netdev - RE: [PATCH] bpf: return EOPNOTSUPP when JIT is needed and not possible

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Date:   Thu, 09 Dec 2021 11:05:18 -0800
From:   John Fastabend <john.fastabend@...il.com>
To:     Thadeu Lima de Souza Cascardo <cascardo@...onical.com>,
        bpf@...r.kernel.org
Cc:     netdev@...r.kernel.org, ast@...nel.org, daniel@...earbox.net,
        linux-kernel@...r.kernel.org
Subject: RE: [PATCH] bpf: return EOPNOTSUPP when JIT is needed and not
 possible

Thadeu Lima de Souza Cascardo wrote:
> When a CBPF program is JITed and CONFIG_BPF_JIT_ALWAYS_ON is enabled, and
> the JIT fails, it would return ENOTSUPP, which is not a valid userspace
> error code.  Instead, EOPNOTSUPP should be returned.
> 
> Fixes: 290af86629b2 ("bpf: introduce BPF_JIT_ALWAYS_ON config")
> Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@...onical.com>
> ---
>  kernel/bpf/core.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
> index de3e5bc6781f..5c89bae0d6f9 100644
> --- a/kernel/bpf/core.c
> +++ b/kernel/bpf/core.c
> @@ -1931,7 +1931,7 @@ struct bpf_prog *bpf_prog_select_runtime(struct bpf_prog *fp, int *err)
>  		fp = bpf_int_jit_compile(fp);
>  		bpf_prog_jit_attempt_done(fp);
>  		if (!fp->jited && jit_needed) {
> -			*err = -ENOTSUPP;
> +			*err = -EOPNOTSUPP;
>  			return fp;
>  		}
>  	} else {
> -- 
> 2.32.0
> 

It seems BPF subsys returns ENOTSUPP in multiple places. This fixes one
paticular case and is user facing. Not sure we want to one-off fix them
here creating user facing changes over multiple kernel versions. On the
fence with this one curious to see what others think. Haven't apps
already adapted to the current convention or they don't care?

.John