[LTP] [PATCH v4 20/31] testcases: sysfs: Add sys_net01

[Cyril Hrubis <chrubis@suse.cz>]

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

Signed-off-by: Cyril Hrubis <chrubis@suse.cz>
---
 include/tst_path_defs.h                      |   1 +
 runtest/sysfs                                |   1 +
 testcases/kernel/sysfs/class/net/.gitignore  |   1 +
 testcases/kernel/sysfs/class/net/Makefile    |   7 +
 testcases/kernel/sysfs/class/net/sys_net01.c | 145 +++++++++++++++++++
 5 files changed, 155 insertions(+)
 create mode 100644 testcases/kernel/sysfs/class/net/.gitignore
 create mode 100644 testcases/kernel/sysfs/class/net/Makefile
 create mode 100644 testcases/kernel/sysfs/class/net/sys_net01.c

diff --git a/include/tst_path_defs.h b/include/tst_path_defs.h
index f2417ecdb..2c9cfcf85 100644
--- a/include/tst_path_defs.h
+++ b/include/tst_path_defs.h
@@ -97,6 +97,7 @@
 #define PATH_CLASS_BDI				"/sys/class/bdi"
 #define PATH_CLASS_HWMON			"/sys/class/hwmon"
 #define PATH_CLASS_LEDS			"/sys/class/leds"
+#define PATH_CLASS_NET				"/sys/class/net"
 #define PATH_CLASS_RTC				"/sys/class/rtc"
 #define PATH_CLASS_THERMAL			"/sys/class/thermal"
 #define PATH_CLASS_WAKEUP			"/sys/class/wakeup"
diff --git a/runtest/sysfs b/runtest/sysfs
index 454042ed0..90e4d2b8e 100644
--- a/runtest/sysfs
+++ b/runtest/sysfs
@@ -15,3 +15,4 @@ sys_leds01 sys_leds01
 sys_wakeup01 sys_wakeup01
 sys_rtc01 sys_rtc01
 sys_thermal01 sys_thermal01
+sys_net01 sys_net01
diff --git a/testcases/kernel/sysfs/class/net/.gitignore b/testcases/kernel/sysfs/class/net/.gitignore
new file mode 100644
index 000000000..f5ef57b75
--- /dev/null
+++ b/testcases/kernel/sysfs/class/net/.gitignore
@@ -0,0 +1 @@
+/sys_net01
diff --git a/testcases/kernel/sysfs/class/net/Makefile b/testcases/kernel/sysfs/class/net/Makefile
new file mode 100644
index 000000000..034038061
--- /dev/null
+++ b/testcases/kernel/sysfs/class/net/Makefile
@@ -0,0 +1,7 @@
+# SPDX-License-Identifier: GPL-2.0-or-later
+# Copyright (c) 2026 Cyril Hrubis <chrubis@suse.cz>
+
+top_srcdir		?= ../../../../..
+
+include $(top_srcdir)/include/mk/testcases.mk
+include $(top_srcdir)/include/mk/generic_leaf_target.mk
diff --git a/testcases/kernel/sysfs/class/net/sys_net01.c b/testcases/kernel/sysfs/class/net/sys_net01.c
new file mode 100644
index 000000000..aa54c0699
--- /dev/null
+++ b/testcases/kernel/sysfs/class/net/sys_net01.c
@@ -0,0 +1,145 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Copyright (c) 2026 Cyril Hrubis <chrubis@suse.cz>
+ */
+
+/*\
+ * Sanity checks for the network interface attributes exported under
+ * /sys/class/net/<iface>/.
+ *
+ * For every network interface the test verifies that:
+ *
+ * - mtu is greater than zero, and for an Ethernet-type interface (type == 1,
+ *   ARPHRD_ETHER, which also covers most virtual/Wi-Fi interfaces on Linux)
+ *   at most 65535, the largest possible IPv4 packet size and comfortably
+ *   above even the largest real-world jumbo frame configurations. Other
+ *   interface types (tunnels, PPP, CAN, ...) are left effectively unbounded
+ *   since their legitimate MTU semantics vary too much to bound generically,
+ *   e.g. a CAN interface reports the size of struct can_frame/canfd_frame
+ *   (16/72) rather than an IP MTU at all.
+ * - addr_len is at most MAX_ADDR_LEN (32), the fixed size of the kernel's
+ *   internal hardware address buffer (include/linux/netdevice.h) and thus a
+ *   hard limit rather than a mere plausibility bound. It is not asserted to
+ *   be non-zero: plenty of legitimate interfaces (PPP, GRE/IPIP/sit tunnels,
+ *   WireGuard, CAN, ...) have no link-layer address at all and report
+ *   addr_len == 0.
+ * - the address has exactly addr_len bytes (colon separated hex octets),
+ *   or is empty when addr_len == 0
+ * - operstate is one of the known states
+ *
+ * Entries directly under /sys/class/net/ that are not actual network
+ * interfaces are skipped: real interfaces are always symlinks to a device
+ * directory (e.g. ../../devices/.../net/eth0), but some drivers also expose
+ * plain control files right there, e.g. bonding_masters (created whenever
+ * the bonding module is loaded, regardless of whether any bond device is
+ * actually configured), used to create/destroy bond devices by writing
+ * ``+bond0``/``-bond0`` to it.
+ */
+
+#include <stdio.h>
+#include <string.h>
+#include <dirent.h>
+#include <limits.h>
+#include <sys/stat.h>
+#include "tst_test.h"
+#include "tst_sysfs_assert.h"
+#include "tst_path_defs.h"
+
+/* include/linux/netdevice.h: fixed size of dev->dev_addr[]. */
+#define MAX_ADDR_LEN 32
+
+/* include/uapi/linux/if_arp.h */
+#define ARPHRD_ETHER 1
+
+/*
+ * The largest possible IPv4 packet size, used as a practical upper bound for
+ * the MTU of an Ethernet-type interface, see the top comment.
+ */
+#define MAX_ETHER_MTU 65535
+
+static const char *const operstates[] = {
+	"unknown", "notpresent", "down", "lowerlayerdown",
+	"testing", "dormant", "up", NULL
+};
+
+static void check_address(const char *iface)
+{
+	char addr[128] = "";
+	int octets;
+	char *p;
+
+	TST_SYSFS_READ_STR(addr, sizeof(addr), PATH_CLASS_NET "/%s/address", iface);
+
+	/* An empty address is valid for an interface with addr_len == 0. */
+	octets = addr[0] ? 1 : 0;
+
+	for (p = addr; *p; p++) {
+		if (*p == ':')
+			octets++;
+	}
+
+	TST_SYSFS_EXP_EQ_LI(octets, PATH_CLASS_NET "/%s/addr_len", iface);
+}
+
+static void check_iface(const char *iface)
+{
+	long type, mtu_max = LONG_MAX;
+
+	tst_res(TINFO, "Checking interface '%s'", iface);
+
+	type = TST_SYSFS_READ_LI(PATH_CLASS_NET "/%s/type", iface);
+
+	if (type == ARPHRD_ETHER)
+		mtu_max = MAX_ETHER_MTU;
+
+	TST_SYSFS_ASSERT_RANGELL(1, mtu_max, PATH_CLASS_NET "/%s/mtu", iface);
+	TST_SYSFS_ASSERT_RANGELL(0, MAX_ADDR_LEN, PATH_CLASS_NET "/%s/addr_len", iface);
+
+	check_address(iface);
+	TST_SYSFS_ASSERT_ONEOF(operstates, PATH_CLASS_NET "/%s/operstate", iface);
+}
+
+static int is_iface(const char *name)
+{
+	struct stat st;
+	char path[PATH_MAX];
+
+	snprintf(path, sizeof(path), PATH_CLASS_NET "/%s", name);
+
+	if (stat(path, &st))
+		return 0;
+
+	return S_ISDIR(st.st_mode);
+}
+
+static void do_test(void)
+{
+	DIR *d;
+	struct dirent *ent;
+	int found = 0;
+
+	d = TST_SYSFS_TRY_OPENDIR(PATH_CLASS_NET);
+
+	while ((ent = SAFE_READDIR(d))) {
+		if (ent->d_name[0] == '.')
+			continue;
+
+		if (!is_iface(ent->d_name)) {
+			tst_res(TINFO, "%s is not a network interface, skipping",
+				ent->d_name);
+			continue;
+		}
+
+		found = 1;
+		check_iface(ent->d_name);
+	}
+
+	SAFE_CLOSEDIR(d);
+
+	if (!found)
+		tst_res(TCONF, "No network interfaces found");
+}
+
+static struct tst_test test = {
+	.test_all = do_test,
+};
-- 
2.54.0


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