selftests: drv-net: add HDS payload sweep test for devmem TCP

Add check_rx_hds test that verifies header/data split works across
payload sizes. The test sweeps payload sizes from 1 byte to 8KB, if any
data propagates up to userspace as SCM_DEVMEM_LINEAR, then the test
fails. This shows that regardless of payload size, ncdevmem's
configuration of hds-thresh to 0 is respected.

Add -L (--fail-on-linear) flag to ncdevmem that causes the receiver to
fail if any SCM_DEVMEM_LINEAR cmsg is received.

Use socat option for fixed block sizing and tcp nodelay to disable
nagle's algo to avoid buffering.

Signed-off-by: Bobby Eshleman <bobbyeshleman@meta.com>
Link: https://patch.msgid.link/20260211-fbnic-tcp-hds-fixes-v1-4-55d050e6f606@meta.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

2 files changed, 28 insertions, 2 deletions

diff --git a/tools/testing/selftests/drivers/net/hw/devmem.py b/tools/testing/selftests/drivers/net/hw/devmem.py
index 45c2d49d55b6..ee863e90d1e0 100755
--- a/tools/testing/selftests/drivers/net/hw/devmem.py
+++ b/tools/testing/selftests/drivers/net/hw/devmem.py
@@ -63,12 +63,29 @@ def check_tx_chunks(cfg) -> None:
     ksft_eq(socat.stdout.strip(), "hello\nworld")
 
 
+def check_rx_hds(cfg) -> None:
+    """Test HDS splitting across payload sizes."""
+    require_devmem(cfg)
+
+    for size in [1, 8, 16, 32, 64, 128, 256, 512, 1024, 2048, 4096, 8192]:
+        port = rand_port()
+        listen_cmd = f"{cfg.bin_local} -L -l -f {cfg.ifname} -s {cfg.addr} -p {port}"
+
+        with bkg(listen_cmd, exit_wait=True) as ncdevmem:
+            wait_port_listen(port)
+            cmd(f"dd if=/dev/zero bs={size} count=1 2>/dev/null | " +
+                f"socat -b {size} -u - TCP{cfg.addr_ipver}:{cfg.baddr}:{port},nodelay",
+                host=cfg.remote, shell=True)
+
+        ksft_eq(ncdevmem.ret, 0, f"HDS failed for payload size {size}")
+
+
 def main() -> None:
     with NetDrvEpEnv(__file__) as cfg:
         cfg.bin_local = path.abspath(path.dirname(__file__) + "/ncdevmem")
         cfg.bin_remote = cfg.remote.deploy(cfg.bin_local)
 
-        ksft_run([check_rx, check_tx, check_tx_chunks],
+        ksft_run([check_rx, check_tx, check_tx_chunks, check_rx_hds],
                  args=(cfg, ))
     ksft_exit()
 
diff --git a/tools/testing/selftests/drivers/net/hw/ncdevmem.c b/tools/testing/selftests/drivers/net/hw/ncdevmem.c
index 16864c844108..e098d6534c3c 100644
--- a/tools/testing/selftests/drivers/net/hw/ncdevmem.c
+++ b/tools/testing/selftests/drivers/net/hw/ncdevmem.c
@@ -98,6 +98,7 @@ static unsigned int ifindex;
 static unsigned int dmabuf_id;
 static uint32_t tx_dmabuf_id;
 static int waittime_ms = 500;
+static bool fail_on_linear;
 
 /* System state loaded by current_config_load() */
 #define MAX_FLOWS	8
@@ -975,6 +976,11 @@ static int do_server(struct memory_buffer *mem)
 					"SCM_DEVMEM_LINEAR. dmabuf_cmsg->frag_size=%u\n",
 					dmabuf_cmsg->frag_size);
 
+				if (fail_on_linear) {
+					pr_err("received SCM_DEVMEM_LINEAR but --fail-on-linear (-L) set");
+					goto err_close_client;
+				}
+
 				continue;
 			}
 
@@ -1398,8 +1404,11 @@ int main(int argc, char *argv[])
 	int is_server = 0, opt;
 	int ret, err = 1;
 
-	while ((opt = getopt(argc, argv, "ls:c:p:v:q:t:f:z:")) != -1) {
+	while ((opt = getopt(argc, argv, "Lls:c:p:v:q:t:f:z:")) != -1) {
 		switch (opt) {
+		case 'L':
+			fail_on_linear = true;
+			break;
 		case 'l':
 			is_server = 1;
 			break;