Subject: Re: Log area on-disk for the journal
To: None <>
From: Ignatios Souvatzis <>
List: tech-kern
Date: 10/21/2006 12:58:05
On Fri, Oct 20, 2006 at 02:40:52PM -0700, Jason Thorpe wrote:
> On Oct 20, 2006, at 2:08 PM, M J Fleming wrote:
> >Wouldn't this rule out the possibility of adding journaling to a pre- 
> >existing
> >filesystem?
> No -- just allocate the inode and mark it as "special" in some way.

Using an inode, and block lists, surely is an elegant way; I think
BSD LFS does it too for some of its meta data (the i file). However,
ISTR that this - using the inode/block allocation used for normal
files also for meta data - was mentioned as problematic wrt. LFS
because in some situations, the filesystem has to fight its normal
operation to make sure it stays consistent, which needs special
effort to do it right.

(Sort of the network layer mixing problems you get with CSLIP or
 PPP with VJ compression enabled if the implementation hasn't be
 done very carefully, or of IP filtering/IP NAT, where you can damage
 higher layers by mistakes made on formally lower layers.)

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