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From: "Björn Töpel" <bjorn.topel@intel.com>
To: Alexei Starovoitov <alexei.starovoitov@gmail.com>,
	Andrii Nakryiko <andrii@kernel.org>
Cc: "Toke Høiland-Jørgensen" <toke@redhat.com>,
	"Björn Töpel" <bjorn.topel@gmail.com>,
	"Alexei Starovoitov" <ast@kernel.org>,
	"Daniel Borkmann" <daniel@iogearbox.net>,
	"Network Development" <netdev@vger.kernel.org>,
	bpf <bpf@vger.kernel.org>,
	"Karlsson, Magnus" <magnus.karlsson@intel.com>,
	"Fijalkowski, Maciej" <maciej.fijalkowski@intel.com>,
	"Jakub Kicinski" <kuba@kernel.org>,
	"Jonathan Lemon" <jonathan.lemon@gmail.com>,
	maximmi@nvidia.com, "David S. Miller" <davem@davemloft.net>,
	"Jesper Dangaard Brouer" <hawk@kernel.org>,
	"John Fastabend" <john.fastabend@gmail.com>,
	"Ciara Loftus" <ciara.loftus@intel.com>,
	weqaar.a.janjua@intel.com, "Marek Majtyka" <alardam@gmail.com>
Subject: Re: [PATCH bpf-next v2 5/8] libbpf, xsk: select AF_XDP BPF program based on kernel version
Date: Wed, 20 Jan 2021 19:30:12 +0100	[thread overview]
Message-ID: <9a624fee-6b49-9f00-3c21-d8ec3026a5a5@intel.com> (raw)
In-Reply-To: <CAADnVQK1vL307SmmUZyuEAmy9S_A2fJwyHryCHBavQ-QDNyxww@mail.gmail.com>

On 2021-01-20 19:25, Alexei Starovoitov wrote:
> On Wed, Jan 20, 2021 at 7:27 AM Björn Töpel <bjorn.topel@intel.com> wrote:
>>
>>>> Would it make sense with some kind of BPF-specific "supported
>>>> features" mechanism? Something else with a bigger scope (whole
>>>> kernel)?
>>>
>>> Heh, in my opinion, yeah. Seems like we'll finally get it for XDP, but
>>> for BPF in general the approach has always been probing AFAICT.
>>>
>>> For the particular case of arguments to helpers, I suppose the verifier
>>> could technically validate value ranges for flags arguments, say. That
>>> would be nice as an early reject anyway, but I'm not sure if it is
>>> possible to add after-the-fact without breaking existing programs
>>> because the verifier can't prove the argument is within the valid range.
>>> And of course it doesn't help you with compatibility with
>>> already-released kernels.
>>>
>>
>> Hmm, think I have a way forward. I'll use BPF_PROG_TEST_RUN.
>>
>> If the load fail for the new helper, fallback to bpf_redirect_map(). Use
>> BPF_PROG_TEST_RUN to make sure that "action via flags" passes.
> 
> +1 to Toke's point. No version checks please.
> One way to detect is to try prog_load. Search for FEAT_* in libbpf.
> Another approach is to scan vmlinux BTF for necessary helpers.
> Currently libbpf is relying on the former.
> I think going forward would be good to detect features via BTF.
> It's going to be much faster and won't create noise for audit that
> could be looking at prog_load calls.
> 

Thanks Alexei. I'll explore both options for the next spin!


Björn

  reply	other threads:[~2021-01-20 18:34 UTC|newest]

Thread overview: 45+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-01-19 15:50 [PATCH bpf-next v2 0/8] Introduce bpf_redirect_xsk() helper Björn Töpel
2021-01-19 15:50 ` [PATCH bpf-next v2 1/8] xdp: restructure redirect actions Björn Töpel
2021-01-20 12:44   ` Toke Høiland-Jørgensen
2021-01-20 13:40     ` Björn Töpel
2021-01-20 14:52       ` Toke Høiland-Jørgensen
2021-01-20 15:49         ` Björn Töpel
2021-01-20 16:30           ` Toke Høiland-Jørgensen
2021-01-20 17:26             ` Björn Töpel
2021-01-19 15:50 ` [PATCH bpf-next v2 2/8] xsk: remove explicit_free parameter from __xsk_rcv() Björn Töpel
2021-01-19 15:50 ` [PATCH bpf-next v2 3/8] xsk: fold xp_assign_dev and __xp_assign_dev Björn Töpel
2021-01-19 15:50 ` [PATCH bpf-next v2 4/8] xsk: register XDP sockets at bind(), and add new AF_XDP BPF helper Björn Töpel
2021-01-20  8:25   ` kernel test robot
2021-01-20  8:41     ` Björn Töpel
2021-01-20  8:50   ` kernel test robot
2021-01-20 12:50   ` Toke Høiland-Jørgensen
2021-01-20 13:25     ` Björn Töpel
2021-01-20 14:54       ` Toke Høiland-Jørgensen
2021-01-20 15:18         ` Björn Töpel
2021-01-20 17:29           ` Toke Høiland-Jørgensen
2021-01-20 18:22             ` Björn Töpel
2021-01-20 20:26               ` Toke Høiland-Jørgensen
2021-01-20 21:15                 ` Alexei Starovoitov
2021-01-21  8:18                   ` Björn Töpel
2021-01-19 15:50 ` [PATCH bpf-next v2 5/8] libbpf, xsk: select AF_XDP BPF program based on kernel version Björn Töpel
2021-01-20 12:52   ` Toke Høiland-Jørgensen
2021-01-20 13:25     ` Björn Töpel
2021-01-20 14:49       ` Björn Töpel
2021-01-20 15:11         ` Toke Høiland-Jørgensen
2021-01-20 15:27           ` Björn Töpel
2021-01-20 17:30             ` Toke Høiland-Jørgensen
2021-01-20 18:25             ` Alexei Starovoitov
2021-01-20 18:30               ` Björn Töpel [this message]
2021-01-20 14:56       ` Toke Høiland-Jørgensen
2021-01-19 15:50 ` [PATCH bpf-next v2 6/8] libbpf, xsk: select bpf_redirect_xsk(), if supported Björn Töpel
2021-01-19 15:50 ` [PATCH bpf-next v2 7/8] selftest/bpf: add XDP socket tests for bpf_redirect_{xsk, map}() Björn Töpel
2021-01-21  7:39   ` Andrii Nakryiko
2021-01-21 12:31     ` Björn Töpel
2021-01-19 15:50 ` [PATCH bpf-next v2 8/8] selftest/bpf: remove a lot of ifobject casting in xdpxceiver Björn Töpel
2021-01-20 13:15 ` [PATCH bpf-next v2 0/8] Introduce bpf_redirect_xsk() helper Maxim Mikityanskiy
2021-01-20 13:27   ` Björn Töpel
2021-01-20 15:57   ` Jesper Dangaard Brouer
2021-01-20 16:19     ` Maciej Fijalkowski
2021-01-21 17:01       ` Jesper Dangaard Brouer
2021-01-22  8:59         ` Magnus Karlsson
2021-01-22  9:45           ` Maciej Fijalkowski

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