[PATCH net-next v2] netdev: clarify GSO vs csum in qstats

[Jakub Kicinski <kuba@kernel.org>]

Could be just me, but I had to pause and double check that the Tx csum
counter in qstat should include GSO'd packets. GSO pretty much implies
csum so one could possibly interpret the csum counter as pure csum offload.

But the counters are based on virtio:

  [tx_needs_csum]
      The number of packets which require checksum calculation by the device.

  [rx_needs_csum]
      The number of packets with VIRTIO_NET_HDR_F_NEEDS_CSUM.

and VIRTIO_NET_HDR_F_NEEDS_CSUM gets set on GSO packets virtio sends.

Clarify this in the spec to avoid any confusion.

Signed-off-by: Jakub Kicinski <kuba@kernel.org>
---
v2:
 - remove the note that almost all GSO types need L4 csum
v1: https://lore.kernel.org/20250213010457.1351376-1-kuba@kernel.org

CC: willemb@google.com
CC: ecree.xilinx@gmail.com
CC: neescoba@cisco.com
---
 Documentation/netlink/specs/netdev.yaml | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/Documentation/netlink/specs/netdev.yaml b/Documentation/netlink/specs/netdev.yaml
index 288923e965ae..48159eb116a4 100644
--- a/Documentation/netlink/specs/netdev.yaml
+++ b/Documentation/netlink/specs/netdev.yaml
@@ -457,6 +457,8 @@ name: netdev
         name: tx-needs-csum
         doc: |
           Number of packets that required the device to calculate the checksum.
+          This counter includes the number of GSO wire packets for which device
+          calculated the L4 checksum.
         type: uint
       -
         name: tx-hw-gso-packets
-- 
2.48.1