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Date: Sun, 10 May 2020 10:05:17 -0700 From: Yonghong Song <yhs@...com> To: Alexei Starovoitov <alexei.starovoitov@...il.com> CC: Andrii Nakryiko <andriin@...com>, bpf <bpf@...r.kernel.org>, Martin KaFai Lau <kafai@...com>, Network Development <netdev@...r.kernel.org>, Alexei Starovoitov <ast@...com>, Daniel Borkmann <daniel@...earbox.net>, Kernel Team <kernel-team@...com> Subject: Re: [PATCH bpf-next v4 12/21] bpf: add PTR_TO_BTF_ID_OR_NULL support On 5/10/20 9:11 AM, Alexei Starovoitov wrote: > On Sat, May 9, 2020 at 10:19 PM Yonghong Song <yhs@...com> wrote: >> >> >> >> On 5/9/20 5:50 PM, Alexei Starovoitov wrote: >>> On Sat, May 09, 2020 at 10:59:12AM -0700, Yonghong Song wrote: >>>> diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c >>>> index a2cfba89a8e1..c490fbde22d4 100644 >>>> --- a/kernel/bpf/btf.c >>>> +++ b/kernel/bpf/btf.c >>>> @@ -3790,7 +3790,10 @@ bool btf_ctx_access(int off, int size, enum bpf_access_type type, >>>> return true; >>>> >>>> /* this is a pointer to another type */ >>>> - info->reg_type = PTR_TO_BTF_ID; >>>> + if (off != 0 && prog->aux->btf_id_or_null_non0_off) >>>> + info->reg_type = PTR_TO_BTF_ID_OR_NULL; >>>> + else >>>> + info->reg_type = PTR_TO_BTF_ID; >>> >>> I think the verifier should be smarter than this. >>> It's too specific and inflexible. All ctx fields of bpf_iter execpt first >>> will be such ? let's figure out a different way to tell verifier about this. >>> How about using typedef with specific suffix? Like: >>> typedef struct bpf_map *bpf_map_or_null; >>> struct bpf_iter__bpf_map { >>> struct bpf_iter_meta *meta; >>> bpf_map_or_null map; >>> }; >>> or use a union with specific second member? Like: >>> struct bpf_iter__bpf_map { >>> struct bpf_iter_meta *meta; >>> union { >>> struct bpf_map *map; >>> long null; >>> }; >>> }; >> >> I have an alternative approach to refactor this for future >> support for map elements as well. >> >> For example, for bpf_map_elements iterator the prog context type >> can be >> struct bpf_iter_bpf_map_elem { >> struct bpf_iter_meta *meta; >> strruct bpf_map *map; >> <key type> *key; >> <value type> *val; >> }; >> >> target will pass the following information to bpf_iter registration: >> arg 1: PTR_TO_BTF_ID >> arg 2: PTR_TO_BTF_ID_OR_NULL >> arg 3: PTR_TO_BUFFER >> arg 4: PTR_TO_BUFFER >> >> verifier will retrieve the reg_type from target. > > you mean to introduce something like 'struct bpf_func_proto' > that describes types of helpers, but instead something similar > to clarify the types in ctx ? That should work. Thanks Yes, this is what I think will be extensible.
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