On Mon Mar 16, 2026 at 7:28 AM EDT, Chengkaitao wrote: > From: Kaitao Cheng <[email protected]> > > Add three kfuncs for BPF linked list queries: > - bpf_list_is_first(head, node): true if node is the first in the list. > - bpf_list_is_last(head, node): true if node is the last in the list. > - bpf_list_empty(head): true if the list has no entries. > > Currently, without these kfuncs, to implement the above functionality > it is necessary to first call bpf_list_pop_front/back to retrieve the > first or last node before checking whether the passed-in node was the > first or last one. After the check, the node had to be pushed back into > the list using bpf_list_push_front/back, which was very inefficient. > > Now, with the bpf_list_is_first/last/empty kfuncs, we can directly > check whether a node is the first, last, or whether the list is empty, > without having to first retrieve the node.
Do you need to expand the exceptions you added in patch 5 for non-owning reference arguments to also hold for this? Checking the selftests, we don't have one where either bpf_list_is_last or bpf_list_is_first return true, can you add one? > > Signed-off-by: Kaitao Cheng <[email protected]> > --- > kernel/bpf/helpers.c | 38 ++++++++++++++++++++++++++++++++++++++ > kernel/bpf/verifier.c | 11 +++++++++++ > 2 files changed, 49 insertions(+) > > diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c > index dc4f8b4eec01..da70dcff4ba8 100644 > --- a/kernel/bpf/helpers.c > +++ b/kernel/bpf/helpers.c > @@ -2518,6 +2518,41 @@ __bpf_kfunc struct bpf_list_node *bpf_list_back(struct > bpf_list_head *head) > return (struct bpf_list_node *)h->prev; > } > > +__bpf_kfunc bool bpf_list_is_first(struct bpf_list_head *head, struct > bpf_list_node *node) > +{ > + struct list_head *h = (struct list_head *)head; > + struct bpf_list_node_kern *kn = (struct bpf_list_node_kern *)node; > + > + if (READ_ONCE(kn->owner) != head) > + return false; > + > + return list_is_first(&kn->list_head, h); > +} > + > +__bpf_kfunc bool bpf_list_is_last(struct bpf_list_head *head, struct > bpf_list_node *node) > +{ > + struct list_head *h = (struct list_head *)head; > + struct bpf_list_node_kern *kn = (struct bpf_list_node_kern *)node; > + > + if (READ_ONCE(kn->owner) != head) > + return false; > + > + return list_is_last(&kn->list_head, h); > +} > + > +__bpf_kfunc bool bpf_list_empty(struct bpf_list_head *head) > +{ > + struct list_head *h = (struct list_head *)head; > + > + /* If list_head was 0-initialized by map, bpf_obj_init_field wasn't > + * called on its fields, so init here > + */ > + if (unlikely(!h->next)) > + INIT_LIST_HEAD(h); > + > + return list_empty(h); > +} > + > __bpf_kfunc struct bpf_rb_node *bpf_rbtree_remove(struct bpf_rb_root *root, > struct bpf_rb_node *node) > { > @@ -4588,6 +4623,9 @@ BTF_ID_FLAGS(func, bpf_list_del, KF_ACQUIRE | > KF_RET_NULL) > BTF_ID_FLAGS(func, bpf_list_front, KF_RET_NULL) > BTF_ID_FLAGS(func, bpf_list_back, KF_RET_NULL) > BTF_ID_FLAGS(func, bpf_list_add_impl) > +BTF_ID_FLAGS(func, bpf_list_is_first) > +BTF_ID_FLAGS(func, bpf_list_is_last) > +BTF_ID_FLAGS(func, bpf_list_empty) > BTF_ID_FLAGS(func, bpf_task_acquire, KF_ACQUIRE | KF_RCU | KF_RET_NULL) > BTF_ID_FLAGS(func, bpf_task_release, KF_RELEASE) > BTF_ID_FLAGS(func, bpf_rbtree_remove, KF_ACQUIRE | KF_RET_NULL) > diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c > index 0a6f2e6a5d28..c2cc622bb3a1 100644 > --- a/kernel/bpf/verifier.c > +++ b/kernel/bpf/verifier.c > @@ -12512,6 +12512,9 @@ enum special_kfunc_type { > KF_bpf_list_del, > KF_bpf_list_front, > KF_bpf_list_back, > + KF_bpf_list_is_first, > + KF_bpf_list_is_last, > + KF_bpf_list_empty, > KF_bpf_cast_to_kern_ctx, > KF_bpf_rdonly_cast, > KF_bpf_rcu_read_lock, > @@ -12574,6 +12577,9 @@ BTF_ID(func, bpf_list_pop_back) > BTF_ID(func, bpf_list_del) > BTF_ID(func, bpf_list_front) > BTF_ID(func, bpf_list_back) > +BTF_ID(func, bpf_list_is_first) > +BTF_ID(func, bpf_list_is_last) > +BTF_ID(func, bpf_list_empty) > BTF_ID(func, bpf_cast_to_kern_ctx) > BTF_ID(func, bpf_rdonly_cast) > BTF_ID(func, bpf_rcu_read_lock) > @@ -12652,6 +12658,9 @@ static const enum special_kfunc_type > bpf_list_api_kfuncs[] = { > KF_bpf_list_del, > KF_bpf_list_front, > KF_bpf_list_back, > + KF_bpf_list_is_first, > + KF_bpf_list_is_last, > + KF_bpf_list_empty, > }; > > /* Kfuncs that take a list node argument (bpf_list_node *). */ > @@ -12660,6 +12669,8 @@ static const enum special_kfunc_type > bpf_list_node_api_kfuncs[] = { > KF_bpf_list_push_back_impl, > KF_bpf_list_add_impl, > KF_bpf_list_del, > + KF_bpf_list_is_first, > + KF_bpf_list_is_last, > }; > > /* Kfuncs that take an rbtree node argument (bpf_rb_node *). */
