netdev - Re: [PATCH v2 bpf-next 2/2] btf: expose API to work with raw btf data

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Date:   Tue, 5 Feb 2019 19:07:11 -0800
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     Andrii Nakryiko <andriin@...com>
Cc:     songliubraving@...com, yhs@...com, ast@...com, kafai@...com,
        netdev@...r.kernel.org, andrii.nakryiko@...il.com,
        daniel@...earbox.net
Subject: Re: [PATCH v2 bpf-next 2/2] btf: expose API to work with raw btf data

On Tue, Feb 05, 2019 at 04:29:49PM -0800, Andrii Nakryiko wrote:
> This patch exposes two new APIs btf__get_raw_data_size() and
> btf__get_raw_data() that allows to get a copy of raw BTF data out of
> struct btf. This is useful for external programs that need to manipulate
> raw data, e.g., pahole using btf__dedup() to deduplicate BTF type info
> and then writing it back to file.
> 
> Signed-off-by: Andrii Nakryiko <andriin@...com>
> Acked-by: Song Liu <songliubraving@...com>
> ---
>  tools/lib/bpf/btf.c      | 10 ++++++++++
>  tools/lib/bpf/btf.h      |  2 ++
>  tools/lib/bpf/libbpf.map |  2 ++
>  3 files changed, 14 insertions(+)
> 
> diff --git a/tools/lib/bpf/btf.c b/tools/lib/bpf/btf.c
> index 1c2ba7182400..34bfb3641aac 100644
> --- a/tools/lib/bpf/btf.c
> +++ b/tools/lib/bpf/btf.c
> @@ -437,6 +437,16 @@ int btf__fd(const struct btf *btf)
>  	return btf->fd;
>  }
>  
> +__u32 btf__get_raw_data_size(const struct btf *btf)
> +{
> +	return btf->data_size;
> +}
> +
> +void btf__get_raw_data(const struct btf *btf, char *data)
> +{
> +	memcpy(data, btf->data, btf->data_size);
> +}

I cannot think of any other way to use this api,
but to call btf__get_raw_data_size() first,
then malloc that much memory and then call btf__get_raw_data()
to store btf into it.

If so, may be api should be single call that allocates, copies,
and returns pointer to new mem and its size?
Probably less error prone?