[PATCH net-next 08/11] selftests: drv-net: ncdevmem: add -n flag to skip NIC configuration

[Bobby Eshleman <bobbyeshleman@gmail.com>]

From: Bobby Eshleman <bobbyeshleman@meta.com>

Add a -n (skip_config) flag that causes ncdevmem to skip NIC
configuration when operating as an RX server. When -n is passed,
ncdevmem skips configuring header split, RSS, and flow steering, as well
as their teardown on exit.

This allows ksft tests to pre-configure the NIC in the host namespace
before launching ncdevmem in the guest namespace. This is needed for
netkit devmem tests where the test harness namespace has direct access
to the NIC and the ncdevmem namespace does not.

Assisted-by: Claude Code:claude-sonnet-4-6
Signed-off-by: Bobby Eshleman <bobbyeshleman@meta.com>
---
 tools/testing/selftests/drivers/net/hw/ncdevmem.c | 58 +++++++++++++----------
 1 file changed, 34 insertions(+), 24 deletions(-)

diff --git a/tools/testing/selftests/drivers/net/hw/ncdevmem.c b/tools/testing/selftests/drivers/net/hw/ncdevmem.c
index e098d6534c3c..d96e8a3b5a65 100644
--- a/tools/testing/selftests/drivers/net/hw/ncdevmem.c
+++ b/tools/testing/selftests/drivers/net/hw/ncdevmem.c
@@ -93,6 +93,7 @@ static char *port;
 static size_t do_validation;
 static int start_queue = -1;
 static int num_queues = -1;
+static int skip_config;
 static char *ifname;
 static unsigned int ifindex;
 static unsigned int dmabuf_id;
@@ -828,7 +829,7 @@ static struct netdev_queue_id *create_queues(void)
 
 static int do_server(struct memory_buffer *mem)
 {
-	struct ethtool_rings_get_rsp *ring_config;
+	struct ethtool_rings_get_rsp *ring_config = NULL;
 	char ctrl_data[sizeof(int) * 20000];
 	size_t non_page_aligned_frags = 0;
 	struct sockaddr_in6 client_addr;
@@ -851,27 +852,29 @@ static int do_server(struct memory_buffer *mem)
 		return -1;
 	}
 
-	ring_config = get_ring_config();
-	if (!ring_config) {
-		pr_err("Failed to get current ring configuration");
-		return -1;
-	}
+	if (!skip_config) {
+		ring_config = get_ring_config();
+		if (!ring_config) {
+			pr_err("Failed to get current ring configuration");
+			return -1;
+		}
 
-	if (configure_headersplit(ring_config, 1)) {
-		pr_err("Failed to enable TCP header split");
-		goto err_free_ring_config;
-	}
+		if (configure_headersplit(ring_config, 1)) {
+			pr_err("Failed to enable TCP header split");
+			goto err_free_ring_config;
+		}
 
-	/* Configure RSS to divert all traffic from our devmem queues */
-	if (configure_rss()) {
-		pr_err("Failed to configure rss");
-		goto err_reset_headersplit;
-	}
+		/* Configure RSS to divert all traffic from our devmem queues */
+		if (configure_rss()) {
+			pr_err("Failed to configure rss");
+			goto err_reset_headersplit;
+		}
 
-	/* Flow steer our devmem flows to start_queue */
-	if (configure_flow_steering(&server_sin)) {
-		pr_err("Failed to configure flow steering");
-		goto err_reset_rss;
+		/* Flow steer our devmem flows to start_queue */
+		if (configure_flow_steering(&server_sin)) {
+			pr_err("Failed to configure flow steering");
+			goto err_reset_rss;
+		}
 	}
 
 	if (bind_rx_queue(ifindex, mem->fd, create_queues(), num_queues, &ys)) {
@@ -1052,13 +1055,17 @@ static int do_server(struct memory_buffer *mem)
 err_unbind:
 	ynl_sock_destroy(ys);
 err_reset_flow_steering:
-	reset_flow_steering();
+	if (!skip_config)
+		reset_flow_steering();
 err_reset_rss:
-	reset_rss();
+	if (!skip_config)
+		reset_rss();
 err_reset_headersplit:
-	restore_ring_config(ring_config);
+	if (!skip_config)
+		restore_ring_config(ring_config);
 err_free_ring_config:
-	ethtool_rings_get_rsp_free(ring_config);
+	if (!skip_config)
+		ethtool_rings_get_rsp_free(ring_config);
 	return err;
 }
 
@@ -1404,7 +1411,7 @@ int main(int argc, char *argv[])
 	int is_server = 0, opt;
 	int ret, err = 1;
 
-	while ((opt = getopt(argc, argv, "Lls:c:p:v:q:t:f:z:")) != -1) {
+	while ((opt = getopt(argc, argv, "Lls:c:p:v:q:t:f:z:n")) != -1) {
 		switch (opt) {
 		case 'L':
 			fail_on_linear = true;
@@ -1436,6 +1443,9 @@ int main(int argc, char *argv[])
 		case 'z':
 			max_chunk = atoi(optarg);
 			break;
+		case 'n':
+			skip_config = 1;
+			break;
 		case '?':
 			fprintf(stderr, "unknown option: %c\n", optopt);
 			break;

-- 
2.52.0