bpf.vger.kernel.org archive mirror
 help / color / mirror / Atom feed
From: "Toke Høiland-Jørgensen" <toke@redhat.com>
To: "Björn Töpel" <bjorn.topel@intel.com>,
	"Björn Töpel" <bjorn.topel@gmail.com>,
	ast@kernel.org, daniel@iogearbox.net, netdev@vger.kernel.org,
	bpf@vger.kernel.org
Cc: magnus.karlsson@intel.com, maciej.fijalkowski@intel.com,
	kuba@kernel.org, jonathan.lemon@gmail.com, maximmi@nvidia.com,
	davem@davemloft.net, hawk@kernel.org, john.fastabend@gmail.com,
	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 16:11:33 +0100	[thread overview]
Message-ID: <87eeif4p96.fsf@toke.dk> (raw)
In-Reply-To: <6cda7383-663e-ed92-45dd-bbf87ca45eef@intel.com>

Björn Töpel <bjorn.topel@intel.com> writes:

> On 2021-01-20 14:25, Björn Töpel wrote:
>> On 2021-01-20 13:52, Toke Høiland-Jørgensen wrote:
>>> Björn Töpel <bjorn.topel@gmail.com> writes:
>>>
>>>> From: Björn Töpel <bjorn.topel@intel.com>
>>>>
>>>> Add detection for kernel version, and adapt the BPF program based on
>>>> kernel support. This way, users will get the best possible performance
>>>> from the BPF program.
>>>
>>> Please do explicit feature detection instead of relying on the kernel
>>> version number; some distro kernels are known to have a creative notion
>>> of their own version, which is not really related to the features they
>>> actually support (I'm sure you know which one I'm referring to ;)).
>>>
>> 
>> Right. For a *new* helper, like bpf_redirect_xsk, we rely on rejection
>> from the verifier to detect support. What about "bpf_redirect_map() now
>> supports passing return value as flags"? Any ideas how to do that in a
>> robust, non-version number-based scheme?
>>
>
> Just so that I understand this correctly. Red^WSome distro vendors
> backport the world, and call that franken kernel, say, 3.10. Is that
> interpretation correct? My hope was that wasn't the case. :-(

Yup, indeed. All kernels shipped for the entire lifetime of RHEL8 think
they are v4.18.0... :/

I don't think we're the only ones doing it (there are examples in the
embedded world as well, for instance, and not sure about the other
enterprise distros), but RHEL is probably the most extreme example.

We could patch the version check in the distro-supplied version of
libbpf, of course, but that doesn't help anyone using upstream versions,
and given the prevalence of vendoring libbpf, I fear that going with the
version check will just result in a bad user experience...

> 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.

-Toke


  reply	other threads:[~2021-01-20 15:16 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 [this message]
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
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

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=87eeif4p96.fsf@toke.dk \
    --to=toke@redhat.com \
    --cc=alardam@gmail.com \
    --cc=ast@kernel.org \
    --cc=bjorn.topel@gmail.com \
    --cc=bjorn.topel@intel.com \
    --cc=bpf@vger.kernel.org \
    --cc=ciara.loftus@intel.com \
    --cc=daniel@iogearbox.net \
    --cc=davem@davemloft.net \
    --cc=hawk@kernel.org \
    --cc=john.fastabend@gmail.com \
    --cc=jonathan.lemon@gmail.com \
    --cc=kuba@kernel.org \
    --cc=maciej.fijalkowski@intel.com \
    --cc=magnus.karlsson@intel.com \
    --cc=maximmi@nvidia.com \
    --cc=netdev@vger.kernel.org \
    --cc=weqaar.a.janjua@intel.com \
    --subject='Re: [PATCH bpf-next v2 5/8] libbpf, xsk: select AF_XDP BPF program based on kernel version' \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).