selftests/bpf: Add read_trace_pipe_iter function

We have two printk tests reading trace_pipe in non blocking way,
with the very same code. Moving that in new read_trace_pipe_iter
function.

Current read_trace_pipe is used from samples/bpf and needs to
do blocking read and printf of the trace_pipe data, using new
read_trace_pipe_iter to implement that.

Both printk tests do early checks for the number of found messages
and can bail earlier, but I did not find any speed difference w/o
that condition, so I did not complicate the change more for that.

Some of the samples/bpf programs use read_trace_pipe function,
so I kept that interface untouched. I did not see any issues with
affected samples/bpf programs other than there's slight change in
read_trace_pipe output. The current code uses puts that adds new
line after the printed string, so we would occasionally see extra
new line. With this patch we read output per lines, so there's no
need to use puts and we can use just printf instead without extra
new line.

Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Yonghong Song <yonghong.song@linux.dev>
Link: https://lore.kernel.org/bpf/20240410140952.292261-1-jolsa@kernel.org

1 files changed, 9 insertions, 27 deletions

diff --git a/tools/testing/selftests/bpf/prog_tests/trace_printk.c b/tools/testing/selftests/bpf/prog_tests/trace_printk.c
index 7b9124d506a5..e56e88596d64 100644
--- a/tools/testing/selftests/bpf/prog_tests/trace_printk.c
+++ b/tools/testing/selftests/bpf/prog_tests/trace_printk.c
@@ -5,18 +5,19 @@
 
 #include "trace_printk.lskel.h"
 
-#define TRACEFS_PIPE	"/sys/kernel/tracing/trace_pipe"
-#define DEBUGFS_PIPE	"/sys/kernel/debug/tracing/trace_pipe"
 #define SEARCHMSG	"testing,testing"
 
+static void trace_pipe_cb(const char *str, void *data)
+{
+	if (strstr(str, SEARCHMSG) != NULL)
+		(*(int *)data)++;
+}
+
 void serial_test_trace_printk(void)
 {
 	struct trace_printk_lskel__bss *bss;
-	int err = 0, iter = 0, found = 0;
 	struct trace_printk_lskel *skel;
-	char *buf = NULL;
-	FILE *fp = NULL;
-	size_t buflen;
+	int err = 0, found = 0;
 
 	skel = trace_printk_lskel__open();
 	if (!ASSERT_OK_PTR(skel, "trace_printk__open"))
@@ -35,16 +36,6 @@ void serial_test_trace_printk(void)
 	if (!ASSERT_OK(err, "trace_printk__attach"))
 		goto cleanup;
 
-	if (access(TRACEFS_PIPE, F_OK) == 0)
-		fp = fopen(TRACEFS_PIPE, "r");
-	else
-		fp = fopen(DEBUGFS_PIPE, "r");
-	if (!ASSERT_OK_PTR(fp, "fopen(TRACE_PIPE)"))
-		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_printk_lskel__detach(skel);
@@ -56,21 +47,12 @@ void serial_test_trace_printk(void)
 		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_printk_ran)
-			break;
-		if (++iter > 1000)
-			break;
-	}
+	ASSERT_OK(read_trace_pipe_iter(trace_pipe_cb, &found, 1000),
+		 "read_trace_pipe_iter");
 
 	if (!ASSERT_EQ(found, bss->trace_printk_ran, "found"))
 		goto cleanup;
 
 cleanup:
 	trace_printk_lskel__destroy(skel);
-	free(buf);
-	if (fp)
-		fclose(fp);
 }