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

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Message-ID: <20191020172503.qeee2olqxxnynm6v@ast-mbp.dhcp.thefacebook.com>
Date:   Sun, 20 Oct 2019 10:25:05 -0700
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     Magnus Karlsson <magnus.karlsson@...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 Sun, Oct 20, 2019 at 10:13:49AM +0200, Magnus Karlsson wrote:
> 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.

Ahh. Right. xskmap explicitly prohibits BTF for key/value.
const struct bpf_map_ops xsk_map_ops = {
        ...
        .map_check_btf = map_check_no_btf,
};
I guess it's time to add support for it.