🚀 go-pugleaf

crj10@phx.cam.ac.uk (Clive Jones) wrote:

>The FreeSpace module knows, initially, how to deal with ADFS, RAMFS, NETFS,
>NFS and SCSIFS. Other filing systems have to register by calling:

(...details of SWIs and handlers deleted...)

Actually using this is a bit tricky. Brian Brunswick has working code which
uses this in Memphis (possibly not the released version). The biggest
problem is that when the FreeSpace module calls your handler routine, you
are in User mode and R13 points to the FreeSpace module's private stack in
it's workspace. This is of zero gauranteed depth ie. you can't use it, so
you have no stack (unless you want to over-write random bits of RMA). So you
need to supply your own stack, or not use any stack, or call SWI OS_EnterOS
to get the SVC stack. You can ease the problem by doing as little work
yourself as possible eg. call SWI OS_FSControl 49 (get free space) to do all
the work for you for free space reason code 2 (the other option for IDEFS
is to call IDEFS_DescribeDisc).

Next problem, FreeSpace calls you with the return address on the stack (the
one you can't use for anything) rather than in LR.

OS_FSControl 49 - reads free space on the disc or image file that holds a
specified object.

Entry:  r0 = 49
        r1 = pinter to name of object (null terminated)
Exit:   r0 = free space
        r1 = largest creatable object
        r2 = disc size

If you pass adfs::4.$.PC.Drive_C.DRDOS.TMP in r1, the information returned
in r0-r2 will be for the PC hard disk image Drive_C and not ADFS drive 4.

All of the above information is in the grey cover photocopied PRMs that were
available at the the Acorn User show.

It's a shame you can't do *ShowFree on a per directory basis, because if you
could then you could get a free space display for your PC partition. Also
since RISC OS 3 can get the free space of any image/disk on any filing
system, it's a shame the FreeSpace module doesn't just use this. Then filing
systems wouldn't have to bother with all this registering lark. These sound
like things for Nick and Andrew's filer improvements package to me.

You can intercept the *Free call made by IDEFSFiler with:

*SetMacro Alias$Free If "<Wimp$State>"="desktop" then ShowFree -FS
<FileSwitch$TemporaryFilingSystem> %0 else %Free %0

This should be enough for you to bolt interactive free space display on top
of any RISC OS 2 filing system you may have, unless IDEFSFiler does a *%Free
rather than *Free in which case you'd have to sit on OS_CLI in some way :-(.

Owen.