On Fri, Sep 04, 2020 at 12:23:55PM +0100, Lorenz Bauer wrote: > Function prototypes using ARG_PTR_TO_BTF_ID currently use two ways to signal > which BTF IDs are acceptable. First, bpf_func_proto.btf_id is an array of > IDs, one for each argument. This array is only accessed up to the highest > numbered argument that uses ARG_PTR_TO_BTF_ID and may therefore be less than > five arguments long. It usually points at a BTF_ID_LIST. Second, check_btf_id > is a function pointer that is called by the verifier if present. It gets the > actual BTF ID of the register, and the argument number we're currently checking. > It turns out that the only user check_arg_btf_id ignores the argument, and is > simply used to check whether the BTF ID matches one of the socket types. I believe the second way, ".check_btf_id", can be removed. It currently ensures it can accept socket types that has "struct sock_common" in it. Since then, btf_struct_ids_match() has been introduced which I think can be used here. A ".btf_id" pointing to the "struct sock_common" alone is enough. If the above is doable, is this change still needed? > > Replace both of these mechanisms with explicit btf_id_sets for each argument > in a function proto. The verifier can now check that a PTR_TO_BTF_ID is one > of several IDs, and the code that does the type checking becomes simpler. > > Add a small optimisation to btf_set_contains for the common case of a set with > a single entry. >
