Subject: Re: LFS frailty vs. datestamping [Was Re: /dev/clock pseudodevice]
To: Greywolf <>
From: Bill Studenmund <>
List: tech-kern
Date: 07/30/2001 11:46:28
On Sat, 28 Jul 2001, Greywolf wrote:

> On Sat, 28 Jul 2001, Bill Sommerfeld wrote:
> # The ability to set the clock backwards may also be used to confuse
> # audit trails and LFSv1, though I think it's fixed in LFSv2.
> ...with all I've been hearing about LFS and seeing the headaches
> concerning it (rearranging the order of data on disk, having a cleanerd,
> and now the above), I posit that LFS is a horribly fragile filesystem
> model, and I'm wondering why we don't do a generic logging/journaling layer
> that can overlay FFS (or any other filesystem we'd like journaling on, but
> FFS comes to mind since it and LFS are the only ones for which we run
> a consistency check at boot time).  Perhaps I'm being a bit simplistic,
> and I'm SURE I'm missing something here (in which case someone will gladly
> thump me soundly with a clue*4, I'm sure), but in concept, it sounds like
> a potentially much better win than LFS is capable of providing.

I've thought about journalizing ffs. While I think it could be useful, I
don't think a layered fs can do it. The fundamental problem is that there
are two sides to a file system, the top and the bottom. Layered file
systems can do lots of nice things on the top side, but they can't do much
of anything on the bottom. Journalizing, though, is all on the bottom side
(it changes how metadata blocks are written). :-(

Don't forget that most file systems that are journalized only journal the
metadata, not the file data. :-)

Take care,