From: "Jonathan Lemon" <jonathan.lemon@gmail.com>
To: "Jesper Dangaard Brouer" <brouer@redhat.com>
Cc: netdev@vger.kernel.org, kernel-team@fb.com,
bjorn.topel@intel.com, magnus.karlsson@intel.com, ast@kernel.org,
daniel@iogearbox.net
Subject: Re: [PATCH v4 bpf-next 1/2] bpf: Allow bpf_map_lookup_elem() on an xskmap
Date: Tue, 04 Jun 2019 10:25:23 -0700 [thread overview]
Message-ID: <87399C88-4388-4857-AD77-E98527DEFDA4@gmail.com> (raw)
In-Reply-To: <20190604184306.362d9d8e@carbon>
On 4 Jun 2019, at 9:43, Jesper Dangaard Brouer wrote:
> On Mon, 3 Jun 2019 09:38:51 -0700
> Jonathan Lemon <jonathan.lemon@gmail.com> wrote:
>
>> Currently, the AF_XDP code uses a separate map in order to
>> determine if an xsk is bound to a queue. Instead of doing this,
>> have bpf_map_lookup_elem() return the queue_id, as a way of
>> indicating that there is a valid entry at the map index.
>
> Just a reminder, that once we choose a return value, there the
> queue_id, then it basically becomes UAPI, and we cannot change it.
Yes - Alexei initially wanted to return the sk_cookie instead, but
that's 64 bits and opens up a whole other can of worms.
> Can we somehow use BTF to allow us to extend this later?
>
> I was also going to point out that, you cannot return a direct pointer
> to queue_id, as BPF-prog side can modify this... but Daniel already
> pointed this out.
So, I see three solutions here (for this and Toke's patchset also,
which is encountering the same problem).
1) add a scratch register (Toke's approach)
2) add a PTR_TO_<type>, which has the access checked. This is the most
flexible approach, but does seem a bit overkill at the moment.
3) add another helper function, say, bpf_map_elem_present() which just
returns a boolean value indicating whether there is a valid map entry
or not.
I was starting to do 2), but wanted to get some more feedback first.
--
Jonathan
next prev parent reply other threads:[~2019-06-04 17:25 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-06-03 16:38 [PATCH v4 bpf-next 0/2] Better handling of xskmap entries Jonathan Lemon
2019-06-03 16:38 ` [PATCH v4 bpf-next 1/2] bpf: Allow bpf_map_lookup_elem() on an xskmap Jonathan Lemon
2019-06-04 14:54 ` Daniel Borkmann
2019-06-04 15:30 ` Daniel Borkmann
2019-06-04 16:43 ` Jesper Dangaard Brouer
2019-06-04 17:25 ` Jonathan Lemon [this message]
2019-06-04 18:12 ` Martin Lau
2019-06-05 8:45 ` Björn Töpel
2019-06-05 15:42 ` Jonathan Lemon
2019-06-04 18:18 ` Björn Töpel
2019-06-04 20:07 ` Toke Høiland-Jørgensen
2019-06-03 16:38 ` [PATCH v4 bpf-next 2/2] libbpf: remove qidconf and better support external bpf programs Jonathan Lemon
2019-06-04 6:06 ` [PATCH v4 bpf-next 0/2] Better handling of xskmap entries Björn Töpel
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