selftests/bpf: Add trace_vprintk test prog

This commit adds a test prog for vprintk which confirms that:
  * bpf_trace_vprintk is writing to /sys/kernel/debug/tracing/trace_pipe
  * __bpf_vprintk macro works as expected
  * >3 args are printed
  * bpf_printk w/ 0 format args compiles
  * bpf_trace_vprintk call w/ a fmt specifier but NULL fmt data fails

Approach and code are borrowed from trace_printk test.
Signed-off-by: Dave Marchevsky <davemarchevsky@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20210917182911.2426606-9-davemarchevsky@fb.com

tools/testing/selftests/bpf/Makefile

@@ -315,7 +315,8 @@ LINKED_SKELS := test_static_linked.skel.h linked_funcs.skel.h		\
 		linked_vars.skel.h linked_maps.skel.h
 
 LSKELS := kfunc_call_test.c fentry_test.c fexit_test.c fexit_sleep.c \
-	test_ksyms_module.c test_ringbuf.c atomics.c trace_printk.c
+	test_ksyms_module.c test_ringbuf.c atomics.c trace_printk.c \
+	trace_vprintk.c
 SKEL_BLACKLIST += $$(LSKELS)
 
 test_static_linked.skel.h-deps := test_static_linked1.o test_static_linked2.o

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

+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2021 Facebook */
+
+#include <test_progs.h>
+
+#include "trace_vprintk.lskel.h"
+
+#define TRACEBUF	"/sys/kernel/debug/tracing/trace_pipe"
+#define SEARCHMSG	"1,2,3,4,5,6,7,8,9,10"
+
+void test_trace_vprintk(void)
+{
+	int err = 0, iter = 0, found = 0;
+	struct trace_vprintk__bss *bss;
+	struct trace_vprintk *skel;
+	char *buf = NULL;
+	FILE *fp = NULL;
+	size_t buflen;
+
+	skel = trace_vprintk__open_and_load();
+	if (!ASSERT_OK_PTR(skel, "trace_vprintk__open_and_load"))
+		goto cleanup;
+
+	bss = skel->bss;
+
+	err = trace_vprintk__attach(skel);
+	if (!ASSERT_OK(err, "trace_vprintk__attach"))
+		goto cleanup;
+
+	fp = fopen(TRACEBUF, "r");
+	if (!ASSERT_OK_PTR(fp, "fopen(TRACEBUF)"))
+		goto cleanup;
+
+	/* We do not want to wait forever if this test fails... */
+	fcntl(fileno(fp), F_SETFL, O_NONBLOCK);
+
+	/* wait for tracepoint to trigger */
+	usleep(1);
+	trace_vprintk__detach(skel);
+
+	if (!ASSERT_GT(bss->trace_vprintk_ran, 0, "bss->trace_vprintk_ran"))
+		goto cleanup;
+
+	if (!ASSERT_GT(bss->trace_vprintk_ret, 0, "bss->trace_vprintk_ret"))
+		goto cleanup;
+
+	/* verify our search string is in the trace buffer */
+	while (getline(&buf, &buflen, fp) >= 0 || errno == EAGAIN) {
+		if (strstr(buf, SEARCHMSG) != NULL)
+			found++;
+		if (found == bss->trace_vprintk_ran)
+			break;
+		if (++iter > 1000)
+			break;
+	}
+
+	if (!ASSERT_EQ(found, bss->trace_vprintk_ran, "found"))
+		goto cleanup;
+
+	if (!ASSERT_LT(bss->null_data_vprintk_ret, 0, "bss->null_data_vprintk_ret"))
+		goto cleanup;
+
+cleanup:
+	trace_vprintk__destroy(skel);
+	free(buf);
+	if (fp)
+		fclose(fp);
+}

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

+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2021 Facebook */
+
+#include "vmlinux.h"
+#include <bpf/bpf_helpers.h>
+#include <bpf/bpf_tracing.h>
+
+char _license[] SEC("license") = "GPL";
+
+int null_data_vprintk_ret = 0;
+int trace_vprintk_ret = 0;
+int trace_vprintk_ran = 0;
+
+SEC("fentry/__x64_sys_nanosleep")
+int sys_enter(void *ctx)
+{
+	static const char one[] = "1";
+	static const char three[] = "3";
+	static const char five[] = "5";
+	static const char seven[] = "7";
+	static const char nine[] = "9";
+	static const char f[] = "%pS\n";
+
+	/* runner doesn't search for \t, just ensure it compiles */
+	bpf_printk("\t");
+
+	trace_vprintk_ret = __bpf_vprintk("%s,%d,%s,%d,%s,%d,%s,%d,%s,%d %d\n",
+		one, 2, three, 4, five, 6, seven, 8, nine, 10, ++trace_vprintk_ran);
+
+	/* non-NULL fmt w/ NULL data should result in error */
+	null_data_vprintk_ret = bpf_trace_vprintk(f, sizeof(f), NULL, 0);
+	return 0;
+}