From mboxrd@z Thu Jan 1 00:00:00 1970 From: Gerrit Renker Subject: [PATCH 11/31] [DCCP]: Make dccp_delta_seqno return signed numbers Date: Tue, 20 Mar 2007 20:06:55 -0300 Message-ID: <20070320230655.GZ17811@ghostprotocols.net> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: netdev@vger.kernel.org To: "David S. Miller" Return-path: Received: from wx-out-0506.google.com ([66.249.82.230]:34121 "EHLO wx-out-0506.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752133AbXCTXHL (ORCPT ); Tue, 20 Mar 2007 19:07:11 -0400 Received: by wx-out-0506.google.com with SMTP id h31so64649wxd for ; Tue, 20 Mar 2007 16:07:11 -0700 (PDT) Content-Disposition: inline Sender: netdev-owner@vger.kernel.org List-Id: netdev.vger.kernel.org Problem: -------- Using dccp_delta_seqno(a, b) produces unusable results when -- by accident or coincidence -- sequence number b precedes a. If e.g. a and b are merely reordered and have a distance 1, their delta_seqno is 2^48-1, which would indicate a loss of 2^48-2 packets. Fix: ---- The fix is by using signed 48-bit arithmetic for dccp_delta_seqno, so that dccp_delta_seqno(a, b) returns: * > 0 if a is `before' b OR * 0 if a == b OR * < 0 and > -2^47 if b is `before' a OR * -2^47 if neither a `before' b nor b `before' a This implements http://www.mail-archive.com/dccp@vger.kernel.org/msg01153.html Signed-off-by: Gerrit Renker Acked-by: Ian McDonald Signed-off-by: Arnaldo Carvalho de Melo --- net/dccp/dccp.h | 7 +++++-- 1 files changed, 5 insertions(+), 2 deletions(-) diff --git a/net/dccp/dccp.h b/net/dccp/dccp.h index 82c618f..e6c95e9 100644 --- a/net/dccp/dccp.h +++ b/net/dccp/dccp.h @@ -113,9 +113,12 @@ static inline void dccp_inc_seqno(u64 *seqno) *seqno = ADD48(*seqno, 1); } -static inline u64 dccp_delta_seqno(u64 seqno1, u64 seqno2) +/* signed mod-2^48 distance: pos. if seqno1 < seqno2, neg. if seqno1 > seqno2 */ +static inline s64 dccp_delta_seqno(const u64 seqno1, const u64 seqno2) { - return ((seqno2 << 16) - (seqno1 << 16)) >> 16; + u64 delta = SUB48(seqno2, seqno1); + + return TO_SIGNED48(delta); } /* is seq1 < seq2 ? */ -- 1.5.0.3