bpftool: Add support for dumping streams

Add support for printing the BPF stream contents of a program in
bpftool. The new bpftool prog tracelog command is extended to take
stdout and stderr arguments, and then the prog specification.

The bpf_prog_stream_read() API added in previous patch is simply reused
to grab data and then it is dumped to the respective file. The stdout
data is sent to stdout, and stderr is printed to stderr.

Cc: Quentin Monnet <qmo@kernel.org>
Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Link: https://lore.kernel.org/r/20250703204818.925464-12-memxor@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

1 files changed, 48 insertions, 1 deletions

diff --git a/tools/bpf/bpftool/prog.c b/tools/bpf/bpftool/prog.c
index deeaa5c1ed7d..9722d841abc0 100644
--- a/tools/bpf/bpftool/prog.c
+++ b/tools/bpf/bpftool/prog.c
@@ -1113,6 +1113,52 @@ static int do_detach(int argc, char **argv)
 	return 0;
 }
 
+enum prog_tracelog_mode {
+	TRACE_STDOUT,
+	TRACE_STDERR,
+};
+
+static int
+prog_tracelog_stream(int prog_fd, enum prog_tracelog_mode mode)
+{
+	FILE *file = mode == TRACE_STDOUT ? stdout : stderr;
+	int stream_id = mode == TRACE_STDOUT ? 1 : 2;
+	char buf[512];
+	int ret;
+
+	ret = 0;
+	do {
+		ret = bpf_prog_stream_read(prog_fd, stream_id, buf, sizeof(buf), NULL);
+		if (ret > 0)
+			fwrite(buf, sizeof(buf[0]), ret, file);
+	} while (ret > 0);
+
+	fflush(file);
+	return ret ? -1 : 0;
+}
+
+static int do_tracelog_any(int argc, char **argv)
+{
+	enum prog_tracelog_mode mode;
+	int fd;
+
+	if (argc == 0)
+		return do_tracelog(argc, argv);
+	if (!is_prefix(*argv, "stdout") && !is_prefix(*argv, "stderr"))
+		usage();
+	mode = is_prefix(*argv, "stdout") ? TRACE_STDOUT : TRACE_STDERR;
+	NEXT_ARG();
+
+	if (!REQ_ARGS(2))
+		return -1;
+
+	fd = prog_parse_fd(&argc, &argv);
+	if (fd < 0)
+		return -1;
+
+	return prog_tracelog_stream(fd, mode);
+}
+
 static int check_single_stdin(char *file_data_in, char *file_ctx_in)
 {
 	if (file_data_in && file_ctx_in &&
@@ -2493,6 +2539,7 @@ static int do_help(int argc, char **argv)
 		"                         [repeat N]\n"
 		"       %1$s %2$s profile PROG [duration DURATION] METRICs\n"
 		"       %1$s %2$s tracelog\n"
+		"       %1$s %2$s tracelog { stdout | stderr } PROG\n"
 		"       %1$s %2$s help\n"
 		"\n"
 		"       " HELP_SPEC_MAP "\n"
@@ -2532,7 +2579,7 @@ static const struct cmd cmds[] = {
 	{ "loadall",	do_loadall },
 	{ "attach",	do_attach },
 	{ "detach",	do_detach },
-	{ "tracelog",	do_tracelog },
+	{ "tracelog",	do_tracelog_any },
 	{ "run",	do_run },
 	{ "profile",	do_profile },
 	{ 0 }