linux-kernel - Re: [PATCH RFC 1/2] perf tools: Support single perf.data file directory

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Date:   Mon, 23 Sep 2019 23:34:27 +0200
From:   Jiri Olsa <jolsa@...hat.com>
To:     Adrian Hunter <adrian.hunter@...el.com>
Cc:     Arnaldo Carvalho de Melo <acme@...nel.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH RFC 1/2] perf tools: Support single perf.data file
 directory

On Mon, Sep 16, 2019 at 11:56:45AM +0300, Adrian Hunter wrote:
> Support directory output that contains a regular perf.data file. This is
> preparation for adding support for putting a copy of /proc/kcore in that
> directory.
> 
> Distinguish the multiple file case from the regular (single) perf.data file
> case by adding data->is_multi_file.

SNIP

>  static int open_file_read(struct perf_data *data)
>  {
>  	struct stat st;
> @@ -302,12 +312,17 @@ static int open_dir(struct perf_data *data)
>  {
>  	int ret;
>  
> -	/*
> -	 * So far we open only the header, so we can read the data version and
> -	 * layout.
> -	 */
> -	if (asprintf(&data->file.path, "%s/header", data->path) < 0)
> -		return -1;
> +	if (perf_data__is_multi_file(data)) {
> +		/*
> +		 * So far we open only the header, so we can read the data version and
> +		 * layout.
> +		 */
> +		if (asprintf(&data->file.path, "%s/header", data->path) < 0)
> +			return -1;
> +	} else {
> +		if (asprintf(&data->file.path, "%s/perf.data", data->path) < 0)
> +			return -1;
> +	}

first, please note that there's support for perf.data directory code,
but it's not been enabled yet, so we can do any changes there without
breaking existing users

currently the logic is prepared to have perf.data DIR_FORMAT feature
to define the layout of the directory

it'd be great to have just single point where we get directory layout,
not checking on files names first and checking on DIR_FORMAT later

also the kcore will be beneficial for other layouts,
so would be great to make it somehow optional/switchable

one of the options could be to have DIR_FORMAT feature as the source
of directory layout and it'd have bitmask of files/dirs (like kcore_dir)
available in the directory

thanks,
jirka