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Important: This document is part of the Legacy section of the ADC Reference Library. This information should not be used for new development.

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SCSI ID from vRefNum

Q: I would like to obtain the SCSI-ID of a disk volume where a certain file is located. What is the way to do it?

A: I assume you've already thought ahead to the cases where the drive in question is not SCSI (e.g., floppy, IDE, RAM disk, etc.)

There are two answers to this question, depending upon whether SCSI Manager 4.3 is present or not. If SCSI Manager 4.3 is not present, you rely on the fact that SCSI devices are at a particular place in the unit table. To summarize Inside Macintosh:Devices, SCSI drivers go in slots 32-40 in the unit table in order, so the driver for SCSI 0 is in slot 32, SCSI 1 is in slot 1, etc.

     slot number = -(refnum-1)

So the driver for SCSI 0 has refnum -33, SCSI 1 has refnum -34, etc.

If SCSI Manager 4.3 is installed, you call the routine SCSILookupRefNumXRef() as documented in Inside Macintosh:Devices on page 4-52 and 4-53.

To detect the presence of SCSI Manager 4.3, check that the trap _SCSIAtomic is unimplemented, as demonstrated in Inside Macintosh:Operating System Utilities on page 8-21 through 8-23. You also want to read the "I Am Curious SCSI" note in the SCSI Samples 1.0 folder on the Tool Chest developer CD

Given that you have a volume reference number, you need to obtain the driver reference number. You get this by calling PBHGetVInfo(), documented in Inside Macintosh:Files on page 2-144.

OSErr   GetDRefNumFromVRefNum(short vRefNum, short *dRefNum)
    HParamBlockRec  pb;
    Str27           volName;
    OSErr           result;

    pb.volumeParam.ioVRefNum = vRefNum;
    pb.volumeParam.ioNamePtr = volName;
    pb.volumeParam.ioVolIndex = 0;  /* use ioVRefNum only,
                                        return volume name */
    result = PBHGetVInfoSync(&pb);
    if (result == noErr)
        *dRefNum = pb.volumeParam.ioVDrvInfo;
    return result;

Given the driver reference number, use the code below (from "I Am Curious SCSI").

 * Get the SCSI Bus ID for a particular driver reference number. This is
 * valid for the original SCSI Manager. Under the asynchronous SCSI Manager,
 * it is needed if the driver did not register with the SCSI Manager.
#define DriverRefNumToSCSI(x)  ((signed short) (~(x) - 32))

 * Return the DeviceIdent for a particular driver by searching the list of
 * registered devices. Return noErr on success, or nsvErr if there is none
        short        driverRefNum,
        DeviceIdent  *deviceIdentPtr
    OSErr            status, scsiStatus;
    SCSI_DriverPB    pb;
    short            targetID;

    status = nsvErr;
    if (AsynchronousSCSIManagerPresent()) {
         * Scan the list of registered drivers for
         * this driverRefNum.
        ClearMemory((ptr) &pb, sizeof pb);
        pb.scsiPBLength = sizeof (SCSI_Driver_PB);
        pb.scsiCompletion = NULL;
        pb.scsiFlags = 0;
        pb.scsiFunctionCode = SCSILookupRefNumXref;
        /* Initialize the DeviceIdent to an
         * "impossible" value to start the scan
         * process. SCSIAction will return the
         * current device in pb.scsiDevice and the
         * next registered device in
         * pb.scsiNextDevice. The do loop examines
         * each registered device in turn. The loop
         * exits when the next device is on an
         * illegal bus. Note that the test must
         * ignore the first value as the current
         * bus (pb.scsiDevice.bus ) contains the
         * "illegal" designation.

         *((long *) &pb.scsiDevice) = -1L;
         do {
            scsiStatus = SCSIAction((SCSI_PB *) &pb);
            if (scsiStatus != noErr) {
                status = scsiStatus;
            if (pb.scsiDriver == driverRefNum /* Is this the driver we want? */
             && pb.scsiDevice.bus != 0xFF) {  /* Is this a real bus? */
                *deviceIdentPtr = pb.scsiDevice;
                status = noErr;
            pb.scsiDevice = pb.scsiNextDevice;
        } while (pb.scsiDevice.bus != 0xFF);
    if (status == nsvErr) {
         * The asynchronous SCSI Manager is missing or the
         * driver didn't register with the SCSI Manager.*/
        targetID = DriverRefNumToSCSI(driverRefNum);
        if (targetID >= 0 && targetID <= 6) {
            deviceIdentPtr->diReserved = 0;
            deviceIdentPtr->diBus = 0;
            deviceIdentPtr->targetID = targetID;
            deviceIdentPtr->LUN = 0;
            status = noErr;
    return (status);

[May 23 1997]

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