[DCCP]: Make dccp_delta_seqno return signed numbers 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@xxxxxxxxxxxxxxx/msg01153.html Signed-off-by: Gerrit Renker <gerrit@xxxxxxxxxxxxxx> Acked-by: Ian McDonald <ian.mcdonald@xxxxxxxxxxx> --- net/dccp/dccp.h | 7 +++++-- 1 file changed, 5 insertions(+), 2 deletions(-) --- a/net/dccp/dccp.h +++ b/net/dccp/dccp.h @@ -113,9 +113,12 @@ static inline void dccp_inc_seqno(u64 *s *seqno = ADD48(*seqno, 1); } -static inline u64 dccp_delta_seqno(u64 seqno1, u64 seqno2) +/* return > 0 if seqno1 is `before' seqno2, <= 0 otherwise */ +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 ? */ - 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
