libcontainer/intelrdt: drop writeFile function

Drop writeFile() as it only had one caller. Stop using os.WriteFile()
for writing to the schemata file so that the writes are unit-testable.
Also, adapt and simplify the testutil helper writeFile() function.

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

Author: marquiz

libcontainer/intelrdt/intelrdt.go

@@ -326,16 +326,6 @@ func getIntelRdtParamString(path, file string) (string, error) {
 	return string(bytes.TrimSpace(contents)), nil
 }
 
-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 {
-		return newLastCmdError(fmt.Errorf("intelrdt: unable to write %v: %w", data, err))
-	}
-	return nil
-}
-
 // Get the read-only L3 cache information
 func getL3CacheInfo() (*L3CacheInfo, error) {
 	l3CacheInfo := &L3CacheInfo{}
@@ -648,9 +638,17 @@ func (m *Manager) Set(container *configs.Config) error {
 		path := filepath.Join(m.GetPath(), "schemata")
 		for _, line := range append([]string{r.L3CacheSchema, r.MemBwSchema}, r.Schemata...) {
 			if line != "" {
-				if err := os.WriteFile(path, []byte(line+"\n"), 0o600); err != nil {
+				f, err := os.OpenFile(path, os.O_WRONLY|os.O_APPEND, 0o600)
+				if err != nil {
+					return err
+				}
+				if _, err := f.Write([]byte(line + "\n")); err != nil {
+					_ = f.Close() // Ignore error, we can't do much about it.
 					return newLastCmdError(fmt.Errorf("intelrdt: unable to write %v: %w", line, err))
 				}
+				if err := f.Close(); err != nil {
+					return newLastCmdError(fmt.Errorf("intelrdt: failed to close file after writing %v: %w", line, err))
+				}
 			}
 		}
 	}

libcontainer/intelrdt/intelrdt_test.go

@@ -106,11 +106,8 @@ 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
+			helper.writeFile("schemata", "")
 
 			intelrdt := newManager(helper.config, "", helper.IntelRdtPath)
 			if err := intelrdt.Set(helper.config); err != nil {

libcontainer/intelrdt/util_test.go

@@ -42,11 +42,9 @@ func NewIntelRdtTestUtil(t *testing.T) *intelRdtTestUtil {
 }
 
 // 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)
-		}
+func (c *intelRdtTestUtil) writeFile(file, contents string) {
+	err := os.WriteFile(filepath.Join(c.IntelRdtPath, file), []byte(contents), 0o600)
+	if err != nil {
+		c.t.Fatal(err)
 	}
 }