Subject: Re: [tcpdump-workers] Current wireless-testing breaks libpcap: mr_alen should be set
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From: Guy Harris <guy@alum.mit.edu>
In-Reply-To: <1267578048.14049.11.camel@mj>
Date: Sat, 6 Mar 2010 13:23:12 -0800
Cc: linux-wireless@vger.kernel.org, netdev@vger.kernel.org,
	Jiri Pirko <jpirko@redhat.com>
Message-Id: <7D621661-59E7-46C4-9E86-1D9654A626E7@alum.mit.edu>
References: <1267578048.14049.11.camel@mj>
To: tcpdump-workers@lists.tcpdump.org
Sender: linux-wireless-owner@vger.kernel.org


On Mar 2, 2010, at 5:00 PM, Pavel Roskin wrote:

> This patch to libpcap helps:
> 
> --- a/pcap-linux.c
> +++ b/pcap-linux.c
> @@ -1563,6 +1563,7 @@ live_open_new(pcap_t *handle, const char
> 			memset(&mr, 0, sizeof(mr));
> 			mr.mr_ifindex = handle->md.ifindex;
> 			mr.mr_type    = PACKET_MR_PROMISC;
> +			mr.mr_alen    = 6;

If there are any network types that support promiscuous mode and have link-layer addresses that aren't 6 octets long, that would still fail.

It sounds as if the fix is not to care about the address length if the address isn't used, so you don't need to get the length right for PACKET_MR_PROMISC or PACKET_MR_ALLMULTI, so libpcap, and other clients setting promiscuous or "show me all multicast packets" mode, don't need to change.  Is that the case?