add '.healing.bin' for tracking currently healing disk (#10573)

add a hint on the disk to allow for tracking fresh disk
being healed, to allow for restartable heals, and also
use this as a way to track and remove disks.

There are more pending changes where we should move
all the disk formatting logic to backend drives, this
PR doesn't deal with this refactor instead makes it
easier to track healing in the future.

cmd/xl-storage.go

@@ -92,8 +92,7 @@ type xlStorage struct {
 	activeIOCount    int32
 
 	diskPath string
-	hostname string
-	endpoint string
+	endpoint Endpoint
 
 	pool sync.Pool
 
@@ -249,7 +248,6 @@ func newLocalXLStorage(path string) (*xlStorage, error) {
 // Initialize a new storage disk.
 func newXLStorage(ep Endpoint) (*xlStorage, error) {
 	path := ep.Path
-	hostname := ep.Host
 	var err error
 	if path, err = getValidPath(path, true); err != nil {
 		return nil, err
@@ -262,8 +260,7 @@ func newXLStorage(ep Endpoint) (*xlStorage, error) {
 
 	p := &xlStorage{
 		diskPath: path,
-		hostname: hostname,
-		endpoint: ep.String(),
+		endpoint: ep,
 		pool: sync.Pool{
 			New: func() interface{} {
 				b := disk.AlignedBlock(readBlockSize)
@@ -319,7 +316,11 @@ func (s *xlStorage) String() string {
 }
 
 func (s *xlStorage) Hostname() string {
-	return s.hostname
+	return s.endpoint.Host
+}
+
+func (s *xlStorage) Endpoint() Endpoint {
+	return s.endpoint
 }
 
 func (*xlStorage) Close() error {
@@ -334,6 +335,13 @@ func (s *xlStorage) IsLocal() bool {
 	return true
 }
 
+func (s *xlStorage) Healing() bool {
+	healingFile := pathJoin(s.diskPath, minioMetaBucket,
+		bucketMetaPrefix, healingTrackerFilename)
+	_, err := os.Stat(healingFile)
+	return err == nil
+}
+
 func (s *xlStorage) waitForLowActiveIO() {
 	max := lowActiveIOWaitMaxN
 	for atomic.LoadInt32(&s.activeIOCount) >= s.maxActiveIOCount {
@@ -439,6 +447,7 @@ type DiskInfo struct {
 	Free      uint64
 	Used      uint64
 	RootDisk  bool
+	Healing   bool
 	Endpoint  string
 	MountPath string
 	ID        string
@@ -462,9 +471,10 @@ func (s *xlStorage) DiskInfo(context.Context) (info DiskInfo, err error) {
 		Total:     di.Total,
 		Free:      di.Free,
 		Used:      di.Total - di.Free,
+		Healing:   s.Healing(),
 		RootDisk:  s.rootDisk,
 		MountPath: s.diskPath,
-		Endpoint:  s.endpoint,
+		Endpoint:  s.endpoint.String(),
 	}
 
 	diskID, err := s.GetDiskID()