On Mon, 6 Feb 2006, Nate Lawson wrote:
Nate Lawson wrote:
Oleg Bulyzhin wrote:
On Mon, Feb 06, 2006 at 02:21:09PM -0800, Nate Lawson wrote:
Oleg Bulyzhin wrote:
nq = q->m_nextpkt;
q->m_nextpkt = NULL;
m->m_pkthdr.csum_flags &= q->m_pkthdr.csum_flags;
- m->m_pkthdr.csum_data += q->m_pkthdr.csum_data;
+ sum = m->m_pkthdr.csum_data + q->m_pkthdr.csum_data;
+ m->m_pkthdr.csum_data = (sum & 0xffff) + (sum >> 16);
m_cat(m, q);
}
#ifdef MAC
...
Sam Leffler mentioned this comment from NetBSD would be helpful. Might you
add it to clear up misunderstandings like I had?
sys/mbuf.h has useful comments not found in the freebsd file:
...
* Note for in-bound TCP/UDP checksums, we expect the csum_data to NOT
* be bit-wise inverted (the final step in the calculation of an IP
* checksum) -- this is so we can accumulate the checksum for fragmented
* packets during reassembly.
*/
This almost makes the carry-folding (including the above change)
unnecessary too. csum_data can accumulate at least 64K terms each
less than 0x10000 before it might have a carry out of its 32-bit int.
I think there can't be 64K fragments, so the unpatched version would
work if the final step did the carry-folding and no intermediate step
assumes that csum_data < 0x10000. I couldn't find any final or
intermediate steps that would cause problems.
Bruce
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