On 7/27/24 8:01 PM, Amery Hung wrote:
This series allows stashing kptr into local kptr. Currently, kptrs are only allowed to be stashed into map value with bpf_kptr_xchg(). A motivating use case of this series is to enable adding referenced kptr to bpf_rbtree or bpf_list by using allocated object as graph node and the storage of referenced kptr. For example, a bpf qdisc [0] enqueuing a referenced kptr to a struct sk_buff* to a bpf_list serving as a fifo: struct skb_node { struct sk_buff __kptr *skb; struct bpf_list_node node; }; private(A) struct bpf_spin_lock fifo_lock; private(A) struct bpf_list_head fifo __contains(skb_node, node); /* In Qdisc_ops.enqueue */ struct skb_node *skbn; skbn = bpf_obj_new(typeof(*skbn)); if (!skbn) goto drop; /* skb is a referenced kptr to struct sk_buff acquired earilier * but not shown in this code snippet. */ skb = bpf_kptr_xchg(&skbn->skb, skb); if (skb) /* should not happen; do something below releasing skb to * satisfy the verifier */ ...bpf_spin_lock(&fifo_lock);bpf_list_push_back(&fifo, &skbn->node); bpf_spin_unlock(&fifo_lock); The implementation first searches for BPF_KPTR when generating program BTF. Then, we teach the verifier that the detination argument of bpf_kptr_xchg() can be local kptr, and use the btf_record in program BTF to check against the source argument. This series is mostly developed by Dave, who kindly helped and sent me the patchset. The selftests in bpf qdisc (WIP) relies on this series to work.
The set lgtm. With the doc fix in the bpf_kptr_xchg, you can carry my Ack. Acked-by: Martin KaFai Lau <martin.lau@xxxxxxxxxx>
