Re: [Qemu-devel] [PATCH 1/2 v2] pci: change default value of rom_bar to 2

["Michael S. Tsirkin" <mst@redhat.com>]

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 <bsd@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.


> > >  I think we really just want to detect
> > > unspecified versus specified, which probably means setting the default
> > > value to something the user can't, or at least wouldn't, specify.
> > > Thanks,
> > > 
> > > Alex
> > 
> > OK but I should be able to query value of each variable and figure
> > out what it means.
> > 
> > We can build a tri-state property type if desired:
> > force on/force off/auto.
> > Just let's not code up random magic values.
> > 0 and 1 for on/off is ugly enough.
> > 
> > 
> > > > 
> > > > >      DEFINE_PROP_BIT("multifunction", PCIDevice, cap_present,
> > > > >                      QEMU_PCI_CAP_MULTIFUNCTION_BITNR, false),
> > > > >      DEFINE_PROP_BIT("command_serr_enable", PCIDevice, cap_present,
> > > > > -- 
> > > > > 1.8.3.1
> > > 
> > > 
> 
>