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

["Daniel T. Lee" <danieltimlee@gmail.com>]

On Sat, Jun 27, 2020 at 5:30 AM Andrii Nakryiko
<andrii.nakryiko@gmail.com> wrote:
>
> On Fri, Jun 26, 2020 at 1:18 AM Daniel T. Lee <danieltimlee@gmail.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@gmail.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
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.

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;
> > +       }
> > +
>
> [...]