netdev - Re: [PATCH 3/3] samples: bpf: refactor BPF map in map test with libbpf

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Message-ID: <CAEf4BzZZxQr4QzTyL-6n0XE=aSBQFhLSNXU=aBxzu5tofgiVRA@mail.gmail.com>
Date:   Fri, 26 Jun 2020 15:19:18 -0700
From:   Andrii Nakryiko <andrii.nakryiko@...il.com>
To:     "Daniel T. Lee" <danieltimlee@...il.com>
Cc:     Daniel Borkmann <daniel@...earbox.net>,
        Alexei Starovoitov <ast@...nel.org>,
        Yonghong Song <yhs@...com>, Martin KaFai Lau <kafai@...com>,
        Andrii Nakryiko <andriin@...com>,
        Networking <netdev@...r.kernel.org>, bpf <bpf@...r.kernel.org>
Subject: Re: [PATCH 3/3] samples: bpf: refactor BPF map in map test with libbpf

On Fri, Jun 26, 2020 at 3:14 PM Daniel T. Lee <danieltimlee@...il.com> wrote:
>
> On Sat, Jun 27, 2020 at 5:30 AM Andrii Nakryiko
> <andrii.nakryiko@...il.com> wrote:
> >
> > On Fri, Jun 26, 2020 at 1:18 AM Daniel T. Lee <danieltimlee@...il.com> wrote:
> > >
> > > From commit 646f02ffdd49 ("libbpf: Add BTF-defined map-in-map
> > > support"), a way to define internal map in BTF-defined map has been
> > > added.
> > >
> > > Instead of using previous 'inner_map_idx' definition, the structure to
> > > be used for the inner map can be directly defined using array directive.
> > >
> > >     __array(values, struct inner_map)
> > >
> > > This commit refactors map in map test program with libbpf by explicitly
> > > defining inner map with BTF-defined format.
> > >
> > > Signed-off-by: Daniel T. Lee <danieltimlee@...il.com>
> > > ---
> >
> > Thanks for the clean up, looks good except that prog NULL check.
> >
>
> I'll fix this NULL check as well too.
>
> > It also seems like this is the last use of bpf_map_def_legacy, do you
> > mind removing it as well?
> >
>
> Actually, there is one more place that uses bpf_map_def_legacy.
> map_perf_test_kern.c is the one, and I'm currently working on it, but
> I'm having difficulty with refactoring this file at the moment.
>
> It has a hash_map map definition named inner_lru_hash_map with
> BPF_F_NUMA_NODE flag and '.numa_node = 0'.
>
> The bpf_map_def in libbpf has the attribute name map_flags but
> it does not have the numa_node attribute. Because the numa node

It does since 1 or 2 days ago ([0])

  [0] https://patchwork.ozlabs.org/project/netdev/patch/20200621062112.3006313-1-andriin@fb.com/


> for bpf_map_def cannot be explicitly specified, this means that there
> is no way to set the numa node where the map will be placed at the
> time of bpf_object__load.
>
> The only approach currently available is not to use libbbpf to handle
> everything (bpf_object_load), but instead to create a map directly with
> specifying numa node (bpf_load approach).
>
>     bpf_create_map_in_map_node
>     bpf_create_map_node
>
> I'm trying to stick with the libbpf implementation only, and I'm wondering
> If I have to create bpf maps manually at _user.c program.
>
> Any advice and suggestions will be greatly appreciated.
>

It should be super straightforward now with a BTF-defined map
supporting numa_node attribute.

> Thanks for your time and effort for the review.
> Daniel.
>
> >
> > >  samples/bpf/Makefile               |  2 +-
> > >  samples/bpf/test_map_in_map_kern.c | 85 +++++++++++++++---------------
> > >  samples/bpf/test_map_in_map_user.c | 53 +++++++++++++++++--
> > >  3 files changed, 91 insertions(+), 49 deletions(-)
> > >
> >
> > [...]
> >
> > >
> > >         snprintf(filename, sizeof(filename), "%s_kern.o", argv[0]);
> > > +       obj = bpf_object__open_file(filename, NULL);
> > > +       if (libbpf_get_error(obj)) {
> >
> > this is right, but...
> >
> > > +               fprintf(stderr, "ERROR: opening BPF object file failed\n");
> > > +               return 0;
> > > +       }
> > >
> > > -       if (load_bpf_file(filename)) {
> > > -               printf("%s", bpf_log_buf);
> > > -               return 1;
> > > +       prog = bpf_object__find_program_by_name(obj, "trace_sys_connect");
> > > +       if (libbpf_get_error(prog)) {
> >
> > this is wrong. Just NULL check. libbpf APIs are not very consistent
> > with what they return, unfortunately.
> >
> > > +               printf("finding a prog in obj file failed\n");
> > > +               goto cleanup;
> > > +       }
> > > +
> >
> > [...]