Path: utzoo!attcan!uunet!mcsun!hp4nl!janus!maarten
From: maarten@janus.UUCP (Maarten Carels)
Newsgroups: comp.sys.mac.programmer
Subject: Re: Telling Floppies from Hard Disks
Message-ID: <785@janus.UUCP>
Date: 24 Aug 89 12:11:27 GMT
References: <1742@cs-spool.calgary.UUCP> <3841@internal.Apple.COM>
Reply-To: maarten@fwi.uva.nl (Maarten Carels)
Organization: Faculteit Wiskunde & Informatica, Universiteit van Amsterdam
Lines: 55


blob@apple.com (Brian Bechtel) writes:
>In article <1742@cs-spool.calgary.UUCP> jamesm@cpsc.ucalgary.ca (Mark 
>James) writes:
>> I'm looking for a method to test a volume to see if it is a floppy or a 
>> hard drive.  I have written an INIT to patch PBMountVol to check an 
... stuff deleted...
>It sounds like what you really want to check is if a device in the drive 
>queue is removable or not.  To do this, examine the four bytes of flags 
>preceeding the drive queue entry for this device.  See Inside Mac 
>IV-181 & 182 for details.  C source is:
Then some C source appears, only the relevant parts kept:

>    d = ... /* pointer to some drive queue element */
>        if (d->dQDrive == driveNumber)   /* is this the drive we want? */
>        {
>            p = (Ptr)d;
>            p -= 3; /* to get to the byte with eject info */
>            if (*p == 8)
****                   ^ This is plain wrong, see below
>                /* non ejectable disk in drive */
>            else
>                /* ejectable disk in drive */

The flag byte tested above contains (IM IV-181):
0	if no disk in drive
1 or 2	if disk in drive
8	if nonejectable disk in drive
$fc-$ff	if disk was ejected within last 1.5 seconds
$48	if disk in drive is nonejectable but driver wants a call

if there is 48 in the flags byte, the disk is considered nonejectable
by both the Finder and Standard File. Unmounting the disk (dragging to
the trash) causes an Eject control call to thye driver, that can be used
to clean up after unmounting (such as updating internal data structures
of the driver).

Code like this (checking for 8, and failing to recognize 48 for non-ejectable
disks) causes problems with some disks (such as mine) in programs like
DiskExpress, PrintQueue (of Super(Laser)Spool, FEdit, to name some.

So, please do not check for only for flags value 8, but also for $48,
or test for the specific bit (3).

--maarten

In real life:	Maarten Carels
		Computer Science Department
		University of Amsterdam
email:		maarten@fwi.uva.nl
-- 
In real life:	Maarten Carels
		Computer Science Department
		University of Amsterdam
email:		maarten@fwi.uva.nl