Subject: Re: [PATCH v5 perf,bpf 07/15] perf, bpf: save bpf_prog_info information as headers to perf.data

From: Jiri Olsa <[email-masked]>
Date: Mon, 4 Mar 2019 14:52:51 +0100

On Wed, Feb 27, 2019 at 09:06:35PM -0800, Song Liu wrote:
> This patch enables perf-record to save bpf_prog_info information as
> headers to perf.data. A new header type HEADER_BPF_PROG_INFO is
> introduced for this data.
> 
> Signed-off-by: Song Liu <[email-masked]>
> ---
>  tools/perf/util/header.c | 143 ++++++++++++++++++++++++++++++++++++++-
>  tools/perf/util/header.h |   1 +
>  2 files changed, 143 insertions(+), 1 deletion(-)
> 
> diff --git a/tools/perf/util/header.c b/tools/perf/util/header.c
> index 4b88de5e9192..16f5bedb0b7d 100644
> --- a/tools/perf/util/header.c
> +++ b/tools/perf/util/header.c
> @@ -18,6 +18,7 @@
>  #include <sys/utsname.h>
>  #include <linux/time64.h>
>  #include <dirent.h>
> +#include <bpf/libbpf.h>
>  
>  #include "evlist.h"
>  #include "evsel.h"
> @@ -39,6 +40,7 @@
>  #include "tool.h"
>  #include "time-utils.h"
>  #include "units.h"
> +#include "bpf-event.h"
>  
>  #include "sane_ctype.h"
>  
> @@ -1074,6 +1076,51 @@ static int write_clockid(struct feat_fd *ff,
>  			sizeof(ff->ph->env.clockid_res_ns));
>  }
>  
> +static int write_bpf_prog_info(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.lock);
> +
> +	root = &env->bpf_progs.infos;
> +	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 bpf_prog_info_node *node;
> +		size_t len;
> +
> +		node = rb_entry(next, struct bpf_prog_info_node, rb_node);
> +		next = rb_next(&node->rb_node);
> +		len = sizeof(struct bpf_prog_info_linear) +
> +			node->info_linear->data_len;
> +
> +		/* before writing to file, translate address to offset */
> +		bpf_program__bpil_addr_to_offs(node->info_linear);
> +		ret = do_write(ff, node->info_linear, len);
> +		bpf_program__bpil_offs_to_addr(node->info_linear);

what's the reason to call this before the error check?

thanks,
jirka

> +		if (ret < 0)
> +			goto out;
> +	}
> +out:
> +	up_read(&env->bpf_progs.lock);
> +	return ret;
> +}

SNIP