On Wed, Aug 27, 2025 at 9:46 AM Leon Hwang <leon.hwang@xxxxxxxxx> wrote:
>
> Add libbpf support for the BPF_F_CPU flag for percpu maps by embedding the
> cpu info into the high 32 bits of:
>
> 1. **flags**: bpf_map_lookup_elem_flags(), bpf_map__lookup_elem(),
> bpf_map_update_elem() and bpf_map__update_elem()
> 2. **opts->elem_flags**: bpf_map_lookup_batch() and
> bpf_map_update_batch()
>
> And the flag can be BPF_F_ALL_CPUS, but cannot be
> 'BPF_F_CPU | BPF_F_ALL_CPUS'.
>
> Behavior:
>
> * If the flag is BPF_F_ALL_CPUS, the update is applied across all CPUs.
> * If the flag is BPF_F_CPU, it updates value only to the specified CPU.
> * If the flag is BPF_F_CPU, lookup value only from the specified CPU.
> * lookup does not support BPF_F_ALL_CPUS.
>
> Signed-off-by: Leon Hwang <leon.hwang@xxxxxxxxx>
> ---
> tools/lib/bpf/bpf.h | 8 ++++++++
> tools/lib/bpf/libbpf.c | 33 +++++++++++++++++++++++++++------
> tools/lib/bpf/libbpf.h | 21 ++++++++-------------
> 3 files changed, 43 insertions(+), 19 deletions(-)
>
[...]
> @@ -10629,6 +10629,27 @@ static int validate_map_op(const struct bpf_map *map, size_t key_sz,
> case BPF_MAP_TYPE_PERCPU_CGROUP_STORAGE: {
> int num_cpu = libbpf_num_possible_cpus();
> size_t elem_sz = roundup(map->def.value_size, 8);
> + __u32 cpu;
> +
> + if (flags & (BPF_F_CPU | BPF_F_ALL_CPUS)) {
> + if ((flags & BPF_F_CPU) && (flags & BPF_F_ALL_CPUS)) {
> + pr_warn("map '%s': can't use BPF_F_CPU and BPF_F_ALL_CPUS at the same time\n",
> + map->name);
> + return -EINVAL;
> + }
> + cpu = flags >> 32;
> + if (cpu >= num_cpu) {
only check this if BPF_F_CPU is set
> + pr_warn("map '%s': cpu %u in flags cannot be GE num cpus %d\n",
"GE"? maybe "CPU #%d is not valid"... (or don't even check cpu value
itself, it's unlikely user using BPF_F_CPU will get it so wrong)
[...]
