CODEWITHSUNDEEP
linuxtcplinux-device-driver
Yifan Sun
Yifan Sun

Reputation: 832

Programming Linux network driver to support turning off TCP checksum offload

I am programming a linux networking driver. It is almost done. When I ping between 2 PCs, everything is perfect. And then I try to use some TCP/UDP protocols, the receiver never replies. I used wireshark to see what happens there, and I found all the TCP packets have incorrect checksum. It is said the wrong checksum is caused by TCP checksum offload. I tried to turn it off with ethtool. When I use sudo ethtool -K uwn0 tx off, it replies me

Cannot get device rx-checksumming settings: Operation not supported
Cannot get device tx-checksumming settings: Operation not supported
Cannot get device scatter-gather settings: Operation not supported
Cannot get device tcp-segmentation-offload settings: Operation not supported
Cannot get device udp-fragmentation-offload settings: Operation not supported
Cannot get device generic-segmentation-offload settings: Operation not supported
Cannot get device generic-receive-offload settings: Operation not supported
Cannot get device flags: Operation not supported

Is there a way to make my driver support tcp checksum offload? Or just compute checksum in software? Thanks

Upvotes: 3

Views: 2745

Answers (1)

cpaasch
cpaasch

Reputation: 101

When setting up your device's interface within your driver, you should unset the flag NETIF_F_HW_CSUM in netdev->hw_features to force TCP to calculate the check-sum in software.

For a example of setting up the hardware's feature-flags, take a look at
lxr.free-electrons.com/source/drivers/net/ethernet/intel/e1000e/netdev.c.

Upvotes: 1

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