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| author | Jakub Kicinski <kuba@kernel.org> | 2026-05-26 09:01:49 -0700 |
|---|---|---|
| committer | Jakub Kicinski <kuba@kernel.org> | 2026-05-28 14:37:47 -0700 |
| commit | 6686e7f03f42c9476770e06e0a030b7267018e71 (patch) | |
| tree | 22abe3148c61e93230f799d3d1e301d4e84c1d6f /Documentation | |
| parent | f94874c38886b4e1adbd3233a313f320966d30ff (diff) | |
| download | linux-next-history-6686e7f03f42c9476770e06e0a030b7267018e71.tar.gz | |
docs: net: add Rx notes to the checksum guide
The Rx checksum processing gives people pause. The two main questions
in my experience are:
- what to do with bad IPv4 checksum; and
- what to do with packets with bad checksum.
Folks often feel the urge to drop the latter, to "avoid overloading
the host".
Reviewed-by: Willem de Bruijn <willemb@google.com>
Link: https://patch.msgid.link/20260526160151.2793354-9-kuba@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Diffstat (limited to 'Documentation')
| -rw-r--r-- | Documentation/networking/checksum-offloads.rst | 17 |
1 files changed, 16 insertions, 1 deletions
diff --git a/Documentation/networking/checksum-offloads.rst b/Documentation/networking/checksum-offloads.rst index 907aed9f3a3b8..d838fe5c16066 100644 --- a/Documentation/networking/checksum-offloads.rst +++ b/Documentation/networking/checksum-offloads.rst @@ -19,7 +19,6 @@ The following technologies are described: Things that should be documented here but aren't yet: -* RX Checksum Offload * CHECKSUM_UNNECESSARY conversion @@ -139,3 +138,19 @@ In Linux, RCO is implemented individually in each encapsulation protocol, and most tunnel types have flags controlling its use. For instance, VXLAN has the configuration flag VXLAN_F_REMCSUM_TX to indicate that RCO should be used when transmitting. + + +RX Checksum Offload +=================== + +RX checksum offload is controlled via NETIF_F_RXCSUM. When disabled the driver +must not set skb->ip_summed on ingress packets. As mentioned, IPv4 checksum +is not offloaded, the RXCSUM feature controls the offload of verification of +transport layer checksums. + +Note that packets with bad TCP/UDP checksums must still be passed +to the stack. skb->ip_summed of such packets can be set to ``CHECKSUM_COMPLETE`` +or left at ``CHECKSUM_NONE``. Drivers **must not discard** packets with +bad TCP/UDP checksum and must not configure the device to drop them. +Checksum validation is relatively inexpensive and having bad packets reflected +in SNMP counters is crucial for network monitoring. |