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Re: OS_GBPB 12 in a Wimp task

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In message <almarsoft.333093024920706560@news.orange.fr>
 on 15 Mar 2012 Rick Murray  wrote:

> On Thu, 15 Mar 2012 02:40:06 -0700 (PDT), Christopher Bazley 
> <cs99cjb@gmail.com> wrote:
> 
> > Incidentally, I am alarmed at some contributors' suggestions that R4 be
> > interpreted as a pointer. Way to let programs crash the operating system!
> > This is not how to implement an opaque handle between user
> 
> I thought it was the FS using R4 as a pointer?

Yes, but Chris is quite right that actually implementing a filing system like
that would be a bad idea.  I'm afraid it was my loose choice of words.  I was
trying to make the point that after the initial call to OS-GBPB with R4=0,
the filing system might return in R4 a value which then does not change over
subsequent calls until finally R4=-1 is returned at the end, so "remembering
previous values of R4" is scarcely an improvement for winding backwards
through the directory.  The filing system might be using R4 as a pointer to a
structure where the actual context is being kept internally.

I should, of course, have used the word "handle".

Implementing a filing system along these lines is problematic in itself, as
the caller is not obliged to keep going till it gets R4=-1, so the filing
system has no way of knowing that the handle and context can be disposed of.

My inclination (from the filing system author's point of view) is that there
are quite a few weird and wonderful filing systems where it would be pretty
hard to treat R4 as a random access file index into the directory.  But I
appreciate that the application author doesn't always have much option if the
application is to multi-task and behave responsively.  Perhaps we need a way
of asking the filing system to go backwards, as well as forwards?!  But that
would involve a new API, which would be even less likely to be achievable
than the alternatives of rewriting FileAction (and other apps) or rewriting
the filing systems!

-- 
Matthew Phillips
Durham

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OS_GBPB 12 in a Wimp task Christopher Bazley <cs99cjb@gmail.com> - 2012-03-06 14:33 -0800
  Re: OS_GBPB 12 in a Wimp task jeff <jeffrey.a.doggett@gmail.com> - 2012-03-07 00:02 -0800
    Re: OS_GBPB 12 in a Wimp task Matthew Phillips <spam2011m@yahoo.co.uk> - 2012-03-08 22:33 +0000
      Re: OS_GBPB 12 in a Wimp task Christopher Bazley <cs99cjb@gmail.com> - 2012-03-10 10:22 -0800
        Re: OS_GBPB 12 in a Wimp task Matthew Phillips <spam2011m@yahoo.co.uk> - 2012-03-10 21:04 +0000
          Re: OS_GBPB 12 in a Wimp task Rick Murray <heyrickmail-usenet@yahoo.co.uk> - 2012-03-10 23:11 +0100
            Re: OS_GBPB 12 in a Wimp task Matthew Phillips <spam2011m@yahoo.co.uk> - 2012-03-11 09:10 +0000
              Re: OS_GBPB 12 in a Wimp task Chris Johnson <chrisjohnson+news@spamcop.net> - 2012-03-11 10:41 +0000
              Re: OS_GBPB 12 in a Wimp task Steve Fryatt <news@stevefryatt.org.uk> - 2012-03-11 11:06 +0000
              Re: OS_GBPB 12 in a Wimp task Rick Murray <heyrickmail-usenet@yahoo.co.uk> - 2012-03-11 17:56 +0100
                Re: OS_GBPB 12 in a Wimp task Gavin Wraith <gavin@wra1th.plus.com> - 2012-03-11 18:25 +0000
                Re: OS_GBPB 12 in a Wimp task Rick Murray <heyrickmail-usenet@yahoo.co.uk> - 2012-03-12 00:33 +0100
                Re: OS_GBPB 12 in a Wimp task Gavin Wraith <gavin@wra1th.plus.com> - 2012-03-12 11:56 +0000
                Re: OS_GBPB 12 in a Wimp task Martin Wuerthner <spamtrap@mw-software.com> - 2012-03-12 16:44 +0100
                Re: OS_GBPB 12 in a Wimp task druck <news@druck.org.uk> - 2012-03-12 20:57 +0000
                Re: OS_GBPB 12 in a Wimp task Martin Wuerthner <spamtrap@mw-software.com> - 2012-03-12 22:26 +0100
                Re: OS_GBPB 12 in a Wimp task Rick Murray <heyrickmail-usenet@yahoo.co.uk> - 2012-03-13 17:50 +0100
                Re: OS_GBPB 12 in a Wimp task jgharston <jgh@arcade.demon.co.uk> - 2012-03-13 10:15 -0700
                Re: OS_GBPB 12 in a Wimp task Matthew Phillips <spam2011m@yahoo.co.uk> - 2012-03-13 07:34 +0000
                Re: OS_GBPB 12 in a Wimp task Rick Murray <heyrickmail-usenet@yahoo.co.uk> - 2012-03-14 06:00 +0100
                Re: OS_GBPB 12 in a Wimp task Christopher Bazley <cs99cjb@gmail.com> - 2012-03-15 02:40 -0700
                Re: OS_GBPB 12 in a Wimp task Rick Murray <heyrickmail-usenet@yahoo.co.uk> - 2012-03-15 14:55 +0100
                Re: OS_GBPB 12 in a Wimp task "Ste (news)" <steve@revi11.plus.com> - 2012-03-15 14:46 +0000
                Re: OS_GBPB 12 in a Wimp task Rick Murray <heyrickmail-usenet@yahoo.co.uk> - 2012-03-15 18:44 +0100
                Re: OS_GBPB 12 in a Wimp task Jeremy Nicoll - news posts <jn.nntp.scrap007@wingsandbeaks.org.uk> - 2012-03-15 19:44 +0000
                Re: OS_GBPB 12 in a Wimp task Alan Adams <alan@adamshome.org.uk> - 2012-03-15 20:36 +0000
                Re: OS_GBPB 12 in a Wimp task Chris Johnson <chrisjohnson+news@spamcop.net> - 2012-03-15 20:26 +0000
                Re: OS_GBPB 12 in a Wimp task Rick Murray <heyrickmail-usenet@yahoo.co.uk> - 2012-03-16 06:12 +0100
                Re: OS_GBPB 12 in a Wimp task Matthew Phillips <spam2011m@yahoo.co.uk> - 2012-03-15 20:34 +0000
                Re: OS_GBPB 12 in a Wimp task Alan Adams <alan@adamshome.org.uk> - 2012-03-15 21:04 +0000
                Re: OS_GBPB 12 in a Wimp task Matthew Phillips <spam2011m@yahoo.co.uk> - 2012-03-16 00:17 +0000
        Re: OS_GBPB 12 in a Wimp task Chris Johnson <chrisjohnson+news@spamcop.net> - 2012-03-10 23:58 +0000
          Re: OS_GBPB 12 in a Wimp task Chris Johnson <chrisjohnson+news@spamcop.net> - 2012-03-11 10:43 +0000
          Re: OS_GBPB 12 in a Wimp task jeff <jeffrey.a.doggett@gmail.com> - 2012-03-12 03:03 -0700
            Re: OS_GBPB 12 in a Wimp task Chris Johnson <chrisjohnson+news@spamcop.net> - 2012-03-12 10:44 +0000
            Re: OS_GBPB 12 in a Wimp task Matthew Phillips <spam2011m@yahoo.co.uk> - 2012-03-13 07:44 +0000
              Re: OS_GBPB 12 in a Wimp task jeff <jeffrey.a.doggett@gmail.com> - 2012-03-13 03:06 -0700
  Re: OS_GBPB 12 in a Wimp task druck <news@druck.org.uk> - 2012-03-07 10:08 +0000

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