Re: [PATCH 2/2] HID: bpf: use __bpf_kfunc instead of noinline

[Andrii Nakryiko]

On Tue, Jan 23, 2024 at 8:46 AM Benjamin Tissoires <bentiss@xxxxxxxxxx> wrote:
>
> Follow the docs at Documentation/bpf/kfuncs.rst:
> - declare the function with `__bpf_kfunc`
> - disables missing prototype warnings, which allows to remove them from
>   include/linux/hid-bpf.h
>
> Removing the prototypes is not an issue because we currently have to
> redeclare them when writing the BPF program. They will eventually be
> generated by bpftool directly AFAIU.
>
> Signed-off-by: Benjamin Tissoires <bentiss@xxxxxxxxxx>
> ---
>  drivers/hid/bpf/hid_bpf_dispatch.c | 22 +++++++++++++++++-----
>  include/linux/hid_bpf.h            | 11 -----------
>  2 files changed, 17 insertions(+), 16 deletions(-)
>
> diff --git a/drivers/hid/bpf/hid_bpf_dispatch.c b/drivers/hid/bpf/hid_bpf_dispatch.c
> index 5111d1fef0d3..119e4f03df55 100644
> --- a/drivers/hid/bpf/hid_bpf_dispatch.c
> +++ b/drivers/hid/bpf/hid_bpf_dispatch.c
> @@ -143,6 +143,11 @@ u8 *call_hid_bpf_rdesc_fixup(struct hid_device *hdev, u8 *rdesc, unsigned int *s
>  }
>  EXPORT_SYMBOL_GPL(call_hid_bpf_rdesc_fixup);
>
> +/* Disables missing prototype warnings */
> +__diag_push();
> +__diag_ignore_all("-Wmissing-prototypes",
> +                 "Global kfuncs as their definitions will be in BTF");
> +

would it be possible to use __bpf_kfunc_start_defs() and
__bpf_kfunc_end_defs() macros instead of explicit __diag push/pop
pairs? It's defined in include/linux/btf.h

>  /**
>   * hid_bpf_get_data - Get the kernel memory pointer associated with the context @ctx
>   *
> @@ -152,7 +157,7 @@ EXPORT_SYMBOL_GPL(call_hid_bpf_rdesc_fixup);
>   *
>   * @returns %NULL on error, an %__u8 memory pointer on success
>   */
> -noinline __u8 *
> +__bpf_kfunc __u8 *
>  hid_bpf_get_data(struct hid_bpf_ctx *ctx, unsigned int offset, const size_t rdwr_buf_size)
>  {
>         struct hid_bpf_ctx_kern *ctx_kern;
> @@ -167,6 +172,7 @@ hid_bpf_get_data(struct hid_bpf_ctx *ctx, unsigned int offset, const size_t rdwr
>
>         return ctx_kern->data + offset;
>  }
> +__diag_pop(); /* missing prototype warnings */
>
>  /*
>   * The following set contains all functions we agree BPF programs
> @@ -274,6 +280,11 @@ static int do_hid_bpf_attach_prog(struct hid_device *hdev, int prog_fd, struct b
>         return fd;
>  }
>
> +/* Disables missing prototype warnings */
> +__diag_push();
> +__diag_ignore_all("-Wmissing-prototypes",
> +                 "Global kfuncs as their definitions will be in BTF");
> +
>  /**
>   * hid_bpf_attach_prog - Attach the given @prog_fd to the given HID device
>   *
> @@ -286,7 +297,7 @@ static int do_hid_bpf_attach_prog(struct hid_device *hdev, int prog_fd, struct b
>   * is pinned to the BPF file system).
>   */
>  /* called from syscall */
> -noinline int
> +__bpf_kfunc int
>  hid_bpf_attach_prog(unsigned int hid_id, int prog_fd, __u32 flags)
>  {
>         struct hid_device *hdev;
> @@ -328,7 +339,7 @@ hid_bpf_attach_prog(unsigned int hid_id, int prog_fd, __u32 flags)
>   *
>   * @returns A pointer to &struct hid_bpf_ctx on success, %NULL on error.
>   */
> -noinline struct hid_bpf_ctx *
> +__bpf_kfunc struct hid_bpf_ctx *
>  hid_bpf_allocate_context(unsigned int hid_id)
>  {
>         struct hid_device *hdev;
> @@ -359,7 +370,7 @@ hid_bpf_allocate_context(unsigned int hid_id)
>   * @ctx: the HID-BPF context to release
>   *
>   */
> -noinline void
> +__bpf_kfunc void
>  hid_bpf_release_context(struct hid_bpf_ctx *ctx)
>  {
>         struct hid_bpf_ctx_kern *ctx_kern;
> @@ -380,7 +391,7 @@ hid_bpf_release_context(struct hid_bpf_ctx *ctx)
>   *
>   * @returns %0 on success, a negative error code otherwise.
>   */
> -noinline int
> +__bpf_kfunc int
>  hid_bpf_hw_request(struct hid_bpf_ctx *ctx, __u8 *buf, size_t buf__sz,
>                    enum hid_report_type rtype, enum hid_class_request reqtype)
>  {
> @@ -448,6 +459,7 @@ hid_bpf_hw_request(struct hid_bpf_ctx *ctx, __u8 *buf, size_t buf__sz,
>         kfree(dma_data);
>         return ret;
>  }
> +__diag_pop(); /* missing prototype warnings */
>
>  /* our HID-BPF entrypoints */
>  BTF_SET8_START(hid_bpf_fmodret_ids)
> diff --git a/include/linux/hid_bpf.h b/include/linux/hid_bpf.h
> index 840cd254172d..7118ac28d468 100644
> --- a/include/linux/hid_bpf.h
> +++ b/include/linux/hid_bpf.h
> @@ -77,17 +77,6 @@ enum hid_bpf_attach_flags {
>  int hid_bpf_device_event(struct hid_bpf_ctx *ctx);
>  int hid_bpf_rdesc_fixup(struct hid_bpf_ctx *ctx);
>
> -/* Following functions are kfunc that we export to BPF programs */
> -/* available everywhere in HID-BPF */
> -__u8 *hid_bpf_get_data(struct hid_bpf_ctx *ctx, unsigned int offset, const size_t __sz);
> -
> -/* only available in syscall */
> -int hid_bpf_attach_prog(unsigned int hid_id, int prog_fd, __u32 flags);
> -int hid_bpf_hw_request(struct hid_bpf_ctx *ctx, __u8 *buf, size_t buf__sz,
> -                      enum hid_report_type rtype, enum hid_class_request reqtype);
> -struct hid_bpf_ctx *hid_bpf_allocate_context(unsigned int hid_id);
> -void hid_bpf_release_context(struct hid_bpf_ctx *ctx);
> -
>  /*
>   * Below is HID internal
>   */
>
> --
> 2.43.0
>
>