Chengkaitao <[email protected]> writes:
> 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.
>
> In previous versions, to implement the above functionality, it was
> 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.
>
> Signed-off-by: Kaitao Cheng <[email protected]>
> ---
> kernel/bpf/helpers.c | 41 +++++++++++++++++++++++++++++++++++++++++
> kernel/bpf/verifier.c | 15 +++++++++++++--
> 2 files changed, 54 insertions(+), 2 deletions(-)
>
> diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c
> index 188840057c7d..2b9f30a36c63 100644
> --- a/kernel/bpf/helpers.c
> +++ b/kernel/bpf/helpers.c
> @@ -2521,6 +2521,44 @@ __bpf_kfunc int bpf_list_add_impl(struct bpf_list_head
> *head,
> return -EINVAL;
> }
>
> +__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 *n = (struct bpf_list_node_kern *)node;
> +
> + if (unlikely(!h->next) || list_empty(h))
> + return false;
Do we need this block?
It sounds like a problem if we end up in the situation where
node->owner points to the uninitialized head - the list is corrupted.
> +
> + if (READ_ONCE(n->owner) != head)
> + return false;
> +
> + return h->next == &n->list_head;
Can we reuse list_is_first() here for simplicity?
> +}
> +
> +__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 *n = (struct bpf_list_node_kern *)node;
> +
> + if (unlikely(!h->next) || list_empty(h))
> + return false;
> +
> + if (READ_ONCE(n->owner) != head)
> + return false;
> +
> + return h->prev == &n->list_head;
Here maybe list_is_last() going to work as well?
> +}
> +
> +__bpf_kfunc bool bpf_list_empty(struct bpf_list_head *head)
> +{
> + struct list_head *h = (struct list_head *)head;
> +
> + if (unlikely(!h->next))
> + return true;
> +
> + return list_empty(h);
> +}
> +
> __bpf_kfunc struct bpf_rb_node *bpf_rbtree_remove(struct bpf_rb_root *root,
> struct bpf_rb_node *node)
> {
> @@ -4591,6 +4629,9 @@ 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 197b972e79a2..e97c7e11bf65 100644
> --- a/kernel/bpf/verifier.c
> +++ b/kernel/bpf/verifier.c
> @@ -12465,6 +12465,9 @@ enum special_kfunc_type {
> KF_bpf_list_front,
> KF_bpf_list_back,
> KF_bpf_list_add_impl,
> + 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,
> @@ -12527,6 +12530,9 @@ BTF_ID(func, bpf_list_del)
> BTF_ID(func, bpf_list_front)
> BTF_ID(func, bpf_list_back)
> BTF_ID(func, bpf_list_add_impl)
> +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)
> @@ -13003,7 +13009,10 @@ static bool is_bpf_list_api_kfunc(u32 btf_id)
> btf_id == special_kfunc_list[KF_bpf_list_del] ||
> btf_id == special_kfunc_list[KF_bpf_list_front] ||
> btf_id == special_kfunc_list[KF_bpf_list_back] ||
> - btf_id == special_kfunc_list[KF_bpf_list_add_impl];
> + btf_id == special_kfunc_list[KF_bpf_list_add_impl] ||
> + btf_id == special_kfunc_list[KF_bpf_list_is_first] ||
> + btf_id == special_kfunc_list[KF_bpf_list_is_last] ||
> + btf_id == special_kfunc_list[KF_bpf_list_empty];
> }
>
> static bool is_bpf_rbtree_api_kfunc(u32 btf_id)
> @@ -13126,7 +13135,9 @@ static bool check_kfunc_is_graph_node_api(struct
> bpf_verifier_env *env,
> ret = (kfunc_btf_id ==
> special_kfunc_list[KF_bpf_list_push_front_impl] ||
> kfunc_btf_id ==
> special_kfunc_list[KF_bpf_list_push_back_impl] ||
> kfunc_btf_id == special_kfunc_list[KF_bpf_list_del] ||
> - kfunc_btf_id ==
> special_kfunc_list[KF_bpf_list_add_impl]);
> + kfunc_btf_id == special_kfunc_list[KF_bpf_list_add_impl]
> ||
> + kfunc_btf_id == special_kfunc_list[KF_bpf_list_is_first]
> ||
> + kfunc_btf_id == special_kfunc_list[KF_bpf_list_is_last]);
> break;
> case BPF_RB_NODE:
> ret = (kfunc_btf_id == special_kfunc_list[KF_bpf_rbtree_remove]
> ||
> --
> 2.50.1 (Apple Git-155)
