netdev - Re: [PATCH net-next v5] rtnetlink: add new RTM

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Message-ID: <1461091667.10638.229.camel@edumazet-glaptop3.roam.corp.google.com>
Date:	Tue, 19 Apr 2016 11:47:47 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	David Miller <davem@...emloft.net>
Cc:	roopa@...ulusnetworks.com, netdev@...r.kernel.org,
	jhs@...atatu.com, tgraf@...g.ch, nicolas.dichtel@...nd.com
Subject: Re: [PATCH net-next v5] rtnetlink: add new RTM_GETSTATS message to
 dump link stats

On Tue, 2016-04-19 at 14:31 -0400, David Miller wrote:

> +#ifndef HAVE_EFFICIENT_UNALIGNED_ACCESS
> +	/* IF necessary, add a zero length NOP attribute so that the
> +	 * nla_data() of the IFLA_STATS64 will be 64-bit aligned.
> +	 *
> +	 * The nlattr header is 4 bytes in size, that's why we test
> +	 * if the skb->data _is_ aligned.  This NOP attribute, plus
> +	 * nlattr header for IFLA_STATS64, will make nla_data() 8-byte
> +	 * aligned.
> +	 */
> +	if (IS_ALIGNED((unsigned long)skb->data, 8)) {
> +		attr = nla_reserve(skb, IFLA_PAD, 0);
> +		if (!attr)
> +			return -EMSGSIZE;
> +	}
> +#endif

Since we want to use this in other places, we could define a helper.

nla_align_64bit(skb, attribute)  or something.