[RFC PATCH bpf-next 3/3] bpf: Add bpf_get_kern_btf_id() tests

[Yonghong Song <yhs@fb.com>]

Two tests are added. One is from John Fastabend ({1]) which tests
tracing style access for xdp program from the kernel ctx.
Another is a tc test to test both kernel ctx tracing style access
and explicit non-ctx type cast.

  [1] https://lore.kernel.org/bpf/20221109215242.1279993-1-john.fastabend@gmail.com/

Signed-off-by: Yonghong Song <yhs@fb.com>
---
 .../bpf/prog_tests/get_kern_btf_id.c          | 81 +++++++++++++++++++
 .../selftests/bpf/progs/get_kern_btf_id.c     | 44 ++++++++++
 2 files changed, 125 insertions(+)
 create mode 100644 tools/testing/selftests/bpf/prog_tests/get_kern_btf_id.c
 create mode 100644 tools/testing/selftests/bpf/progs/get_kern_btf_id.c

diff --git a/tools/testing/selftests/bpf/prog_tests/get_kern_btf_id.c b/tools/testing/selftests/bpf/prog_tests/get_kern_btf_id.c
new file mode 100644
index 000000000000..205631916564
--- /dev/null
+++ b/tools/testing/selftests/bpf/prog_tests/get_kern_btf_id.c
@@ -0,0 +1,81 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <test_progs.h>
+#include <network_helpers.h>
+#include "get_kern_btf_id.skel.h"
+
+static void test_xdp(void)
+{
+	struct get_kern_btf_id *skel;
+	int err, prog_fd;
+	char buf[128];
+
+	LIBBPF_OPTS(bpf_test_run_opts, topts,
+		.data_in = &pkt_v4,
+		.data_size_in = sizeof(pkt_v4),
+		.data_out = buf,
+		.data_size_out = sizeof(buf),
+		.repeat = 1,
+	);
+
+	skel = get_kern_btf_id__open();
+	if (!ASSERT_OK_PTR(skel, "skel_open"))
+		return;
+
+	bpf_program__set_autoload(skel->progs.md_xdp, true);
+	err = get_kern_btf_id__load(skel);
+	if (!ASSERT_OK(err, "skel_load"))
+		goto out;
+
+	prog_fd = bpf_program__fd(skel->progs.md_xdp);
+	err = bpf_prog_test_run_opts(prog_fd, &topts);
+	ASSERT_OK(err, "test_run");
+	ASSERT_EQ(topts.retval, XDP_PASS, "xdp test_run retval");
+
+	ASSERT_EQ(skel->bss->ifindex, 1, "xdp_md ifindex");
+	ASSERT_EQ(skel->bss->ifindex, skel->bss->ingress_ifindex, "xdp_md ingress_ifindex");
+	ASSERT_STREQ(skel->bss->name, "lo", "xdp_md name");
+	ASSERT_NEQ(skel->bss->inum, 0, "xdp_md inum");
+
+out:
+	get_kern_btf_id__destroy(skel);
+}
+
+static void test_tc(void)
+{
+	struct get_kern_btf_id *skel;
+	int err, prog_fd;
+
+	LIBBPF_OPTS(bpf_test_run_opts, topts,
+		.data_in = &pkt_v4,
+		.data_size_in = sizeof(pkt_v4),
+		.repeat = 1,
+	);
+
+	skel = get_kern_btf_id__open();
+	if (!ASSERT_OK_PTR(skel, "skel_open"))
+		return;
+
+	bpf_program__set_autoload(skel->progs.md_skb, true);
+	err = get_kern_btf_id__load(skel);
+	if (!ASSERT_OK(err, "skel_load"))
+		goto out;
+
+	prog_fd = bpf_program__fd(skel->progs.md_skb);
+	err = bpf_prog_test_run_opts(prog_fd, &topts);
+	ASSERT_OK(err, "test_run");
+	ASSERT_EQ(topts.retval, 0, "tc test_run retval");
+
+	ASSERT_EQ(skel->bss->meta_len, 0, "skb meta_len");
+	ASSERT_EQ(skel->bss->frag0_len, 0, "skb frag0_len");
+
+out:
+	get_kern_btf_id__destroy(skel);
+}
+
+void test_get_kern_btf_id(void)
+{
+	if (test__start_subtest("xdp"))
+		test_xdp();
+	if (test__start_subtest("tc"))
+		test_tc();
+}
diff --git a/tools/testing/selftests/bpf/progs/get_kern_btf_id.c b/tools/testing/selftests/bpf/progs/get_kern_btf_id.c
new file mode 100644
index 000000000000..b530c7c52ff3
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/get_kern_btf_id.c
@@ -0,0 +1,44 @@
+#include "vmlinux.h"
+#include <bpf/bpf_helpers.h>
+#include <bpf/bpf_core_read.h>
+
+#define	IFNAMSIZ 16
+
+int ifindex, ingress_ifindex;
+char name[IFNAMSIZ];
+unsigned int inum;
+int meta_len, frag0_len;
+
+extern void *bpf_get_kern_btf_id(void *, __u32) __ksym;
+
+SEC("?xdp")
+int md_xdp(struct xdp_md *ctx)
+{
+	struct xdp_buff *kctx = bpf_get_kern_btf_id(ctx, 0);
+	struct net_device *dev;
+
+	dev = kctx->rxq->dev;
+	ifindex = dev->ifindex;
+	inum = dev->nd_net.net->ns.inum;
+	__builtin_memcpy(name, dev->name, IFNAMSIZ);
+	ingress_ifindex = ctx->ingress_ifindex;
+	return XDP_PASS;
+}
+
+SEC("?tc")
+int md_skb(struct __sk_buff *skb)
+{
+	struct sk_buff *kskb = bpf_get_kern_btf_id(skb, 0);
+	struct skb_shared_info *shared_info;
+
+	/* Simulate the following kernel macro:
+	 *   #define skb_shinfo(SKB) ((struct skb_shared_info *)(skb_end_pointer(SKB)))
+	 */
+	shared_info = bpf_get_kern_btf_id(kskb->head + kskb->end,
+		bpf_core_type_id_kernel(struct skb_shared_info));
+	meta_len = shared_info->meta_len;
+	frag0_len = shared_info->frag_list->len;
+	return 0;
+}
+
+char _license[] SEC("license") = "GPL";
-- 
2.30.2