linux-kernel - Re: [PATCH] net: bpf: make bpf_ktime_get

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Date:   Sun, 26 Apr 2020 09:08:26 -0700
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     Maciej Żenczykowski <zenczykowski@...il.com>
Cc:     Maciej Żenczykowski <maze@...gle.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Linux Network Development Mailing List 
        <netdev@...r.kernel.org>, LKML <linux-kernel@...r.kernel.org>,
        "David S . Miller" <davem@...emloft.net>
Subject: Re: [PATCH] net: bpf: make bpf_ktime_get_ns() available to non GPL programs

On Mon, Apr 20, 2020 at 11:47 AM Maciej Żenczykowski
<zenczykowski@...il.com> wrote:
>
> From: Maciej Żenczykowski <maze@...gle.com>
>
> The entire implementation is in kernel/bpf/helpers.c:
>
> BPF_CALL_0(bpf_ktime_get_ns) {
>        /* NMI safe access to clock monotonic */
>        return ktime_get_mono_fast_ns();
> }
>
> const struct bpf_func_proto bpf_ktime_get_ns_proto = {
>        .func           = bpf_ktime_get_ns,
>        .gpl_only       = false,
>        .ret_type       = RET_INTEGER,
> };
>
> and this was presumably marked GPL due to kernel/time/timekeeping.c:
>   EXPORT_SYMBOL_GPL(ktime_get_mono_fast_ns);
>
> and while that may make sense for kernel modules (although even that
> is doubtful), there is currently AFAICT no other source of time
> available to ebpf.
>
> Furthermore this is really just equivalent to clock_gettime(CLOCK_MONOTONIC)
> which is exposed to userspace (via vdso even to make it performant)...
>
> As such, I see no reason to keep the GPL restriction.
> (In the future I'd like to have access to time from Apache licensed ebpf code)
>
> Signed-off-by: Maciej Żenczykowski <maze@...gle.com>

The issue of compatibility with apache licensed bpf progs was
brought up few times in the past.
The patch indeed will clear this hurdle.
Applied.