Subject: Re: [PATCH v3 perf,bpf 08/11] perf, bpf: save btf information as headers to perf.data

From: Jiri Olsa <[email-masked]>
Date: Mon, 18 Feb 2019 00:06:30 +0100

On Fri, Feb 15, 2019 at 01:53:51PM -0800, Song Liu wrote:
> This patch enables perf-record to save btf information as headers to
> perf.data A new header type HEADER_BTF is introduced for this data.
> 
> Signed-off-by: Song Liu <[email-masked]>
> ---
>  tools/perf/util/header.c | 99 +++++++++++++++++++++++++++++++++++++++-
>  tools/perf/util/header.h |  1 +
>  2 files changed, 99 insertions(+), 1 deletion(-)
> 
> diff --git a/tools/perf/util/header.c b/tools/perf/util/header.c
> index 0889ad797940..2de4f4e9b590 100644
> --- a/tools/perf/util/header.c
> +++ b/tools/perf/util/header.c
> @@ -1127,6 +1127,45 @@ static int write_bpf_prog_info(struct feat_fd *ff,
>  	return ret;
>  }
>  
> +static int write_btf(struct feat_fd *ff,
> +		     struct perf_evlist *evlist __maybe_unused)
> +{
> +	struct perf_env *env = &ff->ph->env;
> +	struct rb_root *root;
> +	struct rb_node *next;
> +	u32 count = 0;
> +	int ret;
> +
> +	down_read(&env->bpf_progs.bpf_info_lock);
> +
> +	root = &env->bpf_progs.btfs;
> +	next = rb_first(root);
> +	while (next) {
> +		++count;
> +		next = rb_next(next);
> +	}
> +
> +	ret = do_write(ff, &count, sizeof(count));
> +
> +	if (ret < 0)
> +		goto out;
> +
> +	next = rb_first(root);
> +	while (next) {
> +		struct btf_node *node;
> +
> +		node = rb_entry(next, struct btf_node, rb_node);
> +		next = rb_next(&node->rb_node);
> +		ret = do_write(ff, node,
> +			       sizeof(struct btf_node) + node->data_size);

hm, you write the whole struct btf_node with struct rb_node? why?

thanks,
jirka