[PATCH bpf-next 2/2] selftests/bpf: add selftests verifying bpf_trace_printk() behaviour

[Alan Maguire]

Simple selftest that verifies bpf_trace_printk() returns a sensible
value and tracing messages appear.

Signed-off-by: Alan Maguire <alan.maguire@xxxxxxxxxx>
---
 .../selftests/bpf/prog_tests/trace_printk.c        | 71 ++++++++++++++++++++++
 tools/testing/selftests/bpf/progs/trace_printk.c   | 21 +++++++
 2 files changed, 92 insertions(+)
 create mode 100644 tools/testing/selftests/bpf/prog_tests/trace_printk.c
 create mode 100644 tools/testing/selftests/bpf/progs/trace_printk.c

diff --git a/tools/testing/selftests/bpf/prog_tests/trace_printk.c b/tools/testing/selftests/bpf/prog_tests/trace_printk.c
new file mode 100644
index 0000000..a850cba
--- /dev/null
+++ b/tools/testing/selftests/bpf/prog_tests/trace_printk.c
@@ -0,0 +1,71 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2020, Oracle and/or its affiliates. */
+
+#include <test_progs.h>
+
+#include "trace_printk.skel.h"
+
+#define TRACEBUF	"/sys/kernel/debug/tracing/trace_pipe"
+#define SEARCHMSG	"testing,testing"
+
+void test_trace_printk(void)
+{
+	int err, duration = 0, found = 0;
+	struct trace_printk *skel;
+	struct trace_printk__bss *bss;
+	char buf[1024];
+	int fd = -1;
+
+	skel = trace_printk__open();
+	if (CHECK(!skel, "skel_open", "failed to open skeleton\n"))
+		return;
+
+	err = trace_printk__load(skel);
+	if (CHECK(err, "skel_load", "failed to load skeleton: %d\n", err))
+		goto cleanup;
+
+	bss = skel->bss;
+
+	err = trace_printk__attach(skel);
+	if (CHECK(err, "skel_attach", "skeleton attach failed: %d\n", err))
+		goto cleanup;
+
+	fd = open(TRACEBUF, O_RDONLY);
+	if (CHECK(fd < 0, "could not open trace buffer",
+		  "error %d opening %s", errno, TRACEBUF))
+		goto cleanup;
+
+	/* We do not want to wait forever if this test fails... */
+	fcntl(fd, F_SETFL, O_NONBLOCK);
+
+	/* wait for tracepoint to trigger */
+	sleep(1);
+	trace_printk__detach(skel);
+
+	if (CHECK(bss->trace_printk_ran == 0,
+		  "bpf_trace_printk never ran",
+		  "ran == %d", bss->trace_printk_ran))
+		goto cleanup;
+
+	if (CHECK(bss->trace_printk_ret <= 0,
+		  "bpf_trace_printk returned <= 0 value",
+		  "got %d", bss->trace_printk_ret))
+		goto cleanup;
+
+	/* verify our search string is in the trace buffer */
+	while (read(fd, buf, sizeof(buf)) >= 0) {
+		if (strstr(buf, SEARCHMSG) != NULL)
+			found++;
+	}
+
+	if (CHECK(!found, "message from bpf_trace_printk not found",
+		  "no instance of %s in %s", SEARCHMSG, TRACEBUF))
+		goto cleanup;
+
+	printf("ran %d times; last return value %d, with %d instances of msg\n",
+	       bss->trace_printk_ran, bss->trace_printk_ret, found);
+cleanup:
+	trace_printk__destroy(skel);
+	if (fd != -1)
+		close(fd);
+}
diff --git a/tools/testing/selftests/bpf/progs/trace_printk.c b/tools/testing/selftests/bpf/progs/trace_printk.c
new file mode 100644
index 0000000..8ff6d49
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/trace_printk.c
@@ -0,0 +1,21 @@
+// SPDX-License-Identifier: GPL-2.0
+// Copyright (c) 2020, Oracle and/or its affiliates.
+
+#include "vmlinux.h"
+#include <bpf/bpf_helpers.h>
+#include <bpf/bpf_tracing.h>
+
+char _license[] SEC("license") = "GPL";
+
+int trace_printk_ret = 0;
+int trace_printk_ran = 0;
+
+SEC("tracepoint/sched/sched_switch")
+int sched_switch(void *ctx)
+{
+	static const char fmt[] = "testing,testing %d\n";
+
+	trace_printk_ret = bpf_trace_printk(fmt, sizeof(fmt),
+					    ++trace_printk_ran);
+	return 0;
+}
-- 
1.8.3.1