next up previous contents
Next: 4.9.2 In-Core File Systems Up: 4.9 File System Types Previous: 4.9 File System Types

   
4.9.1 Stateless File Systems

A stateless file system does not create a ``wrapping'' vnode

  
Figure: Vnode Structure in a Stateless File System
2.6in

Figure: Vnode Structure in a Stateless File System


\epsfig{file=figures/fs-stateless.eps}




2.1in


\epsfig{file=figures/fs-stateless.eps}


for every vnode in the interposed file system. As shown in Figure fig-fs-stateless, there is only one new vnode created, as is needed for every file system: the root (Y2) of the interposing file system Y.

This file system type is quite limited. The only time that something interesting can happen is when the file system's mount point is crossed. I expect very few useful file systems to fall into this category. An example is Crossfs (Appendix sec-appendix-typical-stateless-crossfs), a file system that performs a stateless event when a lookup operation traverses into it from the file system it is mounted on. A typical event might be to print a message on the system console that includes the uid and gid of process that crossed into this file system.


next up previous contents
Next: 4.9.2 In-Core File Systems Up: 4.9 File System Types Previous: 4.9 File System Types
Erez Zadok
1999-12-07