netdev - Re: [PATCH v4 bpf-next 10/14] bpf: allow to specify kernel module BTFs when attaching BPF programs

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Message-ID: <20201202205809.qwbismdmmtrcsar7@ast-mbp>
Date:   Wed, 2 Dec 2020 12:58:09 -0800
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     Andrii Nakryiko <andrii@...nel.org>
Cc:     bpf@...r.kernel.org, netdev@...r.kernel.org, ast@...com,
        daniel@...earbox.net, kernel-team@...com
Subject: Re: [PATCH v4 bpf-next 10/14] bpf: allow to specify kernel module
 BTFs when attaching BPF programs

On Tue, Dec 01, 2020 at 04:16:12PM -0800, Andrii Nakryiko wrote:
> diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
> index c3458ec1f30a..60b95b51ccb8 100644
> --- a/include/uapi/linux/bpf.h
> +++ b/include/uapi/linux/bpf.h
> @@ -558,6 +558,7 @@ union bpf_attr {
>  		__u32		line_info_cnt;	/* number of bpf_line_info records */
>  		__u32		attach_btf_id;	/* in-kernel BTF type id to attach to */
>  		__u32		attach_prog_fd; /* 0 to attach to vmlinux */
> +		__u32		attach_btf_obj_id; /* vmlinux/module BTF object ID for BTF type */

I think the uapi should use attach_btf_obj_fd here.
Everywhere else uapi is using FDs to point to maps, progs, BTFs of progs.
BTF of a module isn't different from BTF of a program.
Looking at libbpf implementation... it has the FD of a module anyway,
since it needs to fetch it to search for the function btf_id in there.
So there won't be any inconvenience for libbpf to pass FD in here.
>From the uapi perspective attach_btf_obj_fd will remove potential
race condition. It's very unlikely race, of course.

The rest of the series look good to me.