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

[Yonghong Song <yonghong.song@xxxxxxxxx>]

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}};
>    ...

What I mean is to add a selftest in tools/testing/selftests/bpf/ directory,
not a test with partial code in the commit message. You can add another
subtest in tools/testing/selftests/bpf/progs/map_in_map.c.

> 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)
>
> New behaviour:
>    # 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=16, 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) = 6
>    bpf(BPF_MAP_CREATE, {map_type=BPF_MAP_TYPE_ARRAY_OF_MAPS, key_size=4,
>      value_size=4, max_entries=2, map_flags=0, inner_map_fd=6,
>      map_name="outer_map", 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) = 7
>    bpf(BPF_MAP_UPDATE_ELEM, {map_fd=7, key=0x7ffc89f2de54,
>      value=0x7ffc89f2de58,flags=BPF_ANY}, 32) = 0
>    bpf(BPF_MAP_UPDATE_ELEM, {map_fd=7, key=0x7ffc89f2de54,
>      value=0x7ffc89f2de58, flags=BPF_ANY}, 32) = 0
>    ...
>    +++ exited with 0 +++
>
> Signed-off-by: Andrey Grafin <conquistador@xxxxxxxxxxxxxx>
> ---
>   tools/lib/bpf/libbpf.c | 4 ++++
>   1 file changed, 4 insertions(+)
>
> diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
> index e067be95da3c..8f4d580187aa 100644
> --- a/tools/lib/bpf/libbpf.c
> +++ b/tools/lib/bpf/libbpf.c
> @@ -70,6 +70,7 @@
>   
>   static struct bpf_map *bpf_object__add_map(struct bpf_object *obj);
>   static bool prog_is_subprog(const struct bpf_object *obj, const struct bpf_program *prog);
> +static int map_set_def_max_entries(struct bpf_map *map);
>   
>   static const char * const attach_type_name[] = {
>   	[BPF_CGROUP_INET_INGRESS]	= "cgroup_inet_ingress",
> @@ -5212,6 +5213,9 @@ static int bpf_object__create_map(struct bpf_object *obj, struct bpf_map *map, b
>   
>   	if (bpf_map_type__is_map_in_map(def->type)) {
>   		if (map->inner_map) {
> +			err = map_set_def_max_entries(map->inner_map);
> +			if (err)
> +				return err;
>   			err = bpf_object__create_map(obj, map->inner_map, true);
>   			if (err) {
>   				pr_warn("map '%s': failed to create inner map: %d\n",