[RFC,1/3] libbpf: Define bpf_get_fd_opts and introduce bpf_map_get_fd_by_id_opts()

From: Roberto Sassu <roberto.sassu@huawei.com>

Define a new data structure called bpf_get_fd_opts, with the member
open_flags, to be used by callers of the _opts variants of
bpf_*_get_fd_by_id() to specify the permissions needed for the file
descriptor to be obtained.

Also, introduce bpf_map_get_fd_by_id_opts(), to let the caller pass a
bpf_get_fd_opts structure.

Finally, keep the existing bpf_map_get_fd_by_id(), and call
bpf_map_get_fd_by_id_opts() with NULL as opts argument, to request
read-write permissions (current behavior).

Signed-off-by: Roberto Sassu <roberto.sassu@huawei.com>
---
 tools/lib/bpf/bpf.c      | 12 +++++++++++-
 tools/lib/bpf/bpf.h      | 10 ++++++++++
 tools/lib/bpf/libbpf.map |  3 ++-
 3 files changed, 23 insertions(+), 2 deletions(-)

On Mon, Sep 26, 2022 at 8:45 AM Roberto Sassu
<roberto.sassu@huaweicloud.com> wrote:
>
> From: Roberto Sassu <roberto.sassu@huawei.com>
>
> Define a new data structure called bpf_get_fd_opts, with the member
> open_flags, to be used by callers of the _opts variants of
> bpf_*_get_fd_by_id() to specify the permissions needed for the file
> descriptor to be obtained.
>
> Also, introduce bpf_map_get_fd_by_id_opts(), to let the caller pass a
> bpf_get_fd_opts structure.
>
> Finally, keep the existing bpf_map_get_fd_by_id(), and call
> bpf_map_get_fd_by_id_opts() with NULL as opts argument, to request
> read-write permissions (current behavior).
>
> Signed-off-by: Roberto Sassu <roberto.sassu@huawei.com>
> ---

looks good overall, but please see two nits below

>  tools/lib/bpf/bpf.c      | 12 +++++++++++-
>  tools/lib/bpf/bpf.h      | 10 ++++++++++
>  tools/lib/bpf/libbpf.map |  3 ++-
>  3 files changed, 23 insertions(+), 2 deletions(-)
>
> diff --git a/tools/lib/bpf/bpf.c b/tools/lib/bpf/bpf.c
> index 1d49a0352836..4b03063edf1d 100644
> --- a/tools/lib/bpf/bpf.c
> +++ b/tools/lib/bpf/bpf.c
> @@ -948,19 +948,29 @@ int bpf_prog_get_fd_by_id(__u32 id)
>         return libbpf_err_errno(fd);
>  }
>
> -int bpf_map_get_fd_by_id(__u32 id)
> +int bpf_map_get_fd_by_id_opts(__u32 id,
> +                             const struct bpf_get_fd_opts *opts)
>  {
>         const size_t attr_sz = offsetofend(union bpf_attr, open_flags);
>         union bpf_attr attr;
>         int fd;
>
> +       if (!OPTS_VALID(opts, bpf_get_fd_opts))
> +               return libbpf_err(-EINVAL);
> +
>         memset(&attr, 0, attr_sz);
>         attr.map_id = id;
> +       attr.open_flags = OPTS_GET(opts, open_flags, 0);
>
>         fd = sys_bpf_fd(BPF_MAP_GET_FD_BY_ID, &attr, attr_sz);
>         return libbpf_err_errno(fd);
>  }
>
> +int bpf_map_get_fd_by_id(__u32 id)
> +{
> +       return bpf_map_get_fd_by_id_opts(id, NULL);
> +}
> +
>  int bpf_btf_get_fd_by_id(__u32 id)
>  {
>         const size_t attr_sz = offsetofend(union bpf_attr, open_flags);
> diff --git a/tools/lib/bpf/bpf.h b/tools/lib/bpf/bpf.h
> index 9c50beabdd14..38a1b7eccfc8 100644
> --- a/tools/lib/bpf/bpf.h
> +++ b/tools/lib/bpf/bpf.h
> @@ -365,7 +365,17 @@ LIBBPF_API int bpf_prog_get_next_id(__u32 start_id, __u32 *next_id);
>  LIBBPF_API int bpf_map_get_next_id(__u32 start_id, __u32 *next_id);
>  LIBBPF_API int bpf_btf_get_next_id(__u32 start_id, __u32 *next_id);
>  LIBBPF_API int bpf_link_get_next_id(__u32 start_id, __u32 *next_id);
> +
> +struct bpf_get_fd_opts {
> +       size_t sz; /* size of this struct for forward/backward compatibility */
> +       __u32 open_flags; /* permissions requested for the operation on fd */
> +       __u32 :0;

this should be size_t: 0

> +};
> +#define bpf_get_fd_opts__last_field open_flags
> +
>  LIBBPF_API int bpf_prog_get_fd_by_id(__u32 id);
> +LIBBPF_API int bpf_map_get_fd_by_id_opts(__u32 id,
> +                                        const struct bpf_get_fd_opts *opts);
>  LIBBPF_API int bpf_map_get_fd_by_id(__u32 id);
>  LIBBPF_API int bpf_btf_get_fd_by_id(__u32 id);
>  LIBBPF_API int bpf_link_get_fd_by_id(__u32 id);
> diff --git a/tools/lib/bpf/libbpf.map b/tools/lib/bpf/libbpf.map
> index c1d6aa7c82b6..2e665b21d84f 100644
> --- a/tools/lib/bpf/libbpf.map
> +++ b/tools/lib/bpf/libbpf.map
> @@ -367,10 +367,11 @@ LIBBPF_1.0.0 {
>                 libbpf_bpf_map_type_str;
>                 libbpf_bpf_prog_type_str;
>                 perf_buffer__buffer;
> -};
> +} LIBBPF_0.8.0;
>

good catch, please send this as a separate fix, thanks!

>  LIBBPF_1.1.0 {
>         global:
> +               bpf_map_get_fd_by_id_opts;
>                 user_ring_buffer__discard;
>                 user_ring_buffer__free;
>                 user_ring_buffer__new;
> --
> 2.25.1
>