On Mon, Nov 2, 2020 at 4:08 PM Song Liu [off-list ref] wrote:

quoted

On Oct 28, 2020, at 5:58 PM, Andrii Nakryiko [off-list ref] wrote:

From: Andrii Nakryiko <redacted>

Add re-usable btf_helpers.{c,h} to provide BTF-related testing routines. Start
with adding a raw BTF dumping helpers.

Raw BTF dump is the most succinct and at the same time a very human-friendly
way to validate exact contents of BTF types. Cross-validate raw BTF dump and
writable BTF in a single selftest. Raw type dump checks also serve as a good
self-documentation.

Signed-off-by: Andrii Nakryiko <andrii@kernel.org>

Acked-by: Song Liu <redacted>

with a couple nits:

[...]

quoted

+
+/* Print raw BTF type dump into a local buffer and return string pointer back.
+ * Buffer *will* be overwritten by subsequent btf_type_raw_dump() calls
+ */
+const char *btf_type_raw_dump(const struct btf *btf, int type_id)
+{
+     static char buf[16 * 1024];
+     FILE *buf_file;
+
+     buf_file = fmemopen(buf, sizeof(buf) - 1, "w");
+     if (!buf_file) {
+             fprintf(stderr, "Failed to open memstream: %d\n", errno);
+             return NULL;
+     }
+
+     fprintf_btf_type_raw(buf_file, btf, type_id);
+     fflush(buf_file);
+     fclose(buf_file);
+
+     return buf;
+}

diff --git a/tools/testing/selftests/bpf/btf_helpers.h b/tools/testing/selftests/bpf/btf_helpers.h
new file mode 100644
index 000000000000..2c9ce1b61dc9
--- /dev/null
+++ b/tools/testing/selftests/bpf/btf_helpers.h

@@ -0,0 +1,12 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/* Copyright (c) 2020 Facebook */
+#ifndef __BTF_HELPERS_H
+#define __BTF_HELPERS_H
+
+#include <stdio.h>
+#include <bpf/btf.h>
+
+int fprintf_btf_type_raw(FILE *out, const struct btf *btf, __u32 id);
+const char *btf_type_raw_dump(const struct btf *btf, int type_id);
+
+#endif

diff --git a/tools/testing/selftests/bpf/prog_tests/btf_write.c b/tools/testing/selftests/bpf/prog_tests/btf_write.c
index 314e1e7c36df..bc1412de1b3d 100644
--- a/tools/testing/selftests/bpf/prog_tests/btf_write.c
+++ b/tools/testing/selftests/bpf/prog_tests/btf_write.c

@@ -2,6 +2,7 @@

/* Copyright (c) 2020 Facebook */
#include <test_progs.h>
#include <bpf/btf.h>
+#include "btf_helpers.h"

static int duration = 0;

@@ -11,12 +12,12 @@ void test_btf_write() {
      const struct btf_member *m;
      const struct btf_enum *v;
      const struct btf_param *p;
-     struct btf *btf;
+     struct btf *btf = NULL;

No need to initialize btf.

quoted

      int id, err, str_off;

      btf = btf__new_empty();
      if (CHECK(IS_ERR(btf), "new_empty", "failed: %ld\n", PTR_ERR(btf)))
-             return;
+             goto err_out;

err_out is not needed either.

eagle eye ;) fixed both

[...]