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Date:      Thu, 14 Mar 2002 12:55:13 -0800
From:      Terry Lambert <tlambert2@mindspring.com>
To:        Attila Nagy <bra@fsn.hu>
Cc:        freebsd-hackers@freebsd.org
Subject:   Re: NULLFS in -STABLE
Message-ID:  <3C910E31.A959274C@mindspring.com>
References:  <Pine.LNX.4.44.0203141053070.26135-100000@scribble.fsn.hu>

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Attila Nagy wrote:
> The only thing, which seems to be changed that the NULLFS mount isn't
> recursive anymore.
> If I have:
> /stuff
> /stuff/.1
> /stuff/.2
> ...
> 
> (.* are directories, each one there is another partition mounted in)
> 
> and I mount /stuff to somewhere else with mount_null, I see only /stuff,
> and empty .* directories. So I have to do:
> mount_null /stuff /other_dir/stuff
> mount_null /stuff/.1 /other_dir/stuff/.1, etc.
> 
> BTW, this is only a minor issue.

THis is actually intentional.  THe mount point traversal occurs
at a covered dev_t/inode pair, and the nullfs has a different
dev_t for the vnode.

When you mount a / from a remote system NFS, you don't get the
/usr or other FS's mounted under it, either.  8-).


> Congratulations to anyone, who did this work!

B.P., Jake, and Russilan are the main guys responsible for
the work, which was mostly locing stuff introduced by changes
in the underlying code, and Russilan's major effor at emulating
the cache coherency for the VOP_GETPAGES/VOP_PUTPAGES to deal
with the cache coherency.  It's a brute-force approach, but it
works, and it was probably easier than getting the other changes
into FreeBSD to clear up the coherency through the paging path
directly.

-- Terry

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