Re: [PATCH 1/2] block: add BPF kfuncs to read blkcg io.stat

[Tejun Heo <tj@kernel.org>]

Hello,

On Fri, Aug 07, 2026 at 12:37:31PM -0700, Ziyang Men wrote:
> +__bpf_kfunc struct blkcg *bpf_get_root_blkcg(void)
> +__bpf_kfunc struct blkcg *bpf_get_blkcg(struct cgroup_subsys_state *css)
> +__bpf_kfunc void bpf_put_blkcg(struct blkcg *blkcg)
> +__bpf_kfunc void bpf_blkcg_flush_stats(struct blkcg *blkcg)

I wonder whether making the above deal with css's would make more sense so
that we don't end up with per-subsystem iterators. If casting to per-subsys
type is necessary, we can provide RCU protected cast kfucns.

> +__bpf_kfunc u64 bpf_blkg_iostat_bytes(struct blkcg_gq *blkg,
> +				      enum blkg_iostat_type rw)
> +__bpf_kfunc u64 bpf_blkg_iostat_ios(struct blkcg_gq *blkg,
> +				    enum blkg_iostat_type rw)
> +__bpf_kfunc u64 bpf_blkg_dev(struct blkcg_gq *blkg)

Ignoring 32bit split reads (do we really care for BPF accesses?), the above
can easily be done with BPF_CORE_READ(), right?

Thanks.

-- 
tejun