netdev - RE: [PATCH v2 bpf-next 10/16] bpf: Add bpf_btf_find_by_name

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Date:   Tue, 27 Apr 2021 14:00:43 -0700
From:   John Fastabend <john.fastabend@...il.com>
To:     Alexei Starovoitov <alexei.starovoitov@...il.com>,
        davem@...emloft.net
Cc:     daniel@...earbox.net, andrii@...nel.org, netdev@...r.kernel.org,
        bpf@...r.kernel.org, kernel-team@...com
Subject: RE: [PATCH v2 bpf-next 10/16] bpf: Add bpf_btf_find_by_name_kind()
 helper.

Alexei Starovoitov wrote:
> From: Alexei Starovoitov <ast@...nel.org>
> 
> Add new helper:
> 
> long bpf_btf_find_by_name_kind(u32 btf_fd, char *name, u32 kind, int flags)
> 	Description
> 		Find given name with given type in BTF pointed to by btf_fd.
> 		If btf_fd is zero look for the name in vmlinux BTF and in module's BTFs.
> 	Return
> 		Returns btf_id and btf_obj_fd in lower and upper 32 bits.
> 
> Signed-off-by: Alexei Starovoitov <ast@...nel.org>
> ---

I'm missing some high-level concept on how this would be used? Where does btf_fd come
from and how is it used so that it doesn't break sig-check?

A use-case I'm trying to fit into this series is how to pass down a BTF fd/object
with the program. I know its not doing CO-RE yet but we would want it to use the
BTF object being passed down for CO-RE eventually. Will there be someway to do
that here? That looks like the btf_fd here.

Thanks,
John