references:
- https://www.ibm.com/developerworks/linux/library/l-linux-filesystem/
- https://unix.stackexchange.com/questions/4402/what-is-a-superblock-inode-dentry-and-a-file
Anatomy of the Linux file system
Inode
An inode (short for "index node") is a bunch of attributes about a file that Linux stores. There is one inode for each file (though with some filesystems, Linux has to create its own inodes because the information is spread around the filesystem). The inode stores information like who owns the file, how big the file is, and who is allowed to open the file. Each inode also contains a number unique to the filesystem partition; it's like a serial number for the file described by that inode.
Dentry
A dentry (short for "directory entry") is what the Linux kernel uses to keep track of the hierarchy of files in directories. Each dentry maps an inode number to a file name and a parent directory.
Superblock
The superblock is a unique data structure in a filesystem (though multiple copies exist to guard against corruption). The superblock holds metadata about the filesystem, like which inode is the top-level directory and the type of filesystem used.
