Here is as promised the patch to take care of the two ambiguous cases stated in http://www.mail-archive.com/dccp@xxxxxxxxxxxxxxx/msg01295.html I have compile-tested it and below is a detailed justification why the use of the (newer variant of) dccp_delta_seqno is equivalent to the old condition. (NB: It might be possible to use a macro instead.) --------------------> Patch <------------------------------------------------- [DCCP]: Remove ambiguity in the way before48 is used This removes two ambiguities in employing the new definition of before48, following the analysis on http://www.mail-archive.com/dccp@xxxxxxxxxxxxxxx/msg01295.html (1) Updating GSR when P.seqno >= S.SWL With the old definition we did not update when P.seqno and S.SWL are 2^47 apart. To ensure the same behaviour as with the old definition, this is replaced with the equivalent condition dccp_delta_seqno(S.SWL, P.seqno) >= 0 (2) Sending SYNC when P.seqno >= S.OSR Here it is debatable whether the new definition causes an ambiguity: the case is similar to (1); and to have consistency with the case (1), we use the equivalent condition dccp_delta_seqno(S.OSR, P.seqno) >= 0 Detailed Justification [not necessarily commit message]: -------------------------------------------------------- dccp_delta_seqno(a, b) returns a value >= 0 if either a is `before' b or a == b, using the new definition: a `before' b <=> 1 <= (b - a) mod 2^48 <= 2^47 - 1. The old and new definition of `before' are identical as long as the modulo-2^48 difference between a and b is not equal to 2^47. In both cases, a test of the form !before(x, y) has been replaced by dccp_delta_seqno(y, x) >= 0. For all values excluding y = (x + 2^47) % 2^48, the equivalence is clear to see. When y = (x + 2^47) % 2^48 then !before(x, y) returned false in the new definition. However, 'dccp_delta_seqno(x, (x+2^47) % 2^48) >= 0' also returns false; hence we have full equivalence. Signed-off-by: Gerrit Renker <gerrit@xxxxxxxxxxxxxx> --- net/dccp/input.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-) --- a/net/dccp/input.c +++ b/net/dccp/input.c @@ -86,7 +86,8 @@ static int dccp_check_seqno(struct sock dh->dccph_type == DCCP_PKT_SYNCACK) { if (between48(DCCP_SKB_CB(skb)->dccpd_ack_seq, dp->dccps_awl, dp->dccps_awh) && - !before48(DCCP_SKB_CB(skb)->dccpd_seq, dp->dccps_swl)) + dccp_delta_seqno(dp->dccps_swl, + DCCP_SKB_CB(skb)->dccpd_seq) >= 0) dccp_update_gsr(sk, DCCP_SKB_CB(skb)->dccpd_seq); else return -1; @@ -203,7 +204,8 @@ static int __dccp_rcv_established(struct if (dp->dccps_role != DCCP_ROLE_CLIENT) goto send_sync; check_seq: - if (!before48(DCCP_SKB_CB(skb)->dccpd_seq, dp->dccps_osr)) { + if (dccp_delta_seqno(dp->dccps_osr, + DCCP_SKB_CB(skb)->dccpd_seq) >= 0) { send_sync: dccp_send_sync(sk, DCCP_SKB_CB(skb)->dccpd_seq, DCCP_PKT_SYNC); - To unsubscribe from this list: send the line "unsubscribe dccp" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
