Re: Brutal Deluxe's holidays project 1: IIgs mount virtual disk image

[Toinet <antoine.vignau@laposte.net>]

On 19 août, 19:44, "ict@ccess" <gids...@sasktel.net> wrote:
> On Aug 19, 4:32 am, "Peter Watson" <paw77@N_O_hotmail_S_P_A_M.com>
> wrote:
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> > "Toinet" <antoine.vig...@laposte.net> wrote in message
>
> >8f27b9af-c978-4b5e-b447-30cc6d76420c@o6g2000yqj.googlegroups.com">news:8f27b9af-c978-4b5e-b447-30cc6d76420c@o6g2000yqj.googlegroups.com...
>
> > > It is not possible to mount a HFS partition nor a DOS 3.x or RDOS 3.x
> > > partition, it is limited to ProDOS files only (140 KB or 800KB). Note
> > > that the files are loaded into memory in one shot. There are no ways
> > > to open files larger than available RAM or >800 KB.
>
> > I understand the size limitation due to loading everything into memory, but
> > I'm curious to know why you couldn't support other disk sizes such as a 1.44
> > MB ProDOS file image?
> > --
> > Peter Watson
> > -- Write to MS-DOS disks on the Apple IIgs?
> > -- Impossible!  ;-)
>
> Exactly!  I think it was gone about the wrong way.  You don't need to
> load the entire disk image into memory.  You just have to load the
> directory and then load files from there.  That way, there are a few
> utilities that can read a dos 3.3 catalog from Prodos.  Really, all
> that is needed is a driver that calculates the offset to a hard drive
> block.  Since it is known that the Prodos catalog starts on block #2
> on any drive, then just add 2 to the starting directory block of the
> disk image.  Any file can also be loaded by adding the files block
> number to the theoretical starting block zero of the disk image.  This
> sounds and is much easier than loading the entire image into memory.
>
> Rob

Rob,

What is theorically possible is not feasible on GS/OS as it is not
reentrant, meaning you cannot tell a low-level device driver read or
write 512/532 bytes blocks from a file which is a high-level call.

If you read the GS/OS reference and the Driver reference, you would
understand it.

I confirm that it sounds and is much easier than loading the entire
image into memory but that is not possible due to GS/OS limitations.

So please forgive me for that useless software ;-)

Antoine