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From:   "David S. Miller" <davem@redhat.com>
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Date:   Thu, 8 Feb 2001 00:14:11 -0800 (PST)
To:     Rusty Russell <rusty@linuxcare.com.au>
Cc:     netdev@oss.sgi.com
Subject: Re: Is mac address reference safe w/ zero copy?
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Rusty Russell writes:
 > Hi Dave, et al,
 > 
 > 	The following code in route.c:ip_route_input_slow()
 > 
 > 		if (dev->hard_header_len) {
 > 			int i;
 > 			unsigned char *p = skb->mac.raw;
 > 			printk(KERN_WARNING "ll header: ");
 > 			for (i=0; i<dev->hard_header_len; i++, p++) {
 > 				printk("%02x", *p);
 > 
 > 	Is this safe w/ paged skbs?  Can I assume this in the ipt_mac
 > mac-address-matching netfilter module (which can only be called on
 > incoming or forwarded packets)?

It is safe unless you can show a place where an ethernet header
lands somewhere other than skb->data on input :-)

Format of input SKBs really have not changed at device header level.

Later,
David S. Miller
davem@redhat.com