From: "Toke Høiland-Jørgensen" <toke@redhat.com>
To: Andrii Nakryiko <andriin@fb.com>,
bpf@vger.kernel.org, netdev@vger.kernel.org, ast@fb.com,
daniel@iogearbox.net
Cc: andrii.nakryiko@gmail.com, kernel-team@fb.com,
Andrii Nakryiko <andriin@fb.com>
Subject: Re: [PATCH v2 bpf-next 3/3] libbpf: add BTF-defined map-in-map support
Date: Tue, 28 Apr 2020 13:03:07 +0200 [thread overview]
Message-ID: <878sifx47o.fsf@toke.dk> (raw)
In-Reply-To: <20200428064140.122796-4-andriin@fb.com>
Andrii Nakryiko <andriin@fb.com> writes:
> As discussed at LPC 2019 ([0]), this patch brings (a quite belated) support
> for declarative BTF-defined map-in-map support in libbpf. It allows to define
> ARRAY_OF_MAPS and HASH_OF_MAPS BPF maps without any user-space initialization
> code involved.
>
> Additionally, it allows to initialize outer map's slots with references to
> respective inner maps at load time, also completely declaratively.
>
> Despite a weak type system of C, the way BTF-defined map-in-map definition
> works, it's actually quite hard to accidentally initialize outer map with
> incompatible inner maps. This being C, of course, it's still possible, but
> even that would be caught at load time and error returned with helpful debug
> log pointing exactly to the slot that failed to be initialized.
>
> As an example, here's a rather advanced HASH_OF_MAPS declaration and
> initialization example, filling slots #0 and #4 with two inner maps:
>
> #include <bpf/bpf_helpers.h>
>
> struct inner_map {
> __uint(type, BPF_MAP_TYPE_ARRAY);
> __uint(max_entries, 1);
> __type(key, int);
> __type(value, int);
> } inner_map1 SEC(".maps"),
> inner_map2 SEC(".maps");
>
> struct outer_hash {
> __uint(type, BPF_MAP_TYPE_HASH_OF_MAPS);
> __uint(max_entries, 5);
> __uint(key_size, sizeof(int));
> __inner(values, struct inner_map);
> } outer_hash SEC(".maps") = {
> .values = {
> [0] = &inner_map2,
> [4] = &inner_map1,
> },
> };
I like the syntax (well, to the extent you can 'like' C syntax and its
esoteric (ab)uses), and am only mildly horrified at what it takes to
achieve it ;)
Acked-by: Toke Høiland-Jørgensen <toke@redhat.com>
next prev parent reply other threads:[~2020-04-28 11:03 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-04-28 6:41 [PATCH v2 bpf-next 0/3] Add BTF-defined map-in-map support to libbpf Andrii Nakryiko
2020-04-28 6:41 ` [PATCH v2 bpf-next 1/3] libbpf: refactor BTF-defined map definition parsing logic Andrii Nakryiko
2020-04-28 6:41 ` [PATCH v2 bpf-next 2/3] libbpf: refactor map creation logic and fix cleanup leak Andrii Nakryiko
2020-04-28 10:48 ` Toke Høiland-Jørgensen
2020-04-28 6:41 ` [PATCH v2 bpf-next 3/3] libbpf: add BTF-defined map-in-map support Andrii Nakryiko
2020-04-28 11:03 ` Toke Høiland-Jørgensen [this message]
2020-04-28 18:03 ` Alexei Starovoitov
2020-04-28 18:35 ` Andrii Nakryiko
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