Re: [bpf-next PATCH 4/4] selftests/bpf: Migrate tcpbpf_user.c to use BPF skeleton

On Thu, Oct 29, 2020 at 4:20 PM Andrii Nakryiko
[off-list ref] wrote:

On Thu, Oct 29, 2020 at 12:57 AM Alexander Duyck
[off-list ref] wrote:

quoted

From: Alexander Duyck <alexanderduyck@fb.com>

Update tcpbpf_user.c to make use of the BPF skeleton. Doing this we can
simplify test_tcpbpf_user and reduce the overhead involved in setting up
the test.

Signed-off-by: Alexander Duyck <alexanderduyck@fb.com>
---

Few suggestions below, but overall looks good:

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

quoted

 .../testing/selftests/bpf/prog_tests/tcpbpf_user.c |   48 +++++++++-----------
 1 file changed, 21 insertions(+), 27 deletions(-)

diff --git a/tools/testing/selftests/bpf/prog_tests/tcpbpf_user.c b/tools/testing/selftests/bpf/prog_tests/tcpbpf_user.c
index 4e1190894e1e..7e92c37976ac 100644
--- a/tools/testing/selftests/bpf/prog_tests/tcpbpf_user.c
+++ b/tools/testing/selftests/bpf/prog_tests/tcpbpf_user.c

@@ -5,6 +5,7 @@

 #include "test_tcpbpf.h"
 #include "cgroup_helpers.h"
+#include "test_tcpbpf_kern.skel.h"

 #define LO_ADDR6 "::1"
 #define CG_NAME "/tcpbpf-user-test"

@@ -162,39 +163,32 @@ static void run_test(int map_fd, int sock_map_fd)

 void test_tcpbpf_user(void)
 {
-       const char *file = "test_tcpbpf_kern.o";
-       int prog_fd, map_fd, sock_map_fd;
-       struct bpf_object *obj;
+       struct test_tcpbpf_kern *skel;
+       int map_fd, sock_map_fd;
+       struct bpf_link *link;
        int cg_fd = -1;
-       int rv;
-
-       cg_fd = cgroup_setup_and_join(CG_NAME);
-       if (CHECK_FAIL(cg_fd < 0))
-               goto err;

-       if (CHECK_FAIL(bpf_prog_load(file, BPF_PROG_TYPE_SOCK_OPS, &obj, &prog_fd))) {
-               fprintf(stderr, "FAILED: load_bpf_file failed for: %s\n", file);
-               goto err;
-       }
+       skel = test_tcpbpf_kern__open_and_load();
+       if (CHECK(!skel, "open and load skel", "failed"))
+               return;

-       rv = bpf_prog_attach(prog_fd, cg_fd, BPF_CGROUP_SOCK_OPS, 0);
-       if (CHECK_FAIL(rv)) {
-               fprintf(stderr, "FAILED: bpf_prog_attach: %d (%s)\n",
-                      errno, strerror(errno));
-               goto err;
-       }
+       cg_fd = test__join_cgroup(CG_NAME);
+       if (CHECK_FAIL(cg_fd < 0))

please use either CHECK() or one of the newer ASSERT_xxx() macro (also
defined in test_progs.h), CHECK_FAIL should be avoided in general.

So the plan I had was to actually move over to the following:
        cg_fd = test__join_cgroup(CG_NAME);
        if (CHECK_FAIL(cg_fd < 0))
                goto cleanup_skel;

It still makes use of CHECK_FAIL but it looks like test__join_cgroup
already takes care of error messaging so using CHECK_FAIL in this case
makes more sense.

In addition I was looking at simplifying the first patch which should
just be the move with minimal changes to allow the functionality to
build as a part of the test_progs framework. The end result should be
the same it just helps to make the fact that the first patch should
just be a move a little more clear.

quoted

+               goto cleanup_skel;

-       map_fd = bpf_find_map(__func__, obj, "global_map");
-       if (CHECK_FAIL(map_fd < 0))
-               goto err;
+       map_fd = bpf_map__fd(skel->maps.global_map);
+       sock_map_fd = bpf_map__fd(skel->maps.sockopt_results);

-       sock_map_fd = bpf_find_map(__func__, obj, "sockopt_results");
-       if (CHECK_FAIL(sock_map_fd < 0))
-               goto err;
+       link = bpf_program__attach_cgroup(skel->progs.bpf_testcb, cg_fd);

you can do skel->links.bpf_testcb = bpf_program__attach_cgroup() and
skeleton's __destroy() call will take care of destroying the link

Okay, I can look into using that. Actually this has me wondering if
there wouldn't be some way to make use of test_tcpbpf_kern__attach to
achieve this in some standard way. I'll get that sorted before I
submit v2.

quoted

+       if (CHECK(IS_ERR(link), "attach_cgroup(estab)", "err: %ld\n",
+                 PTR_ERR(link)))

there is a convenient ASSERT_OK_PTR() specifically for pointers like
this (and NULL ones as well, of course); saves a lot of typing and
encapsulates error extraction internally.

I'll update the code to address that.