netdev - Re: [PATCH bpf v2] xsk: improve documentation for AF

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Date:   Sun, 20 Oct 2019 10:13:49 +0200
From:   Magnus Karlsson <magnus.karlsson@...il.com>
To:     Alexei Starovoitov <alexei.starovoitov@...il.com>
Cc:     Magnus Karlsson <magnus.karlsson@...el.com>,
        Björn Töpel <bjorn.topel@...el.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Network Development <netdev@...r.kernel.org>,
        Jonathan Lemon <jonathan.lemon@...il.com>,
        "open list:DOCUMENTATION" <linux-doc@...r.kernel.org>,
        bpf <bpf@...r.kernel.org>
Subject: Re: [PATCH bpf v2] xsk: improve documentation for AF_XDP

On Sat, Oct 19, 2019 at 11:48 AM Alexei Starovoitov
<alexei.starovoitov@...il.com> wrote:
>
> On Fri, Oct 18, 2019 at 11:33:40AM +0200, Magnus Karlsson wrote:
> > +
> > +   #include <linux/bpf.h>
> > +   #include "bpf_helpers.h"
> > +
> > +   #define MAX_SOCKS 16
> > +
> > +   struct {
> > +        __uint(type, BPF_MAP_TYPE_XSKMAP);
> > +        __uint(max_entries, MAX_SOCKS);
> > +        __uint(key_size, sizeof(int));
> > +        __uint(value_size, sizeof(int));
> > +   } xsks_map SEC(".maps");
> > +
> > +   struct {
> > +        __uint(type, BPF_MAP_TYPE_PERCPU_ARRAY);
> > +        __uint(max_entries, 1);
> > +        __type(key, int);
> > +        __type(value, unsigned int);
> > +   } rr_map SEC(".maps");
>
> hmm. does xsks_map compile?

Yes. Actually, I wrote a new sample to demonstrate this feature and to
test the code above. I will send that patch set (contains some small
additions to libbpf also to be able to support this) to bpf-next.
Though, if I used the __type declarations of the rr_map PERCPU_ARRAY I
got this warning: "pr_warning("Error in
bpf_create_map_xattr(%s):%s(%d). Retrying without BTF.\n")", so I had
to change it to the type above that is also used for SOCKMAP. Some
enablement that is missing for XSKMAP? Have not dug into it.

> > +
> > +   SEC("xdp_sock") int xdp_sock_prog(struct xdp_md *ctx)
> > +   {
> > +     int key = 0, idx;
> > +     unsigned int *rr;
> > +
> > +     rr = bpf_map_lookup_elem(&rr_map, &key);
> > +     if (!rr)
> > +        return XDP_ABORTED;
>
> could you please use global data and avoid lookup?
> The run-time will be much faster.

Good idea. Will do and change the new sample app too.