From: "Toke Høiland-Jørgensen" <toke@redhat.com>
To: Jakub Kicinski <kuba@kernel.org>,
Andrii Nakryiko <andrii.nakryiko@gmail.com>
Cc: Networking <netdev@vger.kernel.org>, bpf <bpf@vger.kernel.org>,
Alexei Starovoitov <ast@kernel.org>,
Daniel Borkmann <daniel@iogearbox.net>,
Martin KaFai Lau <kafai@fb.com>, Song Liu <songliubraving@fb.com>,
Yonghong Song <yhs@fb.com>, Andrii Nakryiko <andriin@fb.com>,
"David S. Miller" <davem@davemloft.net>,
Jesper Dangaard Brouer <brouer@redhat.com>,
John Fastabend <john.fastabend@gmail.com>,
Lorenz Bauer <lmb@cloudflare.com>, Andrey Ignatov <rdna@fb.com>
Subject: Re: [PATCH bpf-next v3 1/4] xdp: Support specifying expected existing program when attaching XDP
Date: Wed, 25 Mar 2020 17:48:57 +0100 [thread overview]
Message-ID: <877dz8peh2.fsf@toke.dk> (raw)
In-Reply-To: <20200324184311.4cfb4911@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com>
Jakub Kicinski <kuba@kernel.org> writes:
> On Tue, 24 Mar 2020 17:54:07 -0700 Andrii Nakryiko wrote:
>> On Tue, Mar 24, 2020 at 11:13 AM Toke Høiland-Jørgensen <toke@redhat.com> wrote:
>> >
>> > From: Toke Høiland-Jørgensen <toke@redhat.com>
>> >
>> > While it is currently possible for userspace to specify that an existing
>> > XDP program should not be replaced when attaching to an interface, there is
>> > no mechanism to safely replace a specific XDP program with another.
>> >
>> > This patch adds a new netlink attribute, IFLA_XDP_EXPECTED_ID, which can be
>> > set along with IFLA_XDP_FD. If set, the kernel will check that the program
>> > currently loaded on the interface matches the expected one, and fail the
>> > operation if it does not. This corresponds to a 'cmpxchg' memory operation.
>> > Setting the new attribute with a negative value means that no program is
>> > expected to be attached, which corresponds to setting the UPDATE_IF_NOEXIST
>> > flag.
>> >
>> > A new companion flag, XDP_FLAGS_EXPECT_ID, is also added to explicitly
>> > request checking of the EXPECTED_ID attribute. This is needed for userspace
>> > to discover whether the kernel supports the new attribute.
>>
>> Doesn't it feel inconsistent in UAPI that FD is used to specify XDP
>> program to be attached, but ID is used to specify expected XDP
>> program? Especially that the same cgroup use case is using
>> (consistently) prog FDs. Or is it another case where XDP needs its own
>> special way?
>
> There was a comment during review of v1, I wish you spoke up then.
>
> The prog ID is what dump returns, so the consistency can go either way
> (note that this API predates object IDs). Since XDP uses IDs internally
> it's just simpler to take prog ID.
>
> But it's a detail, so if you feel strongly I don't really mind.
Using an FD instead of an ID does make this more extensible (such as
supporting bpf_link FDs in the future; see my other reply to Alexei). So
I'll respin this, and switch it back to EXPECTED_FD.
-Toke
next prev parent reply other threads:[~2020-03-25 16:49 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-03-24 18:12 [PATCH bpf-next v3 0/4] XDP: Support atomic replacement of XDP interface attachments Toke Høiland-Jørgensen
2020-03-24 18:12 ` [PATCH bpf-next v3 1/4] xdp: Support specifying expected existing program when attaching XDP Toke Høiland-Jørgensen
2020-03-24 19:40 ` Jakub Kicinski
2020-03-25 0:54 ` Andrii Nakryiko
2020-03-25 1:43 ` Jakub Kicinski
2020-03-25 16:48 ` Toke Høiland-Jørgensen [this message]
2020-03-25 1:46 ` Alexei Starovoitov
2020-03-25 16:48 ` Toke Høiland-Jørgensen
2020-03-24 18:12 ` [PATCH bpf-next v3 2/4] tools: Add EXPECTED_ID-related definitions in if_link.h Toke Høiland-Jørgensen
2020-03-24 18:12 ` [PATCH bpf-next v3 3/4] libbpf: Add function to set link XDP fd while specifying old program Toke Høiland-Jørgensen
2020-03-24 18:12 ` [PATCH bpf-next v3 4/4] selftests/bpf: Add tests for attaching XDP programs Toke Høiland-Jørgensen
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