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Linux File Systems
Linux is incredibly versatile in that it is capable of supporting a large number of different file systems including, but not limited to:
The numerous file systems are collated in a hierarchical tree structure and viewed by the system as a single file system entity. New file systems are mounted (that is, a file system is associated with a storage device in Linux) to this tree as they are added to the system[5].
Virtual File System
Referring back to Figure 23.1, the Virtual File System (VFS) plays a key role in facilitating the inclusion of the many file systems. It provides a level of abstraction, creating a unified interface between the individual file systems and the rest of the kernel. It is the root level of the file-system interface and is responsible for tracking all currently-supported and mounted file systems. Figure 23.6 represents the interactions between the VFS and the real file systems (in this instance we are only demonstrating the vfat and ext2 file systems).
The buffer cache is used as a common data buffer from the hardware devices, speeding up file system access to the physical devices holding the file systems. It is independent of the file systems and as such keeps these file systems independent from the supporting device drivers and media.
During the navigation of mounted file systems inodes are continuously read or written, so the VFS maintains an inode cache to speed up access to the mounted file systems. (Note — inode stands for index node and is a data structure found within Unix file systems, containing all the information about a file system object).
The VFS also maintains a cache of directory entries to speed up access to those most commonly in use. When a directory is looked up by a file system, its details are added to the cache and can be accessed more quickly the next time the same directory is looked up. The VFS uses a form of Least Recently Used (LRU) retention of cache entries. As a directory entry is added to the cache, those used previously are moved down a level. When the cache is full, the entry at the lowest level will be discarded as the next entry is added[5].
![Linux virtual file system interactions[5].png](/uploads/images/editor/20200710/191601Linux virtual file system interactions[5].png "Linux virtual file system interactions[5].png")
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