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

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Date:   Mon, 21 Feb 2022 19:24:28 +0100
From:   Jiri Olsa <olsajiri@...il.com>
To:     "Bayduraev, Alexey V" <alexey.v.bayduraev@...ux.intel.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 Mon, Feb 21, 2022 at 04:24:28PM +0300, Bayduraev, Alexey V wrote:
> 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?

how about something like below (with your change)

jirka


---
diff --git a/tools/perf/util/data.c b/tools/perf/util/data.c
index 15a4547d608e..d3382098d6f9 100644
--- a/tools/perf/util/data.c
+++ b/tools/perf/util/data.c
@@ -52,8 +52,10 @@ int perf_data__create_dir(struct perf_data *data, int nr)
 			goto out_err;
 
 		ret = open(file->path, O_RDWR|O_CREAT|O_TRUNC, S_IRUSR|S_IWUSR);
-		if (ret < 0)
+		if (ret < 0) {
+			ret = -errno;
 			goto out_err;
+		}
 
 		file->fd = ret;
 	}