Re: [Qemu-devel] [PATCH] pc: cleanup 1.4 compat support

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

On Mon, Aug 19, 2013 at 09:04:28AM -0300, Eduardo Habkost wrote:
> On Sun, Aug 18, 2013 at 04:50:02PM +0300, Michael S. Tsirkin wrote:
> > Make 1.4 compat code call the 1.6 one, reducing
> > code duplication. Add comment explaining why we can't
> > make 1.4 call 1.5 as usual.
> > 
> > Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
> > ---
> >  hw/i386/pc_piix.c | 4 ++--
> >  hw/i386/pc_q35.c  | 4 ++--
> >  2 files changed, 4 insertions(+), 4 deletions(-)
> > 
> > diff --git a/hw/i386/pc_piix.c b/hw/i386/pc_piix.c
> > index 15c932e..86cfadc 100644
> > --- a/hw/i386/pc_piix.c
> > +++ b/hw/i386/pc_piix.c
> > @@ -272,8 +272,8 @@ static void pc_init_pci_1_4(QEMUMachineInitArgs *args)
> >  {
> >      x86_cpu_compat_set_features("n270", FEAT_1_ECX, 0, CPUID_EXT_MOVBE);
> >      x86_cpu_compat_set_features("Westmere", FEAT_1_ECX, 0, CPUID_EXT_PCLMULQDQ);
> > -    has_pci_info = false;
> > -    pc_init_pci(args);
> > +    /* 1.5 was special - it enabled pvpanic in builtin machine */
> > +    pc_init_pci_1_6(args);
> >  }
> >  
> 
> I find this confusing (and probably it will be even more confusing when
> people read this code a few years from now). I would prefer the
> following pattern:
> 
> static void pc_compat_1_5()
> {
> 	/* do 1.5 stuff (possibly undoing 1.6 stuff) */
> 	has_pvpanic = true;
> }
> 
> static void pc_init_pci_1_5()
> {
> 	pc_compat_1_5();
> 	pc_init_pci();
> }
> 
> static void pc_compat_1_4()
> {
> 	pc_compat_1_5();
> 	/* do 1.4 stuff (possibly undoing 1.5 stuff) */
> 	has_pvpanic = false;
> }
> 
> static void pc_init_pci_1_4()
> {
> 	pc_compat_1_4();
> 	pc_init_pci();
> }
> 
> static void pc_compat_1_3()
> {
> 	pc_compat_1_3();
> 	/* do 1.3 stuff (possibly undoing 1.4 stuff) */
> }
> 
> static void pc_init_pci_1_3()
> {
> 	pc_compat_1_3();
> 	pc_init_pci();
> }
> 
> Otherwise the same problem may happen again in the future.

Sure, why not. Want to send a patch like this?
Prefer a patch on top of this one, or instead of it?

> 
> With this, we could even reuse the same pc_compat_*() functions on
> pc_piix.c and pc_q35.c.

That would be nice.

> >  static void pc_init_pci_1_3(QEMUMachineInitArgs *args)
> > diff --git a/hw/i386/pc_q35.c b/hw/i386/pc_q35.c
> > index 09d8183..8d62700 100644
> > --- a/hw/i386/pc_q35.c
> > +++ b/hw/i386/pc_q35.c
> > @@ -239,8 +239,8 @@ static void pc_q35_init_1_4(QEMUMachineInitArgs *args)
> >  {
> >      x86_cpu_compat_set_features("n270", FEAT_1_ECX, 0, CPUID_EXT_MOVBE);
> >      x86_cpu_compat_set_features("Westmere", FEAT_1_ECX, 0, CPUID_EXT_PCLMULQDQ);
> > -    has_pci_info = false;
> > -    pc_q35_init(args);
> > +    /* 1.5 was special - it enabled pvpanic in builtin machine */
> > +    pc_q35_init_1_6(args);
> >  }
> >  
> >  static QEMUMachine pc_q35_machine_v1_6 = {
> > -- 
> > MST
> 
> -- 
> Eduardo