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To: tlambert2@mindspring.com
Cc: "Patrick W. Penzias Dirks" <pwd@apple.com>,
	FreeBSD-FS@FreeBSD.ORG, FreeBSD-Arch@FreeBSD.ORG
Subject: Re: Support for pivot_root-like system call? 
In-Reply-To: <3B2096AB.309B2D14@mindspring.com> 
Date: Fri, 08 Jun 2001 08:30:11 -0700
From: Peter Wemm <peter@wemm.org>
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Terry Lambert wrote:
> "Patrick W. Penzias Dirks" wrote:
> > 
> > Hi,
> > 
> > I'm the filesystems tech lead in Apple's Mac OS X Core OS group.
> > Prompted by the needs of, among others, virus protection software
> > developers who want to be able to mount "on" the root directory to
> > intercept ALL filesystem calls in the system, I'm contemplating
> > implementation of a new system call in Mac OS X to do something like
> > Linux's pivot_root system call:
> > 
> >         int pivot_root(const char *new_root, const char *put_old);
> > 
> > (which basically installs "new_root" as the new "/" [root_vnode] in
> > the system and transfers the current root directory to the pathname
> > specified my "put_old")
> 
> It doesn't work in FreeBSD proper because of cache coherency
> bugs that have been around since 1995, but:
> 
> mount -t nullfs / /put_old # or wherever
> mount -t <whatever> /
> 
> Would do what you want, I think.

Terry, the 'cache coherency' bugs have been fixed in -current for ~8
months now (September 2000).  The infrastructure changes for this are
subject to a call-for-review right now for a merge to 4.x. 

Cheers,
-Peter
--
Peter Wemm - peter@FreeBSD.org; peter@yahoo-inc.com; peter@netplex.com.au
"All of this is for nothing if we don't go to the stars" - JMS/B5


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