netdev - Re: [PATCH] net: skb: move enum skb_drop

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Date:   Fri, 11 Mar 2022 14:23:13 -0800
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     Menglong Dong <menglong8.dong@...il.com>
Cc:     Jakub Kicinski <kuba@...nel.org>, David Ahern <dsahern@...nel.org>,
        Neil Horman <nhorman@...driver.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>, Martin Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...nel.org>,
        David Miller <davem@...emloft.net>,
        Menglong Dong <imagedong@...cent.com>,
        Eric Dumazet <edumazet@...gle.com>,
        Talal Ahmad <talalahmad@...gle.com>,
        Kees Cook <keescook@...omium.org>,
        Alexander Lobakin <alobakin@...me>,
        LKML <linux-kernel@...r.kernel.org>,
        netdev <netdev@...r.kernel.org>, bpf <bpf@...r.kernel.org>,
        Mengen Sun <mengensun@...cent.com>,
        Hao Peng <flyingpeng@...cent.com>
Subject: Re: [PATCH] net: skb: move enum skb_drop_reason to uapi

On Thu, Mar 10, 2022 at 8:58 PM Menglong Dong <menglong8.dong@...il.com> wrote:
>
> On Fri, Mar 11, 2022 at 11:54 AM Jakub Kicinski <kuba@...nel.org> wrote:
> >
> > On Fri, 11 Mar 2022 11:28:28 +0800 menglong8.dong@...il.com wrote:
> > > From: Menglong Dong <imagedong@...cent.com>
> > >
> > > Move the definition of 'enum skb_drop_reason' in 'skbuff.h' to the uapi
> > > header 'net_dropmon.h', therefore some users, such as eBPF program, can
> > > make use of it.
> >
> > BPF does not need an enum definition to be part of the uAPI to make use
> > of it. BTF should encode the values, and CO-RE can protect from them
> > changing, AFAIU. I think we need a better example user / justification.
>
> There is something wrong with my description, it's not the eBPF, but the user
> program that loads eBPF.
>
> In my case, I'll pass the packet info (protocol, ip, port, etc) and drop reason
> to user space by eBPF that is attached on the kfree_skb() tracepoint.
>
> In the user space, I'll custom the description for drop reasons and convert them
> from int to string. Therefore, I need to use 'enum skb_drop_reason' in my
> user space code.

As Jakub said there is no reason to expose this in uapi.

> For now, I copied the definition of 'enum skb_drop_reason' to my code,
> and I think it's better to make them uapi, considering someone else may
> use it this way too.

No. Please use CO-RE and vmlinux.h instead.