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H A Dip_fragment.cdiff 6623e3b24a5ebb07e81648c478d286a1329ab891 Wed Jan 05 08:52:55 CET 2011 Eric Dumazet <eric.dumazet@gmail.com> ipv4: IP defragmentation must be ECN aware

RFC3168 (The Addition of Explicit Congestion Notification to IP)
states :

5.3. Fragmentation

ECN-capable packets MAY have the DF (Don't Fragment) bit set.
Reassembly of a fragmented packet MUST NOT lose indications of
congestion. In other words, if any fragment of an IP packet to be
reassembled has the CE codepoint set, then one of two actions MUST be
taken:

* Set the CE codepoint on the reassembled packet. However, this
MUST NOT occur if any of the other fragments contributing to
this reassembly carries the Not-ECT codepoint.

* The packet is dropped, instead of being reassembled, for any
other reason.

This patch implements this requirement for IPv4, choosing the first
action :

If one fragment had NO-ECT codepoint
reassembled frame has NO-ECT
ElIf one fragment had CE codepoint
reassembled frame has CE

Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>