netdev - Re: [PATCH bpf v2 3/4] bpf: Use EOPNOTSUPP in bpf_tcp_check

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Date:   Mon, 31 Jan 2022 12:55:25 -0800
From:   John Fastabend <john.fastabend@...il.com>
To:     Maxim Mikityanskiy <maximmi@...dia.com>,
        John Fastabend <john.fastabend@...il.com>
Cc:     bpf@...r.kernel.org, Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>, netdev@...r.kernel.org,
        Tariq Toukan <tariqt@...dia.com>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        KP Singh <kpsingh@...nel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Petar Penkov <ppenkov@...gle.com>,
        Lorenz Bauer <lmb@...udflare.com>,
        Eric Dumazet <edumazet@...gle.com>
Subject: Re: [PATCH bpf v2 3/4] bpf: Use EOPNOTSUPP in bpf_tcp_check_syncookie

Maxim Mikityanskiy wrote:
> On 2022-01-25 09:06, John Fastabend wrote:
> > Maxim Mikityanskiy wrote:
> >> When CONFIG_SYN_COOKIES is off, bpf_tcp_check_syncookie returns
> >> ENOTSUPP. It's a non-standard and deprecated code. The related function
> >> bpf_tcp_gen_syncookie and most of the other functions use EOPNOTSUPP if
> >> some feature is not available. This patch changes ENOTSUPP to EOPNOTSUPP
> >> in bpf_tcp_check_syncookie.
> >>
> >> Fixes: 399040847084 ("bpf: add helper to check for a valid SYN cookie")
> >> Signed-off-by: Maxim Mikityanskiy <maximmi@...dia.com>
> >> Reviewed-by: Tariq Toukan <tariqt@...dia.com>
> > 
> > This came up in another thread? Or was it the same and we lost the context
> > in the commit msg. Either way I don't think we should start one-off
> > changing these user facing error codes. Its not the only spot we do this
> > and its been this way for sometime.
> > 
> > Is it causing a real problem?
> 
> I'm not aware of anyone complaining about it. It's just a cleanup to use 
> the proper error code, since ENOTSUPP is a non-standard one (used in 
> NFS?), for example, strerror() returns "Unknown error 524" instead of 
> "Operation not supported".
> 
> Source: Documentation/dev-tools/checkpatch.rst:

iirc we didn't change the other ones so I see no reason to change this. Its
not great, but anything using it has already figured it out and it is
user facing.