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From: Jason Wang <jasowang@redhat.com>
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Date: Mon, 14 Dec 2015 14:26:41 +0800
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Subject: Re: [Qemu-devel] [PATCH v3 6/7] vmxnet3: Introduce 'x-disable-pcie'
 backword compatability property
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To: Shmulik Ladkani <shmulik.ladkani@ravellosystems.com>, Dmitry Fleytman <dmitry@daynix.com>
Cc: idan.brown@ravellosystems.com, qemu-devel@nongnu.org



On 12/12/2015 08:00 PM, Shmulik Ladkani wrote:
> Following the previous patch which changed vmxnet3 to be a pci express
> device, this patch introduces a boolean property 'x-disable-pcie' whose
> default is false.
>
> Setting 'x-disable-pcie' to 'on' preserves the old 'pci device' (non
> express) behavior. This allows migration to older versions.
>
> Signed-off-by: Shmulik Ladkani <shmulik.ladkani@ravellosystems.com>
> ---
>  hw/net/vmxnet3.c    | 2 ++
>  include/hw/compat.h | 4 ++++
>  2 files changed, 6 insertions(+)
>
> diff --git a/hw/net/vmxnet3.c b/hw/net/vmxnet3.c
> index 7ded287..f9cd02b 100644
> --- a/hw/net/vmxnet3.c
> +++ b/hw/net/vmxnet3.c
> @@ -2610,6 +2610,8 @@ static Property vmxnet3_properties[] = {
>      DEFINE_NIC_PROPERTIES(VMXNET3State, conf),
>      DEFINE_PROP_BIT("x-old-msi-offsets", VMXNET3State, compat_flags,
>                      VMXNET3_COMPAT_FLAG_OLD_MSI_OFFSETS_BIT, false),
> +    DEFINE_PROP_BIT("x-disable-pcie", VMXNET3State, compat_flags,
> +                    VMXNET3_COMPAT_FLAG_DISABLE_PCIE_BIT, false),
>      DEFINE_PROP_END_OF_LIST(),
>  };
>  
> diff --git a/include/hw/compat.h b/include/hw/compat.h
> index 01e326d..642b082 100644
> --- a/include/hw/compat.h
> +++ b/include/hw/compat.h
> @@ -22,6 +22,10 @@
>              .driver   = "vmxnet3",\
>              .property = "x-old-msi-offsets",\
>              .value    = "on",\
> +        },{\
> +            .driver   = "vmxnet3",\
> +            .property = "x-disable-pcie",\
> +            .value    = "on",\
>          },
>  
>  #define HW_COMPAT_2_3 \

Same as patch 3. Too late for 2.5, need do this for HW_COMPAT_2_5.

Just for pcie, another choice is a new type with "is_express = true".
But both method looks good to me.