netdev - Re: [RFC PATCH v1 bpf-next 0/4] Support associating BPF programs with struct

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Message-ID: <CAEf4BzZhRtswXo_x0Oks-VvcmCLHUdKPKGtELPSECDtxyAEoKg@mail.gmail.com>
Date: Mon, 13 Oct 2025 17:10:56 -0700
From: Andrii Nakryiko <andrii.nakryiko@...il.com>
To: Amery Hung <ameryhung@...il.com>
Cc: bpf@...r.kernel.org, netdev@...r.kernel.org, alexei.starovoitov@...il.com, 
	andrii@...nel.org, daniel@...earbox.net, tj@...nel.org, martin.lau@...nel.org, 
	kernel-team@...a.com
Subject: Re: [RFC PATCH v1 bpf-next 0/4] Support associating BPF programs with struct_ops

On Fri, Oct 10, 2025 at 10:49 AM Amery Hung <ameryhung@...il.com> wrote:
>
> This patchset adds a new BPF command BPF_STRUCT_OPS_ASSOCIATE_PROG to
> the bpf() syscall to allow associating a BPF program with a struct_ops.
> The command is introduced to address a emerging need from struct_ops
> users. As the number of subsystems adopting struct_ops grows, more
> users are building their struct_ops-based solution with some help from
> other BPF programs. For exmample, scx_layer uses a syscall program as
> a user space trigger to refresh layers [0]. It also uses tracing program
> to infer whether a task is using GPU and needs to be prioritized [1]. In
> these use cases, when there are multiple struct_ops instances, the
> struct_ops kfuncs called from different BPF programs, whether struct_ops
> or not needs to be able to refer to a specific one, which currently is
> not possible.
>
> The new BPF command will allow users to explicitly associate a BPF
> program with a struct_ops map. The libbpf wrapper can be called after
> loading programs and before attaching programs and struct_ops.
>
> Internally, it will set prog->aux->st_ops_assoc to the struct_ops
> struct (i.e., kdata). struct_ops kfuncs can then get the associated
> struct_ops by adding a "__prog" argument. The value of the speical
> argument will be fixed up by the verifier during verification.
>
> The command conceptually associates the implementation of BPF programs
> with struct_ops map, not the attachment. A program associated with the
> map will take a refcount of it so that st_ops_assoc always points to a
> valid struct_ops struct. However, the struct_ops can be in an
> uninitialized or unattached state. The struct_ops implementer will be
> responsible to maintain and check the state of the associated
> struct_ops before accessing it.
>
> We can also consider support associating struct_ops link with BPF
> programs, which on one hand make struct_ops implementer's job easier,
> but might complicate libbpf workflow and does not apply to legacy
> struct_ops attachment.
>
> [0] https://github.com/sched-ext/scx/blob/main/scheds/rust/scx_layered/src/bpf/main.bpf.c#L557
> [1] https://github.com/sched-ext/scx/blob/main/scheds/rust/scx_layered/src/bpf/main.bpf.c#L754
>
> Amery Hung (4):
>   bpf: Allow verifier to fixup kernel module kfuncs
>   bpf: Support associating BPF program with struct_ops
>   libbpf: Add bpf_struct_ops_associate_prog() API
>   selftests/bpf: Test BPF_STRUCT_OPS_ASSOCIATE_PROG command
>

please also drop RFC from the next revision

>  include/linux/bpf.h                           |  11 ++
>  include/uapi/linux/bpf.h                      |  16 +++
>  kernel/bpf/bpf_struct_ops.c                   |  32 ++++++
>  kernel/bpf/core.c                             |   6 +
>  kernel/bpf/syscall.c                          |  38 +++++++
>  kernel/bpf/verifier.c                         |   3 +-
>  tools/include/uapi/linux/bpf.h                |  16 +++
>  tools/lib/bpf/bpf.c                           |  18 +++
>  tools/lib/bpf/bpf.h                           |  19 ++++
>  tools/lib/bpf/libbpf.map                      |   1 +
>  .../bpf/prog_tests/test_struct_ops_assoc.c    |  76 +++++++++++++
>  .../selftests/bpf/progs/struct_ops_assoc.c    | 105 ++++++++++++++++++
>  .../selftests/bpf/test_kmods/bpf_testmod.c    |  17 +++
>  .../bpf/test_kmods/bpf_testmod_kfunc.h        |   1 +
>  14 files changed, 357 insertions(+), 2 deletions(-)
>  create mode 100644 tools/testing/selftests/bpf/prog_tests/test_struct_ops_assoc.c
>  create mode 100644 tools/testing/selftests/bpf/progs/struct_ops_assoc.c
>
> --
> 2.47.3
>