Re[2]: Intercepting file system calls (read, write, open, close, etc)
Re[2]: Intercepting file system calls (read, write, open, close, etc)
- Subject: Re[2]: Intercepting file system calls (read, write, open, close, etc)
- From: Igor Shmukler <email@hidden>
- Date: Fri, 19 Nov 2004 05:28:14 +0300
> >> 1. Try VFS Stacking ? Or over-riding V-node ops ?
> >
> > Was support for VFS stacking removed? I was warned of such a year or
> > two ago, and stopped my VFS efforts at that point (also trying to
> > intercept file system calls).
>
> Stacking filesystems in the BSD model doesn't work very well. It gets
> expensive very quickly, and locking can become a nightmare. It's also
> often not really what you want; the above is a good example of that.
The above being - ?
SunOS is a proof that BSD model and stackable VFS do work well together.
The reason locking in an operating system such as a BSD would problematic is because VFS is very complex. It needed flattening back in 1998 right after VM became stable. Now to support MP kernel locking is more complex than ever. That does not mean that things ought to be this way. Implementing a stackable FS is relatively straightforward if you start from the right place - vnode interface. If done correctly stackable does not create any problems with locking that would not be present in a leaf design.
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