Re: [Qemu-devel] [PATCH] pc/fwcfg: unbreak migration from qemu-2.5 and qemu-2.6 during firmware boot

[Igor Mammedov <imammedo@redhat.com>]

On Mon, 24 Apr 2017 16:13:17 -0300
Eduardo Habkost <ehabkost@redhat.com> wrote:

> On Mon, Apr 24, 2017 at 08:58:17PM +0200, Igor Mammedov wrote:
> [...]
> > diff --git a/hw/i386/pc.c b/hw/i386/pc.c
> > index f3b372a18f..3f2d96da64 100644
> > --- a/hw/i386/pc.c
> > +++ b/hw/i386/pc.c
> > @@ -1047,7 +1047,7 @@ static void load_linux(PCMachineState *pcms,
> >      fw_cfg_add_i32(fw_cfg, FW_CFG_SETUP_SIZE, setup_size);
> >      fw_cfg_add_bytes(fw_cfg, FW_CFG_SETUP_DATA, setup, setup_size);
> >  
> > -    if (fw_cfg_dma_enabled(fw_cfg)) {
> > +    if (!pcmc->linuxboot_dma_disabled && fw_cfg_dma_enabled(fw_cfg)) {
> 
> Why not name the flag just "linuxboot_dma", set it to true by
> default at pc_machine_class_init(), and avoid the double
> negative?
to avoid setting it to true somewhere else, so less thing could go wrong
but is you prefer *_enable variant I can switch to it.

> 
> [...]
> > diff --git a/include/hw/i386/pc.h b/include/hw/i386/pc.h
> > index f278b3ae89..ff6f13b61b 100644
> > --- a/include/hw/i386/pc.h
> > +++ b/include/hw/i386/pc.h
> > @@ -151,6 +151,8 @@ struct PCMachineClass {
> >      bool save_tsc_khz;
> >      /* generate legacy CPU hotplug AML */
> >      bool legacy_cpu_hotplug;
> > +
> 
> A one-line description of the consequences of setting/clearing
> the flag would be nice.
will fix in v2

> 
> > +    bool linuxboot_dma_disabled;
> >  };
> >  
> >  #define TYPE_PC_MACHINE "generic-pc-machine"
> > @@ -432,10 +434,6 @@ bool e820_get_entry(int, uint32_t, uint64_t *, uint64_t *);
> >  #define PC_COMPAT_2_6 \
> >      HW_COMPAT_2_6 \
> >      {\
> > -        .driver   = "fw_cfg_io",\
> > -        .property = "dma_enabled",\
> > -        .value    = "off",\
> > -    },{\
> >          .driver   = TYPE_X86_CPU,\
> >          .property = "cpuid-0xb",\
> >          .value    = "off",\
> > -- 
> > 2.11.0 (Apple Git-81)
> > 
>