add LKD 13.md

README.md

@@ -59,6 +59,7 @@ Linux Kernel Development
 10. [Chapter 10: Kernel Synchronization Methods](./linux-kernel-development/chapter-10.md)
 11. [Chapter 11: Timers and Time Management](./linux-kernel-development/chapter-11.md)
 12. [Chapter 12: Memory Management](./linux-kernel-development/chapter-12.md)
+13. (-) [Chapter 13: The Virtual Filesystem](./linux-kernel-development/chapter-13.md)
 
 Paper Review
 ---

linux-kernel-development/chapter-13.md

@@ -0,0 +1,17 @@
+# Chapter 13: The Virtual Filesystem
+The `Virtual Filesystem` (VFS) is the subsystem of the kernel that implements the file and filesystem-related interfaces to user-space. All filesystems rely on the VFS not only to coexist but also to interoperate. This enables programs to use standard Unix system calls to read and write to different filesystems, even on different media.
+
+## Common Filesystem interfaces
+The VFS enables system calls work between different filesystems and media. New filesystems and new Virtual of storage media can find their way into Linux, and programs need not be rewritten or even recompiled.
+
+
+## Filesystem Abstraction
+Ther kernel implements an abstraction layer around its low-level filesystem interface. This abstraction layer works by defining the basic conceptual interfaces and data structures that all filesystems support.
+
+
+## Unix Filesystem
+Unix has provided four basic filesystem-related abstractions:
+- `file`:
+- `directory entries`:
+- `inodes`:
+- `mount points`: