP_STRING("romfile", PCIDevice, romfile), > >> > > > > - DEFINE_PROP_UINT32("rombar", PCIDevice, rom_bar, 1), > >> > > > > + /* > >> > > > > + * 0 = disable > >> > > > > + * 1 = user requested on, force loading even if rom > >> > > > > blacklisted > >> > > > > + * 2 = enabled but disables loading of blacklisted roms > >> > > > > (default) > >> > > > > + */ > >> > > > > + DEFINE_PROP_UINT32("rombar", PCIDevice, rom_bar, 2), > >> > > > > >> > > > How do users figure out this interface? > >> > > > Read code? > >> > > > Could we add a bit property rombarforce=on/off instead? > >> > > > Seems better. > >> > > > > >> > > > Maybe we should teach bool type visitors > >> > > > about 0 and 1 being legal values > >> > > > (call out to int visitor, then check value 0 or 1), > >> > > > then rombar can be changed to bit property too. > >> > > > > >> > > > Also, this will need QMP support right? > >> > > > IIUC rombar is not exposed in QMP ATM. > >> > > > >> > > rombarforce seems very redundant for a user interface; rombar=1 "expose > >> > > the ROM BAR of the device", rombarforce=1 "yes, really expose the ROM > >> > > BAR of the device". > >> > > >> > Not really. > >> > In this design, rombarforce=yes means "expose ROM BAR of the device", > >> > rombar should not be exposed to users - it's a compatibility property > >> > used for cross-version migration. > >> > > >> > > Even if force implies rombar, > >> > > I don't think that's > >> > > very easy to code in libvirt. > >> > > >> > Libvirt doesn't touch rombar AFAIK. > >> > >> It does > >> > >> http://libvirt.org/formatdomain.html#elementsNICSROM > >> > >> <rom bar='off'> > > > > > > Got it, thanks. So if you think the right thing > > to do for users it to interpret rom=on as > > meaning "force" then just do that. > > Use some new hidden field for machine compatibility. > > Even if we use another variable for machine compatibility, > we can't assume rom=on means force. > > "force" is that special case where even if the rom is blacklisted, > loading is attempted. (Please see 2/2 v2] vfio: blacklist loading of unstable > roms) > For now, the usecase is to get around when there is a new rom to test. > > A tristate property seems better, with an approach that addresses your > concerns > about random values that could confuse users.
I suspect there are ways to parse the opts for a given device to find whether rombar was specified so we don't need to create a magic "unset" value. We just need to dig through the obfuscation of the opts code.