[PATCH bpf-next v7 11/17] selftests/bpf: Verify xdp_metadata xdp->af_xdp path

[Stanislav Fomichev <sdf@google.com>]

- create new netns
- create veth pair (veTX+veRX)
- setup AF_XDP socket for both interfaces
- attach bpf to veRX
- send packet via veTX
- verify the packet has expected metadata at veRX

Cc: John Fastabend <john.fastabend@gmail.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Martin KaFai Lau <martin.lau@linux.dev>
Cc: Jakub Kicinski <kuba@kernel.org>
Cc: Willem de Bruijn <willemb@google.com>
Cc: Jesper Dangaard Brouer <brouer@redhat.com>
Cc: Anatoly Burakov <anatoly.burakov@intel.com>
Cc: Alexander Lobakin <alexandr.lobakin@intel.com>
Cc: Magnus Karlsson <magnus.karlsson@gmail.com>
Cc: Maryam Tahhan <mtahhan@redhat.com>
Cc: xdp-hints@xdp-project.net
Cc: netdev@vger.kernel.org
Signed-off-by: Stanislav Fomichev <sdf@google.com>
---
 tools/testing/selftests/bpf/Makefile          |   2 +-
 .../selftests/bpf/prog_tests/xdp_metadata.c   | 410 ++++++++++++++++++
 .../selftests/bpf/progs/xdp_metadata.c        |  64 +++
 .../selftests/bpf/progs/xdp_metadata2.c       |  23 +
 tools/testing/selftests/bpf/xdp_metadata.h    |  15 +
 5 files changed, 513 insertions(+), 1 deletion(-)
 create mode 100644 tools/testing/selftests/bpf/prog_tests/xdp_metadata.c
 create mode 100644 tools/testing/selftests/bpf/progs/xdp_metadata.c
 create mode 100644 tools/testing/selftests/bpf/progs/xdp_metadata2.c
 create mode 100644 tools/testing/selftests/bpf/xdp_metadata.h

diff --git a/tools/testing/selftests/bpf/Makefile b/tools/testing/selftests/bpf/Makefile
index 205e8c3c346a..5356f317bc62 100644
--- a/tools/testing/selftests/bpf/Makefile
+++ b/tools/testing/selftests/bpf/Makefile
@@ -527,7 +527,7 @@ TRUNNER_BPF_PROGS_DIR := progs
 TRUNNER_EXTRA_SOURCES := test_progs.c cgroup_helpers.c trace_helpers.c	\
 			 network_helpers.c testing_helpers.c		\
 			 btf_helpers.c flow_dissector_load.h		\
-			 cap_helpers.c test_loader.c
+			 cap_helpers.c test_loader.c xsk.c
 TRUNNER_EXTRA_FILES := $(OUTPUT)/urandom_read $(OUTPUT)/bpf_testmod.ko	\
 		       $(OUTPUT)/liburandom_read.so			\
 		       $(OUTPUT)/xdp_synproxy				\
diff --git a/tools/testing/selftests/bpf/prog_tests/xdp_metadata.c b/tools/testing/selftests/bpf/prog_tests/xdp_metadata.c
new file mode 100644
index 000000000000..bb62d9d6bce0
--- /dev/null
+++ b/tools/testing/selftests/bpf/prog_tests/xdp_metadata.c
@@ -0,0 +1,410 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <test_progs.h>
+#include <network_helpers.h>
+#include "xdp_metadata.skel.h"
+#include "xdp_metadata2.skel.h"
+#include "xdp_metadata.h"
+#include "xsk.h"
+
+#include <bpf/btf.h>
+#include <linux/errqueue.h>
+#include <linux/if_link.h>
+#include <linux/net_tstamp.h>
+#include <linux/udp.h>
+#include <sys/mman.h>
+#include <net/if.h>
+#include <poll.h>
+
+#define TX_NAME "veTX"
+#define RX_NAME "veRX"
+
+#define UDP_PAYLOAD_BYTES 4
+
+#define AF_XDP_SOURCE_PORT 1234
+#define AF_XDP_CONSUMER_PORT 8080
+
+#define UMEM_NUM 16
+#define UMEM_FRAME_SIZE XSK_UMEM__DEFAULT_FRAME_SIZE
+#define UMEM_SIZE (UMEM_FRAME_SIZE * UMEM_NUM)
+#define XDP_FLAGS XDP_FLAGS_DRV_MODE
+#define QUEUE_ID 0
+
+#define TX_ADDR "10.0.0.1"
+#define RX_ADDR "10.0.0.2"
+#define PREFIX_LEN "8"
+#define FAMILY AF_INET
+
+#define SYS(cmd) ({ \
+	if (!ASSERT_OK(system(cmd), (cmd))) \
+		goto out; \
+})
+
+struct xsk {
+	void *umem_area;
+	struct xsk_umem *umem;
+	struct xsk_ring_prod fill;
+	struct xsk_ring_cons comp;
+	struct xsk_ring_prod tx;
+	struct xsk_ring_cons rx;
+	struct xsk_socket *socket;
+};
+
+static int open_xsk(const char *ifname, struct xsk *xsk)
+{
+	int mmap_flags = MAP_PRIVATE | MAP_ANONYMOUS | MAP_NORESERVE;
+	const struct xsk_socket_config socket_config = {
+		.rx_size = XSK_RING_PROD__DEFAULT_NUM_DESCS,
+		.tx_size = XSK_RING_PROD__DEFAULT_NUM_DESCS,
+		.libbpf_flags = XSK_LIBBPF_FLAGS__INHIBIT_PROG_LOAD,
+		.xdp_flags = XDP_FLAGS,
+		.bind_flags = XDP_COPY,
+	};
+	const struct xsk_umem_config umem_config = {
+		.fill_size = XSK_RING_PROD__DEFAULT_NUM_DESCS,
+		.comp_size = XSK_RING_CONS__DEFAULT_NUM_DESCS,
+		.frame_size = XSK_UMEM__DEFAULT_FRAME_SIZE,
+		.flags = XDP_UMEM_UNALIGNED_CHUNK_FLAG,
+	};
+	__u32 idx;
+	u64 addr;
+	int ret;
+	int i;
+
+	xsk->umem_area = mmap(NULL, UMEM_SIZE, PROT_READ | PROT_WRITE, mmap_flags, -1, 0);
+	if (!ASSERT_NEQ(xsk->umem_area, MAP_FAILED, "mmap"))
+		return -1;
+
+	ret = xsk_umem__create(&xsk->umem,
+			       xsk->umem_area, UMEM_SIZE,
+			       &xsk->fill,
+			       &xsk->comp,
+			       &umem_config);
+	if (!ASSERT_OK(ret, "xsk_umem__create"))
+		return ret;
+
+	ret = xsk_socket__create(&xsk->socket, ifname, QUEUE_ID,
+				 xsk->umem,
+				 &xsk->rx,
+				 &xsk->tx,
+				 &socket_config);
+	if (!ASSERT_OK(ret, "xsk_socket__create"))
+		return ret;
+
+	/* First half of umem is for TX. This way address matches 1-to-1
+	 * to the completion queue index.
+	 */
+
+	for (i = 0; i < UMEM_NUM / 2; i++) {
+		addr = i * UMEM_FRAME_SIZE;
+		printf("%p: tx_desc[%d] -> %lx\n", xsk, i, addr);
+	}
+
+	/* Second half of umem is for RX. */
+
+	ret = xsk_ring_prod__reserve(&xsk->fill, UMEM_NUM / 2, &idx);
+	if (!ASSERT_EQ(UMEM_NUM / 2, ret, "xsk_ring_prod__reserve"))
+		return ret;
+	if (!ASSERT_EQ(idx, 0, "fill idx != 0"))
+		return -1;
+
+	for (i = 0; i < UMEM_NUM / 2; i++) {
+		addr = (UMEM_NUM / 2 + i) * UMEM_FRAME_SIZE;
+		printf("%p: rx_desc[%d] -> %lx\n", xsk, i, addr);
+		*xsk_ring_prod__fill_addr(&xsk->fill, i) = addr;
+	}
+	xsk_ring_prod__submit(&xsk->fill, ret);
+
+	return 0;
+}
+
+static void close_xsk(struct xsk *xsk)
+{
+	if (xsk->umem)
+		xsk_umem__delete(xsk->umem);
+	if (xsk->socket)
+		xsk_socket__delete(xsk->socket);
+	munmap(xsk->umem, UMEM_SIZE);
+}
+
+static void ip_csum(struct iphdr *iph)
+{
+	__u32 sum = 0;
+	__u16 *p;
+	int i;
+
+	iph->check = 0;
+	p = (void *)iph;
+	for (i = 0; i < sizeof(*iph) / sizeof(*p); i++)
+		sum += p[i];
+
+	while (sum >> 16)
+		sum = (sum & 0xffff) + (sum >> 16);
+
+	iph->check = ~sum;
+}
+
+static int generate_packet(struct xsk *xsk, __u16 dst_port)
+{
+	struct xdp_desc *tx_desc;
+	struct udphdr *udph;
+	struct ethhdr *eth;
+	struct iphdr *iph;
+	void *data;
+	__u32 idx;
+	int ret;
+
+	ret = xsk_ring_prod__reserve(&xsk->tx, 1, &idx);
+	if (!ASSERT_EQ(ret, 1, "xsk_ring_prod__reserve"))
+		return -1;
+
+	tx_desc = xsk_ring_prod__tx_desc(&xsk->tx, idx);
+	tx_desc->addr = idx % (UMEM_NUM / 2) * UMEM_FRAME_SIZE;
+	printf("%p: tx_desc[%u]->addr=%llx\n", xsk, idx, tx_desc->addr);
+	data = xsk_umem__get_data(xsk->umem_area, tx_desc->addr);
+
+	eth = data;
+	iph = (void *)(eth + 1);
+	udph = (void *)(iph + 1);
+
+	memcpy(eth->h_dest, "\x00\x00\x00\x00\x00\x02", ETH_ALEN);
+	memcpy(eth->h_source, "\x00\x00\x00\x00\x00\x01", ETH_ALEN);
+	eth->h_proto = htons(ETH_P_IP);
+
+	iph->version = 0x4;
+	iph->ihl = 0x5;
+	iph->tos = 0x9;
+	iph->tot_len = htons(sizeof(*iph) + sizeof(*udph) + UDP_PAYLOAD_BYTES);
+	iph->id = 0;
+	iph->frag_off = 0;
+	iph->ttl = 0;
+	iph->protocol = IPPROTO_UDP;
+	ASSERT_EQ(inet_pton(FAMILY, TX_ADDR, &iph->saddr), 1, "inet_pton(TX_ADDR)");
+	ASSERT_EQ(inet_pton(FAMILY, RX_ADDR, &iph->daddr), 1, "inet_pton(RX_ADDR)");
+	ip_csum(iph);
+
+	udph->source = htons(AF_XDP_SOURCE_PORT);
+	udph->dest = htons(dst_port);
+	udph->len = htons(sizeof(*udph) + UDP_PAYLOAD_BYTES);
+	udph->check = 0;
+
+	memset(udph + 1, 0xAA, UDP_PAYLOAD_BYTES);
+
+	tx_desc->len = sizeof(*eth) + sizeof(*iph) + sizeof(*udph) + UDP_PAYLOAD_BYTES;
+	xsk_ring_prod__submit(&xsk->tx, 1);
+
+	ret = sendto(xsk_socket__fd(xsk->socket), NULL, 0, MSG_DONTWAIT, NULL, 0);
+	if (!ASSERT_GE(ret, 0, "sendto"))
+		return ret;
+
+	return 0;
+}
+
+static void complete_tx(struct xsk *xsk)
+{
+	__u32 idx;
+	__u64 addr;
+
+	if (ASSERT_EQ(xsk_ring_cons__peek(&xsk->comp, 1, &idx), 1, "xsk_ring_cons__peek")) {
+		addr = *xsk_ring_cons__comp_addr(&xsk->comp, idx);
+
+		printf("%p: refill idx=%u addr=%llx\n", xsk, idx, addr);
+		*xsk_ring_prod__fill_addr(&xsk->fill, idx) = addr;
+		xsk_ring_prod__submit(&xsk->fill, 1);
+	}
+}
+
+static void refill_rx(struct xsk *xsk, __u64 addr)
+{
+	__u32 idx;
+
+	if (ASSERT_EQ(xsk_ring_prod__reserve(&xsk->fill, 1, &idx), 1, "xsk_ring_prod__reserve")) {
+		printf("%p: complete idx=%u addr=%llx\n", xsk, idx, addr);
+		*xsk_ring_prod__fill_addr(&xsk->fill, idx) = addr;
+		xsk_ring_prod__submit(&xsk->fill, 1);
+	}
+}
+
+static int verify_xsk_metadata(struct xsk *xsk)
+{
+	const struct xdp_desc *rx_desc;
+	struct pollfd fds = {};
+	struct xdp_meta *meta;
+	struct ethhdr *eth;
+	struct iphdr *iph;
+	__u64 comp_addr;
+	void *data;
+	__u64 addr;
+	__u32 idx;
+	int ret;
+
+	ret = recvfrom(xsk_socket__fd(xsk->socket), NULL, 0, MSG_DONTWAIT, NULL, NULL);
+	if (!ASSERT_EQ(ret, 0, "recvfrom"))
+		return -1;
+
+	fds.fd = xsk_socket__fd(xsk->socket);
+	fds.events = POLLIN;
+
+	ret = poll(&fds, 1, 1000);
+	if (!ASSERT_GT(ret, 0, "poll"))
+		return -1;
+
+	ret = xsk_ring_cons__peek(&xsk->rx, 1, &idx);
+	if (!ASSERT_EQ(ret, 1, "xsk_ring_cons__peek"))
+		return -2;
+
+	rx_desc = xsk_ring_cons__rx_desc(&xsk->rx, idx);
+	comp_addr = xsk_umem__extract_addr(rx_desc->addr);
+	addr = xsk_umem__add_offset_to_addr(rx_desc->addr);
+	printf("%p: rx_desc[%u]->addr=%llx addr=%llx comp_addr=%llx\n",
+	       xsk, idx, rx_desc->addr, addr, comp_addr);
+	data = xsk_umem__get_data(xsk->umem_area, addr);
+
+	/* Make sure we got the packet offset correctly. */
+
+	eth = data;
+	ASSERT_EQ(eth->h_proto, htons(ETH_P_IP), "eth->h_proto");
+	iph = (void *)(eth + 1);
+	ASSERT_EQ((int)iph->version, 4, "iph->version");
+
+	/* custom metadata */
+
+	meta = data - sizeof(struct xdp_meta);
+
+	if (!ASSERT_NEQ(meta->rx_timestamp, 0, "rx_timestamp"))
+		return -1;
+
+	if (!ASSERT_NEQ(meta->rx_hash, 0, "rx_hash"))
+		return -1;
+
+	xsk_ring_cons__release(&xsk->rx, 1);
+	refill_rx(xsk, comp_addr);
+
+	return 0;
+}
+
+void test_xdp_metadata(void)
+{
+	struct xdp_metadata2 *bpf_obj2 = NULL;
+	struct xdp_metadata *bpf_obj = NULL;
+	struct bpf_program *new_prog, *prog;
+	struct nstoken *tok = NULL;
+	__u32 queue_id = QUEUE_ID;
+	struct bpf_map *prog_arr;
+	struct xsk tx_xsk = {};
+	struct xsk rx_xsk = {};
+	__u32 val, key = 0;
+	int retries = 10;
+	int rx_ifindex;
+	int sock_fd;
+	int ret;
+
+	/* Setup new networking namespace, with a veth pair. */
+
+	SYS("ip netns add xdp_metadata");
+	tok = open_netns("xdp_metadata");
+	SYS("ip link add numtxqueues 1 numrxqueues 1 " TX_NAME
+	    " type veth peer " RX_NAME " numtxqueues 1 numrxqueues 1");
+	SYS("ip link set dev " TX_NAME " address 00:00:00:00:00:01");
+	SYS("ip link set dev " RX_NAME " address 00:00:00:00:00:02");
+	SYS("ip link set dev " TX_NAME " up");
+	SYS("ip link set dev " RX_NAME " up");
+	SYS("ip addr add " TX_ADDR "/" PREFIX_LEN " dev " TX_NAME);
+	SYS("ip addr add " RX_ADDR "/" PREFIX_LEN " dev " RX_NAME);
+
+	rx_ifindex = if_nametoindex(RX_NAME);
+
+	/* Setup separate AF_XDP for TX and RX interfaces. */
+
+	ret = open_xsk(TX_NAME, &tx_xsk);
+	if (!ASSERT_OK(ret, "open_xsk(TX_NAME)"))
+		goto out;
+
+	ret = open_xsk(RX_NAME, &rx_xsk);
+	if (!ASSERT_OK(ret, "open_xsk(RX_NAME)"))
+		goto out;
+
+	bpf_obj = xdp_metadata__open();
+	if (!ASSERT_OK_PTR(bpf_obj, "open skeleton"))
+		goto out;
+
+	prog = bpf_object__find_program_by_name(bpf_obj->obj, "rx");
+	bpf_program__set_ifindex(prog, rx_ifindex);
+	bpf_program__set_flags(prog, BPF_F_XDP_DEV_BOUND_ONLY);
+
+	if (!ASSERT_OK(xdp_metadata__load(bpf_obj), "load skeleton"))
+		goto out;
+
+	/* Make sure we can't add dev-bound programs to prog maps. */
+	prog_arr = bpf_object__find_map_by_name(bpf_obj->obj, "prog_arr");
+	if (!ASSERT_OK_PTR(prog_arr, "no prog_arr map"))
+		goto out;
+
+	val = bpf_program__fd(prog);
+	if (!ASSERT_ERR(bpf_map__update_elem(prog_arr, &key, sizeof(key),
+					     &val, sizeof(val), BPF_ANY),
+			"update prog_arr"))
+		goto out;
+
+	/* Attach BPF program to RX interface. */
+
+	ret = bpf_xdp_attach(rx_ifindex,
+			     bpf_program__fd(bpf_obj->progs.rx),
+			     XDP_FLAGS, NULL);
+	if (!ASSERT_GE(ret, 0, "bpf_xdp_attach"))
+		goto out;
+
+	sock_fd = xsk_socket__fd(rx_xsk.socket);
+	ret = bpf_map_update_elem(bpf_map__fd(bpf_obj->maps.xsk), &queue_id, &sock_fd, 0);
+	if (!ASSERT_GE(ret, 0, "bpf_map_update_elem"))
+		goto out;
+
+	/* Send packet destined to RX AF_XDP socket. */
+	if (!ASSERT_GE(generate_packet(&tx_xsk, AF_XDP_CONSUMER_PORT), 0,
+		       "generate AF_XDP_CONSUMER_PORT"))
+		goto out;
+
+	/* Verify AF_XDP RX packet has proper metadata. */
+	if (!ASSERT_GE(verify_xsk_metadata(&rx_xsk), 0,
+		       "verify_xsk_metadata"))
+		goto out;
+
+	complete_tx(&tx_xsk);
+
+	/* Make sure freplace correctly picks up original bound device
+	 * and doesn't crash.
+	 */
+
+	bpf_obj2 = xdp_metadata2__open();
+	if (!ASSERT_OK_PTR(bpf_obj2, "open skeleton"))
+		goto out;
+
+	new_prog = bpf_object__find_program_by_name(bpf_obj2->obj, "freplace_rx");
+	bpf_program__set_attach_target(new_prog, bpf_program__fd(prog), "rx");
+
+	if (!ASSERT_OK(xdp_metadata2__load(bpf_obj2), "load freplace skeleton"))
+		goto out;
+
+	if (!ASSERT_OK(xdp_metadata2__attach(bpf_obj2), "attach freplace"))
+		goto out;
+
+	/* Send packet to trigger . */
+	if (!ASSERT_GE(generate_packet(&tx_xsk, AF_XDP_CONSUMER_PORT), 0,
+		       "generate freplace packet"))
+		goto out;
+
+	while (!retries--) {
+		if (bpf_obj2->bss->called)
+			break;
+		usleep(10);
+	}
+	ASSERT_GT(bpf_obj2->bss->called, 0, "not called");
+
+out:
+	close_xsk(&rx_xsk);
+	close_xsk(&tx_xsk);
+	xdp_metadata2__destroy(bpf_obj2);
+	xdp_metadata__destroy(bpf_obj);
+	if (tok)
+		close_netns(tok);
+	system("ip netns del xdp_metadata");
+}
diff --git a/tools/testing/selftests/bpf/progs/xdp_metadata.c b/tools/testing/selftests/bpf/progs/xdp_metadata.c
new file mode 100644
index 000000000000..77678b034389
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/xdp_metadata.c
@@ -0,0 +1,64 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <vmlinux.h>
+#include "xdp_metadata.h"
+#include <bpf/bpf_helpers.h>
+#include <bpf/bpf_endian.h>
+
+struct {
+	__uint(type, BPF_MAP_TYPE_XSKMAP);
+	__uint(max_entries, 4);
+	__type(key, __u32);
+	__type(value, __u32);
+} xsk SEC(".maps");
+
+struct {
+	__uint(type, BPF_MAP_TYPE_PROG_ARRAY);
+	__uint(max_entries, 1);
+	__type(key, __u32);
+	__type(value, __u32);
+} prog_arr SEC(".maps");
+
+extern int bpf_xdp_metadata_rx_timestamp(const struct xdp_md *ctx,
+					 __u64 *timestamp) __ksym;
+extern int bpf_xdp_metadata_rx_hash(const struct xdp_md *ctx,
+				    __u32 *hash) __ksym;
+
+SEC("xdp")
+int rx(struct xdp_md *ctx)
+{
+	void *data, *data_meta;
+	struct xdp_meta *meta;
+	u64 timestamp = -1;
+	int ret;
+
+	/* Reserve enough for all custom metadata. */
+
+	ret = bpf_xdp_adjust_meta(ctx, -(int)sizeof(struct xdp_meta));
+	if (ret != 0)
+		return XDP_DROP;
+
+	data = (void *)(long)ctx->data;
+	data_meta = (void *)(long)ctx->data_meta;
+
+	if (data_meta + sizeof(struct xdp_meta) > data)
+		return XDP_DROP;
+
+	meta = data_meta;
+
+	/* Export metadata. */
+
+	/* We expect veth bpf_xdp_metadata_rx_timestamp to return 0 HW
+	 * timestamp, so put some non-zero value into AF_XDP frame for
+	 * the userspace.
+	 */
+	bpf_xdp_metadata_rx_timestamp(ctx, &timestamp);
+	if (timestamp == 0)
+		meta->rx_timestamp = 1;
+
+	bpf_xdp_metadata_rx_hash(ctx, &meta->rx_hash);
+
+	return bpf_redirect_map(&xsk, ctx->rx_queue_index, XDP_PASS);
+}
+
+char _license[] SEC("license") = "GPL";
diff --git a/tools/testing/selftests/bpf/progs/xdp_metadata2.c b/tools/testing/selftests/bpf/progs/xdp_metadata2.c
new file mode 100644
index 000000000000..cf69d05451c3
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/xdp_metadata2.c
@@ -0,0 +1,23 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <vmlinux.h>
+#include "xdp_metadata.h"
+#include <bpf/bpf_helpers.h>
+#include <bpf/bpf_endian.h>
+
+extern int bpf_xdp_metadata_rx_hash(const struct xdp_md *ctx,
+				    __u32 *hash) __ksym;
+
+int called;
+
+SEC("freplace/rx")
+int freplace_rx(struct xdp_md *ctx)
+{
+	u32 hash = 0;
+	/* Call _any_ metadata function to make sure we don't crash. */
+	bpf_xdp_metadata_rx_hash(ctx, &hash);
+	called++;
+	return XDP_PASS;
+}
+
+char _license[] SEC("license") = "GPL";
diff --git a/tools/testing/selftests/bpf/xdp_metadata.h b/tools/testing/selftests/bpf/xdp_metadata.h
new file mode 100644
index 000000000000..f6780fbb0a21
--- /dev/null
+++ b/tools/testing/selftests/bpf/xdp_metadata.h
@@ -0,0 +1,15 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#pragma once
+
+#ifndef ETH_P_IP
+#define ETH_P_IP 0x0800
+#endif
+
+#ifndef ETH_P_IPV6
+#define ETH_P_IPV6 0x86DD
+#endif
+
+struct xdp_meta {
+	__u64 rx_timestamp;
+	__u32 rx_hash;
+};
-- 
2.39.0.314.g84b9a713c41-goog