[PATCH net-next 3/4] selftests/net: Add netkit io_uring ZC test for large rx_buf_len

[Daniel Borkmann <daniel@iogearbox.net>]

Add test_iou_zcrx_large_buf, which runs iou-zcrx with rx_buf_len >
page size (-x 2) through a netkit-leased RX queue. The netkit ifindex
is opaque to io_uring, but rx_page_size is honoured by the leased
physical qops via netif_mp_open_rxq()'s lease redirect.

Originally, I also added a BIG TCP variant on top, but dropped it
here as fbnic (and the QEMU fbnic model) has no BIG TCP support
to exercise it as this point.

Tested against the QEMU fbnic emulation. The new test exercises
the > page rx_buf_len path only when the leased NIC advertises
QCFG_RX_PAGE_SIZE; otherwise it skips.

For fbnic, I used Bjorn's patches locally [0]:

  # ./nk_qlease.py
  TAP version 13
  1..5
  ok 1 nk_qlease.test_iou_zcrx
  ok 2 nk_qlease.test_iou_zcrx_large_buf
  ok 3 nk_qlease.test_attrs
  ok 4 nk_qlease.test_attach_xdp_with_mp
  ok 5 nk_qlease.test_destroy
  # Totals: pass:5 fail:0 xfail:0 xpass:0 skip:0 error:0

Without those patches (aka not advertising QCFG_RX_PAGE_SIZE):

  # ./nk_qlease.py
  TAP version 13
  1..5
  ok 1 nk_qlease.test_iou_zcrx
  ok 2 nk_qlease.test_iou_zcrx_large_buf # SKIP Large chunks are not supported -95
  ok 3 nk_qlease.test_attrs
  ok 4 nk_qlease.test_attach_xdp_with_mp
  ok 5 nk_qlease.test_destroy
  # Totals: pass:4 fail:0 xfail:0 xpass:0 skip:1 error:0

Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/netdev/20260522113225.241337-1-bjorn@kernel.org/ [0]
---
 .../selftests/drivers/net/hw/nk_qlease.py     | 86 ++++++++++++++++++-
 1 file changed, 85 insertions(+), 1 deletion(-)

diff --git a/tools/testing/selftests/drivers/net/hw/nk_qlease.py b/tools/testing/selftests/drivers/net/hw/nk_qlease.py
index fee114676fd8..90d688453ddf 100755
--- a/tools/testing/selftests/drivers/net/hw/nk_qlease.py
+++ b/tools/testing/selftests/drivers/net/hw/nk_qlease.py
@@ -32,6 +32,15 @@ from lib.py import (
 )
 from lib.py import KsftSkipEx, CmdExitFailure
 
+# iou-zcrx exits with 42 from setup_zcrx() when the NIC does not advertise
+# QCFG_RX_PAGE_SIZE (or otherwise rejects the requested rx_buf_len).
+SKIP_CODE = 42
+
+
+def _restore_hugepages(count):
+    with open("/proc/sys/vm/nr_hugepages", "w", encoding="utf-8") as f:
+        f.write(str(count))
+
 
 def _create_netkit_pair(cfg, rxqueues=2):
     if cfg.nk_host_ifname:
@@ -188,6 +197,75 @@ def test_iou_zcrx(cfg) -> None:
         cmd(tx_cmd, host=cfg.remote)
 
 
+def test_iou_zcrx_large_buf(cfg) -> None:
+    """iou-zcrx with rx_buf_len > page size, going through a netkit-leased
+    queue. Exercises the queue rx-buf-len path via netif_mp_open_rxq()'s
+    lease redirect: the netkit ifindex is opaque to io_uring, but
+    rx_page_size is honoured by the *physical* qops because the lease
+    pointer rewrites the request from netkit onto the leased physical
+    rxq before supported_params/validate_qcfg are consulted.
+    """
+    cfg.require_ipver("6")
+    src_queue, nk_queue = _setup_lease(cfg)
+    defer(_teardown_netkit, cfg)
+    ethnl = EthtoolFamily()
+
+    with open("/proc/sys/vm/nr_hugepages", "r+", encoding="utf-8") as f:
+        nr_hugepages = int(f.read().strip())
+        if nr_hugepages < 64:
+            f.seek(0)
+            f.write("64")
+            defer(_restore_hugepages, nr_hugepages)
+
+    rings = ethnl.rings_get({"header": {"dev-index": cfg.ifindex}})
+    rx_rings = rings["rx"]
+    hds_thresh = rings.get("hds-thresh", 0)
+
+    ethnl.rings_set(
+        {
+            "header": {"dev-index": cfg.ifindex},
+            "tcp-data-split": "enabled",
+            "hds-thresh": 0,
+            "rx": 64,
+        }
+    )
+    defer(
+        ethnl.rings_set,
+        {
+            "header": {"dev-index": cfg.ifindex},
+            "tcp-data-split": "unknown",
+            "hds-thresh": hds_thresh,
+            "rx": rx_rings,
+        },
+    )
+
+    ethtool(f"-X {cfg.ifname} equal {src_queue}")
+    defer(ethtool, f"-X {cfg.ifname} default")
+
+    flow_rule_id = set_flow_rule(cfg, src_queue)
+    defer(ethtool, f"-N {cfg.ifname} delete {flow_rule_id}")
+
+    # -x 2 asks iou-zcrx for rx_buf_len = 2 * page_size (8 KiB on x86_64),
+    # backed by a 2 MiB hugepage area so the chunks are physically
+    # contiguous, which is what zcrx requires for non-default rx_buf_len.
+    rx_cmd = (
+        f"ip netns exec {cfg.netns.name} {cfg.bin_local} "
+        f"-s -p {cfg.port} -i {cfg.nk_guest_ifname} -q {nk_queue} -x 2"
+    )
+    tx_cmd = f"{cfg.bin_remote} -c -h {cfg.nk_guest_ipv6} -p {cfg.port} -l 12840"
+
+    # Probe via -d (dry run): exits with SKIP_CODE if the leased physical
+    # qops doesn't advertise QCFG_RX_PAGE_SIZE (e.g. older bnxt FW/HW).
+    probe = cmd(rx_cmd + " -d", fail=False)
+    if probe.ret == SKIP_CODE:
+        msg = probe.stdout.strip() or "rx_buf_len not supported by leased NIC"
+        raise KsftSkipEx(msg)
+
+    with bkg(rx_cmd, exit_wait=True):
+        wait_port_listen(cfg.port, proto="tcp", ns=cfg.netns)
+        cmd(tx_cmd, host=cfg.remote)
+
+
 def test_attrs(cfg) -> None:
     cfg.require_ipver("6")
     src_queue, nk_queue = _setup_lease(cfg)
@@ -350,7 +428,13 @@ def main() -> None:
         cfg.port = rand_port()
 
         ksft_run(
-            [test_iou_zcrx, test_attrs, test_attach_xdp_with_mp, test_destroy],
+            [
+                test_iou_zcrx,
+                test_iou_zcrx_large_buf,
+                test_attrs,
+                test_attach_xdp_with_mp,
+                test_destroy,
+            ],
             args=(cfg,),
         )
     ksft_exit()
-- 
2.43.0