samples, bpf: Move read_trace_pipe to trace_helpers

To reduce the reliance of trace samples (trace*_user) on bpf_load,
move read_trace_pipe to trace_helpers. By moving this bpf_loader helper
elsewhere, trace functions can be easily migrated to libbbpf.

Signed-off-by: Daniel T. Lee <danieltimlee@gmail.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Andrii Nakryiko <andriin@fb.com>
Link: https://lore.kernel.org/bpf/20200321100424.1593964-2-danieltimlee@gmail.com

tools/testing/selftests/bpf/trace_helpers.c

@@ -4,12 +4,15 @@
 #include <string.h>
 #include <assert.h>
 #include <errno.h>
+#include <fcntl.h>
 #include <poll.h>
 #include <unistd.h>
 #include <linux/perf_event.h>
 #include <sys/mman.h>
 #include "trace_helpers.h"
 
+#define DEBUGFS "/sys/kernel/debug/tracing/"
+
 #define MAX_SYMS 300000
 static struct ksym syms[MAX_SYMS];
 static int sym_cnt;
@@ -86,3 +89,23 @@ long ksym_get_addr(const char *name)
 
 	return 0;
 }
+
+void read_trace_pipe(void)
+{
+	int trace_fd;
+
+	trace_fd = open(DEBUGFS "trace_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);
+		}
+	}
+}

tools/testing/selftests/bpf/trace_helpers.h

@@ -12,5 +12,6 @@ struct ksym {
 int load_kallsyms(void);
 struct ksym *ksym_search(long key);
 long ksym_get_addr(const char *name);
+void read_trace_pipe(void);
 
 #endif