【openEuler 22.09】Add sysfs file to overlayfs to display mount information

【项目难度】：基础
【项目描述】：
    在实际生产环境中不断出现overlayfs没有真正卸掉的出现了诸如quota统计数据持续增长等问题。对于现网环境目前没有好的办法去界定该类情况。overlayfs在实际使用过程中是有很多限制但是并没有在代码层面直接做限制，所以在使用过程会出现操作错误引入的一些奇怪的问题，往往这类问题表露出来的现象是比较奇怪的，定位起来比较耗时。基于这样的背景overlayfs的维测功能需要增强。
构想：
在“/sys/fs/“目录下增加overlayfs的目录，目录下记录各个挂载点的挂载信息，只有overlayfs被真正卸载掉目录下对应的目录才会删除。
目录结构构想如下，其中目录名称组成结构为："merge_主设备号_次设备号"
![目录结构构想](https://foruda.gitee.com/images/1666156487418949351/cba9e119_11013349.png "image_2022-10-19_13-14-03.png")
【产出标准】：
    1. 在"/sys/fs"目录下增加overlayfs目录，目录下记录各个挂载点的挂载信息
    2. 只有在overlayfs被真正卸载掉时，目录下对应的目录才会被删除
【技术要求】：
    1. C语言
    2. Linux kernel
    3. 存储
【导师姓名/导师邮箱】：yebin10@huawei.com
【成果提交仓库】：https://gitee.com/openeuler/kernel/tree/openEuler-22.09/
【相关参考资料】：https://gitee.com/openeuler/kernel

本次活动将面向全球学生，题目内容请同时提交中英文版本。

project name：Add sysfs file for overlayfs
【Difficulty】：basic
【Description】：
    In the actual production environment, Overlayfs often occurs some problems, such as continuous growth of quota statistics. There is no good way to define this category for the current environment. Overlayfs has many restrictions in the actual use process but it has not directly restricted at the code level. Therefore, some strange problems introduced in operation errors will occur during the use process. It is time-consuming. Based on this background, Overlayfs's maintenance function needs to be enhanced.
    This patch add sysfs file for overlayfs to recording the mount information. The sysfs file will be deleted only when Overlayfs is truly unloaded.
Idea:
    Add the directory of overlayfs under the directory "/sys/fs/", and the directory records the mount information of each mount point, and the corresponding directory under the directory will be deleted only when the overlayfs is really unmounted.
    The directory structure is conceived as follows, where the directory name composition structure is: "merge_primary_secondary_device_number"
![directory structure](https://foruda.gitee.com/images/1666157758052245227/b8128449_11013349.png "image_2022-10-19_13-14-03.png")
【Output Requirements】：
    1. Add the directory "/sys/fs" to the directory overlayfs, which records the mount information of each mount point
    2. Only when overlayfs is actually unmounted, the corresponding directory will be deleted
【Technical Requirements】：
    1. C language
    2. Linux kernel
    3. storage
【Mentor/Email】：yebin10@huawei.com
【Project Repository】：https://gitee.com/openeuler/kernel/tree/openEuler-22.09/
【Notes】：https://gitee.com/openeuler/kernel

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