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

[Eduardo Habkost]

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?

[...]
> 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.

> +    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)
> 

-- 
Eduardo