libcontainer: intelrdt: add user-friendly diagnostics for Intel RDT operation errors

Linux kernel v4.15 introduces better diagnostics for Intel RDT operation
errors. If any error returns when making new directories or writing to
any of the control file in resctrl filesystem, reading file
/sys/fs/resctrl/info/last_cmd_status could provide more information that
can be conveyed in the error returns from file operations.

Some examples:
  echo "L3:0=f3;1=ff" > /sys/fs/resctrl/container_id/schemata
  -bash: echo: write error: Invalid argument
  cat /sys/fs/resctrl/info/last_cmd_status
  mask f3 has non-consecutive 1-bits

  echo "MB:0=0;1=110" > /sys/fs/resctrl/container_id/schemata
  -bash: echo: write error: Invalid argument
  cat /sys/fs/resctrl/info/last_cmd_status
  MB value 0 out of range [10,100]

  cd /sys/fs/resctrl
  mkdir 1 2 3 4 5 6 7 8
  mkdir: cannot create directory '8': No space left on device
  cat /sys/fs/resctrl/info/last_cmd_status
  out of CLOSIDs

See 'last_cmd_status' for more details in kernel documentation:
https://www.kernel.org/doc/Documentation/x86/intel_rdt_ui.txt

In runc, we could append the diagnostics information to the error
message of Intel RDT operation errors to provide more user-friendly
information.

Signed-off-by: Xiaochen Shen <xiaochen.shen@intel.com>

libcontainer/intelrdt/intelrdt.go

@@ -439,6 +439,22 @@ func getMemBwInfo() (*MemBwInfo, error) {
 	return memBwInfo, nil
 }
 
+// Get diagnostics for last filesystem operation error from file info/last_cmd_status
+func getLastCmdStatus() (string, error) {
+	rootPath, err := getIntelRdtRoot()
+	if err != nil {
+		return "", err
+	}
+
+	path := filepath.Join(rootPath, "info")
+	lastCmdStatus, err := getIntelRdtParamString(path, "last_cmd_status")
+	if err != nil {
+		return "", err
+	}
+
+	return lastCmdStatus, nil
+}
+
 // WriteIntelRdtTasks writes the specified pid into the "tasks" file
 func WriteIntelRdtTasks(dir string, pid int) error {
 	if dir == "" {
@@ -637,21 +653,21 @@ func (m *IntelRdtManager) Set(container *configs.Config) error {
 		// Write a single joint schema string to schemata file
 		if l3CacheSchema != "" && memBwSchema != "" {
 			if err := writeFile(path, "schemata", l3CacheSchema+"\n"+memBwSchema); err != nil {
-				return err
+				return NewLastCmdError(err)
 			}
 		}
 
 		// Write only L3 cache schema string to schemata file
 		if l3CacheSchema != "" && memBwSchema == "" {
 			if err := writeFile(path, "schemata", l3CacheSchema); err != nil {
-				return err
+				return NewLastCmdError(err)
 			}
 		}
 
 		// Write only memory bandwidth schema string to schemata file
 		if l3CacheSchema == "" && memBwSchema != "" {
 			if err := writeFile(path, "schemata", memBwSchema); err != nil {
-				return err
+				return NewLastCmdError(err)
 			}
 		}
 	}
@@ -662,11 +678,11 @@ func (m *IntelRdtManager) Set(container *configs.Config) error {
 func (raw *intelRdtData) join(id string) (string, error) {
 	path := filepath.Join(raw.root, id)
 	if err := os.MkdirAll(path, 0755); err != nil {
-		return "", err
+		return "", NewLastCmdError(err)
 	}
 
 	if err := WriteIntelRdtTasks(path, raw.pid); err != nil {
-		return "", err
+		return "", NewLastCmdError(err)
 	}
 	return path, nil
 }
@@ -692,3 +708,23 @@ func IsNotFound(err error) bool {
 	_, ok := err.(*NotFoundError)
 	return ok
 }
+
+type LastCmdError struct {
+	LastCmdStatus string
+	Err           error
+}
+
+func (e *LastCmdError) Error() string {
+	return fmt.Sprintf(e.Err.Error() + ", last_cmd_status: " + e.LastCmdStatus)
+}
+
+func NewLastCmdError(err error) error {
+	lastCmdStatus, err1 := getLastCmdStatus()
+	if err1 == nil {
+		return &LastCmdError{
+			LastCmdStatus: lastCmdStatus,
+			Err:           err,
+		}
+	}
+	return err
+}