diff options
Diffstat (limited to 'include/linux')
| -rw-r--r-- | include/linux/igmp.h | 167 |
1 files changed, 159 insertions, 8 deletions
diff --git a/include/linux/igmp.h b/include/linux/igmp.h index 073b30a9b850..3a2d35a9f307 100644 --- a/include/linux/igmp.h +++ b/include/linux/igmp.h @@ -92,15 +92,166 @@ struct ip_mc_list { struct rcu_head rcu; }; +/* RFC3376, relevant sections: + * - 4.1.1. Maximum Response Code + * - 4.1.7. QQIC (Querier's Query Interval Code) + * + * For both MRC and QQIC, values >= 128 use the same floating-point + * encoding as follows: + * + * 0 1 2 3 4 5 6 7 + * +-+-+-+-+-+-+-+-+ + * |1| exp | mant | + * +-+-+-+-+-+-+-+-+ + */ +#define IGMPV3_FP_EXP(value) (((value) >> 4) & 0x07) +#define IGMPV3_FP_MAN(value) ((value) & 0x0f) + +/* 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 */ -#define IGMPV3_MASK(value, nb) ((nb)>=32 ? (value) : ((1<<(nb))-1) & (value)) -#define IGMPV3_EXP(thresh, nbmant, nbexp, value) \ - ((value) < (thresh) ? (value) : \ - ((IGMPV3_MASK(value, nbmant) | (1<<(nbmant))) << \ - (IGMPV3_MASK((value) >> (nbmant), nbexp) + (nbexp)))) - -#define IGMPV3_QQIC(value) IGMPV3_EXP(0x80, 4, 3, value) -#define IGMPV3_MRC(value) IGMPV3_EXP(0x80, 4, 3, value) + +/* IGMPv3 MRC/QQIC 8-bit exponential field decode + * + * RFC3376, 4.1.1 & 4.1.7. defines the decoding formula: + * 0 1 2 3 4 5 6 7 + * +-+-+-+-+-+-+-+-+ + * |1| exp | mant | + * +-+-+-+-+-+-+-+-+ + * Max Resp Time = (mant | 0x10) << (exp + 3) + * QQI = (mant | 0x10) << (exp + 3) + */ +static inline unsigned long igmpv3_exp_field_decode(const u8 code) +{ + if (code < IGMPV3_EXP_MIN_THRESHOLD) { + return code; + } else { + unsigned long mc_man, mc_exp; + + mc_exp = IGMPV3_FP_EXP(code); + mc_man = IGMPV3_FP_MAN(code); + + return (mc_man | 0x10) << (mc_exp + 3); + } +} + +/* Calculate Max Resp Time from Maximum Response Code + * + * RFC3376, relevant sections: + * - 4.1.1. Maximum Response Code + * - 8.3. Query Response Interval + * + * After decode, MRC represents the Maximum Response Time (MRT) in + * units of 0.1 seconds (100 ms). + */ +static inline unsigned long igmpv3_mrt(const struct igmpv3_query *ih3) +{ + return igmpv3_exp_field_decode(ih3->code); +} + +/* Calculate Querier's Query Interval from Querier's Query Interval Code + * + * 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) + * + * After decode, QQIC represents the Querier's Query Interval in units + * of seconds. + */ +static inline unsigned long igmpv3_qqi(const struct igmpv3_query *ih3) +{ + return igmpv3_exp_field_decode(ih3->qqic); +} static inline int ip_mc_may_pull(struct sk_buff *skb, unsigned int len) { |