[LTP] [PATCH v2 21/31] testcases: sysfs: Add sys_net02

A test for /sys/class/net/*/* files.

This test, unlike sys_net01, creates a virtual ethernet interface so
that it can change various attributes and verify that they are mirrored
into the sysfs correctly.

Signed-off-by: Cyril Hrubis <[email protected]>
---
 runtest/sysfs                                 |   1 +
 testcases/kernel/sysfs/class/net/.gitignore   |   1 +
 testcases/kernel/sysfs/class/net/sys_net02.c  | 179 ++++++++++++++++++
 .../kernel/sysfs/class/net/sys_net_common.h   |  80 ++++++++
 4 files changed, 261 insertions(+)
 create mode 100644 testcases/kernel/sysfs/class/net/sys_net02.c
 create mode 100644 testcases/kernel/sysfs/class/net/sys_net_common.h

diff --git a/runtest/sysfs b/runtest/sysfs
index 90e4d2b8e..fee8a0b2b 100644
--- a/runtest/sysfs
+++ b/runtest/sysfs
@@ -16,3 +16,4 @@ sys_wakeup01 sys_wakeup01
 sys_rtc01 sys_rtc01
 sys_thermal01 sys_thermal01
 sys_net01 sys_net01
+sys_net02 sys_net02
diff --git a/testcases/kernel/sysfs/class/net/.gitignore b/testcases/kernel/sysfs/class/net/.gitignore
index f5ef57b75..b70d02158 100644
--- a/testcases/kernel/sysfs/class/net/.gitignore
+++ b/testcases/kernel/sysfs/class/net/.gitignore
@@ -1 +1,2 @@
 /sys_net01
+/sys_net02
diff --git a/testcases/kernel/sysfs/class/net/sys_net02.c b/testcases/kernel/sysfs/class/net/sys_net02.c
new file mode 100644
index 000000000..f8f564c1f
--- /dev/null
+++ b/testcases/kernel/sysfs/class/net/sys_net02.c
@@ -0,0 +1,179 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Copyright (c) 2026 Cyril Hrubis <[email protected]>
+ */
+
+/*\
+ * Verifies that the link state attributes exported under
+ * /sys/class/net/<iface>/ correctly mirror the administrative state of a
+ * veth peer.
+ *
+ * A veth device's carrier is expected to be up only while its peer is up:
+ * veth_open()/veth_close() call netif_carrier_on()/netif_carrier_off() based
+ * on whether the peer is running. The test creates a veth pair and checks
+ * that bringing the peer down and back up is reflected in:
+ *
+ * - carrier - 1 while the peer is up, 0 while it is down
+ * - operstate - "up" while the peer is up, "lowerlayerdown" while it is down
+ * - carrier_up_count / carrier_down_count - incremented by exactly one on
+ *   each corresponding transition
+ * - carrier_changes - always equal to carrier_up_count + carrier_down_count
+ *
+ * Note this only checks the values synchronously after each netlink state
+ * change (which is itself synchronous), it does not use poll(2)/select(2):
+ * unlike some other sysfs attributes, /sys/class/net/<iface>/carrier does not
+ * support poll() based notification on Linux, link state changes are
+ * reported to userspace via rtnetlink instead.
+ *
+ * The test also checks attributes that are not tied to the peer's state:
+ *
+ * - mtu - directly writable via sysfs; a few valid values are written and
+ *   read back, and one syntactically invalid value is rejected (with the mtu
+ *   left unchanged)
+ * - address - read-only in sysfs, changed via rtnetlink instead (the
+ *   interface is brought down first since most drivers require this); while
+ *   doing so, the IFF_UP bit in "flags" is also cross-checked against the
+ *   interface's own administrative state
+ * - netdev_group and ifalias - directly writable via sysfs, a value is
+ *   written and read back
+ *
+ * This needs root to create the veth pair.
+ */
+
+#include <stdio.h>
+#include <string.h>
+#include <unistd.h>
+#include <net/if.h>
+
+#include "tst_test.h"
+#include "tst_netdevice.h"
+#include "tst_sysfs_assert.h"
+
+#define IFNAME1 "ltp_vethp1"
+#define IFNAME2 "ltp_vethp2"
+#define IFACE_PATH "/sys/class/net/" IFNAME1
+
+static int veth_created;
+
+static long read_mtu(void)
+{
+	return TST_SYSFS_READ_LI(IFACE_PATH "/mtu");
+}
+
+#include "sys_net_common.h"
+
+static void setup(void)
+{
+	CREATE_VETH_PAIR(IFNAME1, IFNAME2);
+	veth_created = 1;
+
+	NETDEV_SET_STATE(IFNAME1, 1);
+	NETDEV_SET_STATE(IFNAME2, 1);
+}
+
+static unsigned long read_flags(void)
+{
+	return TST_SYSFS_READ_LX(IFACE_PATH "/flags");
+}
+
+static void check_address(void)
+{
+	static const unsigned char new_addr[6] = {0x02, 0, 0, 0, 0, 0x01};
+	char actual[32];
+	long iff_up;
+
+	tst_res(TINFO, "IFNAME1 is up before the address change");
+	iff_up = read_flags() & IFF_UP;
+	TST_EXP_EQ_LI(iff_up, IFF_UP);
+
+	NETDEV_SET_STATE(IFNAME1, 0);
+	tst_res(TINFO, "IFNAME1 is down for the address change");
+	iff_up = read_flags() & IFF_UP;
+	TST_EXP_EQ_LI(iff_up, 0);
+
+	NETDEV_SET_HWADDR(IFNAME1, new_addr, sizeof(new_addr));
+	NETDEV_SET_STATE(IFNAME1, 1);
+	tst_res(TINFO, "IFNAME1 is up again after the address change");
+	iff_up = read_flags() & IFF_UP;
+	TST_EXP_EQ_LI(iff_up, IFF_UP);
+
+	TST_SYSFS_READ_STR(actual, sizeof(actual), IFACE_PATH "/address");
+
+	TST_EXP_EQ_STR(actual, "02:00:00:00:00:01");
+}
+
+static void check_netdev_group(void)
+{
+	long group;
+
+	if (FILE_PRINTF(IFACE_PATH "/netdev_group", "%d", 7)) {
+		tst_res(TFAIL, "Failed to set netdev_group");
+		return;
+	}
+
+	group = TST_SYSFS_READ_LI(IFACE_PATH "/netdev_group");
+
+	TST_EXP_EQ_LI(group, 7);
+}
+
+static void check_ifalias(void)
+{
+	char alias[64];
+
+	if (FILE_PRINTF(IFACE_PATH "/ifalias", "%s", "ltp-test-alias")) {
+		tst_res(TFAIL, "Failed to set ifalias");
+		return;
+	}
+
+	TST_SYSFS_READ_STR(alias, sizeof(alias), IFACE_PATH "/ifalias");
+	TST_EXP_EQ_STR(alias, "ltp-test-alias");
+}
+
+static void run(void)
+{
+	struct netdev_state s0, s1, s2;
+
+	read_state(&s0);
+	check_state(&s0, 1, "up", "both ends up");
+
+	NETDEV_SET_STATE(IFNAME2, 0);
+	read_state(&s1);
+	check_state(&s1, 0, "lowerlayerdown", "peer down");
+	check_state_delta(&s0, &s1, 0, 1, "peer down transition");
+
+	NETDEV_SET_STATE(IFNAME2, 1);
+	read_state(&s2);
+	check_state(&s2, 1, "up", "peer back up");
+	check_state_delta(&s1, &s2, 1, 0, "peer up transition");
+
+	check_mtu_valid(68);
+	check_mtu_valid(1500);
+	check_mtu_valid(9000);
+	check_mtu_valid(65535);
+	check_mtu_invalid("-1");
+	check_mtu_invalid("0");
+	check_mtu_invalid("67");
+	check_mtu_invalid("70000");
+
+	check_address();
+
+	check_netdev_group();
+	check_ifalias();
+}
+
+static void cleanup(void)
+{
+	if (veth_created)
+		NETDEV_REMOVE_DEVICE(IFNAME1);
+}
+
+static struct tst_test test = {
+	.test_all = run,
+	.setup = setup,
+	.cleanup = cleanup,
+	.needs_root = 1,
+	.needs_kconfigs = (const char *const[]){
+		"CONFIG_VETH",
+		NULL
+	},
+};
diff --git a/testcases/kernel/sysfs/class/net/sys_net_common.h b/testcases/kernel/sysfs/class/net/sys_net_common.h
new file mode 100644
index 000000000..7b0346c9c
--- /dev/null
+++ b/testcases/kernel/sysfs/class/net/sys_net_common.h
@@ -0,0 +1,80 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Copyright (c) 2026 Cyril Hrubis <[email protected]>
+ */
+
+#ifndef SYS_NET_COMMON
+#define SYS_NET_COMMON
+
+struct netdev_state {
+	long carrier;
+	long carrier_changes;
+	long carrier_up_count;
+	long carrier_down_count;
+	char operstate[32];
+};
+
+static void read_state(struct netdev_state *st)
+{
+	st->carrier = TST_SYSFS_READ_LI(IFACE_PATH "/carrier");
+	st->carrier_changes = TST_SYSFS_READ_LI(IFACE_PATH "/carrier_changes");
+	st->carrier_up_count = TST_SYSFS_READ_LI(IFACE_PATH "/carrier_up_count");
+	st->carrier_down_count = TST_SYSFS_READ_LI(IFACE_PATH "/carrier_down_count");
+	TST_SYSFS_READ_STR(st->operstate, sizeof(st->operstate), IFACE_PATH "/operstate");
+}
+
+static void check_state(const struct netdev_state *st, long carrier,
+			const char *operstate, const char *desc)
+{
+	tst_res(TINFO, "%s", desc);
+
+	TST_EXP_EQ_LI(st->carrier, carrier);
+	TST_EXP_EQ_STR(st->operstate, operstate);
+	TST_EXP_EQ_LI(st->carrier_changes,
+		      st->carrier_up_count + st->carrier_down_count);
+}
+
+static void check_state_delta(const struct netdev_state *prev,
+			      const struct netdev_state *cur, long up_delta,
+			      long down_delta, const char *desc)
+{
+	long got_up = cur->carrier_up_count - prev->carrier_up_count;
+	long got_down = cur->carrier_down_count - prev->carrier_down_count;
+	long got_changes = cur->carrier_changes - prev->carrier_changes;
+
+	tst_res(TINFO, "%s", desc);
+
+	TST_EXP_EQ_LI(got_up, up_delta);
+	TST_EXP_EQ_LI(got_down, down_delta);
+	TST_EXP_EQ_LI(got_changes, up_delta + down_delta);
+}
+
+static void check_mtu_valid(long mtu)
+{
+	char mtu_str[16];
+
+	snprintf(mtu_str, sizeof(mtu_str), "%ld", mtu);
+
+	if (FILE_PRINTF(IFACE_PATH "/mtu", "%s", mtu_str)) {
+		tst_res(TFAIL, "Failed to set mtu to %ld", mtu);
+		return;
+	}
+
+	TST_EXP_EQ_LI(read_mtu(), mtu);
+}
+
+static void check_mtu_invalid(const char *mtu_str)
+{
+	long before = read_mtu();
+
+	if (!FILE_PRINTF(IFACE_PATH "/mtu", "%s", mtu_str)) {
+		tst_res(TFAIL, "Writing mtu '%s' unexpectedly succeeded",
+			mtu_str);
+		return;
+	}
+
+	tst_res(TINFO, "Writing mtu '%s' was rejected as expected", mtu_str);
+	TST_EXP_EQ_LI(read_mtu(), before);
+}
+
+#endif /* SYS_NET_COMMON */
-- 
2.54.0


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