From: David Miller <davem@davemloft.net>
Date: Sat, 26 Dec 2009 19:44:18 -0800 (PST)

From: Stephen Hemminger <redacted>
Date: Sat, 26 Dec 2009 14:05:44 -0800

quoted

Other drivers may have same problem, I really think this ought
to be done at higher level.

I tend to agree with you, and I thought we had handled all
cases.  Let's simply make AF_PACKET linearize the link
level header before sending things out to the transmit path.

I can work on this if you want.

Actually Stephen, I took a look and I can't see how AF_PACKET
can create this situation.

It always copies into the linear area of the SKB it allocates
for sendmsg() processing.  Whether the data comes from sendmsg
data or the mmap() ring buffer.