Re: [PATCH bpf v2] libbpf: Apply map_set_def_max_entries() for inner_maps on creation

[Martin KaFai Lau <martin.lau@linux.dev>]

On 1/12/24 4:10 AM, Andrey Grafin wrote:
> This patch allows to create BPF_MAP_TYPE_ARRAY_OF_MAPS and
> BPF_MAP_TYPE_HASH_OF_MAPS with values of BPF_MAP_TYPE_PERF_EVENT_ARRAY.
> 
> Previous behaviour created a zero filled btf_map_def for inner maps and
> tried to use it for a map creation but the linux kernel forbids to create
> a BPF_MAP_TYPE_PERF_EVENT_ARRAY map with max_entries=0.
> 
> A simple bpf snippet to reproduce:
>    struct inner_map {
>      __uint(type, BPF_MAP_TYPE_PERF_EVENT_ARRAY);
>      __uint(key_size, sizeof(int));
>      __uint(value_size, sizeof(u32));
>    } inner_map0 SEC(".maps"), inner_map1 SEC(".maps");
> 
>    struct {
>      __uint(type, BPF_MAP_TYPE_ARRAY_OF_MAPS);
>      __uint(max_entries, 2);
>      __type(key, u32);
>      __array(values, struct inner_map);
>    } outer_map SEC(".maps") = {
>      .values = {&inner_map0, &inner_map1}};
>    ...
> 
> Previous behaviour:
>    # sudo bpftool prog load ./bpf_sample.elf /sys/fs/bpf/test
>      libbpf: map 'outer_map': failed to create inner map: -22
>      libbpf: map 'outer_map': failed to create: Invalid argument(-22)
>      libbpf: failed to load object './bpf_sample.elf'
>      Error: failed to load object file
> 
>    # sudo strace -e bpf bpftool prog load ./bpf_sample.elf /sys/fs/bpf/test
>    ...
>    bpf(BPF_MAP_CREATE, {map_type=BPF_MAP_TYPE_PERF_EVENT_ARRAY, key_size=4,
>      value_size=4, max_entries=16, map_flags=0, inner_map_fd=0,
>      map_name="inner_map0", map_ifindex=0, btf_fd=0, btf_key_type_id=0,
>      btf_value_type_id=0, btf_vmlinux_value_type_id=0, map_extra=0}, 72) = 4
>    bpf(BPF_MAP_CREATE, {map_type=BPF_MAP_TYPE_PERF_EVENT_ARRAY, key_size=4,
>      value_size=4, max_entries=16, map_flags=0, inner_map_fd=0,
>      map_name="inner_map1", map_ifindex=0, btf_fd=0, btf_key_type_id=0,
>      btf_value_type_id=0, btf_vmlinux_value_type_id=0, map_extra=0}, 72) = 5
>    bpf(BPF_MAP_CREATE, {map_type=BPF_MAP_TYPE_PERF_EVENT_ARRAY, key_size=4,
>      value_size=4, max_entries=0, map_flags=0, inner_map_fd=0,
>      map_name="outer_map.inner", map_ifindex=0, btf_fd=0,
>      btf_key_type_id=0, btf_value_type_id=0, btf_vmlinux_value_type_id=0,
>      map_extra=0}, 72) = -1 EINVAL (Invalid argument)

The change makes sense. Please help to add a real selftest to catch future 
regression. I believe it is what Yonghong has already asked in v1. Some of the 
existing "progs/*map_in_map*.c" may be a good candidate to add this test case.

pw-bot: cr