Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
MIME-Version: 1.0
References: <20200420184750.218489-1-zenczykowski@gmail.com>
In-Reply-To: <20200420184750.218489-1-zenczykowski@gmail.com>
From:   Alexei Starovoitov <alexei.starovoitov@gmail.com>
Date:   Sun, 26 Apr 2020 09:08:26 -0700
Message-ID: <CAADnVQ+oVnmpMbmt482pUs+Nb8tny3_WGPbqTtWvVpCJZsbEKQ@mail.gmail.com>
Subject: Re: [PATCH] net: bpf: make bpf_ktime_get_ns() available to non GPL programs
To:     =?UTF-8?Q?Maciej_=C5=BBenczykowski?= <zenczykowski@gmail.com>
Cc:     =?UTF-8?Q?Maciej_=C5=BBenczykowski?= <maze@google.com>,
        Alexei Starovoitov <ast@kernel.org>,
        Daniel Borkmann <daniel@iogearbox.net>,
        Linux Network Development Mailing List 
        <netdev@vger.kernel.org>, LKML <linux-kernel@vger.kernel.org>,
        "David S . Miller" <davem@davemloft.net>
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On Mon, Apr 20, 2020 at 11:47 AM Maciej =C5=BBenczykowski
<zenczykowski@gmail.com> wrote:
>
> From: Maciej =C5=BBenczykowski <maze@google.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 =3D {
>        .func           =3D bpf_ktime_get_ns,
>        .gpl_only       =3D false,
>        .ret_type       =3D 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_MONOTON=
IC)
> 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 =C5=BBenczykowski <maze@google.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.