selftests/bpf: Extend netkit tests to validate set {head,tail}room

Extend the netkit selftests to specify and validate the {head,tail}room
on the netdevice:

# ./vmtest.sh -- ./test_progs -t netkit
[...]
./test_progs -t netkit
[ 1.174147] bpf_testmod: loading out-of-tree module taints kernel.
[ 1.174585] bpf_testmod: module verification failed: signature and/or required key missing - tainting kernel
[ 1.422307] tsc: Refined TSC clocksource calibration: 3407.983 MHz
[ 1.424511] clocksource: tsc: mask: 0xffffffffffffffff max_cycles: 0x311fc3e5084, max_idle_ns: 440795359833 ns
[ 1.428092] clocksource: Switched to clocksource tsc
#363 tc_netkit_basic:OK
#364 tc_netkit_device:OK
#365 tc_netkit_multi_links:OK
#366 tc_netkit_multi_opts:OK
#367 tc_netkit_neigh_links:OK
#368 tc_netkit_pkt_type:OK
#369 tc_netkit_scrub:OK
Summary: 7/0 PASSED, 0 SKIPPED, 0 FAILED

Signed-off-by: Daniel Borkmann <[e-mail]>
Acked-by: Nikolay Aleksandrov <[e-mail]>
Link: https://lore.kernel.org/bpf/[e-mail]

tools/testing/selftests/bpf/prog_tests/tc_netkit.c

···
 #include "netlink_helpers.h"
 #include "tc_helpers.h"
 
+#define NETKIT_HEADROOM	32
+#define NETKIT_TAILROOM	8
+
 #define MARK		42
 #define PRIO		0xeb9f
 #define ICMP_ECHO	8
+
+#define FLAG_ADJUST_ROOM (1 << 0)
+#define FLAG_SAME_NETNS  (1 << 1)
 
 struct icmphdr {
 	__u8		type;
···
 };
 
 static int create_netkit(int mode, int policy, int peer_policy, int *ifindex,
-			 bool same_netns, int scrub, int peer_scrub)
+			 int scrub, int peer_scrub, __u32 flags)
 {
 	struct rtnl_handle rth = { .fd = -1 };
 	struct iplink_req req = {};
···
 	addattr32(&req.n, sizeof(req), IFLA_NETKIT_SCRUB, scrub);
 	addattr32(&req.n, sizeof(req), IFLA_NETKIT_PEER_SCRUB, peer_scrub);
 	addattr32(&req.n, sizeof(req), IFLA_NETKIT_MODE, mode);
+	if (flags & FLAG_ADJUST_ROOM) {
+		addattr16(&req.n, sizeof(req), IFLA_NETKIT_HEADROOM, NETKIT_HEADROOM);
+		addattr16(&req.n, sizeof(req), IFLA_NETKIT_TAILROOM, NETKIT_TAILROOM);
+	}
 	addattr_nest_end(&req.n, data);
 	addattr_nest_end(&req.n, linkinfo);
 
···
 				 " addr ee:ff:bb:cc:aa:dd"),
 				 "set hwaddress");
 	}
-	if (same_netns) {
+	if (flags & FLAG_SAME_NETNS) {
 		ASSERT_OK(system("ip link set dev " netkit_peer " up"),
 				 "up peer");
 		ASSERT_OK(system("ip addr add dev " netkit_peer " 10.0.0.2/24"),
···
 	int err, ifindex;
 
 	err = create_netkit(NETKIT_L2, NETKIT_PASS, NETKIT_PASS,
-			    &ifindex, false, NETKIT_SCRUB_DEFAULT,
-			    NETKIT_SCRUB_DEFAULT);
+			    &ifindex, NETKIT_SCRUB_DEFAULT,
+			    NETKIT_SCRUB_DEFAULT, 0);
 	if (err)
 		return;
 
···
 	int err, ifindex;
 
 	err = create_netkit(mode, NETKIT_PASS, NETKIT_PASS,
-			    &ifindex, false, NETKIT_SCRUB_DEFAULT,
-			    NETKIT_SCRUB_DEFAULT);
+			    &ifindex, NETKIT_SCRUB_DEFAULT,
+			    NETKIT_SCRUB_DEFAULT, 0);
 	if (err)
 		return;
 
···
 	int err, ifindex;
 
 	err = create_netkit(mode, NETKIT_PASS, NETKIT_PASS,
-			    &ifindex, false, NETKIT_SCRUB_DEFAULT,
-			    NETKIT_SCRUB_DEFAULT);
+			    &ifindex, NETKIT_SCRUB_DEFAULT,
+			    NETKIT_SCRUB_DEFAULT, 0);
 	if (err)
 		return;
 
···
 	int err, ifindex, ifindex2;
 
 	err = create_netkit(NETKIT_L3, NETKIT_PASS, NETKIT_PASS,
-			    &ifindex, true, NETKIT_SCRUB_DEFAULT,
-			    NETKIT_SCRUB_DEFAULT);
+			    &ifindex, NETKIT_SCRUB_DEFAULT,
+			    NETKIT_SCRUB_DEFAULT, FLAG_SAME_NETNS);
 	if (err)
 		return;
 
···
 	int err, ifindex;
 
 	err = create_netkit(mode, NETKIT_PASS, NETKIT_PASS,
-			    &ifindex, false, NETKIT_SCRUB_DEFAULT,
-			    NETKIT_SCRUB_DEFAULT);
+			    &ifindex, NETKIT_SCRUB_DEFAULT,
+			    NETKIT_SCRUB_DEFAULT, 0);
 	if (err)
 		return;
 
···
 	struct bpf_link *link;
 
 	err = create_netkit(mode, NETKIT_PASS, NETKIT_PASS,
-			    &ifindex, true, NETKIT_SCRUB_DEFAULT,
-			    NETKIT_SCRUB_DEFAULT);
+			    &ifindex, NETKIT_SCRUB_DEFAULT,
+			    NETKIT_SCRUB_DEFAULT, FLAG_SAME_NETNS);
 	if (err)
 		return;
 
···
 	serial_test_tc_netkit_pkt_type_mode(NETKIT_L3);
 }
 
-static void serial_test_tc_netkit_scrub_type(int scrub)
+static void serial_test_tc_netkit_scrub_type(int scrub, bool room)
 {
 	LIBBPF_OPTS(bpf_netkit_opts, optl);
 	struct test_tc_link *skel;
···
 	int err, ifindex;
 
 	err = create_netkit(NETKIT_L2, NETKIT_PASS, NETKIT_PASS,
-			    &ifindex, false, scrub, scrub);
+			    &ifindex, scrub, scrub,
+			    room ? FLAG_ADJUST_ROOM : 0);
 	if (err)
 		return;
 
···
 	ASSERT_EQ(skel->bss->seen_tc8, true, "seen_tc8");
 	ASSERT_EQ(skel->bss->mark, scrub == NETKIT_SCRUB_NONE ? MARK : 0, "mark");
 	ASSERT_EQ(skel->bss->prio, scrub == NETKIT_SCRUB_NONE ? PRIO : 0, "prio");
+	ASSERT_EQ(skel->bss->headroom, room ? NETKIT_HEADROOM : 0, "headroom");
+	ASSERT_EQ(skel->bss->tailroom, room ? NETKIT_TAILROOM : 0, "tailroom");
 cleanup:
 	test_tc_link__destroy(skel);
 
···
 
 void serial_test_tc_netkit_scrub(void)
 {
-	serial_test_tc_netkit_scrub_type(NETKIT_SCRUB_DEFAULT);
-	serial_test_tc_netkit_scrub_type(NETKIT_SCRUB_NONE);
+	serial_test_tc_netkit_scrub_type(NETKIT_SCRUB_DEFAULT, false);
+	serial_test_tc_netkit_scrub_type(NETKIT_SCRUB_NONE, true);
 }

tools/testing/selftests/bpf/progs/test_tc_link.c

···
 #include <linux/if_packet.h>
 #include <bpf/bpf_endian.h>
 #include <bpf/bpf_helpers.h>
+#include <bpf/bpf_core_read.h>
 
 char LICENSE[] SEC("license") = "GPL";
 
···
 bool seen_mcast;
 
 int mark, prio;
+unsigned short headroom, tailroom;
 
 SEC("tc/ingress")
 int tc1(struct __sk_buff *skb)
···
 	return TCX_PASS;
 }
 
+struct sk_buff {
+	struct net_device *dev;
+};
+
+struct net_device {
+	unsigned short needed_headroom;
+	unsigned short needed_tailroom;
+};
+
 SEC("tc/egress")
 int tc8(struct __sk_buff *skb)
 {
+	struct net_device *dev = BPF_CORE_READ((struct sk_buff *)skb, dev);
+
 	seen_tc8 = true;
 	mark = skb->mark;
 	prio = skb->priority;
+	headroom = BPF_CORE_READ(dev, needed_headroom);
+	tailroom = BPF_CORE_READ(dev, needed_tailroom);
 	return TCX_PASS;
 }