Re: [RFC][PATCH v3 07/15] libbpf: Introduce bpf_obj_get_opts()

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On Fri, Jul 22, 2022 at 10:20 AM Roberto Sassu <roberto.sassu@xxxxxxxxxx> wrote:
>
> Introduce bpf_obj_get_opts(), to let the caller pass the needed permissions
> for the operation. Keep the existing bpf_obj_get() to request read-write
> permissions.
>
> bpf_obj_get() allows the caller to get a file descriptor from a pinned
> object with the provided pathname. Specifying permissions has only effect
> on maps (for links, the permission must be always read-write).
>
> Signed-off-by: Roberto Sassu <roberto.sassu@xxxxxxxxxx>
> ---
>  tools/lib/bpf/bpf.c      | 12 +++++++++++-
>  tools/lib/bpf/bpf.h      |  2 ++
>  tools/lib/bpf/libbpf.map |  1 +
>  3 files changed, 14 insertions(+), 1 deletion(-)
>
> diff --git a/tools/lib/bpf/bpf.c b/tools/lib/bpf/bpf.c
> index 5f2785a4c358..0df088890864 100644
> --- a/tools/lib/bpf/bpf.c
> +++ b/tools/lib/bpf/bpf.c
> @@ -577,18 +577,28 @@ int bpf_obj_pin(int fd, const char *pathname)
>         return libbpf_err_errno(ret);
>  }
>
> -int bpf_obj_get(const char *pathname)
> +int bpf_obj_get_opts(const char *pathname,
> +                    const struct bpf_get_fd_opts *opts)

I'm still not sure whether it's a good idea to mix get_fd with
obj_get/pin operations? [1] seems more clear.
It just so happens that (differently named) flags in BPF_OBJ_GET and
BPF_XXX_GET_FD_BY_ID align, but maybe we shouldn't depend on it?

Also, it seems only bpf_map_get_fd_by_id currently accepts flags? So
this sharing makes even more sense?

[1] https://lore.kernel.org/bpf/20220719194028.4180569-1-jevburton.kernel@xxxxxxxxx/





>  {
>         union bpf_attr attr;
>         int fd;
>
> +       if (!OPTS_VALID(opts, bpf_get_fd_opts))
> +               return libbpf_err(-EINVAL);
> +
>         memset(&attr, 0, sizeof(attr));
>         attr.pathname = ptr_to_u64((void *)pathname);
> +       attr.file_flags = OPTS_GET(opts, flags, 0);
>
>         fd = sys_bpf_fd(BPF_OBJ_GET, &attr, sizeof(attr));
>         return libbpf_err_errno(fd);
>  }
>
> +int bpf_obj_get(const char *pathname)
> +{
> +       return bpf_obj_get_opts(pathname, NULL);
> +}
> +
>  int bpf_prog_attach(int prog_fd, int target_fd, enum bpf_attach_type type,
>                     unsigned int flags)
>  {
> diff --git a/tools/lib/bpf/bpf.h b/tools/lib/bpf/bpf.h
> index b75fd9d37bad..e0c5018cc131 100644
> --- a/tools/lib/bpf/bpf.h
> +++ b/tools/lib/bpf/bpf.h
> @@ -279,6 +279,8 @@ struct bpf_get_fd_opts {
>  };
>  #define bpf_get_fd_opts__last_field flags
>
> +LIBBPF_API int bpf_obj_get_opts(const char *pathname,
> +                               const struct bpf_get_fd_opts *opts);
>  LIBBPF_API int bpf_obj_get(const char *pathname);
>
>  struct bpf_prog_attach_opts {
> diff --git a/tools/lib/bpf/libbpf.map b/tools/lib/bpf/libbpf.map
> index dba97d2ef8a9..55516b19e22f 100644
> --- a/tools/lib/bpf/libbpf.map
> +++ b/tools/lib/bpf/libbpf.map
> @@ -368,4 +368,5 @@ LIBBPF_1.0.0 {
>                 bpf_map_get_fd_by_id_opts;
>                 bpf_btf_get_fd_by_id_opts;
>                 bpf_link_get_fd_by_id_opts;
> +               bpf_obj_get_opts;
>  };
> --
> 2.25.1
>



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