linux-kernel - Re: [PATCH v2 1/9] libbpf: Introduce bpf_map_get_fd_by_id

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Date:   Fri, 3 Jun 2022 13:58:58 -0700
From:   Andrii Nakryiko <andrii.nakryiko@...il.com>
To:     Roberto Sassu <roberto.sassu@...wei.com>
Cc:     Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        KP Singh <kpsingh@...nel.org>, bpf <bpf@...r.kernel.org>,
        Networking <netdev@...r.kernel.org>,
        "open list:KERNEL SELFTEST FRAMEWORK" 
        <linux-kselftest@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 1/9] libbpf: Introduce bpf_map_get_fd_by_id_flags()

On Thu, Jun 2, 2022 at 7:38 AM Roberto Sassu <roberto.sassu@...wei.com> wrote:
>
> Introduce bpf_map_get_fd_by_id_flags(), to let a caller specify the open
> flags needed for the operation. This could make an operation succeed, if
> access to a map is restricted (i.e. it allows only certain operations).
>
> Signed-off-by: Roberto Sassu <roberto.sassu@...wei.com>
> ---
>  tools/lib/bpf/bpf.c      | 8 +++++++-
>  tools/lib/bpf/bpf.h      | 1 +
>  tools/lib/bpf/libbpf.map | 1 +
>  3 files changed, 9 insertions(+), 1 deletion(-)
>
> diff --git a/tools/lib/bpf/bpf.c b/tools/lib/bpf/bpf.c
> index 240186aac8e6..33bac2006043 100644
> --- a/tools/lib/bpf/bpf.c
> +++ b/tools/lib/bpf/bpf.c
> @@ -1047,18 +1047,24 @@ 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_flags(__u32 id, __u32 flags)

let's go the OPTS route instead so that we don't have to add any more
new variants? We can probably use common bpf_get_fd_by_id_opts for
map/prog/link/btf get_fd_by_id operations (and let's add all variants
for consistency)?


>  {
>         union bpf_attr attr;
>         int fd;
>
>         memset(&attr, 0, sizeof(attr));
>         attr.map_id = id;
> +       attr.open_flags = flags;
>
>         fd = sys_bpf_fd(BPF_MAP_GET_FD_BY_ID, &attr, sizeof(attr));
>         return libbpf_err_errno(fd);
>  }
>
> +int bpf_map_get_fd_by_id(__u32 id)
> +{
> +       return bpf_map_get_fd_by_id_flags(id, 0);
> +}
> +
>  int bpf_btf_get_fd_by_id(__u32 id)
>  {
>         union bpf_attr attr;
> diff --git a/tools/lib/bpf/bpf.h b/tools/lib/bpf/bpf.h
> index cabc03703e29..20e4c852362d 100644
> --- a/tools/lib/bpf/bpf.h
> +++ b/tools/lib/bpf/bpf.h
> @@ -438,6 +438,7 @@ 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);
>  LIBBPF_API int bpf_prog_get_fd_by_id(__u32 id);
> +LIBBPF_API int bpf_map_get_fd_by_id_flags(__u32 id, __u32 flags);
>  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 38e284ff057d..019278e66836 100644
> --- a/tools/lib/bpf/libbpf.map
> +++ b/tools/lib/bpf/libbpf.map
> @@ -466,6 +466,7 @@ LIBBPF_1.0.0 {
>                 libbpf_bpf_link_type_str;
>                 libbpf_bpf_map_type_str;
>                 libbpf_bpf_prog_type_str;
> +               bpf_map_get_fd_by_id_flags;
>
>         local: *;
>  };
> --
> 2.25.1
>