Merge Pull Request from: @hiixfj 
 
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.

category: feature
bugzilla：<https://gitee.com/openeuler/kernel/issues/I5WIS5>
CVE: NA

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Put a hook function in file_system_type,
and register sysfs after do_add_mount().

Signed-off-by: hiyoyolumi 862127279@qq.com 
 
Link:https://gitee.com/openeuler/kernel/pulls/149 
Reviewed-by: Zheng Zengkai <zhengzengkai@huawei.com> 
Signed-off-by: Zheng Zengkai <zhengzengkai@huawei.com>