On Sat Mar 21, 2026 at 9:01 PM EDT, Emil Tsalapatis wrote: > 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? >
I misread the selftests, my bad. The tests pass fine, and we just have to keep an owning reference of the nodes around to pass to the helpers. Reviewed-by: Emil Tsalapatis <[email protected]> >> >> 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 *). */
