[PATCH net-next v3 0/5] net: bridge: mcast: support exponential field encoding

Ujjal Roy
2026-04-03T15:01:00Z

Description:
This series addresses a mismatch in how multicast query
intervals and response codes are handled across IPv4 (IGMPv3)
and IPv6 (MLDv2). While decoding logic currently exists,
the corresponding encoding logic is missing during query
packet generation. This leads to incorrect intervals being
transmitted when values exceed their linear thresholds.

The patches introduce a unified floating-point encoding
approach based on RFC3376 and RFC3810, ensuring that large
intervals are correctly represented in QQIC and MRC fields
using the exponent-mantissa format.

Key Changes:
* ipv4: igmp: get rid of IGMPV3_{QQIC,MRC} and simplify calculation
Removes legacy macros in favor of a cleaner, unified
calculation for retrieving intervals from encoded fields,
improving code maintainability.

* ipv6: mld: rename mldv2_mrc() and add mldv2_qqi()
Standardizes MLDv2 terminology by renaming mldv2_mrc()
to mldv2_mrd() (Maximum Response Delay) and introducing
a new API mldv2_qqi for QQI calculation, improving code
readability.

* ipv4: igmp: encode multicast exponential fields
Introduces the logic to dynamically calculate the exponent
and mantissa using bit-scan (fls). This ensures QQIC and
MRC fields (8-bit) are properly encoded when transmitting
query packets with intervals that exceed their respective
linear threshold value of 128 (for QQI/MRT).

* ipv6: mld: encode multicast exponential fields
Applies similar encoding logic for MLDv2. This ensures
QQIC (8-bit) and MRC (16-bit) fields are properly encoded
when transmitting query packets with intervals that exceed
their respective linear thresholds (128 for QQI; 32768
for MRD).

* selftests: net: bridge: add tests for MRC and QQIC validation
Updates bridge selftests to validate both linear and non-linear
(exponential) encoding for MRC and QQIC fields, ensuring
protocol compliance across IGMPv3 and MLDv2.

Impact:
These changes ensure that multicast queriers and listeners
stay synchronized on timing intervals, preventing protocol
timeouts or premature group membership expiration caused
by incorrectly formatted packet headers.

Test results:
Giving results only from vlmc_query_intvl_test and vlmc_query_response_intvl_test
of the script bridge_vlan_mcast.sh.
Without patchset, here is the result.
- TEST: Vlan multicast snooping enable [ OK ]
- TEST: Vlan mcast_query_interval global option default value [ OK ]
- Vlan 10 mcast_query_interval (QQIC) test cases:
- TEST: Number of tagged IGMPv2 general query [ OK ]
- TEST: IGMPv3 QQIC linear value 60 [ OK ]
- TEST: MLDv2 QQIC linear value 60 [ OK ]
- TEST: IGMPv3 QQIC non linear value 160 [FAIL]
- Wrong QQIC in sent tagged IGMPv3 general queries
- TEST: MLDv2 QQIC non linear value 160 [FAIL]
- Wrong QQIC in sent tagged MLDv2 general queries
- TEST: Vlan mcast_query_response_interval global option default value [ OK ]
- Vlan 10 mcast_query_response_interval (MRC) test cases:
- TEST: IGMPv3 MRC linear value 60 [ OK ]
- TEST: IGMPv3 MRC non linear value 160 [FAIL]
- Wrong MRC in sent tagged IGMPv3 general queries
- TEST: MLDv2 MRC linear value 30000 [ OK ]
- TEST: MLDv2 MRC non linear value 60000 [FAIL]
- Wrong MRC in sent tagged MLDv2 general queries
With these patchset, here is the result.
* TEST: Vlan multicast snooping enable [ OK ]
* TEST: Vlan mcast_query_interval global option default value [ OK ]
* Vlan 10 mcast_query_interval (QQIC) test cases:
* TEST: Number of tagged IGMPv2 general query [ OK ]
* TEST: IGMPv3 QQIC linear value 60 [ OK ]
* TEST: MLDv2 QQIC linear value 60 [ OK ]
* TEST: IGMPv3 QQIC non linear value 160 [ OK ]
* TEST: MLDv2 QQIC non linear value 160 [ OK ]
* TEST: Vlan mcast_query_response_interval global option default value [ OK ]
* Vlan 10 mcast_query_response_interval (MRC) test cases:
* TEST: IGMPv3 MRC linear value 60 [ OK ]
* TEST: IGMPv3 MRC non linear value 160 [ OK ]
* TEST: MLDv2 MRC linear value 30000 [ OK ]
* TEST: MLDv2 MRC non linear value 60000 [ OK ]

v3:
- Updated the series title for better clarity; old one is here
https://lore.kernel.org/all/20260326150742.50289-1-royujjal@gmail.com/
- Added key changes section for new selftests patch
- Updated netdev style comments and addressed review comments
- Fixed MLDv2 MRC conversion logic during query generation
- Mentioned intervals in units wherever applicable
- Dropped type casting and fixed indentations

v2:
- Retargeted the series to net-next as suggested
- Fixed a compilation warning in the MLD rename change
- Kept reverse xmas tree order in IGMP exponential encoding change
- Added bridge selftests to validate IGMPv3 Query MRC and QQIC handling

Ujjal Roy (5):
ipv4: igmp: get rid of IGMPV3_{QQIC,MRC} and simplify calculation
ipv6: mld: rename mldv2_mrc() and add mldv2_qqi()
ipv4: igmp: encode multicast exponential fields
ipv6: mld: encode multicast exponential fields
selftests: net: bridge: add tests for MRC and QQIC validation

include/linux/igmp.h | 171 +++++++++++++++-
include/net/mld.h | 190 +++++++++++++++++-
net/bridge/br_multicast.c | 22 +-
net/ipv4/igmp.c | 6 +-
net/ipv6/mcast.c | 19 +-
.../selftests/net/forwarding/.gitignore | 2 +
.../testing/selftests/net/forwarding/Makefile | 10 +
.../net/forwarding/bridge_vlan_mcast.sh | 157 ++++++++++++++-
.../selftests/net/forwarding/mc_decode.c | 73 +++++++
.../selftests/net/forwarding/mc_encode.c | 78 +++++++
10 files changed, 675 insertions(+), 53 deletions(-)
create mode 100644 tools/testing/selftests/net/forwarding/mc_decode.c
create mode 100644 tools/testing/selftests/net/forwarding/mc_encode.c

base-commit: 8b0e64d6c9e7feec5ba5643b4fa8b7fd54464778
--
2.43.0