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, 40 insertions, 23 deletions

diff --git a/tools/testing/selftests/bpf/trace_helpers.c b/tools/testing/selftests/bpf/trace_helpers.c
index 7f45b4cb41fe..70e29f316fe7 100644
--- a/tools/testing/selftests/bpf/trace_helpers.c
+++ b/tools/testing/selftests/bpf/trace_helpers.c
@@ -233,29 +233,6 @@ out:
 	return err;
 }
 
-void read_trace_pipe(void)
-{
-	int trace_fd;
-
-	if (access(TRACEFS_PIPE, F_OK) == 0)
-		trace_fd = open(TRACEFS_PIPE, O_RDONLY, 0);
-	else
-		trace_fd = open(DEBUGFS_PIPE, O_RDONLY, 0);
-	if (trace_fd < 0)
-		return;
-
-	while (1) {
-		static char buf[4096];
-		ssize_t sz;
-
-		sz = read(trace_fd, buf, sizeof(buf) - 1);
-		if (sz > 0) {
-			buf[sz] = 0;
-			puts(buf);
-		}
-	}
-}
-
 ssize_t get_uprobe_offset(const void *addr)
 {
 	size_t start, end, base;
@@ -413,3 +390,43 @@ out:
 	close(fd);
 	return err;
 }
+
+int read_trace_pipe_iter(void (*cb)(const char *str, void *data), void *data, int iter)
+{
+	size_t buflen, n;
+	char *buf = NULL;
+	FILE *fp = NULL;
+
+	if (access(TRACEFS_PIPE, F_OK) == 0)
+		fp = fopen(TRACEFS_PIPE, "r");
+	else
+		fp = fopen(DEBUGFS_PIPE, "r");
+	if (!fp)
+		return -1;
+
+	 /* We do not want to wait forever when iter is specified. */
+	if (iter)
+		fcntl(fileno(fp), F_SETFL, O_NONBLOCK);
+
+	while ((n = getline(&buf, &buflen, fp) >= 0) || errno == EAGAIN) {
+		if (n > 0)
+			cb(buf, data);
+		if (iter && !(--iter))
+			break;
+	}
+
+	free(buf);
+	if (fp)
+		fclose(fp);
+	return 0;
+}
+
+static void trace_pipe_cb(const char *str, void *data)
+{
+	printf("%s", str);
+}
+
+void read_trace_pipe(void)
+{
+	read_trace_pipe_iter(trace_pipe_cb, NULL, 0);
+}