linux-kernel - Re: [PATCH] drivers/vfio: Fix an 8-byte alignment issue

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Message-ID: <5cfa9ed2b8eee3622715a7c0c62b09461dea607c.camel@perches.com>
Date:   Thu, 18 Oct 2018 10:20:10 -0700
From:   Joe Perches <joe@...ches.com>
To:     Wenwen Wang <wang6495@....edu>
Cc:     Kangjie Lu <kjlu@....edu>,
        Alex Williamson <alex.williamson@...hat.com>,
        "open list:VFIO DRIVER" <kvm@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] drivers/vfio: Fix an 8-byte alignment issue

On Wed, 2018-10-17 at 13:18 -0500, Wenwen Wang wrote:
> This patch adds a 4-byte reserved field in the structure
> vfio_eeh_pe_op to make sure that the u64 fields in the structure
> vfio_eeh_pe_err are 8-byte aligned.
> 
> Signed-off-by: Wenwen Wang <wang6495@....edu>
> ---
>  include/uapi/linux/vfio.h | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/include/uapi/linux/vfio.h b/include/uapi/linux/vfio.h
> index 1aa7b82..3e71ded 100644
> --- a/include/uapi/linux/vfio.h
> +++ b/include/uapi/linux/vfio.h
> @@ -729,6 +729,7 @@ struct vfio_eeh_pe_op {
>  	__u32 argsz;
>  	__u32 flags;
>  	__u32 op;
> +	__u32 __res;
>  	union {
>  		struct vfio_eeh_pe_err err;
>  	};

Why use an anonymous union for a single element?
Why not make struct vfio_eeh_pe_err __aligned(8)?
Why not make the u64 structure elements of
struct ufio_eeh_pe_err __aligned_u64?