From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-173.mta1.migadu.com (out-173.mta1.migadu.com [95.215.58.173]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 474D736654B for ; Wed, 4 Mar 2026 03:30:23 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=95.215.58.173 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1772595025; cv=none; b=A15qaA+56r6Fox9qDKGEj6sZK165KF3s6RfqrvE69+y1TOvbHJTvD5oL1xPN7DruiObB30Q3HvCM96KPf+qd8b3Lp5z4QjMUb7oixShbUysgtloqQ4gOcSAFgFxK0Fi79+ks2zGIY5BRiTsxsPORXqxQQTYE3m3o/Wy08EGcCYQ= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1772595025; c=relaxed/simple; bh=bDCY9qCxVKnxLg3h4cj0UKd9B7rYQLhMIbEpt8gfe6A=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=EJbjRhlU56qUl9c7Rfs2Adlet8oX4/1MFxvHjBGBqYiQHZmAHpBya6Tlr6Pu7WHCBmzIlywoEpk9MSjfiCj3VTlI40jEUp4xuidchay/8BsbOhvC0GLGOA5EEifqAKTpSrnqIilpp45M1AuUfxklN/swu6SL5OkZCFKWDstFBio= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b=G0AdRvAo; arc=none smtp.client-ip=95.215.58.173 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b="G0AdRvAo" Message-ID: <37bdb73c-095b-4239-806b-8ea51a2d27a5@linux.dev> DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1772595021; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=IF19acMeWMRHcUxQEGDqRzSYniGKihuY5dnjFgK3H60=; b=G0AdRvAo7QD7wr9mBKAD7wEFsfqbfNKYvOr4+My07wQRoohB7N07BRrbtL7EWuZoEBQw0i KeXF0itWiJf0DjM2VnH0BYW1pjKdHqw8yMFOSlcG7LjoUZN0Cy0sMQZeRVhrfXSrEvSfcH jkqKGt+T+AntkWyR97oQwxUQ7BcYq7g= Date: Wed, 4 Mar 2026 11:30:07 +0800 Precedence: bulk X-Mailing-List: linux-kselftest@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Subject: Re: [PATCH v4 5/6] bpf: add bpf_list_is_first/last/empty kfuncs Content-Language: en-US To: Chengkaitao , martin.lau@linux.dev, ast@kernel.org, daniel@iogearbox.net, andrii@kernel.org, eddyz87@gmail.com, song@kernel.org, yonghong.song@linux.dev, john.fastabend@gmail.com, kpsingh@kernel.org, sdf@fomichev.me, haoluo@google.com, jolsa@kernel.org, shuah@kernel.org, chengkaitao@kylinos.cn, linux-kselftest@vger.kernel.org Cc: bpf@vger.kernel.org, linux-kernel@vger.kernel.org References: <20260303135219.33726-1-pilgrimtao@gmail.com> <20260303135219.33726-6-pilgrimtao@gmail.com> X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Leon Hwang In-Reply-To: <20260303135219.33726-6-pilgrimtao@gmail.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Migadu-Flow: FLOW_OUT On 3/3/26 21:52, Chengkaitao wrote: > From: Kaitao Cheng > > 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 > --- > 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 488810da8f30..3a64a9bab06b 100644 > --- a/kernel/bpf/helpers.c > +++ b/kernel/bpf/helpers.c > @@ -2523,6 +2523,44 @@ __bpf_kfunc int bpf_list_add_impl(struct bpf_list_head *head, > return 0; > } > > +__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; > + > + if (READ_ONCE(n->owner) != head) > + return false; > + > + return h->next == &n->list_head; > +} > + > +__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; > +} > + bpf_list_is_first() and bpf_list_is_last() are nearly identical. The duplicated code should be avoided. > +__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; NIT: A comment here explaining why !h->next returns true would be helpful. Thanks, Leon > + > + return list_empty(h); > +} > + > __bpf_kfunc struct bpf_rb_node *bpf_rbtree_remove(struct bpf_rb_root *root, > struct bpf_rb_node *node) > { > @@ -4593,6 +4631,9 @@ 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 6dfd4afff1cf..78652ccd2a89 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] ||