heal: Avoid deadline error with very large objects (minio#140) (minio#20586)

Healing a large object with a normal scan mode where no parts read 
is involved can still fail after 30 seconds if an object has

There are too many parts when hard disks are being used mainly. 
The reason is there is a general deadline that checks for all parts we 
do a deadline per part.

Author: vadmeste

cmd/xl-storage-disk-id-check.go

@@ -509,9 +509,7 @@ func (p *xlStorageDiskIDCheck) CheckParts(ctx context.Context, volume string, pa
 	}
 	defer done(0, &err)
 
-	return xioutil.WithDeadline[*CheckPartsResp](ctx, globalDriveConfig.GetMaxTimeout(), func(ctx context.Context) (res *CheckPartsResp, err error) {
-		return p.storage.CheckParts(ctx, volume, path, fi)
-	})
+	return p.storage.CheckParts(ctx, volume, path, fi)
 }
 
 func (p *xlStorageDiskIDCheck) DeleteBulk(ctx context.Context, volume string, paths ...string) (err error) {

cmd/xl-storage.go

@@ -2367,6 +2367,41 @@ func (s *xlStorage) AppendFile(ctx context.Context, volume string, path string,
 	return nil
 }
 
+// checkPart is a light check of an existing and size of a part, without doing a bitrot operation
+// For any unexpected error, return checkPartUnknown (zero)
+func (s *xlStorage) checkPart(volumeDir, path, dataDir string, partNum int, expectedSize int64, skipAccessCheck bool) (resp int) {
+	partPath := pathJoin(path, dataDir, fmt.Sprintf("part.%d", partNum))
+	filePath := pathJoin(volumeDir, partPath)
+	st, err := Lstat(filePath)
+	if err != nil {
+		if osIsNotExist(err) {
+			if !skipAccessCheck {
+				// Stat a volume entry.
+				if verr := Access(volumeDir); verr != nil {
+					if osIsNotExist(verr) {
+						resp = checkPartVolumeNotFound
+					}
+					return
+				}
+			}
+		}
+		if osErrToFileErr(err) == errFileNotFound {
+			resp = checkPartFileNotFound
+		}
+		return
+	}
+	if st.Mode().IsDir() {
+		resp = checkPartFileNotFound
+		return
+	}
+	// Check if shard is truncated.
+	if st.Size() < expectedSize {
+		resp = checkPartFileCorrupt
+		return
+	}
+	return checkPartSuccess
+}
+
 // CheckParts check if path has necessary parts available.
 func (s *xlStorage) CheckParts(ctx context.Context, volume string, path string, fi FileInfo) (*CheckPartsResp, error) {
 	volumeDir, err := s.getVolDir(volume)
@@ -2385,36 +2420,12 @@ func (s *xlStorage) CheckParts(ctx context.Context, volume string, path string,
 	}
 
 	for i, part := range fi.Parts {
-		partPath := pathJoin(path, fi.DataDir, fmt.Sprintf("part.%d", part.Number))
-		filePath := pathJoin(volumeDir, partPath)
-		st, err := Lstat(filePath)
+		resp.Results[i], err = xioutil.WithDeadline[int](ctx, globalDriveConfig.GetMaxTimeout(), func(ctx context.Context) (int, error) {
+			return s.checkPart(volumeDir, path, fi.DataDir, part.Number, fi.Erasure.ShardFileSize(part.Size), skipAccessChecks(volume)), nil
+		})
 		if err != nil {
-			if osIsNotExist(err) {
-				if !skipAccessChecks(volume) {
-					// Stat a volume entry.
-					if verr := Access(volumeDir); verr != nil {
-						if osIsNotExist(verr) {
-							resp.Results[i] = checkPartVolumeNotFound
-						}
-						continue
-					}
-				}
-			}
-			if osErrToFileErr(err) == errFileNotFound {
-				resp.Results[i] = checkPartFileNotFound
-			}
-			continue
-		}
-		if st.Mode().IsDir() {
-			resp.Results[i] = checkPartFileNotFound
-			continue
-		}
-		// Check if shard is truncated.
-		if st.Size() < fi.Erasure.ShardFileSize(part.Size) {
-			resp.Results[i] = checkPartFileCorrupt
-			continue
+			return nil, err
 		}
-		resp.Results[i] = checkPartSuccess
 	}
 
 	return &resp, nil
@@ -2546,17 +2557,7 @@ func (s *xlStorage) Delete(ctx context.Context, volume string, path string, dele
 }
 
 func skipAccessChecks(volume string) (ok bool) {
-	for _, prefix := range []string{
-		minioMetaTmpDeletedBucket,
-		minioMetaTmpBucket,
-		minioMetaMultipartBucket,
-		minioMetaBucket,
-	} {
-		if strings.HasPrefix(volume, prefix) {
-			return true
-		}
-	}
-	return ok
+	return strings.HasPrefix(volume, minioMetaBucket)
 }
 
 // RenameData - rename source path to destination path atomically, metadata and data directory.