selftests/bpf: Add test verifying bpf_ringbuf_reserve retval use in map ops

Add a test_ringbuf_map_key test prog, borrowing heavily from extant
test_ringbuf.c. The program tries to use the result of
bpf_ringbuf_reserve as map_key, which was not possible before previouis
commits in this series. The test runner added to prog_tests/ringbuf.c
verifies that the program loads and does basic sanity checks to confirm
that it runs as expected.

Also, refactor test_ringbuf such that runners for existing test_ringbuf
and newly-added test_ringbuf_map_key are subtests of 'ringbuf' top-level
test.

Signed-off-by: Dave Marchevsky <[e-mail]>
Acked-by: Yonghong Song <[e-mail]>
Acked-by: Andrii Nakryiko <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Alexei Starovoitov <[e-mail]>

tools/testing/selftests/bpf/Makefile

···
 		test_subskeleton.skel.h test_subskeleton_lib.skel.h	\
 		test_usdt.skel.h
 
-LSKELS := fentry_test.c fexit_test.c fexit_sleep.c \
-	test_ringbuf.c atomics.c trace_printk.c trace_vprintk.c \
-	map_ptr_kern.c core_kern.c core_kern_overflow.c
+LSKELS := fentry_test.c fexit_test.c fexit_sleep.c atomics.c 		\
+	trace_printk.c trace_vprintk.c map_ptr_kern.c 			\
+	core_kern.c core_kern_overflow.c test_ringbuf.c			\
+	test_ringbuf_map_key.c
+
 # Generate both light skeleton and libbpf skeleton for these
 LSKELS_EXTRA := test_ksyms_module.c test_ksyms_weak.c kfunc_call_test.c \
 	kfunc_call_test_subprog.c

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

···
 #include <linux/perf_event.h>
 #include <linux/ring_buffer.h>
 #include "test_ringbuf.lskel.h"
+#include "test_ringbuf_map_key.lskel.h"
 
 #define EDONE 7777
 
···
 	}
 }
 
+static struct test_ringbuf_map_key_lskel *skel_map_key;
 static struct test_ringbuf_lskel *skel;
 static struct ring_buffer *ringbuf;
 
···
 	return (void *)(long)ring_buffer__poll(ringbuf, timeout);
 }
 
-void test_ringbuf(void)
+static void ringbuf_subtest(void)
 {
 	const size_t rec_sz = BPF_RINGBUF_HDR_SZ + sizeof(struct sample);
 	pthread_t thread;
···
 cleanup:
 	ring_buffer__free(ringbuf);
 	test_ringbuf_lskel__destroy(skel);
+}
+
+static int process_map_key_sample(void *ctx, void *data, size_t len)
+{
+	struct sample *s;
+	int err, val;
+
+	s = data;
+	switch (s->seq) {
+	case 1:
+		ASSERT_EQ(s->value, 42, "sample_value");
+		err = bpf_map_lookup_elem(skel_map_key->maps.hash_map.map_fd,
+					  s, &val);
+		ASSERT_OK(err, "hash_map bpf_map_lookup_elem");
+		ASSERT_EQ(val, 1, "hash_map val");
+		return -EDONE;
+	default:
+		return 0;
+	}
+}
+
+static void ringbuf_map_key_subtest(void)
+{
+	int err;
+
+	skel_map_key = test_ringbuf_map_key_lskel__open();
+	if (!ASSERT_OK_PTR(skel_map_key, "test_ringbuf_map_key_lskel__open"))
+		return;
+
+	skel_map_key->maps.ringbuf.max_entries = getpagesize();
+	skel_map_key->bss->pid = getpid();
+
+	err = test_ringbuf_map_key_lskel__load(skel_map_key);
+	if (!ASSERT_OK(err, "test_ringbuf_map_key_lskel__load"))
+		goto cleanup;
+
+	ringbuf = ring_buffer__new(skel_map_key->maps.ringbuf.map_fd,
+				   process_map_key_sample, NULL, NULL);
+	if (!ASSERT_OK_PTR(ringbuf, "ring_buffer__new"))
+		goto cleanup;
+
+	err = test_ringbuf_map_key_lskel__attach(skel_map_key);
+	if (!ASSERT_OK(err, "test_ringbuf_map_key_lskel__attach"))
+		goto cleanup_ringbuf;
+
+	syscall(__NR_getpgid);
+	ASSERT_EQ(skel_map_key->bss->seq, 1, "skel_map_key->bss->seq");
+	err = ring_buffer__poll(ringbuf, -1);
+	ASSERT_EQ(err, -EDONE, "ring_buffer__poll");
+
+cleanup_ringbuf:
+	ring_buffer__free(ringbuf);
+cleanup:
+	test_ringbuf_map_key_lskel__destroy(skel_map_key);
+}
+
+void test_ringbuf(void)
+{
+	if (test__start_subtest("ringbuf"))
+		ringbuf_subtest();
+	if (test__start_subtest("ringbuf_map_key"))
+		ringbuf_map_key_subtest();
 }

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

···
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2022 Meta Platforms, Inc. and affiliates. */
+
+#include <linux/bpf.h>
+#include <bpf/bpf_helpers.h>
+#include "bpf_misc.h"
+
+char _license[] SEC("license") = "GPL";
+
+struct sample {
+	int pid;
+	int seq;
+	long value;
+	char comm[16];
+};
+
+struct {
+	__uint(type, BPF_MAP_TYPE_RINGBUF);
+} ringbuf SEC(".maps");
+
+struct {
+	__uint(type, BPF_MAP_TYPE_HASH);
+	__uint(max_entries, 1000);
+	__type(key, struct sample);
+	__type(value, int);
+} hash_map SEC(".maps");
+
+/* inputs */
+int pid = 0;
+
+/* inner state */
+long seq = 0;
+
+SEC("fentry/" SYS_PREFIX "sys_getpgid")
+int test_ringbuf_mem_map_key(void *ctx)
+{
+	int cur_pid = bpf_get_current_pid_tgid() >> 32;
+	struct sample *sample, sample_copy;
+	int *lookup_val;
+
+	if (cur_pid != pid)
+		return 0;
+
+	sample = bpf_ringbuf_reserve(&ringbuf, sizeof(*sample), 0);
+	if (!sample)
+		return 0;
+
+	sample->pid = pid;
+	bpf_get_current_comm(sample->comm, sizeof(sample->comm));
+	sample->seq = ++seq;
+	sample->value = 42;
+
+	/* test using 'sample' (PTR_TO_MEM | MEM_ALLOC) as map key arg
+	 */
+	lookup_val = (int *)bpf_map_lookup_elem(&hash_map, sample);
+
+	/* workaround - memcpy is necessary so that verifier doesn't
+	 * complain with:
+	 *   verifier internal error: more than one arg with ref_obj_id R3
+	 * when trying to do bpf_map_update_elem(&hash_map, sample, &sample->seq, BPF_ANY);
+	 *
+	 * Since bpf_map_lookup_elem above uses 'sample' as key, test using
+	 * sample field as value below
+	 */
+	__builtin_memcpy(&sample_copy, sample, sizeof(struct sample));
+	bpf_map_update_elem(&hash_map, &sample_copy, &sample->seq, BPF_ANY);
+
+	bpf_ringbuf_submit(sample, 0);
+	return 0;
+}