From owner-freebsd-arch  Fri Jun  8  2:10:45 2001
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Date: Fri, 08 Jun 2001 02:11:07 -0700
From: Terry Lambert <tlambert2@mindspring.com>
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To: "Patrick W. Penzias Dirks" <pwd@apple.com>
Cc: FreeBSD-FS@FreeBSD.ORG, FreeBSD-Arch@FreeBSD.ORG
Subject: Re: Support for pivot_root-like system call?
References: <200106072103.f57L37l26327@scv2.apple.com>
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"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.

Really, the BSD way of doing this is to stack an FS with the
feature you want on top of the one without the feature in it.

-- Terry

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