linux-kernel - Re: [PATCH core] perf data: Adding error message if perf_data__create

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Date:   Mon, 21 Feb 2022 16:24:28 +0300
From:   "Bayduraev, Alexey V" <alexey.v.bayduraev@...ux.intel.com>
To:     Jiri Olsa <olsajiri@...il.com>
Cc:     Arnaldo Carvalho de Melo <acme@...nel.org>,
        Jiri Olsa <jolsa@...hat.com>,
        Namhyung Kim <namhyung@...nel.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Andi Kleen <ak@...ux.intel.com>,
        Adrian Hunter <adrian.hunter@...el.com>,
        Alexander Antonov <alexander.antonov@...ux.intel.com>,
        Alexei Budankov <abudankov@...wei.com>
Subject: Re: [PATCH core] perf data: Adding error message if
 perf_data__create_dir fails

On 21.02.2022 1:43, Jiri Olsa wrote:
> On Fri, Feb 18, 2022 at 06:23:40PM +0300, Alexey Bayduraev wrote:
>> There is no notification about data directory creation failure. Add it.
>>
>> Signed-off-by: Alexey Bayduraev <alexey.v.bayduraev@...ux.intel.com>
>> ---
>>  tools/perf/builtin-record.c | 4 +++-
>>  1 file changed, 3 insertions(+), 1 deletion(-)
>>
>> diff --git a/tools/perf/builtin-record.c b/tools/perf/builtin-record.c
>> index 0bc6529814b2..0306d5911de2 100644
>> --- a/tools/perf/builtin-record.c
>> +++ b/tools/perf/builtin-record.c
>> @@ -1186,8 +1186,10 @@ static int record__mmap_evlist(struct record *rec,
>>  
>>  	if (record__threads_enabled(rec)) {
>>  		ret = perf_data__create_dir(&rec->data, evlist->core.nr_mmaps);
>> -		if (ret)
>> +		if (ret) {
>> +			pr_err("Failed to create data directory: %s\n", strerror(errno));
> 
> errno will be misleading in here, because perf_data__create_dir
> calls other syscalls on error path

Mostly I want to output something like:

  Failed to create data dir: Too many open files

This will trigger the user to increase the open files limit.
Would it be better to place such message to perf_data__create_dir after 
open() syscall?

Regards,
Alexey

> 
> jirka
> 
>>  			return ret;
>> +		}
>>  		for (i = 0; i < evlist->core.nr_mmaps; i++) {
>>  			if (evlist->mmap)
>>  				evlist->mmap[i].file = &rec->data.dir.files[i];
>> -- 
>> 2.19.0
>>