linux-kernel - Re: [RFC PATCH bpf-next v6 05/12] libbpf: introduce bpf_map__attach_struct_ops

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Message-Id: <bec784d0d78a505dfbfbd17ffe95840dc356c80ceec2a96f9659b442b64c92c6@mail.kernel.org>
Date: Wed,  4 Feb 2026 09:28:42 +0000 (UTC)
From: bot+bpf-ci@...nel.org
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Subject: Re: [RFC PATCH bpf-next v6 05/12] libbpf: introduce bpf_map__attach_struct_ops_opts()

> diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
> index 0c8bf0b5c..70a00da54 100644
> --- a/tools/lib/bpf/libbpf.c
> +++ b/tools/lib/bpf/libbpf.c

[ ... ]

> @@ -13503,7 +13510,9 @@ struct bpf_link *bpf_map__attach_struct_ops(const struct bpf_map *map)
>  		return &link->link;
>  	}
>
> -	fd = bpf_link_create(map->fd, 0, BPF_STRUCT_OPS, NULL);
> +	link_opts.cgroup.relative_fd = OPTS_GET(opts, relative_fd, 0);
> +
> +	fd = bpf_link_create(map->fd, 0, BPF_STRUCT_OPS, &link_opts);

The expected_revision field from bpf_struct_ops_opts is defined in the public
API but doesn't appear to be forwarded here. bpf_link_create() reads
opts->cgroup.expected_revision for BPF_STRUCT_OPS, and similar functions like
bpf_program__attach_cgroup_opts() forward all fields including expected_revision.

Was the expected_revision field intentionally left unused, or should there be a
line here like:

    link_opts.cgroup.expected_revision = OPTS_GET(opts, expected_revision, 0);

Note: A later commit in this series (e83943e72 "libbpf: Support passing
user-defined flags for struct_ops") adds forwarding for the flags field, but
expected_revision remains unused through the end of the series.

> diff --git a/tools/lib/bpf/libbpf.h b/tools/lib/bpf/libbpf.h
> index dfc37a615..5aef44bcf 100644
> --- a/tools/lib/bpf/libbpf.h
> +++ b/tools/lib/bpf/libbpf.h
> @@ -920,6 +920,20 @@ bpf_program__attach_cgroup_opts(const struct bpf_program *prog, int cgroup_fd,
>  struct bpf_map;
>
>  LIBBPF_API struct bpf_link *bpf_map__attach_struct_ops(const struct bpf_map *map);
> +
> +struct bpf_struct_ops_opts {
> +	/* size of this struct, for forward/backward compatibility */
> +	size_t sz;
> +	__u32 flags;
> +	__u32 relative_fd;
> +	__u64 expected_revision;
                ^^^^^^^^^^^^^^^^^
The expected_revision field is defined here but is not read by
bpf_map__attach_struct_ops_opts() in libbpf.c, so any value set by users
will be silently ignored.

> +	size_t :0;
> +};


---
AI reviewed your patch. Please fix the bug or email reply why it's not a bug.
See: https://github.com/kernel-patches/vmtest/blob/master/ci/claude/README.md

CI run summary: https://github.com/kernel-patches/bpf/actions/runs/21665371660

AI-authorship-score: low
AI-authorship-explanation: The commit follows standard libbpf API extension patterns with consistent naming and structure typical of experienced kernel developers.
issues-found: 1
issue-severity-score: low
issue-severity-explanation: The expected_revision field in the public API struct is silently ignored, which could confuse users but does not cause system instability or crashes.