On Mon, Jun 22, 2026 at 7:37 AM Leon Hwang <[email protected]> wrote: > > 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 <[email protected]> > --- > tools/lib/bpf/features.c | 35 +++++++++++++++++++++++++++++++++ > tools/lib/bpf/libbpf_internal.h | 2 ++ > 2 files changed, 37 insertions(+) >
lgtm Acked-by: Andrii Nakryiko <[email protected]> > diff --git a/tools/lib/bpf/features.c b/tools/lib/bpf/features.c > index b7e388f99d0b..ef9581c11303 100644 > --- a/tools/lib/bpf/features.c > +++ b/tools/lib/bpf/features.c > @@ -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) > diff --git a/tools/lib/bpf/libbpf_internal.h b/tools/lib/bpf/libbpf_internal.h > index 04cd303fb5a8..47ae39125f68 100644 > --- a/tools/lib/bpf/libbpf_internal.h > +++ b/tools/lib/bpf/libbpf_internal.h > @@ -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, > }; > > -- > 2.54.0 >
