netdev - Re: [PATCH bpf-next v7 2/6] bpf: Support associating BPF program with struct

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Message-ID: <CAEf4Bzb0Lqthpnhp+O8gGENVUsd78oiQcRTQx-TudbpWPZTxAA@mail.gmail.com>
Date: Tue, 25 Nov 2025 15:54:16 -0800
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: [PATCH bpf-next v7 2/6] bpf: Support associating BPF program with struct_ops

On Fri, Nov 21, 2025 at 3:13 PM Amery Hung <ameryhung@...il.com> wrote:
>
> Add a new BPF command BPF_PROG_ASSOC_STRUCT_OPS to allow associating
> a BPF program with a struct_ops map. This command takes a file
> descriptor of a struct_ops map and a BPF program and set
> prog->aux->st_ops_assoc to the kdata of the struct_ops map.
>
> The command does not accept a struct_ops program nor a non-struct_ops
> map. Programs of a struct_ops map is automatically associated with the
> map during map update. If a program is shared between two struct_ops
> maps, prog->aux->st_ops_assoc will be poisoned to indicate that the
> associated struct_ops is ambiguous. The pointer, once poisoned, cannot
> be reset since we have lost track of associated struct_ops. For other
> program types, the associated struct_ops map, once set, cannot be
> changed later. This restriction may be lifted in the future if there is
> a use case.
>
> A kernel helper bpf_prog_get_assoc_struct_ops() can be used to retrieve
> the associated struct_ops pointer. The returned pointer, if not NULL, is
> guaranteed to be valid and point to a fully updated struct_ops struct.
> For struct_ops program reused in multiple struct_ops map, the return
> will be NULL.
>
> prog->aux->st_ops_assoc is protected by bumping the refcount for
> non-struct_ops programs and RCU for struct_ops programs. Since it would
> be inefficient to track programs associated with a struct_ops map, every
> non-struct_ops program will bump the refcount of the map to make sure
> st_ops_assoc stays valid. For a struct_ops program, it is protected by
> RCU as map_free will wait for an RCU grace period before disassociating
> the program with the map. The helper must be called in BPF program
> context or RCU read-side critical section.
>
> struct_ops implementers should note that the struct_ops returned may not
> be initialized nor attached yet. The struct_ops implementer will be
> responsible for tracking and checking the state of the associated
> struct_ops map if the use case expects an initialized or attached
> struct_ops.
>
> Signed-off-by: Amery Hung <ameryhung@...il.com>
> ---
>  include/linux/bpf.h            | 16 +++++++
>  include/uapi/linux/bpf.h       | 17 +++++++
>  kernel/bpf/bpf_struct_ops.c    | 88 ++++++++++++++++++++++++++++++++++
>  kernel/bpf/core.c              |  3 ++
>  kernel/bpf/syscall.c           | 46 ++++++++++++++++++
>  tools/include/uapi/linux/bpf.h | 17 +++++++
>  6 files changed, 187 insertions(+)
>

LGTM

Acked-by: Andrii Nakryiko <andrii@...nel.org>

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