Subject: Re: mnt_leaf, v_vnlock, VLAYER
To: None <>
From: Matthew Mondor <>
List: tech-kern
Date: 12/05/2005 08:10:00
On Mon, 5 Dec 2005 01:21:50 -0500 (EST)
der Mouse <mouse@Rodents.Montreal.QC.CA> wrote:

> It did this by representing each Unix-layer file with two VMS-layer
> files, one containing the contents and the other containing the name
> mapping.  They were called things like HSHUECOG.HSN and HSHUECOG.HSH
> (details are probably wrong), and, in particular, to use the
> terminology somewhat loosely, there were two underneath-layer vnodes
> for many mount-point-layer vnodes.  (Not all; if the name were all
> lowercase, conformed to VMS conventions, and did not collide with the
> mapping scheme's names, it was not mapped.)  I can see NetBSD use for
> such things in, for example, running atop msdosfs....
> We (=NetBSD) may decide we don't care about supporting any such
> filesystems, but if so, we should make that decision consciously,
> rather than by not realizing the possibility exists.


I have seen UMSDOS support on Linux which was similar;  Of course, using
it brings a number of serious performance and security drawbacks,
though.  Apparently some people found it useful to not have to deal with
slices and labels, so some newbie-targetted Linux distributions used
UMSDOS and gained some popularity (hmm if my memory isn't too bad
possibly that zipslack was an adapted slackware for UMSDOS distributed
in zip format, for instance).

Perhaps that it's still used and such distributions still maintained;  I
didn't have much contacts with Linux beginners since approximately 7
years back (I was providing free tech support to users on a regular
basis on dalnet #linux back then and do remember the problems people
experienced under UMSDOS, though) so I'm probably way behind on news.
I personally don't know any experienced Linux user using UMSDOS so
the actual usefulness might be fairly limited...

In the case of a flash device which uses MSDOS for instance, we can
simply already mount it as-is, for ISO9660 we have Rock Ridge...

If we can't alter the disk structure of a system but must run NetBSD on
it temporarily for a particular reason, we have live CDs and/or boot
floppies already (although, potentially that in this case, if we
supported such a feature, it would be possible to have the /home of a
live CD in a directory on an existing filesystem directory)...

Any ideas for other potential uses?

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