netdev - RE: [PATCH iproute2] ip xfrm: support 64bit kernel and 32bit userspace

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Date:	Fri, 28 Nov 2014 10:47:59 +0000
From:	David Laight <David.Laight@...LAB.COM>
To:	"'roy.qing.li@...il.com'" <roy.qing.li@...il.com>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: RE: [PATCH iproute2] ip xfrm: support 64bit kernel and 32bit
 userspace

From: roy.qing.li@...il.com
> From: Li RongQing <roy.qing.li@...il.com>
> 
> The size of struct xfrm_userpolicy_info is 168 bytes for 64bit kernel, and
> 164 bytes for 32bit userspace because of the different alignment. and lead
> to "ip xfrm" be unable to work.
> 
> add a pad in struct xfrm_userpolicy_info, and enable it by set
> KERNEL_64_USERSPACE_32 to y
...
> diff --git a/include/linux/xfrm.h b/include/linux/xfrm.h
> index fa2ecb2..009510c 100644
> --- a/include/linux/xfrm.h
> +++ b/include/linux/xfrm.h
> @@ -407,6 +407,9 @@ struct xfrm_userpolicy_info {
>  	/* Automatically expand selector to include matching ICMP payloads. */
>  #define XFRM_POLICY_ICMP	2
>  	__u8				share;
> +#ifdef KNL_64_US_32
> +	int				pad;
> +#endif
>  };

You could add __attribute__((aligned(8))) to the structure to pad it on
all systems.

Or find the 64bit member and add __attribute__((aligned(4))) to that member
so that the 64bit version doesn't get padded.
That will make the field more expensive to access on systems that can't
do misaligned memory transfers.

	David



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