Re: 4th set of permission bits?

[Marcus Brinkmann]

On Sat, Dec 02, 2000 at 02:31:20PM +0800, Robert Marlow wrote:
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> > > Hmm... I keep reading over and over and I don't see how my idea doesn't
> > > work... maybe an example and you can show me where it is flawed.
> > > 
> > > say a file begins with the permissions following:
> > > 
> > > rwxr-xr-xr-x
> > > 
> > > ie, the last 3 bits for the non logged-in user is defaulted to
> > > the same as that of worlds (the 2nd set of 3 bits).
> > 
> > Explain to me how this "is defaulted to" should work in your opinion.
> > Defaulted to by whom? At which time?
> 
> What I was thinking was, defaulted by the system. ie it's always defaulted
> to the same as world unless different permissions are explicitly defined.

That doesn't make sense. There is no way to decide if the permissions are
explicitely defined or not. With three bits for rwx, there is no room for
"value undefined" as in perl, for example. That's exactly what the extra bit
is about we are talking, to say "undefined", or better "don't use them".
 
> Ahh, that does make your meaning much more clear. I'm seeing now why the 
> permissions
> would typically have to default to --- rather than just being the same as 
> world. How much trouble would it be to cause it to default differently just
> in the case of the non logged-in user though? (for the user I mean, I already
> realise the coding would likely be a pain in the *&$) Would it be more 
> confusing to
> a user to have to specify an extra flag in order to change the way the extra
> permissions default or would it be more confusing to just have it default to
> the same as world and perhaps have it seem a bit unintuitive for it to no 
> longer
> default to ---?

There are definitely too many "defaults" in the abov paragraph for me to
decide if what you say has any meaning to me :) Sorry, you have to get more
technical, or we will never be able to sort out what it is you imagine.
Describe a sequence of commands or something and what behaviour you expect
(which permissions are set, and where they come from).

> If an extra flag is required to be set, what does that default to? if it 
> defaults
> to the same as the world permissions, (ie not specifying the flag implies this
> default) wouldn't that be the same as doing what I'm trying to do?

This is what is currently done now, and yes, it is probably what you mean,
but see above.

But it is undecided if we want this behaviour to be default, or default to
using the extra rwx set of bits and set them to ---. This is a decision we
have not made yet.

> And if someone
> wants it to default to --- instead, wouldn't that be just the same as 
> specifying
> the permission as 0?

Almost. He would set the permission to 0 AND set the extra bit to use this
instead world. But this would not be a "default", but an explicit setting to
---.

> This is as much effort as specifying a flag to do it.

I still think you have not understood good enough that a bit has only two
states, on or off, and not "undefined". We don't have fuzzy logic in PC
hardware :)

> Also, I finally had a look at that ACL stuff. I think using ACL would be much
> more conveniant

You are invited to make a design and implement it. The Hurd allows arbitrary
extensions of the system by the user. This is not an exclusive or decision.

Marcus

-- 
`Rhubarb is no Egyptian god.' Debian http://www.debian.org brinkmd@debian.org
Marcus Brinkmann              GNU    http://www.gnu.org    marcus@gnu.org
Marcus.Brinkmann@ruhr-uni-bochum.de
http://www.marcus-brinkmann.de