netdev - Re: [PATCH v3 bpf-next 3/4] btf: expose API to work with raw btf

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Message-ID: <e4c11465-31a9-5dd3-7408-b0d5665bc391@fb.com>
Date:   Fri, 8 Feb 2019 17:12:53 +0000
From:   Yonghong Song <yhs@...com>
To:     Andrii Nakryiko <andriin@...com>,
        "alexei.starovoitov@...il.com" <alexei.starovoitov@...il.com>,
        "andrii.nakryiko@...il.com" <andrii.nakryiko@...il.com>,
        Song Liu <songliubraving@...com>,
        "Alexei Starovoitov" <ast@...com>, Martin Lau <kafai@...com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        Kernel Team <Kernel-team@...com>,
        "daniel@...earbox.net" <daniel@...earbox.net>
Subject: Re: [PATCH v3 bpf-next 3/4] btf: expose API to work with raw btf_ext
 data



On 2/7/19 6:55 PM, Andrii Nakryiko wrote:
> This patch changes struct btf_ext to retain original data in sequential
> block of memory, which makes it possible to expose
> btf_ext__get_raw_data() interface, that's similar to
> btf__get_raw_data(), allowing users of libbpf to get access to raw
> representation of .BTF.ext section.
> 
> Signed-off-by: Andrii Nakryiko <andriin@...com>
> ---
>   tools/lib/bpf/btf.c      | 85 +++++++++++++++++++++-------------------
>   tools/lib/bpf/btf.h      |  2 +
>   tools/lib/bpf/libbpf.map |  1 +
>   3 files changed, 47 insertions(+), 41 deletions(-)
> 
> diff --git a/tools/lib/bpf/btf.c b/tools/lib/bpf/btf.c
> index 8730f6c3be9e..c87cc3d71b9f 100644
> --- a/tools/lib/bpf/btf.c
> +++ b/tools/lib/bpf/btf.c
> @@ -41,9 +41,8 @@ struct btf {
>   
>   struct btf_ext_info {
>   	/*
> -	 * info points to a deep copy of the individual info section
> -	 * (e.g. func_info and line_info) from the .BTF.ext.
> -	 * It does not include the __u32 rec_size.
> +	 * info points to the individual info section (e.g. func_info and
> +	 * line_info) from the .BTF.ext. It does not include the __u32 rec_size.
>   	 */
>   	void *info;
>   	__u32 rec_size;
> @@ -51,8 +50,13 @@ struct btf_ext_info {
>   };
>   
>   struct btf_ext {
> +	union {
> +		struct btf_ext_header *hdr;
> +		void *data;
> +	};
>   	struct btf_ext_info func_info;
>   	struct btf_ext_info line_info;
> +	__u32 data_size;
>   };
>   
>   struct btf_ext_info_sec {
> @@ -603,19 +607,13 @@ struct btf_ext_sec_copy_param {
>   };
>   
>   static int btf_ext_copy_info(struct btf_ext *btf_ext,
> -			     __u8 *data, __u32 data_size,
>   			     struct btf_ext_sec_copy_param *ext_sec)

Overall looks good. Since we do not really "copy" info any more,
rather we try to "setup" info based on btf_ext. Maybe changing
all function and structure names with "_copy_" to "_setup_"?

>   {
> -	const struct btf_ext_header *hdr = (struct btf_ext_header *)data;
>   	const struct btf_ext_info_sec *sinfo;
>   	struct btf_ext_info *ext_info;
>   	__u32 info_left, record_size;
>   	/* The start of the info sec (including the __u32 record_size). */
> -	const void *info;
> -
> -	/* data and data_size do not include btf_ext_header from now on */
> -	data = data + hdr->hdr_len;
> -	data_size -= hdr->hdr_len;
> +	void *info;
[...]