linux-kernel - Re: [PATCH] vDPA: fix incorrect VDPA_ATTR

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Date: Tue, 16 Apr 2024 15:18:26 +0800
From: Jason Wang <jasowang@...hat.com>
To: kovalev@...linux.org
Cc: mst@...hat.com, parav@...dia.com, edumazet@...gle.com, elic@...dia.com, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] vDPA: fix incorrect VDPA_ATTR_MAX value

On Tue, Apr 16, 2024 at 12:39 AM <kovalev@...linux.org> wrote:
>
> From: Vasiliy Kovalev <kovalev@...linux.org>
>
> The VDPA_ATTR_MAX value should correspond to the index of the last
> available member of the structure, not their total number.

I think it's too late to change. More below.

>
> Otherwise, it can lead to interpretation errors in other functions
> when the structure (.maxattr = VDPA_ATTR_MAX) member is actually
> incremented by one and refers to invalid data.
>
> Fixes: 33b347503f01 ("vdpa: Define vdpa mgmt device, ops and a netlink interface")
> Signed-off-by: Vasiliy Kovalev <kovalev@...linux.org>
> ---
>  include/uapi/linux/vdpa.h | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/include/uapi/linux/vdpa.h b/include/uapi/linux/vdpa.h
> index 43c51698195ceb..ab132a09565232 100644
> --- a/include/uapi/linux/vdpa.h
> +++ b/include/uapi/linux/vdpa.h
> @@ -74,7 +74,8 @@ enum vdpa_attr {
>         VDPA_ATTR_DEV_BLK_CFG_FLUSH,            /* u8 */
>
>         /* new attributes must be added above here */
> -       VDPA_ATTR_MAX,
> +       __VDPA_ATTR_MAX,
> +       VDPA_ATTR_MAX   = __VDPA_ATTR_MAX - 1,

Having a MAX in uapi is problematic as it may confuse the userspace. I
think the correct way is to drop it from uAPI.

Thanks

>  };
>
>  #endif
> --
> 2.33.8
>
>