Technical Q&As

FL07 - PBXGetVolInfo Glue (30-July-98)

Q What is the glue for calling PBXGetVolInfoSync and PBXGetVolInfoAsync?


A Here is the glue that you need:

#if GENERATINGCFM
         
#include <Traps.h>
#include <FSM.h>
         
// kFSMXGetVolInfo was not introduced until Universal Interfaces 3.0.1.
         
#if UNIVERSAL_INTERFACES_VERSION < 0x0301
    enum {
        kFSMXGetVolInfo = 0x0012
    };
#endif
         
// Define the ProcInfoType value for the PBXGetVolInfo routines.
         
enum {
    uppXGetVolInfoProcInfo = kRegisterBased |
        RESULT_SIZE(SIZE_CODE(sizeof(OSErr))) |
        REGISTER_RESULT_LOCATION(kRegisterD0) |
        REGISTER_ROUTINE_PARAMETER(1, kRegisterD0, kFourByteCode) |
        REGISTER_ROUTINE_PARAMETER(2, kRegisterD1, kFourByteCode) |
        REGISTER_ROUTINE_PARAMETER(3, kRegisterA0, SIZE_CODE(sizeof(XVolumeParamPtr)))
};
         
// Glue for the sync routine.
         
extern pascal OSErr PBXGetVolInfoSync(XVolumeParamPtr paramBlock)
{
    return CallOSTrapUniversalProc(GetOSTrapAddress(_FSDispatch), uppXGetVolInfoProcInfo,
        kFSMXGetVolInfo,            // selector   in D0
        _FSDispatch,                // trap word  in D1
        paramBlock                  // paramBlock in A0
    );
}
         
// Glue for the async routine.
         
extern pascal OSErr PBXGetVolInfoAsync(XVolumeParamPtr paramBlock)
{
    return CallOSTrapUniversalProc(GetOSTrapAddress(_FSDispatch), uppXGetVolInfoProcInfo,
        kFSMXGetVolInfo,            // selector   in D0
        _FSDispatch | kAsyncMask,   // trap word  in D1
        paramBlock                  // paramBlock in A0
    );
}
         
#endif

IMPORTANT:
While the glue in this Q&A has always been correct, DTS has given out incorrect glue for PBXGetVolInfoSync to a number of individual developers. This glue appears to work, but there is a distinct chance it will cause the computer to crash eventually. If you are using this incorrect glue, you should update to the glue given above as soon as possible.

You can recognize the incorrect glue by looking at the ProcInfoType it constructs. The ProcInfoType construction code for the incorrect glue is shown below.

// WARNING: Do not use this code
#define PROCINFO \
    kRegisterBased | \
    RESULT_SIZE(SIZE_CODE(sizeof(OSErr))) | \
    REGISTER_RESULT_LOCATION(kRegisterD0) | \
    REGISTER_ROUTINE_PARAMETER(1, kRegisterD0, kTwoByteCode) | \
    REGISTER_ROUTINE_PARAMETER(2, kRegisterA0, SIZE_CODE(sizeof(XVolumeParamPtr)))
// WARNING: Do not use this code

This ProcInfoType is incorrect because it does not describe the use of 68K register D1 as an implicit parameter to PBXGetVolInfoSync. Register D1 determines whether the trap runs synchronously or asynchronously. If you fail to set it up, the trap may run asynchronously (based on the previous contents of register D1) which, depending on a variety of circumstances, may crash the computer.

For more information on how to build glue for calling classic 68K code from CFM, including OS traps like PBXGetVolInfoSync, read Technote 1127 In Search of Missing Links.

-- Mark Cookson
-- Revised by Quinn "The Eskimo!"
Worldwide Developer Technical Support


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