perf stat: reject --field-separator and --json-output combination

Specifying --field-separator option is stating you want CSV output.
Passing both --field-separator and --json-output is then stating
you want output to be in CSV and JSON format at same time.

Currently this combination is not rejected, and the outcome
is a malformed combination of CSV and JSON output.
This is because of inconsistencies in various printing functions,
some of them have if-else chains that start with
"Should I print JSON?", and some start with "Should I print CSV?".

Example of current output:
$ tools/perf/perf stat -x , -j -e cpu-migrations true
{"counter-value" : "0.000000", "unit" : "", "event" : "cpu-migrations", "event-runtime" : 474817, "pcnt-running" : 100.00,,

Instead reject the option combination,
with a helpful error message and non-zero exit code.

Example of new output:
$ tools/perf/perf stat -x , -j true
cannot use both --field-separator and --json-output

 Usage: perf stat [<options>] [<command>]

    -x, --field-separator <separator>
                          print counts with custom separator
    -j, --json-output     print counts in JSON format

Signed-off-by: Ivan Lazaric <ivan.lazaric1@gmail.com>
Signed-off-by: Namhyung Kim <namhyung@kernel.org>

1 files changed, 12 insertions, 0 deletions

diff --git a/tools/perf/tests/shell/stat.sh b/tools/perf/tests/shell/stat.sh
index 1e17bee026bd..649de1166fed 100755
--- a/tools/perf/tests/shell/stat.sh
+++ b/tools/perf/tests/shell/stat.sh
@@ -535,6 +535,17 @@ test_stat_delay() {
   echo "stat -D test [Success]"
 }
 
+test_csv_json_fail() {
+  echo "stat -x <sep> -j test"
+  if perf stat -x , -j true > /dev/null 2>&1
+  then
+    echo "stat -x <sep> -j test [Failed - command should have errored]"
+    err=1
+  else
+    echo "stat -x <sep> -j test [Success]"
+  fi
+}
+
 test_default_stat
 test_null_stat
 test_offline_cpu_stat
@@ -551,6 +562,7 @@ test_stat_detailed
 test_stat_repeat
 test_stat_pid
 test_stat_delay
+test_csv_json_fail
 
 cleanup
 exit $err