libcontainer/intelrdt: rewrite writeFile()

Stop using os.WriteFile() so that the writes are unit-testable. Also
remove now stale helper function from tests.

Signed-off-by: Markus Lehtonen <[email protected]>

Author: marquiz

libcontainer/intelrdt/intelrdt.go

@@ -330,7 +330,16 @@ func writeFile(dir, file, data string) error {
 	if dir == "" {
 		return fmt.Errorf("no such directory for %s", file)
 	}
-	if err := os.WriteFile(filepath.Join(dir, file), []byte(data+"\n"), 0o600); err != nil {
+
+	f, err := os.OpenFile(filepath.Join(dir, file), os.O_WRONLY|os.O_APPEND, 0o600)
+	if err != nil {
+		return fmt.Errorf("failed to open file %s: %w", file, err)
+	}
+	_, err = f.Write([]byte(data + "\n"))
+	if errc := f.Close(); errc != nil && err == nil {
+		err = errc
+	}
+	if err != nil {
 		return newLastCmdError(fmt.Errorf("intelrdt: unable to write %v: %w", data, err))
 	}
 	return nil

libcontainer/intelrdt/intelrdt_test.go

@@ -106,11 +106,10 @@ func TestIntelRdtSet(t *testing.T) {
 		t.Run(tc.name, func(t *testing.T) {
 			helper := NewIntelRdtTestUtil(t)
 			helper.config.IntelRdt = tc.config
-
-			helper.writeFileContents(map[string]string{
-				/* Common initial value for all test cases */
-				"schemata": "MB:0=100\nL3:0=ffff\nL2:0=ffffffff\n",
-			})
+			// Pre-create an empty schemata file
+			if err := os.WriteFile(filepath.Join(helper.IntelRdtPath, "schemata"), []byte{}, 0o600); err != nil {
+				t.Fatal(err)
+			}
 
 			intelrdt := newManager(helper.config, "", helper.IntelRdtPath)
 			if err := intelrdt.Set(helper.config); err != nil {

libcontainer/intelrdt/util_test.go

@@ -40,13 +40,3 @@ func NewIntelRdtTestUtil(t *testing.T) *intelRdtTestUtil {
 	}
 	return &intelRdtTestUtil{config: config, IntelRdtPath: testIntelRdtPath, t: t}
 }
-
-// Write the specified contents on the mock of the specified Intel RDT "resource control" files
-func (c *intelRdtTestUtil) writeFileContents(fileContents map[string]string) {
-	for file, contents := range fileContents {
-		err := writeFile(c.IntelRdtPath, file, contents)
-		if err != nil {
-			c.t.Fatal(err)
-		}
-	}
-}