netdev - Re: [PATCH v3 bpf-next 2/9] bpf, xdp: maintain info on attached XDP BPF programs in net

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Date:   Tue, 21 Jul 2020 23:48:41 -0700
From:   Andrii Nakryiko <andrii.nakryiko@...il.com>
To:     David Ahern <dsahern@...il.com>
Cc:     Andrii Nakryiko <andriin@...com>, bpf <bpf@...r.kernel.org>,
        Networking <netdev@...r.kernel.org>,
        Alexei Starovoitov <ast@...com>,
        Daniel Borkmann <daniel@...earbox.net>,
        Kernel Team <kernel-team@...com>
Subject: Re: [PATCH v3 bpf-next 2/9] bpf, xdp: maintain info on attached XDP
 BPF programs in net_device

On Thu, Jul 16, 2020 at 1:31 PM Andrii Nakryiko
<andrii.nakryiko@...il.com> wrote:
>
> On Thu, Jul 16, 2020 at 12:01 PM David Ahern <dsahern@...il.com> wrote:
> >
> > On 7/15/20 10:55 PM, Andrii Nakryiko wrote:
> > > Instead of delegating to drivers, maintain information about which BPF
> > > programs are attached in which XDP modes (generic/skb, driver, or hardware)
> > > locally in net_device. This effectively obsoletes XDP_QUERY_PROG command.
> > >
> > > Such re-organization simplifies existing code already. But it also allows to
> > > further add bpf_link-based XDP attachments without drivers having to know
> > > about any of this at all, which seems like a good setup.
> > > XDP_SETUP_PROG/XDP_SETUP_PROG_HW are just low-level commands to driver to
> > > install/uninstall active BPF program. All the higher-level concerns about
> > > prog/link interaction will be contained within generic driver-agnostic logic.
> > >
> > > All the XDP_QUERY_PROG calls to driver in dev_xdp_uninstall() were removed.
> > > It's not clear for me why dev_xdp_uninstall() were passing previous prog_flags
> > > when resetting installed programs. That seems unnecessary, plus most drivers
> > > don't populate prog_flags anyways. Having XDP_SETUP_PROG vs XDP_SETUP_PROG_HW
> > > should be enough of an indicator of what is required of driver to correctly
> > > reset active BPF program. dev_xdp_uninstall() is also generalized as an
> > > iteration over all three supported mode.
> > >
> > > Signed-off-by: Andrii Nakryiko <andriin@...com>
> > > ---
> > >  include/linux/netdevice.h |  17 +++-
> > >  net/core/dev.c            | 158 +++++++++++++++++++++-----------------
> >
> > Similar to my comment on a v1 patch, this change is doing multiple
> > things that really should be split into 2 patches - one moving code
> > around and the second making the change you want. As is the patch is
> > difficult to properly review.
> >
>
> You mean xdp_uninstall? In patch 1 leave it as three separate
> sections, but switch to different querying. And then in a separate
> patch do a loop?
>
> Alright, I'll split that up as well. But otherwise I don't really see
> much more opportunities to split it.

So I ended up not doing that. Given dev_xdp_uninstall() is just 15
lines of code, half of which are trivial, it just doesn't make sense
to split dev_xdp_uninstall() refactor into two phases.

>
> > Given that you need a v4 anyways, can you split this patch into 2?