Re: [PATCH v4 net 0/6] xsk: fix AF_XDP multi-buffer Tx descriptor reclaim

On 07/19, Maciej Fijalkowski wrote:

v3:
https://lore.kernel.org/netdev/20260714140722.111645-1-maciej.fijalkowski@intel.com/T/ (local)
v3->v4:

* Return standalone invalid Tx descriptors through the completion ring in
  both the generic and zero-copy Tx paths. Advancing the Tx-ring consumer
  releases only the ring slot; returning the descriptor address through
  the CQ also transfers ownership of the corresponding UMEM frame back to
  userspace.

* Remove xsk_tx_batch::consumed_descs. With standalone invalid descriptors
  now reclaimed through the CQ, every descriptor permanently removed from
  the Tx ring is represented by either tx_descs or reclaim_descs. Use
  their sum for Tx-consumer advancement, shared-UMEM fairness accounting,
  and progress detection.

* Ensure that generic reclaim-only processing publishes the updated
  Tx-ring consumer even when no packet was submitted to the networking
  stack.

* Update the XSK selftests to count every descriptor submitted to the Tx
  ring as an expected CQ entry, while continuing to count only valid
  packets as expected Rx traffic. This covers standalone invalid
  descriptors, invalid multi-buffer packets, oversized packets, and the
  non-verbatim STAT_TX_INVALID tests.

* Update the AF_XDP documentation to describe the completion ring as an
  ownership-transfer mechanism and document that standalone, invalid
  multi-buffer, and oversized Tx packets are reclaimed through the CQ.

* Add Jason's tags

Acked-by: Stanislav Fomichev <sdf@fomichev.me>

Kudos for updating the doc with the new expectations! (and I still hope
that we can separately redo the generic tx path)