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libbpf: Probe percpu data feature

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libbpf needs a reliable way to distinguish kernels that can support
global percpu data from those that cannot.

Add a dedicated feature probe, so libbpf can make capability decisions
early and fail predictably when global percpu data is unavailable.

Signed-off-by: Leon Hwang <leon.hwang@linux.dev>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Reviewed-by: Emil Tsalapatis <emil@etsalapatis.com>
Acked-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20260813152324.97937-5-leon.hwang@linux.dev
This commit is contained in:
Leon Hwang 2026-08-13 23:23:17 +08:00 committed by Andrii Nakryiko
parent 6e61f4f8b0
commit 3634e4f2dc
2 changed files with 37 additions and 0 deletions
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35
tools/lib/bpf/features.c
View File

@ -620,6 +620,38 @@ static int probe_bpf_syscall_common_attrs(int token_fd)
return probe_sys_bpf_ext();
}
static int probe_kern_percpu_data(int token_fd)
{
struct bpf_insn insns[] = {
BPF_LD_MAP_VALUE(BPF_REG_1, 0, 0),
BPF_LDX_MEM(BPF_DW, BPF_REG_0, BPF_REG_1, 0),
BPF_EXIT_INSN(),
};
LIBBPF_OPTS(bpf_map_create_opts, map_opts,
.token_fd = token_fd,
.map_flags = token_fd ? BPF_F_TOKEN_FD : 0,
);
LIBBPF_OPTS(bpf_prog_load_opts, prog_opts,
.token_fd = token_fd,
.prog_flags = token_fd ? BPF_F_TOKEN_FD : 0,
);
int ret, map, insn_cnt = ARRAY_SIZE(insns);
map = bpf_map_create(BPF_MAP_TYPE_PERCPU_ARRAY, "libbpf_percpu", sizeof(int), 8, 1,
&map_opts);
if (map < 0) {
pr_warn("Error in %s(): %s. Couldn't create simple percpu_array map.\n",
__func__, errstr(map));
return map;
}
insns[0].imm = map;
ret = bpf_prog_load(BPF_PROG_TYPE_SOCKET_FILTER, NULL, "GPL", insns, insn_cnt, &prog_opts);
close(map);
return probe_fd(ret);
}
typedef int (*feature_probe_fn)(int /* token_fd */);
static struct kern_feature_cache feature_cache;
@ -707,6 +739,9 @@ static struct kern_feature_desc {
[FEAT_BPF_SYSCALL_COMMON_ATTRS] = {
"BPF syscall common attributes support", probe_bpf_syscall_common_attrs,
},
[FEAT_PERCPU_DATA] = {
"kernel supports percpu data", probe_kern_percpu_data,
},
};
bool feat_supported(struct kern_feature_cache *cache, enum kern_feature_id feat_id)

2
tools/lib/bpf/libbpf_internal.h
View File

@ -401,6 +401,8 @@ enum kern_feature_id {
FEAT_BTF_LAYOUT,
/* Kernel supports BPF syscall common attributes */
FEAT_BPF_SYSCALL_COMMON_ATTRS,
/* Kernel supports percpu data */
FEAT_PERCPU_DATA,
__FEAT_CNT,
};