Re: [Qemu-devel] [PATCH] pc: reduce duplication in compat machine types

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

On Mon, Mar 26, 2012 at 03:12:37PM +0200, Andreas Färber wrote:
> Am 26.03.2012 11:40, schrieb Michael S. Tsirkin:
> > Make it easier to add compat properties, by
> > adding macros for properties duplicated across
> > machine types.
> > 
> > Note: there could be bugs in compat properties,
> > this patch does not attempt to address them,
> > the code is bug for bug identical to the original.
> > 
> > Tested by: generated a preprocessed file, sorted and
> > compared to sorted original.
> > Lightly tested on x86_64.
> > 
> > Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
> > ---
> > 
> > I've put the above on my branch as it's needed for
> > fixing balloon pci class. Let me know if there are
> > any objections.
> 
> Better reusing code is certainly a good idea. I wonder though if we
> might ever get into a situation where things change back and forth. I'd
> hope that properties are processed top to bottom so that, e.g.,
> PC_COMPAT_1_0, { ... } can overwrite 0_15 compat properties inherited
> through 1_0.
> 
> Andreas

There are some properties like that currently.
For example, see ide-drive "ver" property or
VGA rombar property.  I'm not sure that's intentional but I kept
it as is.

In that case we can simply keep it out of
the common macros, that's what I did. There's no rule that says
we must have everything in there.

> > 
> >  hw/pc_piix.c |  288 +++++++++++++++-------------------------------------------
> >  1 files changed, 73 insertions(+), 215 deletions(-)
> > 
> > diff --git a/hw/pc_piix.c b/hw/pc_piix.c
> > index 3f99f9a..e39ef69 100644
> > --- a/hw/pc_piix.c
> > +++ b/hw/pc_piix.c
> > @@ -372,50 +372,69 @@ static QEMUMachine pc_machine_v1_1 = {
> >      .is_default = 1,
> >  };
> >  
> > +#define PC_COMPAT_1_0 \
> > +        {\
> > +            .driver   = "pc-sysfw",\
> > +            .property = "rom_only",\
> > +            .value    = stringify(1),\
> > +        }, {\
> > +            .driver   = "isa-fdc",\
> > +            .property = "check_media_rate",\
> > +            .value    = "off",\
> > +        }
> > +
> >  static QEMUMachine pc_machine_v1_0 = {
> >      .name = "pc-1.0",
> >      .desc = "Standard PC",
> >      .init = pc_init_pci,
> >      .max_cpus = 255,
> >      .compat_props = (GlobalProperty[]) {
> > -        {
> > -            .driver   = "pc-sysfw",
> > -            .property = "rom_only",
> > -            .value    = stringify(1),
> > -        }, {
> > -            .driver   = "isa-fdc",
> > -            .property = "check_media_rate",
> > -            .value    = "off",
> > -        },
> > +        PC_COMPAT_1_0,
> >          { /* end of list */ }
> >      },
> >  };
> [snip]
> 
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