netdev - Re: [PATCH bpf-next 08/15] bpf: introduce new bpf AF_XDP map type BPF_MAP_TYPE

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Message-ID: <CAF=yD-+W8=wDXc1=wHi8KF0whgyFLqvo=tROOq16XfA7MDkR+Q@mail.gmail.com>
Date:   Tue, 24 Apr 2018 12:56:04 -0400
From:   Willem de Bruijn <willemdebruijn.kernel@...il.com>
To:     Björn Töpel <bjorn.topel@...il.com>
Cc:     "Karlsson, Magnus" <magnus.karlsson@...el.com>,
        Alexander Duyck <alexander.h.duyck@...el.com>,
        Alexander Duyck <alexander.duyck@...il.com>,
        John Fastabend <john.fastabend@...il.com>,
        Alexei Starovoitov <ast@...com>,
        Jesper Dangaard Brouer <brouer@...hat.com>,
        Daniel Borkmann <daniel@...earbox.net>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        Network Development <netdev@...r.kernel.org>,
        Björn Töpel <bjorn.topel@...el.com>,
        michael.lundkvist@...csson.com,
        "Brandeburg, Jesse" <jesse.brandeburg@...el.com>,
        "Singhai, Anjali" <anjali.singhai@...el.com>,
        "Zhang, Qi Z" <qi.z.zhang@...el.com>
Subject: Re: [PATCH bpf-next 08/15] bpf: introduce new bpf AF_XDP map type BPF_MAP_TYPE_XSKMAP

On Mon, Apr 23, 2018 at 9:56 AM, Björn Töpel <bjorn.topel@...il.com> wrote:
> From: Björn Töpel <bjorn.topel@...el.com>
>
> The xskmap is yet another BPF map, very much inspired by
> dev/cpu/sockmap, and is a holder of AF_XDP sockets. A user application
> adds AF_XDP sockets into the map, and by using the bpf_redirect_map
> helper, an XDP program can redirect XDP frames to an AF_XDP socket.
>
> Note that a socket that is bound to certain ifindex/queue index will
> *only* accept XDP frames from that netdev/queue index. If an XDP
> program tries to redirect from a netdev/queue index other than what
> the socket is bound to, the frame will not be received on the socket.
>
> A socket can reside in multiple maps.
>
> Signed-off-by: Björn Töpel <bjorn.topel@...el.com>

> +struct xsk_map_entry {
> +       struct xdp_sock *xs;
> +       struct rcu_head rcu;
> +};

> +struct xdp_sock *__xsk_map_lookup_elem(struct bpf_map *map, u32 key)
> +{
> +       struct xsk_map *m = container_of(map, struct xsk_map, map);
> +       struct xsk_map_entry *entry;
> +
> +       if (key >= map->max_entries)
> +               return NULL;
> +
> +       entry = READ_ONCE(m->xsk_map[key]);
> +       return entry ? entry->xs : NULL;
> +}

This dynamically allocated structure adds an extra cacheline lookup. If
xdp_sock gets an rcu_head, it can be linked into the map directly.