btrfs-progs: tests: add run_mayfail_stdout helper

Add a variant of mayfail helper that will duplicate the output to
results log and also provides it to the caller for processing. Can be
used for catching unsupported functionality or other special cases.

Signed-off-by: David Sterba <dsterba@suse.com>

tests/common

@@ -216,6 +216,52 @@ run_mayfail()
 	fi
 }
 
+# Same as run_mayfail but does not fail the test if it's handled gracefully by
+# the caller, unexpected failure like segfault or abort will exit forcibly,
+# output is logged
+#
+# NOTE: we don't use pipefail to avoid disturbing the rest of the caller
+# script, so here we use a temporary output file.  Pipes are not supported,
+# store the output to a variable for further processing.
+run_mayfail_stdout()
+{
+	local spec
+	local ins
+	local ret
+
+	tmp_output=$(mktemp --tmpdir btrfs-progs-test--mayfail-stdtout.XXXXXX)
+
+	ins=$(_get_spec_ins "$@")
+	spec=$(($ins-1))
+	spec=$(_cmd_spec "${@:$spec}")
+	set -- "${@:1:$(($ins-1))}" $spec "${@: $ins}"
+	echo "====== RUN MAYFAIL $@" >> "$RESULTS" 2>&1
+	if [[ $TEST_LOG =~ tty ]]; then echo "CMD(mayfail): $@" > /dev/tty; fi
+	if [ "$1" = 'root_helper' ]; then
+		"$@" 2>&1 > "$tmp_output"
+	else
+		$INSTRUMENT "$@" 2>&1 > "$tmp_output"
+	fi
+	ret=$?
+
+	cat "$tmp_output" >> "$RESULTS"
+	cat "$tmp_output"
+	rm -- "$tmp_output"
+
+	if [ "$ret" != 0 ]; then
+		echo "failed (ignored, ret=$ret): $@" >> "$RESULTS"
+		if [ "$ret" == 139 ]; then
+			_fail "mayfail: returned code 139 (SEGFAULT), not ignored"
+		elif [ "$ret" == 134 ]; then
+			_fail "mayfail: returned code 134 (SIGABRT), not ignored"
+		fi
+		return "$ret"
+	fi
+	# return the command code and let the caller decide what to do based
+	# on the stdout
+	return "$ret"
+}
+
 # first argument is error message to print if it fails, otherwise
 # same as run_check but expects the command to fail, output is logged
 run_mustfail()