netdev - Re: [PATCH bpf-next] bpf: Add LINK_DETACH for iter and perf links

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Message-ID: <3381e84d-2027-489a-b3e6-7ee16e2b14a2@linux.dev>
Date: Wed, 6 Aug 2025 11:44:23 -0700
From: Yonghong Song <yonghong.song@...ux.dev>
To: Florian Lehner <dev@...-flo.net>
Cc: bpf@...r.kernel.org, ast@...nel.org, daniel@...earbox.net,
 andrii@...nel.org, martin.lau@...ux.dev, eddyz87@...il.com, song@...nel.org,
 john.fastabend@...il.com, kpsingh@...nel.org, sdf@...ichev.me,
 haoluo@...gle.com, jolsa@...nel.org, davem@...emloft.net, kuba@...nel.org,
 hawk@...nel.org, netdev@...r.kernel.org
Subject: Re: [PATCH bpf-next] bpf: Add LINK_DETACH for iter and perf links



On 8/6/25 11:38 AM, Florian Lehner wrote:
> On Tue, Aug 05, 2025 at 02:07:20PM -0700, Yonghong Song wrote:
>>
>> On 8/1/25 5:10 AM, Florian Lehner wrote:
>>> 73b11c2a introduced LINK_DETACH and implemented it for some link types,
>>> like xdp, netns and others.
>>>
>>> This patch implements LINK_DETACH for perf and iter links, re-using
>>> existing link release handling code.
> [..]
>>>    static void bpf_iter_link_dealloc(struct bpf_link *link)
>>>    {
>>>    	struct bpf_iter_link *iter_link =
>>> @@ -490,6 +496,7 @@ static int bpf_iter_link_fill_link_info(const struct bpf_link *link,
>>>    static const struct bpf_link_ops bpf_iter_link_lops = {
>>>    	.release = bpf_iter_link_release,
>>> +	.detach = bpf_iter_link_detach,
>> Not sure how useful for this one. For bpf_iter programs,
>> the loaded prog will expect certain bpt_iter (e.g., bpf_map_elem, bpf_map, ...).
>> So even if you have detach, you won't be able to attach to a different
>> bpf_iter flavor.
>>
>> Do you have a use case for this one?
>>
> A key reason for adding this was to enable the temporary disabling and re-enabling of
> an attached BPF program while keeping the same bpf_iter flavor. If you don't think
> this is a strong enough use case, I'm open to removing this from the patch.
>
>>>    static void bpf_perf_link_dealloc(struct bpf_link *link)
>>>    {
>>>    	struct bpf_perf_link *perf_link = container_of(link, struct bpf_perf_link, link);
>>> @@ -4027,6 +4033,7 @@ static void bpf_perf_link_show_fdinfo(const struct bpf_link *link,
>>>    static const struct bpf_link_ops bpf_perf_link_lops = {
>>>    	.release = bpf_perf_link_release,
>>> +	.detach = bpf_perf_link_detach,
>> This one may be possible. You might be able to e.g., try a different bpf_cookie, or
>> different perf event.
>>
> The primary use case for this feature is to allow for the temporary disabling of
> uprobes that are attached using bpf_perf_links.

Okay, you patch looks good to me.

Acked-by: Yonghong Song <yonghong.song@...ux.dev>