I have read a bunch of articles, but still cannot get an idea of ACL, so I have following questions.   What are benefits of using ACL over old permissions (0777 for example) and changing file owner, group etc ? (Only one for me as I guess is multiple user can have different permission for one file)   How ACL is implemented ? Does it use inode data ?    Is there any connection between extended attributes(xattr) ? Does VFS have support for extended attributes  ? Or this is FS specific` feature ?   Please help to understand this, maybe there some good articles about this ?Thanks 
ACL and plain old permissions
linux;permissions;filesystems;acl;xattr