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Date: Fri, 15 Dec 2023 16:19:02 -0800
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Subject: Re: [PATCH bpf-next v13 07/14] bpf: pass attached BTF to the
 bpf_struct_ops subsystem
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To: Kui-Feng Lee <sinquersw@gmail.com>, thinker.li@gmail.com
Cc: kuifeng@meta.com, bpf@vger.kernel.org, ast@kernel.org, song@kernel.org,
 kernel-team@meta.com, andrii@kernel.org, drosen@google.com
References: <20231209002709.535966-1-thinker.li@gmail.com>
 <20231209002709.535966-8-thinker.li@gmail.com>
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 <e2222287-6438-4de7-a747-9e04c5fd3f55@gmail.com>
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From: Martin KaFai Lau <martin.lau@linux.dev>
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On 12/15/23 2:10 PM, Kui-Feng Lee wrote:
> 
> 
> On 12/14/23 18:44, Martin KaFai Lau wrote:
>> On 12/8/23 4:27 PM, thinker.li@gmail.com wrote:
>>> @@ -681,15 +682,30 @@ static struct bpf_map *bpf_struct_ops_map_alloc(union 
>>> bpf_attr *attr)
>>>       struct bpf_struct_ops_map *st_map;
>>>       const struct btf_type *t, *vt;
>>>       struct bpf_map *map;
>>> +    struct btf *btf;
>>>       int ret;
>>> -    st_ops_desc = bpf_struct_ops_find_value(btf_vmlinux, 
>>> attr->btf_vmlinux_value_type_id);
>>> -    if (!st_ops_desc)
>>> -        return ERR_PTR(-ENOTSUPP);
>>> +    if (attr->value_type_btf_obj_fd) {
>>> +        /* The map holds btf for its whole life time. */
>>> +        btf = btf_get_by_fd(attr->value_type_btf_obj_fd);
>>> +        if (IS_ERR(btf))
>>> +            return ERR_PTR(PTR_ERR(btf));
>>
>>              return ERR_CAST(btf);
>>
>> It needs to check for btf_is_module:
>>
>>          if (!btf_is_module(btf)) {
>>              btf_put(btf);
>>              return ERR_PTR(-EINVAL);
>>          }
> 
> Even btf is btf_vmlinux the kernel's btf, it still works.

btf could be a bpf program's btf. It needs to ensure it is a kernel module btf 
here.

> Although libbpf pass 0 as the value of value_type_btf_obj_fd for
> btf_vmlinux now, it should be OK for a user space loader to
> pass a fd of btf_vmlinux.
> 
> WDYT?