Subject: Re: path component substitutions (was diskless booting)
To: Jan-Simon Pendry <pendry@vangogh.CS.Berkeley.EDU>
From: Ty Sarna <>
List: tech-kern
Date: 03/15/1994 15:12:11
Jan-Simon Pendry wrote:
> 4.4-lite already has a union filesystem which would seem
> to answer most of your requirements in a much more general
> way.  the man page is appended.  in particular, see the examples.

No, it provides a very diferent set of functionality.  @subs are a
screwdriver, union mounts/TFS are hammers.  Sure, one can use a
screwdriver to pound in a nail and one might be able to use a claw hammer
to screw in a screw, but you're better off using the right tool for the
job. Arguing wether screwdrivers or hammers are better is pointless --
ideally one would have both in one's toolbox.

> i'd like to know what additional functionality you think is required.

@subs have no additional state that nees to be set up on each machine on
each boot (mounts). They work both per-file and per-directory. (or
can you union mount files? would you even want to?). Also, files from
all the different "views" of a filesystem are all right there and easy
to deal with under @subs, while under union/TFS mounting you have to go
somewhere else to access them -- normally your view contains ONLY the
files from your view.

Then, there are a while variety of problems which @subs don't cover. As
I said, I believe the two schemes are complementary.

Ty Sarna                 "As you know, Joel, children have always looked        up to cowboys as role models. And vice versa."