XL: Rename, cleanup and add more comments. (#1769)

- xl-v1-bucket.go - removes a whole bunch of code.
- {xl-v1,fs-v1}-metadata.go - add a lot of comments and rename functions
   appropriately.

erasure.go

@@ -16,11 +16,7 @@
 
 package main
 
-import (
-	"errors"
-
-	"github.com/klauspost/reedsolomon"
-)
+import "github.com/klauspost/reedsolomon"
 
 // erasure storage layer.
 type erasure struct {
@@ -30,9 +26,6 @@ type erasure struct {
 	storageDisks []StorageAPI
 }
 
-// errUnexpected - returned for any unexpected error.
-var errUnexpected = errors.New("Unexpected error - please report at https://github.com/minio/minio/issues")
-
 // newErasure instantiate a new erasure.
 func newErasure(disks []StorageAPI) *erasure {
 	// Initialize E.

fs-v1-metadata.go

@@ -44,28 +44,42 @@ func (m fsMetaV1) WriteTo(writer io.Writer) (n int64, err error) {
 	return int64(p), err
 }
 
-// SearchObjectPart - search object part name and etag.
-func (m fsMetaV1) SearchObjectPart(number int) int {
+// ObjectPartIndex - returns the index of matching object part number.
+func (m fsMetaV1) ObjectPartIndex(partNumber int) (partIndex int) {
 	for i, part := range m.Parts {
-		if number == part.Number {
-			return i
+		if partNumber == part.Number {
+			partIndex = i
+			return partIndex
 		}
 	}
 	return -1
 }
 
 // AddObjectPart - add a new object part in order.
-func (m *fsMetaV1) AddObjectPart(number int, name string, etag string, size int64) {
-	m.Parts = append(m.Parts, objectPartInfo{
-		Number: number,
-		Name:   name,
-		ETag:   etag,
-		Size:   size,
-	})
+func (m *fsMetaV1) AddObjectPart(partNumber int, partName string, partETag string, partSize int64) {
+	partInfo := objectPartInfo{
+		Number: partNumber,
+		Name:   partName,
+		ETag:   partETag,
+		Size:   partSize,
+	}
+
+	// Update part info if it already exists.
+	for i, part := range m.Parts {
+		if partNumber == part.Number {
+			m.Parts[i] = partInfo
+			return
+		}
+	}
+
+	// Proceed to include new part info.
+	m.Parts = append(m.Parts, partInfo)
+
+	// Parts in fsMeta should be in sorted order by part number.
 	sort.Sort(byPartNumber(m.Parts))
 }
 
-// readFSMetadata - read `fs.json`.
+// readFSMetadata - returns the object metadata `fs.json` content.
 func (fs fsObjects) readFSMetadata(bucket, object string) (fsMeta fsMetaV1, err error) {
 	r, err := fs.storage.ReadFile(bucket, path.Join(object, fsMetaJSONFile), int64(0))
 	if err != nil {
@@ -79,10 +93,17 @@ func (fs fsObjects) readFSMetadata(bucket, object string) (fsMeta fsMetaV1, err
 	return fsMeta, nil
 }
 
-// writeFSMetadata - write `fs.json`.
-func (fs fsObjects) writeFSMetadata(bucket, prefix string, fsMeta fsMetaV1) error {
-	// Initialize metadata map, save all erasure related metadata.
+// newFSMetaV1 - initializes new fsMetaV1.
+func newFSMetaV1() (fsMeta fsMetaV1) {
+	fsMeta = fsMetaV1{}
+	fsMeta.Version = "1"
+	fsMeta.Format = "fs"
 	fsMeta.Minio.Release = minioReleaseTag
+	return fsMeta
+}
+
+// writeFSMetadata - writes `fs.json` metadata.
+func (fs fsObjects) writeFSMetadata(bucket, prefix string, fsMeta fsMetaV1) error {
 	w, err := fs.storage.CreateFile(bucket, path.Join(prefix, fsMetaJSONFile))
 	if err != nil {
 		return err

fs-v1-multipart.go

@@ -63,9 +63,8 @@ func (fs fsObjects) newMultipartUploadCommon(bucket string, object string, meta
 		meta = make(map[string]string)
 	}
 
-	fsMeta := fsMetaV1{}
-	fsMeta.Format = "fs"
-	fsMeta.Version = "1"
+	// Initialize `fs.json` values.
+	fsMeta := newFSMetaV1()
 
 	// This lock needs to be held for any changes to the directory contents of ".minio/multipart/object/"
 	nsMutex.Lock(minioMetaBucket, pathJoin(mpartMetaPrefix, bucket, object))
@@ -454,7 +453,7 @@ func (fs fsObjects) listObjectPartsCommon(bucket, object, uploadID string, partN
 		return ListPartsInfo{}, toObjectErr(err, minioMetaBucket, uploadIDPath)
 	}
 	// Only parts with higher part numbers will be listed.
-	partIdx := fsMeta.SearchObjectPart(partNumberMarker)
+	partIdx := fsMeta.ObjectPartIndex(partNumberMarker)
 	parts := fsMeta.Parts
 	if partIdx != -1 {
 		parts = fsMeta.Parts[partIdx+1:]
@@ -642,7 +641,7 @@ func (fs fsObjects) abortMultipartUploadCommon(bucket, object, uploadID string)
 	// the object, if yes do not attempt to delete 'uploads.json'.
 	uploadIDs, err := getUploadIDs(bucket, object, fs.storage)
 	if err == nil {
-		uploadIDIdx := uploadIDs.SearchUploadID(uploadID)
+		uploadIDIdx := uploadIDs.Index(uploadID)
 		if uploadIDIdx != -1 {
 			uploadIDs.Uploads = append(uploadIDs.Uploads[:uploadIDIdx], uploadIDs.Uploads[uploadIDIdx+1:]...)
 		}

httprange.go

@@ -28,13 +28,10 @@ const (
 )
 
 // InvalidRange - invalid range
-type InvalidRange struct {
-	Start  int64
-	Length int64
-}
+type InvalidRange struct{}
 
 func (e InvalidRange) Error() string {
-	return fmt.Sprintf("Invalid range start:%d length:%d", e.Start, e.Length)
+	return "The requested range is not satisfiable"
 }
 
 // HttpRange specifies the byte range to be sent to the client.

object-handlers.go

@@ -136,7 +136,7 @@ func (api objectAPIHandlers) GetObjectHandler(w http.ResponseWriter, r *http.Req
 		writeErrorResponse(w, r, apiErr, r.URL.Path)
 		return
 	}
-	defer readCloser.Close() // Close after this handler returns.
+	defer readCloser.Close()
 
 	// Set standard object headers.
 	setObjectHeaders(w, objInfo, hrange)

tree-walk-xl.go

@@ -54,9 +54,7 @@ func (xl xlObjects) listDir(bucket, prefixDir string, filter func(entry string)
 
 	// Return the first success entry based on the selected random disk.
 	for listErrCount < len(xl.storageDisks) {
-		// Choose a random disk on each attempt, do not hit the same disk all the time.
-		randIndex := rand.Intn(len(xl.storageDisks) - 1)
-		disk := xl.storageDisks[randIndex] // Pick a random disk.
+		disk := xl.getRandomDisk() // Choose a random disk on each attempt.
 		if entries, err = disk.ListDir(bucket, prefixDir); err == nil {
 			// Skip the entries which do not match the filter.
 			for i, entry := range entries {
@@ -85,6 +83,7 @@ func (xl xlObjects) listDir(bucket, prefixDir string, filter func(entry string)
 // getRandomDisk - gives a random disk at any point in time from the
 // available pool of disks.
 func (xl xlObjects) getRandomDisk() (disk StorageAPI) {
+	rand.Seed(time.Now().UTC().UnixNano())
 	randIndex := rand.Intn(len(xl.storageDisks) - 1)
 	disk = xl.storageDisks[randIndex] // Pick a random disk.
 	return disk

xl-v1-bucket.go

@@ -64,234 +64,102 @@ func (xl xlObjects) MakeBucket(bucket string) error {
 	if volumeExistsErrCnt == len(xl.storageDisks) {
 		return toObjectErr(errVolumeExists, bucket)
 	} else if createVolErr > len(xl.storageDisks)-xl.writeQuorum {
-		// Return errWriteQuorum if errors were more than
-		// allowed write quorum.
+		// Return errWriteQuorum if errors were more than allowed write quorum.
 		return toObjectErr(errWriteQuorum, bucket)
 	}
 	return nil
 }
 
-// getAllBucketInfo - list bucket info from all disks.
-// Returns error slice indicating the failed volume stat operations.
-func (xl xlObjects) getAllBucketInfo(bucketName string) ([]BucketInfo, []error) {
-	// Create errs and volInfo slices of storageDisks size.
-	var errs = make([]error, len(xl.storageDisks))
-	var volsInfo = make([]VolInfo, len(xl.storageDisks))
+// getBucketInfo - returns the BucketInfo from one of the disks picked
+// at random.
+func (xl xlObjects) getBucketInfo(bucketName string) (bucketInfo BucketInfo, err error) {
+	// Count for errors encountered.
+	var bucketErrCount = 0
 
-	// Allocate a new waitgroup.
-	var wg = &sync.WaitGroup{}
-	for index, disk := range xl.storageDisks {
-		wg.Add(1)
-		// Stat volume on all the disks in a routine.
-		go func(index int, disk StorageAPI) {
-			defer wg.Done()
-			volInfo, err := disk.StatVol(bucketName)
-			if err != nil {
-				errs[index] = err
-				return
-			}
-			volsInfo[index] = volInfo
-			errs[index] = nil
-		}(index, disk)
-	}
-
-	// Wait for all the Stat operations to finish.
-	wg.Wait()
-
-	// Return the concocted values.
-	var bucketsInfo = make([]BucketInfo, len(xl.storageDisks))
-	for _, volInfo := range volsInfo {
-		if IsValidBucketName(volInfo.Name) {
-			bucketsInfo = append(bucketsInfo, BucketInfo{
+	// Return the first successful lookup from a random list of disks.
+	for bucketErrCount < len(xl.storageDisks) {
+		disk := xl.getRandomDisk() // Choose a random disk on each attempt.
+		var volInfo VolInfo
+		volInfo, err = disk.StatVol(bucketName)
+		if err == nil {
+			bucketInfo = BucketInfo{
 				Name:    volInfo.Name,
 				Created: volInfo.Created,
-			})
-		}
-	}
-	return bucketsInfo, errs
-}
-
-// listAllBucketInfo - list all stat volume info from all disks.
-// Returns
-// - stat volume info for all online disks.
-// - boolean to indicate if healing is necessary.
-// - error if any.
-func (xl xlObjects) listAllBucketInfo(bucketName string) ([]BucketInfo, bool, error) {
-	bucketsInfo, errs := xl.getAllBucketInfo(bucketName)
-	notFoundCount := 0
-	for _, err := range errs {
-		if err == errVolumeNotFound {
-			notFoundCount++
-			// If we have errors with file not found greater than allowed read
-			// quorum we return err as errFileNotFound.
-			if notFoundCount > len(xl.storageDisks)-xl.readQuorum {
-				return nil, false, errVolumeNotFound
 			}
+			return bucketInfo, nil
 		}
+		bucketErrCount++ // Update error count.
 	}
-
-	// Calculate online disk count.
-	onlineDiskCount := 0
-	for index := range errs {
-		if errs[index] == nil {
-			onlineDiskCount++
-		}
-	}
-
-	var heal bool
-	// If online disks count is lesser than configured disks, most
-	// probably we need to heal the file, additionally verify if the
-	// count is lesser than readQuorum, if not we throw an error.
-	if onlineDiskCount < len(xl.storageDisks) {
-		// Online disks lesser than total storage disks, needs to be
-		// healed. unless we do not have readQuorum.
-		heal = true
-		// Verify if online disks count are lesser than readQuorum
-		// threshold, return an error if yes.
-		if onlineDiskCount < xl.readQuorum {
-			return nil, false, errReadQuorum
-		}
-	}
-
-	// Return success.
-	return bucketsInfo, heal, nil
+	return BucketInfo{}, err
 }
 
 // Checks whether bucket exists.
-func (xl xlObjects) isBucketExist(bucketName string) bool {
+func (xl xlObjects) isBucketExist(bucket string) bool {
+	nsMutex.RLock(bucket, "")
+	defer nsMutex.RUnlock(bucket, "")
+
 	// Check whether bucket exists.
-	_, _, err := xl.listAllBucketInfo(bucketName)
+	_, err := xl.getBucketInfo(bucket)
 	if err != nil {
 		if err == errVolumeNotFound {
 			return false
 		}
-		errorIf(err, "Stat failed on bucket "+bucketName+".")
+		errorIf(err, "Stat failed on bucket "+bucket+".")
 		return false
 	}
 	return true
 }
 
-// GetBucketInfo - get bucket info.
+// GetBucketInfo - returns BucketInfo for a bucket.
 func (xl xlObjects) GetBucketInfo(bucket string) (BucketInfo, error) {
 	// Verify if bucket is valid.
 	if !IsValidBucketName(bucket) {
 		return BucketInfo{}, BucketNameInvalid{Bucket: bucket}
 	}
-
 	nsMutex.RLock(bucket, "")
 	defer nsMutex.RUnlock(bucket, "")
-
-	// List and figured out if we need healing.
-	bucketsInfo, heal, err := xl.listAllBucketInfo(bucket)
+	bucketInfo, err := xl.getBucketInfo(bucket)
 	if err != nil {
 		return BucketInfo{}, toObjectErr(err, bucket)
 	}
+	return bucketInfo, nil
+}
 
-	// Heal for missing entries.
-	if heal {
-		go func() {
-			// Create bucket if missing on disks.
-			for index, bktInfo := range bucketsInfo {
-				if bktInfo.Name != "" {
+// listBuckets - returns list of all buckets from a disk picked at random.
+func (xl xlObjects) listBuckets() (bucketsInfo []BucketInfo, err error) {
+	// Count for errors encountered.
+	var listBucketsErrCount = 0
+
+	// Return the first successful lookup from a random list of disks.
+	for listBucketsErrCount < len(xl.storageDisks) {
+		disk := xl.getRandomDisk() // Choose a random disk on each attempt.
+		var volsInfo []VolInfo
+		volsInfo, err = disk.ListVols()
+		if err == nil {
+			// NOTE: The assumption here is that volumes across all disks in
+			// readQuorum have consistent view i.e they all have same number
+			// of buckets. This is essentially not verified since healing
+			// should take care of this.
+			var bucketsInfo []BucketInfo
+			for _, volInfo := range volsInfo {
+				// StorageAPI can send volume names which are incompatible
+				// with buckets, handle it and skip them.
+				if !IsValidBucketName(volInfo.Name) {
 					continue
 				}
-				// Bucketinfo name would be an empty string, create it.
-				xl.storageDisks[index].MakeVol(bucket)
+				bucketsInfo = append(bucketsInfo, BucketInfo{
+					Name:    volInfo.Name,
+					Created: volInfo.Created,
+				})
 			}
-		}()
-	}
-
-	// From all bucketsInfo, calculate the actual usage values.
-	var total, free int64
-	var bucketInfo BucketInfo
-	for _, bucketInfo = range bucketsInfo {
-		if bucketInfo.Name == "" {
-			continue
+			return bucketsInfo, nil
 		}
-		free += bucketInfo.Free
-		total += bucketInfo.Total
+		listBucketsErrCount++ // Update error count.
 	}
-
-	// Update the aggregated values.
-	bucketInfo.Free = free
-	bucketInfo.Total = total
-
-	return BucketInfo{
-		Name:    bucket,
-		Created: bucketInfo.Created,
-		Total:   bucketInfo.Total,
-		Free:    bucketInfo.Free,
-	}, nil
+	return nil, err
 }
 
-func (xl xlObjects) listBuckets() ([]BucketInfo, error) {
-	// Initialize sync waitgroup.
-	var wg = &sync.WaitGroup{}
-
-	// Success vols map carries successful results of ListVols from each disks.
-	var successVols = make([][]VolInfo, len(xl.storageDisks))
-	for index, disk := range xl.storageDisks {
-		wg.Add(1) // Add each go-routine to wait for.
-		go func(index int, disk StorageAPI) {
-			// Indicate wait group as finished.
-			defer wg.Done()
-
-			// Initiate listing.
-			volsInfo, _ := disk.ListVols()
-			successVols[index] = volsInfo
-		}(index, disk)
-	}
-
-	// Wait for all the list volumes running in parallel to finish.
-	wg.Wait()
-
-	// From success vols map calculate aggregated usage values.
-	var volsInfo []VolInfo
-	var total, free int64
-	for _, volsInfo = range successVols {
-		var volInfo VolInfo
-		for _, volInfo = range volsInfo {
-			if volInfo.Name == "" {
-				continue
-			}
-			if !IsValidBucketName(volInfo.Name) {
-				continue
-			}
-			break
-		}
-		free += volInfo.Free
-		total += volInfo.Total
-	}
-
-	// Save the updated usage values back into the vols.
-	for index, volInfo := range volsInfo {
-		volInfo.Free = free
-		volInfo.Total = total
-		volsInfo[index] = volInfo
-	}
-
-	// NOTE: The assumption here is that volumes across all disks in
-	// readQuorum have consistent view i.e they all have same number
-	// of buckets. This is essentially not verified since healing
-	// should take care of this.
-	var bucketsInfo []BucketInfo
-	for _, volInfo := range volsInfo {
-		// StorageAPI can send volume names which are incompatible
-		// with buckets, handle it and skip them.
-		if !IsValidBucketName(volInfo.Name) {
-			continue
-		}
-		bucketsInfo = append(bucketsInfo, BucketInfo{
-			Name:    volInfo.Name,
-			Created: volInfo.Created,
-			Total:   volInfo.Total,
-			Free:    volInfo.Free,
-		})
-	}
-	return bucketsInfo, nil
-}
-
-// ListBuckets - list buckets.
+// ListBuckets - lists all the buckets, sorted by its name.
 func (xl xlObjects) ListBuckets() ([]BucketInfo, error) {
 	bucketInfos, err := xl.listBuckets()
 	if err != nil {
@@ -302,7 +170,7 @@ func (xl xlObjects) ListBuckets() ([]BucketInfo, error) {
 	return bucketInfos, nil
 }
 
-// DeleteBucket - delete a bucket.
+// DeleteBucket - deletes a bucket.
 func (xl xlObjects) DeleteBucket(bucket string) error {
 	// Verify if bucket is valid.
 	if !IsValidBucketName(bucket) {

xl-v1-metadata.go

@@ -100,63 +100,73 @@ func (t byPartNumber) Len() int           { return len(t) }
 func (t byPartNumber) Swap(i, j int)      { t[i], t[j] = t[j], t[i] }
 func (t byPartNumber) Less(i, j int) bool { return t[i].Number < t[j].Number }
 
-// SearchObjectPart - searches for part name and etag, returns the
-// index if found.
-func (m xlMetaV1) SearchObjectPart(number int) int {
+// ObjectPartIndex - returns the index of matching object part number.
+func (m xlMetaV1) ObjectPartIndex(partNumber int) (index int) {
 	for i, part := range m.Parts {
-		if number == part.Number {
-			return i
+		if partNumber == part.Number {
+			index = i
+			return index
 		}
 	}
 	return -1
 }
 
 // AddObjectPart - add a new object part in order.
-func (m *xlMetaV1) AddObjectPart(number int, name string, etag string, size int64) {
+func (m *xlMetaV1) AddObjectPart(partNumber int, partName string, partETag string, partSize int64) {
 	partInfo := objectPartInfo{
-		Number: number,
-		Name:   name,
-		ETag:   etag,
-		Size:   size,
+		Number: partNumber,
+		Name:   partName,
+		ETag:   partETag,
+		Size:   partSize,
 	}
+
+	// Update part info if it already exists.
 	for i, part := range m.Parts {
-		if number == part.Number {
+		if partNumber == part.Number {
 			m.Parts[i] = partInfo
 			return
 		}
 	}
+
+	// Proceed to include new part info.
 	m.Parts = append(m.Parts, partInfo)
+
+	// Parts in xlMeta should be in sorted order by part number.
 	sort.Sort(byPartNumber(m.Parts))
 }
 
-// getPartIndexOffset - given an offset for the whole object, return the part and offset in that part.
-func (m xlMetaV1) getPartIndexOffset(offset int64) (partIndex int, partOffset int64, err error) {
+// objectToPartOffset - translate offset of an object to offset of its individual part.
+func (m xlMetaV1) objectToPartOffset(offset int64) (partIndex int, partOffset int64, err error) {
 	partOffset = offset
+	// Seek until object offset maps to a particular part offset.
 	for i, part := range m.Parts {
 		partIndex = i
+		// Last part can be of '0' bytes, treat it specially and
+		// return right here.
 		if part.Size == 0 {
 			return partIndex, partOffset, nil
 		}
+		// Offset is smaller than size we have reached the proper part offset.
 		if partOffset < part.Size {
 			return partIndex, partOffset, nil
 		}
+		// Continue to towards the next part.
 		partOffset -= part.Size
 	}
-	// Offset beyond the size of the object
-	err = errUnexpected
-	return 0, 0, err
+	// Offset beyond the size of the object return InvalidRange.
+	return 0, 0, InvalidRange{}
 }
 
-// readXLMetadata - read xl metadata.
+// readXLMetadata - returns the object metadata `xl.json` content from
+// one of the disks picked at random.
 func (xl xlObjects) readXLMetadata(bucket, object string) (xlMeta xlMetaV1, err error) {
 	// Count for errors encountered.
 	var xlJSONErrCount = 0
 
-	// Return the first success entry based on the selected random disk.
+	// Return the first successful lookup from a random list of disks.
 	for xlJSONErrCount < len(xl.storageDisks) {
 		var r io.ReadCloser
-		// Choose a random disk on each attempt, do not hit the same disk all the time.
-		disk := xl.getRandomDisk() // Pick a random disk.
+		disk := xl.getRandomDisk() // Choose a random disk on each attempt.
 		r, err = disk.ReadFile(bucket, path.Join(object, xlMetaJSONFile), int64(0))
 		if err == nil {
 			defer r.Close()
@@ -170,23 +180,29 @@ func (xl xlObjects) readXLMetadata(bucket, object string) (xlMeta xlMetaV1, err
 	return xlMetaV1{}, err
 }
 
-// writeXLJson - write `xl.json` on all disks in order.
-func (xl xlObjects) writeXLMetadata(bucket, prefix string, xlMeta xlMetaV1) error {
-	var wg = &sync.WaitGroup{}
-	var mErrs = make([]error, len(xl.storageDisks))
-
-	// Initialize metadata map, save all erasure related metadata.
+// newXLMetaV1 - initializes new xlMetaV1.
+func newXLMetaV1(dataBlocks, parityBlocks int) (xlMeta xlMetaV1) {
+	xlMeta = xlMetaV1{}
 	xlMeta.Version = "1"
 	xlMeta.Format = "xl"
 	xlMeta.Minio.Release = minioReleaseTag
 	xlMeta.Erasure.Algorithm = erasureAlgorithmKlauspost
-	xlMeta.Erasure.DataBlocks = xl.dataBlocks
-	xlMeta.Erasure.ParityBlocks = xl.parityBlocks
+	xlMeta.Erasure.DataBlocks = dataBlocks
+	xlMeta.Erasure.ParityBlocks = parityBlocks
 	xlMeta.Erasure.BlockSize = erasureBlockSize
-	xlMeta.Erasure.Distribution = xl.getDiskDistribution()
+	xlMeta.Erasure.Distribution = randErasureDistribution(dataBlocks + parityBlocks)
+	return xlMeta
+}
 
+// writeXLMetadata - write `xl.json` on all disks in order.
+func (xl xlObjects) writeXLMetadata(bucket, prefix string, xlMeta xlMetaV1) error {
+	var wg = &sync.WaitGroup{}
+	var mErrs = make([]error, len(xl.storageDisks))
+
+	// Start writing `xl.json` to all disks in parallel.
 	for index, disk := range xl.storageDisks {
 		wg.Add(1)
+		// Write `xl.json` in a routine.
 		go func(index int, disk StorageAPI, metadata xlMetaV1) {
 			defer wg.Done()
 
@@ -197,8 +213,10 @@ func (xl xlObjects) writeXLMetadata(bucket, prefix string, xlMeta xlMetaV1) erro
 				return
 			}
 
-			// Save the order.
+			// Save the disk order index.
 			metadata.Erasure.Index = index + 1
+
+			// Marshal metadata to the writer.
 			_, mErr = metadata.WriteTo(metaWriter)
 			if mErr != nil {
 				if mErr = safeCloseAndRemove(metaWriter); mErr != nil {
@@ -208,6 +226,7 @@ func (xl xlObjects) writeXLMetadata(bucket, prefix string, xlMeta xlMetaV1) erro
 				mErrs[index] = mErr
 				return
 			}
+			// Verify if close fails with an error.
 			if mErr = metaWriter.Close(); mErr != nil {
 				if mErr = safeCloseAndRemove(metaWriter); mErr != nil {
 					mErrs[index] = mErr
@@ -223,7 +242,6 @@ func (xl xlObjects) writeXLMetadata(bucket, prefix string, xlMeta xlMetaV1) erro
 	// Wait for all the routines.
 	wg.Wait()
 
-	// FIXME: check for quorum.
 	// Return the first error.
 	for _, err := range mErrs {
 		if err == nil {
@@ -234,11 +252,18 @@ func (xl xlObjects) writeXLMetadata(bucket, prefix string, xlMeta xlMetaV1) erro
 	return nil
 }
 
-// getDiskDistribution - get disk distribution.
-func (xl xlObjects) getDiskDistribution() []int {
-	var distribution = make([]int, len(xl.storageDisks))
-	for index := range xl.storageDisks {
-		distribution[index] = index + 1
+// randErasureDistribution - uses Knuth Fisher-Yates shuffle algorithm.
+func randErasureDistribution(numBlocks int) []int {
+	distribution := make([]int, numBlocks)
+	for i := 0; i < numBlocks; i++ {
+		distribution[i] = i + 1
 	}
+	/*
+		for i := 0; i < numBlocks; i++ {
+			// Choose index uniformly in [i, numBlocks-1]
+			r := i + rand.Intn(numBlocks-i)
+			distribution[r], distribution[i] = distribution[i], distribution[r]
+		}
+	*/
 	return distribution
 }

xl-v1-multipart-common.go

@@ -60,7 +60,8 @@ func (u *uploadsV1) AddUploadID(uploadID string, initiated time.Time) {
 	sort.Sort(byInitiatedTime(u.Uploads))
 }
 
-func (u uploadsV1) SearchUploadID(uploadID string) int {
+// Index - returns the index of matching the upload id.
+func (u uploadsV1) Index(uploadID string) int {
 	for i, u := range u.Uploads {
 		if u.UploadID == uploadID {
 			return i
@@ -90,7 +91,7 @@ func (u uploadsV1) WriteTo(writer io.Writer) (n int64, err error) {
 	return int64(m), err
 }
 
-// getUploadIDs - get saved upload id's.
+// getUploadIDs - get all the saved upload id's.
 func getUploadIDs(bucket, object string, storageDisks ...StorageAPI) (uploadIDs uploadsV1, err error) {
 	uploadJSONPath := path.Join(mpartMetaPrefix, bucket, object, uploadsJSONFile)
 	var errs = make([]error, len(storageDisks))
@@ -258,7 +259,7 @@ func cleanupUploadedParts(bucket, object, uploadID string, storageDisks ...Stora
 
 // listUploadsInfo - list all uploads info.
 func (xl xlObjects) listUploadsInfo(prefixPath string) (uploads []uploadInfo, err error) {
-	disk := xl.getRandomDisk()
+	disk := xl.getRandomDisk() // Choose a random disk on each attempt.
 	splitPrefixes := strings.SplitN(prefixPath, "/", 3)
 	uploadIDs, err := getUploadIDs(splitPrefixes[1], splitPrefixes[2], disk)
 	if err != nil {

xl-v1-multipart.go

@@ -57,7 +57,7 @@ func (xl xlObjects) newMultipartUploadCommon(bucket string, object string, meta
 		meta = make(map[string]string)
 	}
 
-	xlMeta := xlMetaV1{}
+	xlMeta := newXLMetaV1(xl.dataBlocks, xl.parityBlocks)
 	// If not set default to "application/octet-stream"
 	if meta["content-type"] == "" {
 		contentType := "application/octet-stream"
@@ -125,11 +125,18 @@ func (xl xlObjects) putObjectPartCommon(bucket string, object string, uploadID s
 	nsMutex.Lock(minioMetaBucket, pathJoin(mpartMetaPrefix, bucket, object, uploadID, strconv.Itoa(partID)))
 	defer nsMutex.Unlock(minioMetaBucket, pathJoin(mpartMetaPrefix, bucket, object, uploadID, strconv.Itoa(partID)))
 
+	uploadIDPath := path.Join(mpartMetaPrefix, bucket, object, uploadID)
+	xlMeta, err := xl.readXLMetadata(minioMetaBucket, uploadIDPath)
+	if err != nil {
+		return "", toObjectErr(err, minioMetaBucket, uploadIDPath)
+	}
+
 	// List all online disks.
 	onlineDisks, higherVersion, err := xl.listOnlineDisks(minioMetaBucket, pathJoin(mpartMetaPrefix, bucket, object, uploadID))
 	if err != nil {
 		return "", toObjectErr(err, bucket, object)
 	}
+	// Increment version only if we have online disks less than configured storage disks.
 	if diskCount(onlineDisks) < len(xl.storageDisks) {
 		higherVersion++
 	}
@@ -193,21 +200,18 @@ func (xl xlObjects) putObjectPartCommon(bucket string, object string, uploadID s
 		return "", err
 	}
 
-	uploadIDPath := path.Join(mpartMetaPrefix, bucket, object, uploadID)
-	xlMeta, err := xl.readXLMetadata(minioMetaBucket, uploadIDPath)
-	if err != nil {
-		return "", toObjectErr(err, minioMetaBucket, uploadIDPath)
-	}
-	xlMeta.Stat.Version = higherVersion
-	xlMeta.AddObjectPart(partID, partSuffix, newMD5Hex, size)
-
 	partPath := path.Join(mpartMetaPrefix, bucket, object, uploadID, partSuffix)
 	err = xl.renameObject(minioMetaBucket, tmpPartPath, minioMetaBucket, partPath)
 	if err != nil {
 		return "", toObjectErr(err, minioMetaBucket, partPath)
 	}
-	if err = xl.writeXLMetadata(minioMetaBucket, path.Join(mpartMetaPrefix, bucket, object, uploadID), xlMeta); err != nil {
-		return "", toObjectErr(err, minioMetaBucket, path.Join(mpartMetaPrefix, bucket, object, uploadID))
+
+	// Once part is successfully committed, proceed with updating XL metadata.
+	xlMeta.Stat.Version = higherVersion
+	xlMeta.AddObjectPart(partID, partSuffix, newMD5Hex, size)
+
+	if err = xl.writeXLMetadata(minioMetaBucket, uploadIDPath, xlMeta); err != nil {
+		return "", toObjectErr(err, minioMetaBucket, uploadIDPath)
 	}
 	return newMD5Hex, nil
 }
@@ -261,7 +265,7 @@ func (xl xlObjects) listObjectPartsCommon(bucket, object, uploadID string, partN
 	}
 
 	// Only parts with higher part numbers will be listed.
-	partIdx := xlMeta.SearchObjectPart(partNumberMarker)
+	partIdx := xlMeta.ObjectPartIndex(partNumberMarker)
 	parts := xlMeta.Parts
 	if partIdx != -1 {
 		parts = xlMeta.Parts[partIdx+1:]
@@ -349,7 +353,7 @@ func (xl xlObjects) CompleteMultipartUpload(bucket string, object string, upload
 
 	// Loop through all parts, validate them and then commit to disk.
 	for i, part := range parts {
-		partIdx := currentXLMeta.SearchObjectPart(part.PartNumber)
+		partIdx := currentXLMeta.ObjectPartIndex(part.PartNumber)
 		if partIdx == -1 {
 			return "", InvalidPart{}
 		}
@@ -414,7 +418,7 @@ func (xl xlObjects) CompleteMultipartUpload(bucket string, object string, upload
 	// the object, if yes do not attempt to delete 'uploads.json'.
 	uploadIDs, err := getUploadIDs(bucket, object, xl.storageDisks...)
 	if err == nil {
-		uploadIDIdx := uploadIDs.SearchUploadID(uploadID)
+		uploadIDIdx := uploadIDs.Index(uploadID)
 		if uploadIDIdx != -1 {
 			uploadIDs.Uploads = append(uploadIDs.Uploads[:uploadIDIdx], uploadIDs.Uploads[uploadIDIdx+1:]...)
 		}
@@ -435,8 +439,7 @@ func (xl xlObjects) CompleteMultipartUpload(bucket string, object string, upload
 	return s3MD5, nil
 }
 
-// abortMultipartUploadCommon - aborts a multipart upload, common
-// function used by both object layers.
+// abortMultipartUploadCommon - aborts a multipart upload, common function used by both object layers.
 func (xl xlObjects) abortMultipartUploadCommon(bucket, object, uploadID string) error {
 	// Verify if bucket is valid.
 	if !IsValidBucketName(bucket) {
@@ -465,7 +468,7 @@ func (xl xlObjects) abortMultipartUploadCommon(bucket, object, uploadID string)
 	// the object, if yes do not attempt to delete 'uploads.json'.
 	uploadIDs, err := getUploadIDs(bucket, object, xl.storageDisks...)
 	if err == nil {
-		uploadIDIdx := uploadIDs.SearchUploadID(uploadID)
+		uploadIDIdx := uploadIDs.Index(uploadID)
 		if uploadIDIdx != -1 {
 			uploadIDs.Uploads = append(uploadIDs.Uploads[:uploadIDIdx], uploadIDs.Uploads[uploadIDIdx+1:]...)
 		}

xl-v1-object.go

@@ -13,6 +13,12 @@ import (
 	"github.com/minio/minio/pkg/mimedb"
 )
 
+// nullReadCloser - returns 0 bytes and io.EOF upon first read attempt.
+type nullReadCloser struct{}
+
+func (n nullReadCloser) Read([]byte) (int, error) { return 0, io.EOF }
+func (n nullReadCloser) Close() error             { return nil }
+
 /// Object Operations
 
 // GetObject - get an object.
@@ -35,16 +41,19 @@ func (xl xlObjects) GetObject(bucket, object string, startOffset int64) (io.Read
 	if err != nil {
 		return nil, toObjectErr(err, bucket, object)
 	}
-
 	// List all online disks.
 	onlineDisks, _, err := xl.listOnlineDisks(bucket, object)
 	if err != nil {
 		return nil, toObjectErr(err, bucket, object)
 	}
+	// For zero byte files, return a null reader.
+	if xlMeta.Stat.Size == 0 {
+		return nullReadCloser{}, nil
+	}
 	erasure := newErasure(onlineDisks) // Initialize a new erasure with online disks
 
 	// Get part index offset.
-	partIndex, offset, err := xlMeta.getPartIndexOffset(startOffset)
+	partIndex, partOffset, err := xlMeta.objectToPartOffset(startOffset)
 	if err != nil {
 		return nil, toObjectErr(err, bucket, object)
 	}
@@ -59,13 +68,14 @@ func (xl xlObjects) GetObject(bucket, object string, startOffset int64) (io.Read
 		defer nsMutex.RUnlock(bucket, object)
 		for ; partIndex < len(xlMeta.Parts); partIndex++ {
 			part := xlMeta.Parts[partIndex]
-			r, err := erasure.ReadFile(bucket, pathJoin(object, part.Name), offset, part.Size)
+			r, err := erasure.ReadFile(bucket, pathJoin(object, part.Name), partOffset, part.Size)
 			if err != nil {
 				fileWriter.CloseWithError(toObjectErr(err, bucket, object))
 				return
 			}
-			// Reset offset to 0 as it would be non-0 only for the first loop if startOffset is non-0.
-			offset = 0
+			// Reset part offset to 0 to read rest of the parts from
+			// the beginning.
+			partOffset = 0
 			if _, err = io.Copy(fileWriter, r); err != nil {
 				switch reader := r.(type) {
 				case *io.PipeReader:
@@ -76,7 +86,7 @@ func (xl xlObjects) GetObject(bucket, object string, startOffset int64) (io.Read
 				fileWriter.CloseWithError(toObjectErr(err, bucket, object))
 				return
 			}
-			// Close the readerCloser that reads multiparts of an object from the xl storage layer.
+			// Close the readerCloser that reads multiparts of an object.
 			// Not closing leaks underlying file descriptors.
 			r.Close()
 		}
@@ -198,12 +208,13 @@ func (xl xlObjects) PutObject(bucket string, object string, size int64, data io.
 	tempErasureObj := path.Join(tmpMetaPrefix, bucket, object, "object1")
 	tempObj := path.Join(tmpMetaPrefix, bucket, object)
 
+	// List all online disks.
 	onlineDisks, higherVersion, err := xl.listOnlineDisks(bucket, object)
 	if err != nil {
 		return "", toObjectErr(err, bucket, object)
 	}
+	// Increment version only if we have online disks less than configured storage disks.
 	if diskCount(onlineDisks) < len(xl.storageDisks) {
-		// Increment version only if we have online disks less than configured storage disks.
 		higherVersion++
 	}
 	erasure := newErasure(onlineDisks) // Initialize a new erasure with online disks
@@ -290,7 +301,7 @@ func (xl xlObjects) PutObject(bucket string, object string, size int64, data io.
 		return "", toObjectErr(err, bucket, object)
 	}
 
-	xlMeta := xlMetaV1{}
+	xlMeta := newXLMetaV1(xl.dataBlocks, xl.parityBlocks)
 	xlMeta.Meta = metadata
 	xlMeta.Stat.Size = size
 	xlMeta.Stat.ModTime = modTime

xl-v1-utils.go

@@ -73,8 +73,8 @@ func (xl xlObjects) statPart(bucket, objectPart string) (fileInfo FileInfo, err
 
 	// Return the first success entry based on the selected random disk.
 	for xlJSONErrCount < len(xl.storageDisks) {
-		// Choose a random disk on each attempt, do not hit the same disk all the time.
-		disk := xl.getRandomDisk() // Pick a random disk.
+		// Choose a random disk on each attempt.
+		disk := xl.getRandomDisk()
 		fileInfo, err = disk.StatFile(bucket, objectPart)
 		if err == nil {
 			return fileInfo, nil