netdev - Re: [PATCH v2 bpf-next 5/5] selftest: Add tests for XDP programs in devmap entries

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Date:   Thu, 28 May 2020 12:25:10 +0200
From:   Jesper Dangaard Brouer <brouer@...hat.com>
To:     Andrii Nakryiko <andrii.nakryiko@...il.com>
Cc:     David Ahern <dsahern@...nel.org>,
        Networking <netdev@...r.kernel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Toke Høiland-Jørgensen <toke@...hat.com>,
        Daniel Borkmann <daniel@...earbox.net>,
        john fastabend <john.fastabend@...il.com>,
        Alexei Starovoitov <ast@...nel.org>, Martin Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        Andrii Nakryiko <andriin@...com>,
        David Ahern <dsahern@...il.com>, brouer@...hat.com
Subject: Re: [PATCH v2 bpf-next 5/5] selftest: Add tests for XDP programs in
 devmap entries

On Thu, 28 May 2020 00:08:34 -0700
Andrii Nakryiko <andrii.nakryiko@...il.com> wrote:

> > diff --git a/tools/testing/selftests/bpf/progs/test_xdp_with_devmap.c b/tools/testing/selftests/bpf/progs/test_xdp_with_devmap.c
> > new file mode 100644
> > index 000000000000..815cd59b4866
> > --- /dev/null
> > +++ b/tools/testing/selftests/bpf/progs/test_xdp_with_devmap.c
> > @@ -0,0 +1,17 @@
> > +// SPDX-License-Identifier: GPL-2.0
> > +
> > +#include <linux/bpf.h>
> > +#include <bpf/bpf_helpers.h>
> > +
> > +struct bpf_map_def SEC("maps") dm_ports = {
> > +       .type = BPF_MAP_TYPE_DEVMAP,
> > +       .key_size = sizeof(__u32),
> > +       .value_size = sizeof(struct devmap_val),
> > +       .max_entries = 4,
> > +};
> > +  
> 
> This is an old syntax for maps, all the selftests were converted to
> BTF-defined maps. Please update.

LOL - The map type BPF_MAP_TYPE_DEVMAP does not support BTF for key and
value, which it what I've been trying to point out... (and yes, I do
have code that makes it work in my tree.).

That said, you should use the new SEC(".maps") definitions, but you
need to use some tricks to avoid a BTF-ID getting generated.  Let me
help you with something that should work:

/* DEVMAP values */
struct devmap_val {
	__u32 ifindex;   /* device index */
};

struct {
	__uint(type, BPF_MAP_TYPE_DEVMAP);
	__uint(key_size, sizeof(u32));
	__uint(value_size, sizeof(struct devmap_val));
	__uint(max_entries, 4);
} dm_ports SEC(".maps");

Notice by setting key_size and value_size, instead of the "__type",
then a BTF-ID will be generated for this map.
Normally with proper BTF it should look like:

struct {
	__uint(type, BPF_MAP_TYPE_DEVMAP);
	__type(key, u32);
	__type(value, struct devmap_val);
	__uint(max_entries, 4);
} dm_ports_with_BTF SEC(".maps");


-- 
Best regards,
  Jesper Dangaard Brouer
  MSc.CS, Principal Kernel Engineer at Red Hat
  LinkedIn: http://www.linkedin.com/in/brouer