Subject: Re: Clean bit bits
To: None <tech-kern@NetBSD.ORG>
From: Waldi Ravens <>
List: tech-kern
Date: 01/20/1996 03:00:54
In <>, Wayne Berke <> wrote:
> In message <>, Waldi Ravens writes:
> > Ignatios Souvatzis wrote:
> > 
> > >    No problem. When newdosfs(8) sets the number of reserved sectors to
> > >    2 instead of the usual 1, the second reserved sector can be used to
> > >    store timestamps and other usefull information (should of course be
> > >    protected by a magic number and checksum).
> > > 
> > > This would not work with original MS-DOS created filesystems, possibly
> > > coexisting on a dual use harddisk or inserted into the floppy disk,
> > > would it?
> > 
> > No, it wouldn't, fsck would either always or never run on such
> > filesystems. But creating a new filesystem is not an extremely
> > complicated operation, is it?
> I think the objection was for filesystems created in MS-DOS and populated
> with files under it.  In that case you wouldn't want to run newdosfs over
> it.

Probably not without running pax or tar first. ;-)

Anyway, I don't see a real problem here. The extra reserved sector
would of course be optional. If it doesn't exist, fsck will always
check (unless disabled in /etc/fstab). So, for those who don't need
the cleanbit/timestamp stuff, there's no _requirement_ to recreate
file systems.

Another point which has been mentioned is compatibility. AFAICS the
extra reserved sector is fully backwards compatible. I cannot test
this with MS-DOS, but I did try under GEMDOS. I created three small
FAT file systems with 2, 4 and 8 reserved sectors. The GEMDOS FAT-fs
driver happily ignores the extra reserved sectors. I expect MS-DOS
will do the same.