linux-kernel - Re: [PATCH bpf-next v2 0/4] Add wakeup

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Message-ID: <CAG2KctpugdYJ5_pGnc+DNLRQb=3NiGRBhzb5DK8Chb=hgmHaGg@mail.gmail.com>
Date: Wed, 21 Jan 2026 15:27:13 -0800
From: Samuel Wu <wusamuel@...gle.com>
To: Andrii Nakryiko <andrii.nakryiko@...il.com>
Cc: Alexei Starovoitov <ast@...nel.org>, Daniel Borkmann <daniel@...earbox.net>, 
	Andrii Nakryiko <andrii@...nel.org>, Martin KaFai Lau <martin.lau@...ux.dev>, 
	Eduard Zingerman <eddyz87@...il.com>, Song Liu <song@...nel.org>, 
	Yonghong Song <yonghong.song@...ux.dev>, John Fastabend <john.fastabend@...il.com>, 
	KP Singh <kpsingh@...nel.org>, Stanislav Fomichev <sdf@...ichev.me>, Hao Luo <haoluo@...gle.com>, 
	Jiri Olsa <jolsa@...nel.org>, Shuah Khan <shuah@...nel.org>, kernel-team@...roid.com, 
	linux-kernel@...r.kernel.org, bpf@...r.kernel.org, 
	linux-kselftest@...r.kernel.org
Subject: Re: [PATCH bpf-next v2 0/4] Add wakeup_source iterators

On Fri, Jan 9, 2026 at 3:37 PM Andrii Nakryiko
<andrii.nakryiko@...il.com> wrote:
>
> On Thu, Jan 8, 2026 at 2:56 PM Samuel Wu <wusamuel@...gle.com> wrote:
> >
> > This patch series introduces BPF iterators for wakeup_source, enabling
> > BPF programs to efficiently traverse a device's wakeup sources.
> >
> > Currently, inspecting wakeup sources typically involves reading interfaces
> > like /sys/class/wakeup/* or debugfs. The repeated syscalls to query the
> > sysfs nodes is inefficient, as there can be hundreds of wakeup_sources, and
> > each wakeup source have multiple stats, with one sysfs node per stat.
> > debugfs is unstable and insecure.
> >
> > This series implements two types of iterators:
> > 1. Standard BPF Iterator: Allows creating a BPF link to iterate over
> >    wakeup sources
> > 2. Open-coded Iterator: Enables the use of wakeup_source iterators directly
> >    within BPF programs
> >
> > Both iterators utilize pre-existing APIs wakeup_sources_walk_* to traverse
> > over the SRCU that backs the list of wakeup_sources.
>
> One reason to add either open-coded iterator or iterator program is
> when you need to work with some kernel object (i.e., if there is some
> additional API that takes that object and somehow manipulates it) or
> if traversal logic is involved in terms of synchronization primitives
> necessary.
>
> In your case neither concern seems to apply. Looking at
> wakeup_sources_walk_* helpers, it's just a simple linked list
> traversal and struct wakeup_source has plenty of plain data fields of
> interest, if I understand correctly. You probably are not intending to
> allow locking it or manipulate wakeirq, is that right?
>

Correct.

> So I'd say you should do this using bpf_for() generic loop and
> bpf_core_cast() helper. The only problem is that wakeup_sources global
> variable is static, so it's not that easy to get its memory address
> (to start iteration). Maybe look into working around that first?
>
> pw-bot: cr
>

I'm thinking I'll have to drop the open-coded iterators patches in the
v3 patchset, and revisit this in a later patchset when we have a clear
use case for it. I'm seeing now that open-coded iterators support was
added around kernel 6.6, so backwards compatibility will be
nontrivial.

>
> >
> > Changes in v2:
> >  - Guard BPF Makefile with CONFIG_PM_SLEEP to fix build errors
> >  - Update copyright from 2025 to 2026
> >  - v1 link: https://lore.kernel.org/all/20251204025003.3162056-1-wusamuel@google.com/
> >
> > Samuel Wu (4):
> >   bpf: Add wakeup_source iterator
> >   bpf: Open coded BPF for wakeup_sources
> >   selftests/bpf: Add tests for wakeup_sources
> >   selftests/bpf: Open coded BPF wakeup_sources test
> >
> >  kernel/bpf/Makefile                           |   3 +
> >  kernel/bpf/helpers.c                          |   3 +
> >  kernel/bpf/wakeup_source_iter.c               | 137 ++++++++
> >  .../testing/selftests/bpf/bpf_experimental.h  |   5 +
> >  tools/testing/selftests/bpf/config            |   1 +
> >  .../bpf/prog_tests/wakeup_source_iter.c       | 323 ++++++++++++++++++
> >  .../selftests/bpf/progs/wakeup_source_iter.c  | 117 +++++++
> >  7 files changed, 589 insertions(+)
> >  create mode 100644 kernel/bpf/wakeup_source_iter.c
> >  create mode 100644 tools/testing/selftests/bpf/prog_tests/wakeup_source_iter.c
> >  create mode 100644 tools/testing/selftests/bpf/progs/wakeup_source_iter.c
> >
> > --
> > 2.52.0.457.g6b5491de43-goog
> >