On Thu, Mar 13, 2025 at 12:03 PM Amery Hung <ameryhung@xxxxxxxxx> wrote:
>
> From: Amery Hung <amery.hung@xxxxxxxxxxxxx>
>
> Add basic kfuncs for working on skb in qdisc.
>
> Both bpf_qdisc_skb_drop() and bpf_kfree_skb() can be used to release
> a reference to an skb. However, bpf_qdisc_skb_drop() can only be called
> in .enqueue where a to_free skb list is available from kernel to defer
> the release. bpf_kfree_skb() should be used elsewhere. It is also used
> in bpf_obj_free_fields() when cleaning up skb in maps and collections.
>
> bpf_skb_get_hash() returns the flow hash of an skb, which can be used
> to build flow-based queueing algorithms.
>
> Finally, allow users to create read-only dynptr via bpf_dynptr_from_skb().
>
> Signed-off-by: Amery Hung <amery.hung@xxxxxxxxxxxxx>
> ---
> include/linux/bpf.h | 1 +
> kernel/bpf/bpf_struct_ops.c | 2 +
> net/sched/bpf_qdisc.c | 93 ++++++++++++++++++++++++++++++++++++-
> 3 files changed, 95 insertions(+), 1 deletion(-)
>
> diff --git a/include/linux/bpf.h b/include/linux/bpf.h
> index 463e922cb0f5..d3b0c4ccaebf 100644
> --- a/include/linux/bpf.h
> +++ b/include/linux/bpf.h
> @@ -1826,6 +1826,7 @@ struct bpf_struct_ops {
> void *cfi_stubs;
> struct module *owner;
> const char *name;
> + const struct btf_type *type;
> struct btf_func_model func_models[BPF_STRUCT_OPS_MAX_NR_MEMBERS];
> };
there is an alternative to this...
> +static int bpf_qdisc_kfunc_filter(const struct bpf_prog *prog, u32 kfunc_id)
> +{
> + if (bpf_Qdisc_ops.type != btf_type_by_id(prog->aux->attach_btf,
> + prog->aux->attach_btf_id))
> + return 0;
> +
> + /* Skip the check when prog->attach_func_name is not yet available
> + * during check_cfg().
> + */
> + if (!btf_id_set8_contains(&qdisc_kfunc_ids, kfunc_id) ||
> + !prog->aux->attach_func_name)
> + return 0;
> +
> + if (bpf_struct_ops_prog_moff(prog) == offsetof(struct Qdisc_ops, enqueue)) {
> + if (btf_id_set_contains(&qdisc_enqueue_kfunc_set, kfunc_id))
> + return 0;
> + }
Instead of logic in this patch and patch 2,
I think it's cleaner to do:
https://lore.kernel.org/all/AM6PR03MB50804BE76B752350307B6B4C99C22@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx/
then in this patch it will be
if (prog->aux->st_ops != &bpf_Qdisc_ops)
and instead of unchecked array accesses in bpf_struct_ops_prog_moff()
it will be prog->aux->attach_st_ops_member_off
Also see flag based approach in Juntong's patch 3+4.
imo it looks cleaner (more extensible with more checks per st_ops hook)
than offsetof() approach above.
