netdev - Re: [PATCH v2 bpf-next 1/2] bpf: Allow bpf_map_lookup

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Date:   Fri, 31 May 2019 19:13:40 +0200
From:   Björn Töpel <bjorn.topel@...il.com>
To:     Jonathan Lemon <jonathan.lemon@...il.com>
Cc:     Björn Töpel <bjorn.topel@...el.com>,
        Netdev <netdev@...r.kernel.org>,
        "Karlsson, Magnus" <magnus.karlsson@...el.com>,
        Kernel Team <kernel-team@...com>, bpf <bpf@...r.kernel.org>
Subject: Re: [PATCH v2 bpf-next 1/2] bpf: Allow bpf_map_lookup_elem() on an xskmap

On Fri, 31 May 2019 at 18:27, Jonathan Lemon <jonathan.lemon@...il.com> wrote:
>
> On 31 May 2019, at 4:49, Björn Töpel wrote:
>
> > On 2019-05-30 20:57, Jonathan Lemon 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.
> >>
> >> Rearrange some xdp_sock members to eliminate structure holes.
> >>
> >> Signed-off-by: Jonathan Lemon <jonathan.lemon@...il.com>
> >> ---
> >>   include/net/xdp_sock.h                            |  6 +++---
> >>   kernel/bpf/verifier.c                             |  6 +++++-
> >>   kernel/bpf/xskmap.c                               |  4 +++-
> >>   .../selftests/bpf/verifier/prevent_map_lookup.c   | 15 ---------------
> >>   4 files changed, 11 insertions(+), 20 deletions(-)
> >>
> >> diff --git a/include/net/xdp_sock.h b/include/net/xdp_sock.h
> >> index d074b6d60f8a..7d84b1da43d2 100644
> >> --- a/include/net/xdp_sock.h
> >> +++ b/include/net/xdp_sock.h
> >> @@ -57,12 +57,12 @@ struct xdp_sock {
> >>      struct net_device *dev;
> >>      struct xdp_umem *umem;
> >>      struct list_head flush_node;
> >> -    u16 queue_id;
> >> -    struct xsk_queue *tx ____cacheline_aligned_in_smp;
> >> -    struct list_head list;
> >> +    u32 queue_id;
> >
> > Why the increase of size?
>
> Currently xskmaps are defined as size=4, so the returned pointer for
> bpf must have that many bytes.  I was kicking around the idea of using
> a union and returning { qid, zc }, but Alexei pointed out that doesn't
> make a good API.
>
> Besides, queue_index in struct xdp_rxq_info is already a u32.

(Resending w/o HTML from mobile client.)

Makes sense. Thanks for clarifying!


Björn

> --
> Jonathan
>