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Differential D57518

loopback: checksum offloading
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Authored by timo.voelker_fh-muenster.de on Jun 10 2026, 7:38 AM.

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Reviewers

tuexen
jhb
glebius
bz
gallatin
pouria

Group Reviewers

Commits

rG265b3e15abf6: loopback: improve checksum offloading
rGfd3582e683d6: loopback: improve checksum offloading
rGd6c4cea7740d: loopback: improve checksum offloading

Summary

Currently the loopback interface does not work with SCTP/TCP/UDP if IFCAP_RXCSUM is disabled and IFCAP_TXCSUM is enabled. This patch fixes that and cleans up checksum offloading-related stuff.

Allow disabling IFCAP_RXCSUM_IPV6 or IFCAP_TXCSUM_IPV6.
Do not pretend the checksum is correct by setting the LO_CSUM_SET flags if IFCAP_RXCSUM_IPV6 or IFCAP_RXCSUM is enabled. Instead, remove the LO_CSUM_SET flags (in case they have been set somehow) if IFCAP_RXCSUM_IPV6 or IFCAP_RXCSUM is disabled.
Do not unset the transmit checksum offload flags LO_CSUM_FEATURES or LO_CSUM_FEATURES6 since they have a meaning for the receive path since D51475 and D54455.

Test Plan

Initially, ssh 127.0.0.1 works. After disabling IFCAP_RXCSUM,

ifconfig lo0 -rxcsum

ssh 127.0.0.1 does not work. It works after this patch has been applied.

Diff Detail

Repository

rG FreeBSD src repository

Lint

Lint Not Applicable

Unit

Tests Not Applicable

Event Timeline

timo.voelker_fh-muenster.de created this revision.Jun 10 2026, 7:38 AM

Herald added subscribers: ziaee, melifaro, ae, imp. · View Herald TranscriptJun 10 2026, 7:38 AM

timo.voelker_fh-muenster.de requested review of this revision.Jun 10 2026, 7:38 AM

pouria added a subscriber: pouria.Jun 11 2026, 3:48 PM

glebius accepted this revision.Jun 11 2026, 4:04 PM

This revision is now accepted and ready to land.Jun 11 2026, 4:04 PM

pouria accepted this revision.Jun 23 2026, 9:51 AM

tuexen accepted this revision.Jun 28 2026, 10:47 AM

Closed by commit rGd6c4cea7740d: loopback: improve checksum offloading (authored by timo.voelker_fh-muenster.de, committed by tuexen). · Explain WhyJun 28 2026, 10:58 AM

This revision was automatically updated to reflect the committed changes.

tuexen added a commit: rGd6c4cea7740d: loopback: improve checksum offloading.

timo.voelker_fh-muenster.de mentioned this in D57988: tests: fix checksum computation.Jul 1 2026, 7:30 AM

tuexen added a commit: rGfd3582e683d6: loopback: improve checksum offloading.Thu, Aug 6, 8:23 AM

tuexen added a commit: rG265b3e15abf6: loopback: improve checksum offloading.Thu, Aug 6, 9:04 AM

tuexen added a reverting change: rG1b8d19dea462: Revert "loopback: improve checksum offloading".Thu, Aug 6, 4:57 PM

Revision Contents
Changeset List

Path

Size

share/

man/

man4/

23 lines

sys/

net/

42 lines

Diff 180869

share/man/man4/lo.4

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sys/net/if_loop.c

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