Re: [PATCH 4/4] samples: bpf: add mthp_ext

[bot+bpf-ci]

> diff --git a/samples/bpf/.gitignore b/samples/bpf/.gitignore
> index 0002cd359fb1..2a73581876b4 100644
> --- a/samples/bpf/.gitignore
> +++ b/samples/bpf/.gitignore

[ ... ]

> diff --git a/samples/bpf/Makefile b/samples/bpf/Makefile
> index 95a4fa1f1e44..357c7d1c45ef 100644
> --- a/samples/bpf/Makefile
> +++ b/samples/bpf/Makefile

[ ... ]

> diff --git a/samples/bpf/mthp_ext.bpf.c b/samples/bpf/mthp_ext.bpf.c
> new file mode 100644
> index 000000000000..bbee3e9f679c

[ ... ]

> diff --git a/samples/bpf/mthp_ext.c b/samples/bpf/mthp_ext.c
> new file mode 100644
> index 000000000000..0e064bad136f
> --- /dev/null
> +++ b/samples/bpf/mthp_ext.c
> @@ -0,0 +1,340 @@
> +// SPDX-License-Identifier: GPL-2.0

[ ... ]

> +int main(int argc, char **argv)
> +{
> +	const char *root_path = DEFAULT_ROOT;
> +	unsigned long threshold = DEFAULT_THRESHOLD_MS;
> +	unsigned long interval = DEFAULT_INTERVAL_MS;
> +	unsigned int init_order = DEFAULT_ORDER;
> +	unsigned int min_mem = DEFAULT_MIN_MEM;
> +	bool fixed = false;
> +	bool debug = false;
> +	struct mthp_ext *skel;
> +	struct bpf_link *iter_link;
> +	struct bpf_link *ops_link;
> +	struct ring_buffer *rb;
> +	int root_fd;
> +	int psi_fd;
> +	int err = 0;
> +	int opt;

[ ... ]

> +	/* Attach struct_ops to root cgroup for mthp_choose */
> +	DECLARE_LIBBPF_OPTS(bpf_struct_ops_opts, opts);
> +	opts.flags = BPF_F_CGROUP_FD;
> +	opts.target_fd = root_fd;
> +	ops_link = bpf_map__attach_struct_ops_opts(skel->maps.mthp_ops, &opts);
                                                   ^^^^^^^^^^^^^^^^^^^^^^^^^^
Will mthp_ext compile with these symbols? A tree-wide grep shows that
bpf_struct_ops_opts, BPF_F_CGROUP_FD, and bpf_map__attach_struct_ops_opts()
do not exist anywhere in the kernel source tree:

  $ git grep -n "struct bpf_struct_ops_opts"
  samples/bpf/mthp_ext.c:260:	DECLARE_LIBBPF_OPTS(bpf_struct_ops_opts, opts);

  $ git grep -n "BPF_F_CGROUP_FD"
  samples/bpf/mthp_ext.c:261:	opts.flags = BPF_F_CGROUP_FD;

  $ git grep -n "bpf_map__attach_struct_ops_opts"
  samples/bpf/mthp_ext.c:263:	ops_link = bpf_map__attach_struct_ops_opts(skel->maps.mthp_ops, &opts);

The struct bpf_struct_ops_opts type is not defined in tools/lib/bpf/libbpf.h.
The BPF_F_CGROUP_FD flag does not appear in include/uapi/linux/bpf.h or any
other header. The bpf_map__attach_struct_ops_opts() function is not declared
in libbpf.h or exported in tools/lib/bpf/libbpf.map.

The only existing libbpf API for struct_ops attachment is:

  tools/lib/bpf/libbpf.h:
    LIBBPF_API struct bpf_link *
    bpf_map__attach_struct_ops(const struct bpf_map *map);

which takes no opts parameter and cannot attach to a specific cgroup fd.

Samples/bpf/Makefile was modified earlier in this commit to add mthp_ext to
tprogs-y, meaning the build system will attempt to compile mthp_ext.c during
make samples/bpf/. That compilation will fail with undefined type, undefined
identifier, and implicit declaration errors.

This looks like it depends on an out-of-tree libbpf extension that adds a
per-cgroup struct_ops attachment API. Is that libbpf patch supposed to be
included earlier in this series, or should the sample use a different attach
mechanism?

> +	err = libbpf_get_error(ops_link);
> +	if (err) {
> +		fprintf(stderr, "ERROR: attach struct_ops failed: %d\n", err);
> +		ops_link = NULL;
> +		goto attach_opts_fail;
> +	}

[ ... ]

> diff --git a/samples/bpf/mthp_ext.h b/samples/bpf/mthp_ext.h
> new file mode 100644
> index 000000000000..33dc01bcebd3

[ ... ]


---
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/25285279315