Re: [bpf-next PATCH v3 5/5] bpf: selftests, test probe_* helpers from SCHED_CLS

[Andrii Nakryiko <andrii.nakryiko@gmail.com>]

On Thu, May 21, 2020 at 7:36 AM John Fastabend <john.fastabend@gmail.com> wrote:
>
> Lets test using probe* in SCHED_CLS network programs as well just
> to be sure these keep working. Its cheap to add the extra test
> and provides a second context to test outside of sk_msg after
> we generalized probe* helpers to all networking types.
>
> Signed-off-by: John Fastabend <john.fastabend@gmail.com>
> ---
>  .../testing/selftests/bpf/prog_tests/skb_helpers.c |   30 ++++++++++++++++++
>  .../testing/selftests/bpf/progs/test_skb_helpers.c |   33 ++++++++++++++++++++
>  2 files changed, 63 insertions(+)
>  create mode 100644 tools/testing/selftests/bpf/prog_tests/skb_helpers.c
>  create mode 100644 tools/testing/selftests/bpf/progs/test_skb_helpers.c
>
> diff --git a/tools/testing/selftests/bpf/prog_tests/skb_helpers.c b/tools/testing/selftests/bpf/prog_tests/skb_helpers.c
> new file mode 100644
> index 0000000..5a865c4
> --- /dev/null
> +++ b/tools/testing/selftests/bpf/prog_tests/skb_helpers.c
> @@ -0,0 +1,30 @@
> +// SPDX-License-Identifier: GPL-2.0
> +#include <test_progs.h>
> +#include <network_helpers.h>
> +
> +void test_skb_helpers(void)
> +{
> +       struct __sk_buff skb = {
> +               .wire_len = 100,
> +               .gso_segs = 8,
> +               .gso_size = 10,
> +       };
> +       struct bpf_prog_test_run_attr tattr = {
> +               .data_in = &pkt_v4,
> +               .data_size_in = sizeof(pkt_v4),
> +               .ctx_in = &skb,
> +               .ctx_size_in = sizeof(skb),
> +               .ctx_out = &skb,
> +               .ctx_size_out = sizeof(skb),
> +       };
> +       struct bpf_object *obj;
> +       int err;
> +
> +       err = bpf_prog_load("./test_skb_helpers.o", BPF_PROG_TYPE_SCHED_CLS, &obj,
> +                           &tattr.prog_fd);

hm... who's destroying bpf_object?


> +       if (CHECK_ATTR(err, "load", "err %d errno %d\n", err, errno))
> +               return;
> +
> +       err = bpf_prog_test_run_xattr(&tattr);
> +       CHECK_ATTR(err != 0, "len", "err %d errno %d\n", err, errno);
> +}
> diff --git a/tools/testing/selftests/bpf/progs/test_skb_helpers.c b/tools/testing/selftests/bpf/progs/test_skb_helpers.c
> new file mode 100644
> index 0000000..05a1260
> --- /dev/null
> +++ b/tools/testing/selftests/bpf/progs/test_skb_helpers.c
> @@ -0,0 +1,33 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +#include "vmlinux.h"
> +#include <bpf/bpf_helpers.h>
> +#include <bpf/bpf_endian.h>
> +
> +int _version SEC("version") = 1;

version is not needed

> +
> +#define TEST_COMM_LEN 10

doesn't matter for this test, but it's 16 everywhere, let's stay consistent

> +
> +struct bpf_map_def SEC("maps") cgroup_map = {
> +       .type                   = BPF_MAP_TYPE_CGROUP_ARRAY,
> +       .key_size               = sizeof(u32),
> +       .value_size             = sizeof(u32),
> +       .max_entries    = 1,
> +};
> +

Please use new BTF syntax for maps

> +char _license[] SEC("license") = "GPL";
> +
> +SEC("classifier/test_skb_helpers")
> +int test_skb_helpers(struct __sk_buff *skb)
> +{
> +       struct task_struct *task;
> +       char *comm[TEST_COMM_LEN];

this is array of pointer, not array of chars

> +       __u32 tpid;
> +       int ctask;
> +
> +       ctask = bpf_current_task_under_cgroup(&cgroup_map, 0);

compiler might complain that ctask is written, but not read. Let's
assign it to some global variable?

> +       task = (struct task_struct *)bpf_get_current_task();
> +
> +       bpf_probe_read_kernel(&tpid , sizeof(tpid), &task->tgid);
> +       bpf_probe_read_kernel_str(&comm, sizeof(comm), &task->comm);
> +       return 0;
> +}
>