On Tuesday, July 8, 2025 4:55 AM, Jakub Kicinski <k...@kernel.org> wrote: >On Tue, 1 Jul 2025 12:29:38 +0800 Song Yoong Siang wrote: >> |<---sizeof(xdp_meta)--| >> | | >> struct xdp_meta rx_desc->address >> ^ ^ >> | | >> +----------+----------------------+------------+------+ >> | headroom | custom metadata | reserved | data | >> +----------+----------------------+------------+------+ >> ^ ^ ^ >> | | | >> struct xdp_meta xdp_buff->data_meta xdp_buff->data >> | | >> |<---sizeof(xdp_meta)--| > >Huh. Did AF_XDP maintainers explicitly sign off on this or it's just how >IGC implementation works and nobody noticed? > Previously, IGC do copy out the Rx hwts from metadata area, so no problem when implementing XDP Rx metadata.
After that, net_device_ops.ndo_get_tstamp() is added into IGC to support timestamping from both free-running clock and adjustable clock. The 2 timers are stored in the metadata area, thus causing the issue. >For normal XDP my understanding is that its the driver's responsibility >to move the "reserved" stuff out of place before presenting the frame to >program. Is it means that driver needs to move out the "reserved" stuff before XDP program and then move back the stuff after XDP program for certain situation, like XDP_PASS? IMHO, if driver is allowed to use some portion of the metadata area, then the packet processing will be more efficiency and also align with the "zero-copy" idea. Any thoughts?
