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This might be useful for some scenarios where > bpf_object contains multiple related freplace BPF programs intended to > replace different sub-programs in target BPF program. In such case all > programs will have the same attach_prog_fd, but different > attach_func_name. It's conveninent to specify such target function names typo: conveninent => convenient > declaratively in SEC() definitions, but attach_prog_fd is a dynamic > runtime setting. > > To simplify such scenario, allow bpf_program__set_attach_target() to > delay BTF ID resolution till the BPF program load time by providing NULL > attach_func_name. In that case the behavior will be similar to using > bpf_object_open_opts.attach_prog_fd (which is marked deprecated since > v0.7), but has the benefit of allowing more control by user in what is > attached to what. Such setup allows having BPF programs attached to > different target attach_prog_fd with target funtions still declaratively > recorded in BPF source code in SEC() definitions. > > Selftests changes in the next patch should make this more obvious. > > Signed-off-by: Andrii Nakryiko Acked-by: Yonghong Song