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From: blob@apple.com (Brian Bechtel)
Newsgroups: comp.sys.mac.programmer
Subject: Re: Telling Floppies from Hard Disks
Message-ID: <3841@internal.Apple.COM>
Date: 23 Aug 89 20:48:05 GMT
References: <1742@cs-spool.calgary.UUCP>
Sender: usenet@Apple.COM
Organization: Apple Computer, Inc.
Lines: 55

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 
> inserted disk for viruses before mounting it and giving a dialog box if 
> it is infected.  The problem is it takes far to long to mount a hard 
> drive this way. 

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:

/* we assume that you get the drive number from some appropriate
   place, such as doing a PBHGetVInfo for the volume or looking directly 
   in the vcb (ackk!)
*/
Boolean
IsEjectable(driveNumber)
short driveNumber
{
    DrvQElPtr   d;
    QHdrPtr     queueHeader;
    Ptr         p;

    queueHeader = GetDrvQHdr();
    d = (DrvQElPtr)queueHeader->qHead;

    while (d != nil)    /* find the appropriate drive # */
    {
        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)
                return false;           /* non ejectable disk in drive */
            else
                return true;
        }
        d = (DrvQElPtr)d->qLink;
    }
    return false;   /* you specified an invalid drive number */
}

Now if you really want to know if a volume is a floppy or not, use 
PBHGetVInfo, and multiply out the ioVNmAlBlks (remember, it's unsigned!) 
times ioVAlBlkSiz.  Currently valid sizes include 400K, 800K, 720K, 1440K. 
How will you handle other sizes from the future?  Nasty.  That's why I 
think you are really asking to detect removable media.

In such an INIT, you might also want to check that the volume isn't 
extremely large (i.e. CD-ROM), so that you don't waste an incredible 
amount of time mounting those volumes, either.

--Brian Bechtel     blob@apple.com     "My opinion, not Apple's"