diff --git a/include/linux/igmp.h b/include/linux/igmp.h index 0e095c9f234e..3a2d35a9f307 100644 --- a/include/linux/igmp.h +++ b/include/linux/igmp.h @@ -109,6 +109,93 @@ struct ip_mc_list { /* IGMPv3 floating-point exponential field min threshold */ #define IGMPV3_EXP_MIN_THRESHOLD 128 +/* IGMPv3 FP max threshold (mant = 0xF, exp = 7) -> 31744 */ +#define IGMPV3_EXP_MAX_THRESHOLD 31744 + +/* V3 exponential field encoding */ + +/* IGMPv3 MRC/QQIC 8-bit exponential field encode + * + * RFC3376, 4.1.1 & 4.1.7. defines only the decoding formula: + * MRT/QQI = (mant | 0x10) << (exp + 3) + * + * but does NOT define the encoding procedure. To derive exponent: + * + * For any value of mantissa and exponent, the decoding formula + * indicates that the "hidden bit" (0x10) is shifted 4 bits left + * to sit above the 4-bit mantissa. The RFC again shifts this + * entire block left by (exp + 3) to reconstruct the value. + * So, 'hidden bit' is the MSB which is shifted by (4 + exp + 3). + * + * Total left shift of the 'hidden bit' = 4 + (exp + 3) = exp + 7. + * This is the MSB at the 0-based bit position: (exp + 7). + * Since fls() is 1-based, fls(value) - 1 = exp + 7. + * + * Therefore: + * exp = fls(value) - 8 + * mant = (value >> (exp + 3)) & 0x0F + * + * Final encoding formula: + * 0x80 | (exp << 4) | mant + * + * Example (value = 3200): + * 0 1 + * 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 + * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + * |0 0 0 0 1 1 0 0 1 0 0 0 0 0 0 0| (value = 3200) + * | ^-^-mant^ ^..(exp+3)..^| exp = 4, mant = 9 + * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + * + * Encoded: + * 0x80 | (4 << 4) | 9 = 0xC9 + */ +static inline u8 igmpv3_exp_field_encode(unsigned long value) +{ + u8 mc_exp, mc_man; + + /* MRC/QQIC < 128 is literal */ + if (value < IGMPV3_EXP_MIN_THRESHOLD) + return value; + + /* Saturate at max representable (mant = 0xF, exp = 7) -> 31744 */ + if (value >= IGMPV3_EXP_MAX_THRESHOLD) + return 0xFF; + + mc_exp = fls(value) - 8; + mc_man = (value >> (mc_exp + 3)) & 0x0F; + + return 0x80 | (mc_exp << 4) | mc_man; +} + +/* Calculate Maximum Response Code from Max Resp Time + * + * RFC3376, relevant sections: + * - 4.1.1. Maximum Response Code + * - 8.3. Query Response Interval + * + * MRC represents the encoded form of Max Resp Time (MRT); once + * decoded, the resulting value is in units of 0.1 seconds (100 ms). + */ +static inline u8 igmpv3_mrc(unsigned long mrt) +{ + return igmpv3_exp_field_encode(mrt); +} + +/* Calculate Querier's Query Interval Code from Querier's Query Interval + * + * RFC3376, relevant sections: + * - 4.1.7. QQIC (Querier's Query Interval Code) + * - 8.2. Query Interval + * - 8.12. Older Version Querier Present Timeout + * (the [Query Interval] in the last Query received) + * + * QQIC represents the encoded form of Querier's Query Interval (QQI); + * once decoded, the resulting value is in units of seconds. + */ +static inline u8 igmpv3_qqic(unsigned long qi) +{ + return igmpv3_exp_field_encode(qi); +} /* V3 exponential field decoding */ diff --git a/net/bridge/br_multicast.c b/net/bridge/br_multicast.c index 1438c023db62..27010744d7ae 100644 --- a/net/bridge/br_multicast.c +++ b/net/bridge/br_multicast.c @@ -934,12 +934,12 @@ static struct sk_buff *br_ip4_multicast_alloc_query(struct net_bridge_mcast *brm size_t pkt_size, igmp_hdr_size; unsigned long now = jiffies; struct igmpv3_query *ihv3; + unsigned long lmqt, mrt; void *csum_start = NULL; __sum16 *csum = NULL; struct sk_buff *skb; struct igmphdr *ih; struct ethhdr *eth; - unsigned long lmqt; struct iphdr *iph; u16 lmqt_srcs = 0; @@ -1004,15 +1004,15 @@ static struct sk_buff *br_ip4_multicast_alloc_query(struct net_bridge_mcast *brm skb_put(skb, 24); skb_set_transport_header(skb, skb->len); + mrt = group ? brmctx->multicast_last_member_interval : + brmctx->multicast_query_response_interval; *igmp_type = IGMP_HOST_MEMBERSHIP_QUERY; switch (brmctx->multicast_igmp_version) { case 2: ih = igmp_hdr(skb); ih->type = IGMP_HOST_MEMBERSHIP_QUERY; - ih->code = (group ? brmctx->multicast_last_member_interval : - brmctx->multicast_query_response_interval) / - (HZ / IGMP_TIMER_SCALE); + ih->code = mrt / (HZ / IGMP_TIMER_SCALE); ih->group = group; ih->csum = 0; csum = &ih->csum; @@ -1021,11 +1021,9 @@ static struct sk_buff *br_ip4_multicast_alloc_query(struct net_bridge_mcast *brm case 3: ihv3 = igmpv3_query_hdr(skb); ihv3->type = IGMP_HOST_MEMBERSHIP_QUERY; - ihv3->code = (group ? brmctx->multicast_last_member_interval : - brmctx->multicast_query_response_interval) / - (HZ / IGMP_TIMER_SCALE); + ihv3->code = igmpv3_mrc(mrt / (HZ / IGMP_TIMER_SCALE)); ihv3->group = group; - ihv3->qqic = brmctx->multicast_query_interval / HZ; + ihv3->qqic = igmpv3_qqic(brmctx->multicast_query_interval / HZ); ihv3->nsrcs = htons(lmqt_srcs); ihv3->resv = 0; ihv3->suppress = sflag;