add initial implementation of remote backing store

This commit implement the BackingStore Interface for remote backing
store.

Signed-off-by: Utkarsh Mani Tripathi <utkarsh.tripathi@mayadata.io>

pkg/scsi/backingstore/remote/remote.go

@@ -0,0 +1,107 @@
+/*
+Copyright 2016 openebs authors All rights reserved.
+
+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 remote
+
+import (
+	"fmt"
+
+	"github.com/gostor/gotgt/pkg/api"
+	"github.com/gostor/gotgt/pkg/scsi"
+	log "github.com/sirupsen/logrus"
+)
+
+func init() {
+	scsi.RegisterBackingStore("RemBs", newRemBs)
+}
+
+// RemBackingStore
+type RemBackingStore struct {
+	scsi.BaseBackingStore
+	// Remote backing store, remote server exposing
+	// read and write methods.
+	RemBs api.RemBackingStore
+}
+
+func newRemBs() (api.BackingStore, error) {
+	return &RemBackingStore{
+		BaseBackingStore: scsi.BaseBackingStore{
+			Name:            "RemBs",
+			OflagsSupported: 0,
+		},
+	}, nil
+}
+
+func (bs *RemBackingStore) Open(dev *api.SCSILu, path string) error {
+	bs.DataSize = uint64(dev.Size)
+	bs.RemBs = scsi.GetTargetBSMap(path)
+	return nil
+}
+
+func (bs *RemBackingStore) Close(dev *api.SCSILu) error {
+	/* TODO return bs.File.Close()*/
+	return nil
+}
+
+func (bs *RemBackingStore) Init(dev *api.SCSILu, Opts string) error {
+	return nil
+}
+
+func (bs *RemBackingStore) Exit(dev *api.SCSILu) error {
+	return nil
+}
+
+func (bs *RemBackingStore) Size(dev *api.SCSILu) uint64 {
+	return bs.DataSize
+}
+
+func (bs *RemBackingStore) Read(offset, tl int64) ([]byte, error) {
+	tmpbuf := make([]byte, tl)
+	length, err := bs.RemBs.ReadAt(tmpbuf, offset)
+	if err != nil {
+		return nil, err
+	}
+	if length != len(tmpbuf) {
+		return nil, fmt.Errorf("Incomplete read expected:%d actual:%d", tl, length)
+	}
+	return tmpbuf, nil
+}
+
+func (bs *RemBackingStore) Write(wbuf []byte, offset int64) error {
+	length, err := bs.RemBs.WriteAt(wbuf, offset)
+	if err != nil {
+		log.Error(err)
+		return err
+	}
+	if length != len(wbuf) {
+		return fmt.Errorf("Incomplete write expected:%d actual:%d", len(wbuf), length)
+	}
+	return nil
+}
+
+func (bs *RemBackingStore) DataAdvise(offset, length int64, advise uint32) error {
+	return nil
+}
+
+func (bs *RemBackingStore) DataSync(offset, length int64) (err error) {
+	_, err = bs.RemBs.Sync()
+	return
+}
+
+func (bs *RemBackingStore) Unmap(bd []api.UnmapBlockDescriptor) (err error) {
+	_, err = bs.RemBs.Unmap()
+	return
+}