[iyonix-support] Re: Bugs in SCSIFS?
- From: davehigton@xxxxxxxxxxxxx
- To: iyonix-support@xxxxxxxxxxxxx
- Date: Thu, 21 Jun 2007 13:45:24 +0100
Quoting John Ballance <jwb@xxxxxxxxxx>:
> hi
>
> davehigton@xxxxxxxxxxxxx wrote:
> >
> > What happens when a drive with a >2GB partition is offered around?
> > Does it become available for block/sector access via FileCore%SCSI?
> >
>
> if memory serves: it is treated as if it is a single file .. hence the
> (current) 2gb filecore file size restriction 'gets in the way' I don't
> remember any attempt to trap this situation..
>
> various strategies have been considered, varying from allowing dosfs to
> have direct disc access in cases where it is happy it is 'talking' to a
> disc, not a file on disc, to a system that 'slices' the dos disc image
> into a sequence of 'small enough' files, much as cdvdburn does for dvd
> iso images.
I've been working on an application that will allow navigation up and
down a directory structure of a memory stick, and will allow saving
of files from it. It's mostly a test bed to see if I understand FAT
formats, but it takes me part way to understanding what DOSFS would
need to do to deal with devices >2GB. My app in principle would work
on devices up to the limit of a SectorOp SWI, but it relies on the
SectorOp SWI's being available for the particular device, which ATM
implies that the device must be mounted.
It seems we're so nearly there. I assume that DOSFS must interface
to FileSwitch, since the way a DOS drive is operated bears little
resemblance to FileCore. So it must already do all we want, except
that it can't operate on big enough devices.
But all that a DOSFS needs, in principle, is a SectorOp read and a
SectorOp write. Clearly we have lower layers that provide them.
What's nice about using them is that you don't have to write a handler
for a USB 8/6/80 protocol (for example); it's already there and tested.
It just looks like such a narrow gap to bridge...
Presumably a key element here is what Service_IdentifyDisc receives
and gives. The other one (chronologically, but more important in
terms of deficiencies) is step 10 on PRM 2-322.
Dave
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