XL: Cleanup and add more comments. (#1807)

xl-v1-common.go

@@ -0,0 +1,112 @@
+/*
+ * Minio Cloud Storage, (C) 2016 Minio, Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package main
+
+import (
+	"math/rand"
+	"path"
+	"sync"
+	"time"
+)
+
+// 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()) // Seed with current time.
+	randIndex := rand.Intn(len(xl.storageDisks) - 1)
+	disk = xl.storageDisks[randIndex] // Pick a random disk.
+	return disk
+}
+
+// This function does the following check, suppose
+// object is "a/b/c/d", stat makes sure that objects ""a/b/c""
+// "a/b" and "a" do not exist.
+func (xl xlObjects) parentDirIsObject(bucket, parent string) bool {
+	var isParentDirObject func(string) bool
+	isParentDirObject = func(p string) bool {
+		if p == "." {
+			return false
+		}
+		if xl.isObject(bucket, p) {
+			// If there is already a file at prefix "p" return error.
+			return true
+		}
+		// Check if there is a file as one of the parent paths.
+		return isParentDirObject(path.Dir(p))
+	}
+	return isParentDirObject(parent)
+}
+
+func (xl xlObjects) isObject(bucket, prefix string) bool {
+	// Create errs and volInfo slices of storageDisks size.
+	var errs = make([]error, len(xl.storageDisks))
+
+	// Allocate a new waitgroup.
+	var wg = &sync.WaitGroup{}
+	for index, disk := range xl.storageDisks {
+		wg.Add(1)
+		// Stat file on all the disks in a routine.
+		go func(index int, disk StorageAPI) {
+			defer wg.Done()
+			_, err := disk.StatFile(bucket, path.Join(prefix, xlMetaJSONFile))
+			if err != nil {
+				errs[index] = err
+				return
+			}
+			errs[index] = nil
+		}(index, disk)
+	}
+
+	// Wait for all the Stat operations to finish.
+	wg.Wait()
+
+	var errFileNotFoundCount int
+	for _, err := range errs {
+		if err != nil {
+			if err == errFileNotFound {
+				errFileNotFoundCount++
+				// If we have errors with file not found greater than allowed read
+				// quorum we return err as errFileNotFound.
+				if errFileNotFoundCount > len(xl.storageDisks)-xl.readQuorum {
+					return false
+				}
+				continue
+			}
+			errorIf(err, "Unable to access file "+path.Join(bucket, prefix))
+			return false
+		}
+	}
+	return true
+}
+
+// statPart - stat a part file.
+func (xl xlObjects) statPart(bucket, objectPart string) (fileInfo FileInfo, err error) {
+	// Count for errors encountered.
+	var xlJSONErrCount = 0
+
+	// Return the first success entry based on the selected random disk.
+	for xlJSONErrCount < len(xl.storageDisks) {
+		// Choose a random disk on each attempt.
+		disk := xl.getRandomDisk()
+		fileInfo, err = disk.StatFile(bucket, objectPart)
+		if err == nil {
+			return fileInfo, nil
+		}
+		xlJSONErrCount++ // Update error count.
+	}
+	return FileInfo{}, err
+}