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Subject: [Bug 194314] [ixgbe] driver makes some dangerous assumptions with
 struct mbuf sizing with IXGBE_RX_COPY_LEN
Date: Thu, 16 Oct 2014 21:37:31 +0000
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https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=194314

--- Comment #8 from Eric Joyner <ricera10@gmail.com> ---
So it sounds like we may just need to change IXGBE_RX_COPY_LEN from a fixed
value of 160 to something that's calculated based on the length of struct m_hdr
and struct m_pkthdr combined.

I think they got 160 by adding together the size of the two header structs (88
in FreeBSD amd64), adding some number (8) to make that size divisible by 32 (96
% 32 == 0), and then subtracted that from MSIZE (256) to get IXGBE_RX_COPY_LEN
(160), while keeping the padding added as IXGBE_RX_COPY_ALIGN.

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