iSulad: implements layers store

Signed-off-by: Nhaozi007 <liuhao27@huawei.com>

src/image/oci/CMakeLists.txt

 # get current directory sources files
 aux_source_directory(${CMAKE_CURRENT_SOURCE_DIR} local_oci_srcs)
-add_subdirectory(graphdriver)
+add_subdirectory(storage)
 
 set(OCI_SRCS
+    ${STORAGE_SRCS}
     ${local_oci_srcs}
-    ${GRAPHDRIVER_SRCS}
     PARENT_SCOPE
     )
 
 set(OCI_INCS
+    ${STORAGE_INCS}
     ${CMAKE_CURRENT_SOURCE_DIR}
-    ${GRAPHDRIVER_INCS}
     PARENT_SCOPE
     )

src/image/oci/storage/CMakeLists.txt

+# get current directory sources files
+aux_source_directory(${CMAKE_CURRENT_SOURCE_DIR} local_storage_srcs)
+add_subdirectory(graphdriver)
+
+set(STORAGE_SRCS
+    ${local_storage_srcs}
+    ${GRAPHDRIVER_SRCS}
+    PARENT_SCOPE
+    )
+
+set(STORAGE_INCS
+    ${CMAKE_CURRENT_SOURCE_DIR}
+    ${GRAPHDRIVER_INCS}
+    PARENT_SCOPE
+    )

src/image/oci/storage/layer.h

+
+/******************************************************************************
+ * Copyright (c) Huawei Technologies Co., Ltd. 2020. All rights reserved.
+ * iSulad licensed under the Mulan PSL v1.
+ * You can use this software according to the terms and conditions of the Mulan PSL v1.
+ * You may obtain a copy of Mulan PSL v1 at:
+ *     http://license.coscl.org.cn/MulanPSL
+ * THIS SOFTWARE IS PROVIDED ON AN "AS IS" BASIS, WITHOUT WARRANTIES OF ANY KIND, EITHER EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO NON-INFRINGEMENT, MERCHANTABILITY OR FIT FOR A PARTICULAR
+ * PURPOSE.
+ * See the Mulan PSL v1 for more details.
+ * Author: liuhao
+ * Create: 2020-03-24
+ * Description: provide layer store function definition
+ ******************************************************************************/
+#ifndef __OCI_STORAGE_LAYER_H
+#define __OCI_STORAGE_LAYER_H
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+struct layer_config {
+    /*configs for graph driver */
+    char *driver_name;
+    char *driver_root;
+    char **driver_opts;
+    size_t driver_opts_len;
+
+};
+
+struct layer_store_ops {
+    int (*init)(const struct im_configs *conf);
+};
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif