[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: * dccp_delta_seqno(a, b) returns > 0 as before if a is `before' b * it returns 0 if a == b * if b precedes a, it returns a value less than 0 * implements http://www.mail-archive.com/dccp@xxxxxxxxxxxxxxx/msg01153.html Furthermore, the patch adds some useful constants and macros for 48-bit sequence number arithmetic. Signed-off-by: Gerrit Renker <gerrit@xxxxxxxxxxxxxx> --- net/dccp/dccp.h | 13 ++++++++++--- 1 file changed, 10 insertions(+), 3 deletions(-) --- a/net/dccp/dccp.h +++ b/net/dccp/dccp.h @@ -98,7 +98,11 @@ extern int sysctl_dccp_tx_qlen; #define S48_NEG_MIN 0x800000000000LL /* 2^47 */ #define DCCP_MAX_SEQNO 0xFFFFFFFFFFFFLL /* 2^48 - 1 */ #define COMPLEMENT48(x) (0x1000000000000LL - (x)) /* 2^48 - x */ - +#define TO_SIGNED48(x) (((x) < S48_NEG_MIN)? (x) : -COMPLEMENT48( (x))) +#define TO_UNSIGNED48(x) (((x) >= 0)? (x) : COMPLEMENT48(-(x))) +#define _add48(a, b) (((a) + (b)) & DCCP_MAX_SEQNO) +#define _sub48(a, b) _add48((a), COMPLEMENT48((b))) + static inline void dccp_set_seqno(u64 *seqno, u64 value) { *seqno = value & DCCP_MAX_SEQNO; @@ -111,9 +115,12 @@ static inline void add48(u64 *seqno, u64 #define sub48(seqno, decr) add48(seqno, COMPLEMENT48((decr))) #define dccp_inc_seqno(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
