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libbpf: Add BPF_F_CPU and BPF_F_ALL_CPUS flags support for percpu maps

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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.

Acked-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Leon Hwang <leon.hwang@linux.dev>
Link: https://lore.kernel.org/r/20260107022022.12843-7-leon.hwang@linux.dev
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
This commit is contained in:
Leon Hwang
2026-01-07 10:20:21 +08:00
committed by Andrii Nakryiko
parent a6d7ceaaeb
commit dc8673b28b
3 changed files with 36 additions and 19 deletions
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21
src/libbpf.h
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@@ -1216,12 +1216,13 @@ LIBBPF_API struct bpf_map *bpf_map__inner_map(struct bpf_map *map);
* @param key_sz size in bytes of key data, needs to match BPF map definition's **key_size**
* @param value pointer to memory in which looked up value will be stored
* @param value_sz size in byte of value data memory; it has to match BPF map
* definition's **value_size**. For per-CPU BPF maps value size has to be
* a product of BPF map value size and number of possible CPUs in the system
* (could be fetched with **libbpf_num_possible_cpus()**). Note also that for
* per-CPU values value size has to be aligned up to closest 8 bytes for
* alignment reasons, so expected size is: `round_up(value_size, 8)
* * libbpf_num_possible_cpus()`.
* definition's **value_size**. For per-CPU BPF maps, value size can be
* `value_size` if either **BPF_F_CPU** or **BPF_F_ALL_CPUS** is specified
* in **flags**, otherwise a product of BPF map value size and number of
* possible CPUs in the system (could be fetched with
* **libbpf_num_possible_cpus()**). Note also that for per-CPU values value
* size has to be aligned up to closest 8 bytes, so expected size is:
* `round_up(value_size, 8) * libbpf_num_possible_cpus()`.
* @param flags extra flags passed to kernel for this operation
* @return 0, on success; negative error, otherwise
*
@@ -1239,13 +1240,7 @@ LIBBPF_API int bpf_map__lookup_elem(const struct bpf_map *map,
* @param key pointer to memory containing bytes of the key
* @param key_sz size in bytes of key data, needs to match BPF map definition's **key_size**
* @param value pointer to memory containing bytes of the value
* @param value_sz size in byte of value data memory; it has to match BPF map
* definition's **value_size**. For per-CPU BPF maps value size has to be
* a product of BPF map value size and number of possible CPUs in the system
* (could be fetched with **libbpf_num_possible_cpus()**). Note also that for
* per-CPU values value size has to be aligned up to closest 8 bytes for
* alignment reasons, so expected size is: `round_up(value_size, 8)
* * libbpf_num_possible_cpus()`.
* @param value_sz refer to **bpf_map__lookup_elem**'s description.'
* @param flags extra flags passed to kernel for this operation
* @return 0, on success; negative error, otherwise
*