Kernel Extensions and Device Support Programming Concepts

Understanding Data Structures and Header Files for Virtual File Systems

These are the data structures used in implementing virtual file systems:

• The vfs structure contains information about a virtual file system as a single entity.
• The vnode structure contains information about a file system object in a virtual file system. There can be multiple v-nodes for a single file system object.
• The gnode structure contains information about a file system object in a physical file system. There is only a single g-node for a given file system object.
• The gfs structure contains information about a file system implementation. This is distinct from the vfs structure, which contains information about an instance of a virtual file system.

The header files contain the structure definitions for the key components of the virtual file system abstraction. Understanding the contents of these files and the relationships between them is essential to an understanding of virtual file systems. The following are the necessary header files:

• sys/vfs.h
• sys/gfs.h
• sys/vnode.h
• sys/vmount.h