feat: add sync() to vfs

新增sync方法，该方法每次调用，会遍历系统内所有的mount点，调用各个文件系统注册
的sync方法，完成对所有已挂载文件系统的sync操作。

close #I480HV
Signed-off-by: NGuangyao Ma <guangyao.ma@outlook.com>
Change-Id: If3b82bbd67eec92223417c35a0e0fe7ba7d25eaa

fs/mount/fs_sync.c

+/*
+ * Copyright (c) 2021-2021 Huawei Device Co., Ltd. All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without modification,
+ * are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this list of
+ *    conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice, this list
+ *    of conditions and the following disclaimer in the documentation and/or other materials
+ *    provided with the distribution.
+ *
+ * 3. Neither the name of the copyright holder nor the names of its contributors may be used
+ *    to endorse or promote products derived from this software without specific prior written
+ *    permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
+ * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
+ * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR
+ * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
+ * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
+ * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS;
+ * OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
+ * WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR
+ * OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
+ * ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+/****************************************************************************
+ * Included Files
+ ****************************************************************************/
+#include "unistd.h"
+#include "fs/mount.h"
+#include "vfs_config.h"
+
+/****************************************************************************
+ * Private Functions
+ ****************************************************************************/
+
+/****************************************************************************
+ * Public Functions
+ ****************************************************************************/
+
+/****************************************************************************
+ * Name: sync
+ *
+ * Description:
+ *   sync() will sync data of every mount point
+ *
+ ****************************************************************************/
+
+void sync(void)
+{
+  int ret;
+  struct Mount *mnt = NULL;
+  LIST_HEAD *mntList = GetMountList();
+
+  VnodeHold();
+  LOS_DL_LIST_FOR_EACH_ENTRY(mnt, mntList, struct Mount, mountList)
+    {
+      if (mnt->ops->Sync != NULL)
+        {
+            ret = mnt->ops->Sync(mnt);
+            if (ret != OK)
+              {
+                PRINT_ERR("sync failed, %s, %s\n", mnt->pathName, strerror(-ret));
+              }
+        }
+    }
+  VnodeDrop();
+}