Reply with LUN busy when there is a read/write error from backend

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

pkg/scsi/backingstore.go

@@ -153,7 +153,7 @@ write:
 		if err != nil {
 			log.Error(err)
 			key = MEDIUM_ERROR
-			asc = ASC_READ_ERROR
+			asc = ASC_WRITE_ERROR
 			goto sense
 		}
 		log.Debugf("write data at 0x%x for length %d", offset, len(wbuf))
@@ -172,7 +172,7 @@ write:
 		if ((opcode != api.WRITE_6) && (scb[1]&0x8 != 0)) || (pg.Data[0]&0x04 == 0) {
 			if err = bs.DataSync(int64(offset), tl); err != nil {
 				key = MEDIUM_ERROR
-				asc = ASC_READ_ERROR
+				asc = ASC_WRITE_ERROR
 				goto sense
 			}
 		}

pkg/scsi/sbc.go

@@ -459,7 +459,9 @@ func SBCReadWrite(host int, cmd *api.SCSICommand) api.SAMStat {
 
 	err, key, asc = bsPerformCommand(dev.Storage, cmd)
 	if err != nil {
-		goto sense
+		log.Errorf("Error from backend: %v", err)
+		BuildSenseData(cmd, key, asc)
+		return api.SAMStatBusy
 	} else {
 		return api.SAMStatGood
 	}