From a80e1217d2a7d8cfdf574db0004ff04346fb65d9 Mon Sep 17 00:00:00 2001
From: Kir Kolyshkin <kolyshkin@gmail.com>
Date: Thu, 7 Oct 2021 20:19:27 -0700
Subject: [PATCH] libct/intelrdt: add Root()

Export getIntelRdtRoot function as Root.

This is needed by google/cadvisor, which is (ab)using GetIntelRdtPath,
removed by commit 7296dc171238291f4.

While at it, do some minimal refactoring to always use Root()
internally, not relying on variable value. Other than that it's just
some renaming.

Signed-off-by: Kir Kolyshkin <kolyshkin@gmail.com>
---
 libcontainer/intelrdt/intelrdt.go | 48 +++++++++++++++----------------
 1 file changed, 23 insertions(+), 25 deletions(-)

diff --git a/libcontainer/intelrdt/intelrdt.go b/libcontainer/intelrdt/intelrdt.go
index dcf231b63..62179f01f 100644
--- a/libcontainer/intelrdt/intelrdt.go
+++ b/libcontainer/intelrdt/intelrdt.go
@@ -185,10 +185,6 @@ const (
 )
 
 var (
-	// The absolute root path of the Intel RDT "resource control" filesystem
-	intelRdtRoot     string
-	intelRdtRootLock sync.Mutex
-
 	// The flag to indicate if Intel RDT/CAT is enabled
 	catEnabled bool
 	// The flag to indicate if Intel RDT/MBA is enabled
@@ -215,9 +211,10 @@ func featuresInit() {
 			return
 		}
 
-		// 2. Check if Intel RDT "resource control" filesystem is mounted
-		// The user guarantees to mount the filesystem
-		if !isIntelRdtMounted() {
+		// 2. Check if Intel RDT "resource control" filesystem is available.
+		// The user guarantees to mount the filesystem.
+		root, err := Root()
+		if err != nil {
 			return
 		}
 
@@ -226,7 +223,7 @@ func featuresInit() {
 		// selectively disabled or enabled by kernel command line
 		// (e.g., rdt=!l3cat,mba) in 4.14 and newer kernel
 		if flagsSet.CAT {
-			if _, err := os.Stat(filepath.Join(intelRdtRoot, "info", "L3")); err == nil {
+			if _, err := os.Stat(filepath.Join(root, "info", "L3")); err == nil {
 				catEnabled = true
 			}
 		}
@@ -236,15 +233,15 @@ func featuresInit() {
 			// depends on MBA
 			mbaEnabled = true
 		} else if flagsSet.MBA {
-			if _, err := os.Stat(filepath.Join(intelRdtRoot, "info", "MB")); err == nil {
+			if _, err := os.Stat(filepath.Join(root, "info", "MB")); err == nil {
 				mbaEnabled = true
 			}
 		}
 		if flagsSet.MBMTotal || flagsSet.MBMLocal || flagsSet.CMT {
-			if _, err := os.Stat(filepath.Join(intelRdtRoot, "info", "L3_MON")); err != nil {
+			if _, err := os.Stat(filepath.Join(root, "info", "L3_MON")); err != nil {
 				return
 			}
-			enabledMonFeatures, err = getMonFeatures(intelRdtRoot)
+			enabledMonFeatures, err = getMonFeatures(root)
 			if err != nil {
 				return
 			}
@@ -282,10 +279,16 @@ func findIntelRdtMountpointDir(f io.Reader) (string, error) {
 	return mi[0].Mountpoint, nil
 }
 
-// Gets the root path of Intel RDT "resource control" filesystem
-func getIntelRdtRoot() (string, error) {
-	intelRdtRootLock.Lock()
-	defer intelRdtRootLock.Unlock()
+// For Root() use only.
+var (
+	intelRdtRoot string
+	rootMu       sync.Mutex
+)
+
+// Root returns the Intel RDT "resource control" filesystem mount point.
+func Root() (string, error) {
+	rootMu.Lock()
+	defer rootMu.Unlock()
 
 	if intelRdtRoot != "" {
 		return intelRdtRoot, nil
@@ -309,11 +312,6 @@ func getIntelRdtRoot() (string, error) {
 	return intelRdtRoot, nil
 }
 
-func isIntelRdtMounted() bool {
-	_, err := getIntelRdtRoot()
-	return err == nil
-}
-
 type cpuInfoFlags struct {
 	CAT bool // Cache Allocation Technology
 	MBA bool // Memory Bandwidth Allocation
@@ -405,7 +403,7 @@ func writeFile(dir, file, data string) error {
 func getL3CacheInfo() (*L3CacheInfo, error) {
 	l3CacheInfo := &L3CacheInfo{}
 
-	rootPath, err := getIntelRdtRoot()
+	rootPath, err := Root()
 	if err != nil {
 		return l3CacheInfo, err
 	}
@@ -435,7 +433,7 @@ func getL3CacheInfo() (*L3CacheInfo, error) {
 func getMemBwInfo() (*MemBwInfo, error) {
 	memBwInfo := &MemBwInfo{}
 
-	rootPath, err := getIntelRdtRoot()
+	rootPath, err := Root()
 	if err != nil {
 		return memBwInfo, err
 	}
@@ -468,7 +466,7 @@ func getMemBwInfo() (*MemBwInfo, error) {
 
 // Get diagnostics for last filesystem operation error from file info/last_cmd_status
 func getLastCmdStatus() (string, error) {
-	rootPath, err := getIntelRdtRoot()
+	rootPath, err := Root()
 	if err != nil {
 		return "", err
 	}
@@ -517,7 +515,7 @@ func IsMBAScEnabled() bool {
 
 // Get the path of the clos group in "resource control" filesystem that the container belongs to
 func (m *intelRdtManager) getIntelRdtPath() (string, error) {
-	rootPath, err := getIntelRdtRoot()
+	rootPath, err := Root()
 	if err != nil {
 		return "", err
 	}
@@ -601,7 +599,7 @@ func (m *intelRdtManager) GetStats() (*Stats, error) {
 	defer m.mu.Unlock()
 	stats := newStats()
 
-	rootPath, err := getIntelRdtRoot()
+	rootPath, err := Root()
 	if err != nil {
 		return nil, err
 	}