Re: How to avoid compilation errors like "error: no member named xxx in strut xxx"?

[Shuyi Cheng <chengshuyi@linux.alibaba.com>]

On 6/16/21 2:02 PM, Andrii Nakryiko wrote:
> On Tue, Jun 15, 2021 at 9:06 PM Shuyi Cheng
> <chengshuyi@linux.alibaba.com> wrote:
>>
>> I am trying to write a bpf program that supports multiple linux kernel
>> versions. However, there are some differences in the definition of
>> struct net in these multiple kernel versions.
>>
>> Therefore, when we include a certain kernel version of vmlinux.h, the
>> compilation error "error: no member named'proc_inum' in strut net" will
>> appear.
>>
>> However, when we include another kernel version of vmlinux.h, the
>> compilation will appear "error: no member named'ns.inum' in strut net".
>>
>> Anakryiko mentioned in the issue of libbpf/libbpf-bootstrap: vmlinux.h
>> is just a convenient way to have most of kernel types defined for you,
>> so that you don't have to re-define them manually. Link here: https:
>> //github.com/libbpf/libbpf-bootstrap/issues/31#issuecomment-861035643
>>
>> But struct net is a very huge structure, and it may be very difficult to
> 
> You don't need to declare the entire struct, it's enough to declare
> only fields that you need and use.
> 
> If the type has incompatible changes between kernel versions (e.g., if
> some field changed it's type), you can use my_type___suffix approach,
> see [0] and struct kernfs_iattrs___old example. Let me know if you
> need more concrete example (but then also provide more concrete
> explanation of what you actually need).
> 
>    [0] https://nakryiko.com/posts/bcc-to-libbpf-howto-guide/#dealing-with-compile-time-if-s-in-bcc
> 
>> add it manually. So, how can we avoid compilation errors like "error: no
>> member named'xxx' in xxx"


Thank you very much, i get it.