On Mon, Mar 4, 2024 at 2:52 PM Eduard Zingerman <eddyz87@xxxxxxxxx> wrote:
>
> Skip load steps for struct_ops maps not marked for automatic creation.
> This should allow to load bpf object in situations like below:
>
> SEC("struct_ops/foo") int BPF_PROG(foo) { ... }
> SEC("struct_ops/bar") int BPF_PROG(bar) { ... }
>
> struct test_ops___v1 {
> int (*foo)(void);
> };
>
> struct test_ops___v2 {
> int (*foo)(void);
> int (*does_not_exist)(void);
> };
>
> SEC(".struct_ops.link")
> struct test_ops___v1 map_for_old = {
> .test_1 = (void *)foo
> };
>
> SEC(".struct_ops.link")
> struct test_ops___v2 map_for_new = {
> .test_1 = (void *)foo,
> .does_not_exist = (void *)bar
> };
>
> Suppose program is loaded on old kernel that does not have definition
> for 'does_not_exist' struct_ops member. After this commit it would be
> possible to load such object file after the following tweaks:
>
> bpf_program__set_autoload(skel->progs.bar, false);
> bpf_map__set_autocreate(skel->maps.map_for_new, false);
>
> Acked-by: David Vernet <void@xxxxxxxxxxxxx>
> Signed-off-by: Eduard Zingerman <eddyz87@xxxxxxxxx>
> ---
> tools/lib/bpf/libbpf.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
> index 2c0cb72bc7a4..25c452c20d7d 100644
> --- a/tools/lib/bpf/libbpf.c
> +++ b/tools/lib/bpf/libbpf.c
> @@ -1209,7 +1209,7 @@ static int bpf_object__init_kern_struct_ops_maps(struct bpf_object *obj)
> for (i = 0; i < obj->nr_maps; i++) {
> map = &obj->maps[i];
>
> - if (!bpf_map__is_struct_ops(map))
> + if (!bpf_map__is_struct_ops(map) || !map->autocreate)
tbh, I'd keep them as separate checks (they check very different
aspects, so feels appropriate to not combine them in one check)
> continue;
>
> err = bpf_map__init_kern_struct_ops(map);
> @@ -8136,7 +8136,7 @@ static int bpf_object_prepare_struct_ops(struct bpf_object *obj)
> int i;
>
> for (i = 0; i < obj->nr_maps; i++)
> - if (bpf_map__is_struct_ops(&obj->maps[i]))
> + if (bpf_map__is_struct_ops(&obj->maps[i]) && obj->maps[i].autocreate)
especially here, this becomes a bit convoluted
how about we make it a bit more verbose, but also straightforward
map = &obj->maps[i];
if (!bpf_map__is_struct_ops(map))
continue;
if (!map->autocreate)
continue;
bpf_map_prepare_vdata(...)
It will also mirror the structure in bpf_object__init_kern_struct_ops_maps()
> bpf_map_prepare_vdata(&obj->maps[i]);
>
> return 0;
> --
> 2.43.0
>
