Subject: Re: FFS journal (mounting just a sub-directory from a filesystem)
To: der Mouse <mouse@Rodents.Montreal.QC.CA>
From: Greg A. Woods <>
List: tech-kern
Date: 07/23/2006 16:27:15
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At Sat, 22 Jul 2006 16:27:37 -0400 (EDT),
der Mouse wrote:
> Altneratively...some time ago, I wrote code that allows me to mount an
> FFS such that the directory that becomes the mount-point root is not
> necessarily the root of the filesystem in the partition.  For example,
> if I have a parititon containing an all-in-one-partition NetBSD
> install, I could mount just its /usr subtree somewhere.

That's a really cool idea!  I've thought in more abstract terms about
something similar ever since I was first exposed to unix.

> This is relevant because there's no reason why we couldn't have a
> journaling FFS set up such that the root of the on-disk filesystem
> contains, say, directories "deleted" and "root", and then have
> "deleted" used internally with "root" being the root of what you see
> when it's mounted.  No hacks to fsck_ffs required; all that changes is
> the mount code, so that when mounted journaled, those two directories
> are required and handled appropriately.  Oh, and newfs_ffs should
> probably be made capable of pre-creating those directories.

Indeed in this application your idea sounds like a perfect solution.

						Greg A. Woods

H:+1 416 218-0098 W:+1 416 489-5852 x122 VE3TCP RoboHack <>
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