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". Signed-off-by: Jakub Kicinski --- Documentation/networking/checksum-offloads.rst | 17 ++++++++++++++++- 1 file changed, 16 insertions(+), 1 deletion(-) diff --git a/Documentation/networking/checksum-offloads.rst b/Documentation/networking/checksum-offloads.rst index 907aed9f3a3b..d838fe5c1606 100644 --- a/Documentation/networking/checksum-offloads.rst +++ b/Documentation/networking/checksum-offloads.rst @@ -19,7 +19,6 @@ take advantage of checksum offload capabilities of various NICs. 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. -- 2.54.0