[PATCH bpf-next 21/29] libbpf: split feature detectors definitions from cached results

Andrii Nakryiko
2024-01-03T22:23:50Z

Split a list of supported feature detectors with their corresponding
callbacks from actual cached supported/missing values. This will allow
to have more flexible per-token or per-object feature detectors in
subsequent refactorings.

Acked-by: John Fastabend <john.fastabend@gmail.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
---
tools/lib/bpf/libbpf.c | 18 ++++++++++++------
1 file changed, 12 insertions(+), 6 deletions(-)

diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index ebcfb2147fbd..95a7d459b842 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -5001,12 +5001,17 @@ enum kern_feature_result {
FEAT_MISSING = 2,
};

+struct kern_feature_cache {
+ enum kern_feature_result res[__FEAT_CNT];
+};
+
typedef int (*feature_probe_fn)(void);

+static struct kern_feature_cache feature_cache;
+
static struct kern_feature_desc {
const char *desc;
feature_probe_fn probe;
- enum kern_feature_result res;
} feature_probes[__FEAT_CNT] = {
[FEAT_PROG_NAME] = {
"BPF program name", probe_kern_prog_name,
@@ -5074,6 +5079,7 @@ static struct kern_feature_desc {
bool kernel_supports(const struct bpf_object *obj, enum kern_feature_id feat_id)
{
struct kern_feature_desc *feat = &feature_probes[feat_id];
+ struct kern_feature_cache *cache = &feature_cache;
int ret;

if (obj && obj->gen_loader)
@@ -5082,19 +5088,19 @@ bool kernel_supports(const struct bpf_object *obj, enum kern_feature_id feat_id)
*/
return true;

- if (READ_ONCE(feat->res) == FEAT_UNKNOWN) {
+ if (READ_ONCE(cache->res[feat_id]) == FEAT_UNKNOWN) {
ret = feat->probe();
if (ret > 0) {
- WRITE_ONCE(feat->res, FEAT_SUPPORTED);
+ WRITE_ONCE(cache->res[feat_id], FEAT_SUPPORTED);
} else if (ret == 0) {
- WRITE_ONCE(feat->res, FEAT_MISSING);
+ WRITE_ONCE(cache->res[feat_id], FEAT_MISSING);
} else {
pr_warn("Detection of kernel %s support failed: %d\n", feat->desc, ret);
- WRITE_ONCE(feat->res, FEAT_MISSING);
+ WRITE_ONCE(cache->res[feat_id], FEAT_MISSING);
}
}

- return READ_ONCE(feat->res) == FEAT_SUPPORTED;
+ return READ_ONCE(cache->res[feat_id]) == FEAT_SUPPORTED;
}

static bool map_is_reuse_compat(const struct bpf_map *map, int map_fd)
--
2.34.1