linux-kernel - Pointer type of _arp in __skb_flow

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Date:   Fri, 31 Mar 2017 20:53:10 +0200
From:   Nicolas Iooss <nicolas.iooss_linux@....org>
To:     "David S. Miller" <davem@...emloft.net>,
        Simon Horman <simon.horman@...ronome.com>,
        netdev@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org
Subject: Pointer type of _arp in __skb_flow_dissect()

Hello,

Linux 4.11-rc4 contains the following code in function
__skb_flow_dissect(), file net/core/flow_dissector.c:

	const struct arphdr *arp;
	struct arphdr *_arp;

	arp = __skb_header_pointer(skb, nhoff, sizeof(_arp), data,
				   hlen, &_arp);

Here _arp and arp are both pointers to arphdr structures. In other calls
to __skb_header_pointer(), the buffer argument (_arp here) would have
been a struct instead of a pointer. What makes ARP packets different in
__skb_flow_dissect()?

Thanks,
Nicolas

PS: the code which I am curious about seems to have been introduced in
4.11-rc1 with commit 55733350e5e8 ("flow disector: ARP support")