> On Apr 13, 2020, at 9:56 PM, Andrii Nakryiko <andriin@xxxxxx> wrote:
>
> For some types of BPF programs that utilize expected_attach_type, libbpf won't
> set load_attr.expected_attach_type, even if expected_attach_type is known from
> section definition. This was done to preserve backwards compatibility with old
> kernels that didn't recognize expected_attach_type attribute yet (which was
> added in 5e43f899b03a ("bpf: Check attach type at prog load time"). But this
> is problematic for some BPF programs that utilize never features that require
> kernel to know specific expected_attach_type (e.g., extended set of return
> codes for cgroup_skb/egress programs).
>
> This patch makes libbpf specify expected_attach_type by default, but also
> detect support for this field in kernel and not set it during program load.
> This allows to have a good metadata for bpf_program
> (e.g., bpf_program__get_extected_attach_type()), but still work with old
> kernels (for cases where it can work at all).
>
> Additionally, due to expected_attach_type being always set for recognized
> program types, bpf_program__attach_cgroup doesn't have to do extra checks to
> determine correct attach type, so remove that additional logic.
>
> Also adjust section_names selftest to account for this change.
>
> More detailed discussion can be found in [0].
>
> [0] https://lore.kernel.org/bpf/20200412003604.GA15986@xxxxxxxxxxxxxxxxxxxxxxxxxxxxx/
>
> Reported-by: Andrey Ignatov <rdna@xxxxxx>
> Signed-off-by: Andrii Nakryiko <andriin@xxxxxx>
Acked-by: Song Liu <songliubraving@xxxxxx>
With one nit below.
> ---
> v1->v2:
> - fixed prog_type/expected_attach_type combo (Andrey);
> - added comment explaining what we are doing in probe_exp_attach_type (Andrey).
>
> tools/lib/bpf/libbpf.c | 127 ++++++++++++------
> .../selftests/bpf/prog_tests/section_names.c | 42 +++---
> 2 files changed, 110 insertions(+), 59 deletions(-)
>
> diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
> index ff9174282a8c..c7393182e2ae 100644
> --- a/tools/lib/bpf/libbpf.c
> +++ b/tools/lib/bpf/libbpf.c
> @@ -178,6 +178,8 @@ struct bpf_capabilities {
> __u32 array_mmap:1;
> /* BTF_FUNC_GLOBAL is supported */
> __u32 btf_func_global:1;
> + /* kernel support for expected_attach_type in BPF_PROG_LOAD */
> + __u32 exp_attach_type:1;
> };
[...]
> -#define BPF_PROG_SEC_IMPL(string, ptype, eatype, is_attachable, btf, atype) \
> - { string, sizeof(string) - 1, ptype, eatype, is_attachable, btf, atype }
> +#define BPF_PROG_SEC_IMPL(string, ptype, eatype, eatype_optional, \
> + attachable, attach_btf) \
> + { \
> + .sec = string, \
> + .len = sizeof(string) - 1, \
> + .prog_type = ptype, \
> + .sec = string, \
Two lines of ".sec = string".
> + .expected_attach_type = eatype, \
> + .is_exp_attach_type_optional = eatype_optional, \
> + .is_attachable = attachable, \
> + .is_attach_btf = attach_btf, \
> + }
