RE: [PATCH bpf-next 3/8] libbpf: further decouple feature checking logic from bpf_object
From: John Fastabend <john.fastabend@gmail.com>
Date: 2023-12-11 21:41:02
Also in:
bpf, linux-fsdevel, linux-security-module
Andrii Nakryiko wrote:
Add feat_supported() helper that accepts feature cache instead of bpf_object. This allows low-level code in bpf.c to not know or care about higher-level concept of bpf_object, yet it will be able to utilize custom feature checking in cases where BPF token might influence the outcome. Signed-off-by: Andrii Nakryiko <andrii@kernel.org> ---
...
quoted hunk ↗ jump to hunk
diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c index a6b8d6f70918..af5e777efcbd 100644 --- a/tools/lib/bpf/libbpf.c +++ b/tools/lib/bpf/libbpf.c@@ -637,6 +637,7 @@ struct elf_state { }; struct usdt_manager; +struct kern_feature_cache; struct bpf_object { char name[BPF_OBJ_NAME_LEN];@@ -5063,17 +5064,14 @@ static struct kern_feature_desc { }, }; -bool kernel_supports(const struct bpf_object *obj, enum kern_feature_id feat_id) +bool feat_supported(struct kern_feature_cache *cache, 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) - /* To generate loader program assume the latest kernel - * to avoid doing extra prog_load, map_create syscalls. - */ - return true; + /* assume global feature cache, unless custom one is provided */ + if (!cache) + cache = &feature_cache;
Why expose a custom cache at all? Where would that be used? I guess we are looking at libbpf_internal APIs so maybe not a big deal.
quoted hunk ↗ jump to hunk
if (READ_ONCE(cache->res[feat_id]) == FEAT_UNKNOWN) { ret = feat->probe();@@ -5090,6 +5088,17 @@ bool kernel_supports(const struct bpf_object *obj, enum kern_feature_id feat_id) return READ_ONCE(cache->res[feat_id]) == FEAT_SUPPORTED; }
Acked-by: John Fastabend <john.fastabend@gmail.com>