floppy.c

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/*
 *  ReactOS Floppy Driver
 *  Copyright (C) 2004, Vizzini (vizzini@plasmic.com)
 *
 *  This program is free software; you can redistribute it and/or modify
 *  it under the terms of the GNU General Public License as published by
 *  the Free Software Foundation; either version 2 of the License, or
 *  (at your option) any later version.
 *
 *  This program is distributed in the hope that it will be useful,
 *  but WITHOUT ANY WARRANTY; without even the implied warranty of
 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *  GNU General Public License for more details.
 *
 *  You should have received a copy of the GNU General Public License along
 *  with this program; if not, write to the Free Software Foundation, Inc.,
 *  51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * PROJECT:         ReactOS Floppy Driver
 * FILE:            floppy.c
 * PURPOSE:         Main floppy driver routines
 * PROGRAMMER:      Vizzini (vizzini@plasmic.com)
 * REVISIONS:
 *                  15-Feb-2004 vizzini - Created
 * NOTES:
 *  - This driver is only designed to work with ISA-bus floppy controllers.  This
 *    won't work on PCI-based controllers or on anything else with level-sensitive
 *    interrupts without modification.  I don't think these controllers exist.
 *
 * ---- General to-do items ----
 * TODO: Figure out why CreateClose isn't called any more.  Seems to correspond
 *       with the driver not being unloadable.
 * TODO: Think about StopDpcQueued -- could be a race; too tired atm to tell
 * TODO: Clean up drive start/stop responsibilities (currently a mess...)
 *
 * ---- Support for proper media detection ----
 * TODO: Handle MFM flag
 * TODO: Un-hardcode the data rate from various places
 * TODO: Proper media detection (right now we're hardcoded to 1.44)
 * TODO: Media detection based on sector 1
 */

#include "precomp.h"

/*
 * Global controller info structures.  Each controller gets one.  Since the system
 * will probably have only one, with four being a very unlikely maximum, a static
 * global array is easiest to deal with.
 */
static CONTROLLER_INFO gControllerInfo[MAX_CONTROLLERS];
static ULONG gNumberOfControllers = 0;

/* Queue thread management */
static KEVENT QueueThreadTerminate;
static PVOID QueueThreadObject;


static VOID NTAPI
MotorStopDpcFunc(PKDPC UnusedDpc, PVOID DeferredContext, PVOID SystemArgument1, PVOID SystemArgument2)
/*
 * FUNCTION: Stop the floppy motor
 * ARGUMENTS:
 *     UnusedDpc: DPC object that's going off
 *     DeferredContext: called with DRIVE_INFO for drive to turn off
 *     SystemArgument1: unused
 *     SystemArgument2: unused
 * NOTES:
 *     - Must set an event to let other threads know we're done turning off the motor
 *     - Called back at DISPATCH_LEVEL
 */
{
    PCONTROLLER_INFO ControllerInfo = (PCONTROLLER_INFO)DeferredContext;

    UNREFERENCED_PARAMETER(SystemArgument1);
    UNREFERENCED_PARAMETER(SystemArgument2);
    UNREFERENCED_PARAMETER(UnusedDpc);

    ASSERT(KeGetCurrentIrql() == DISPATCH_LEVEL);
    ASSERT(ControllerInfo);

    TRACE_(FLOPPY, "MotorStopDpcFunc called\n");

    HwTurnOffMotor(ControllerInfo);
    ControllerInfo->StopDpcQueued = FALSE;
    KeSetEvent(&ControllerInfo->MotorStoppedEvent, EVENT_INCREMENT, FALSE);
}


VOID NTAPI
StartMotor(PDRIVE_INFO DriveInfo)
/*
 * FUNCTION: Start the motor, taking into account proper handling of the timer race
 * ARGUMENTS:
 *     DriveInfo: drive to start
 * NOTES:
 *     - Never call HwTurnOnMotor() directly
 *     - This protocol manages a race between the cancel timer and the requesting thread.
 *       You wouldn't want to turn on the motor and then cancel the timer, because the
 *       cancel dpc might fire in the meantime, and that'd un-do what you just did.  If you
 *       cancel the timer first, but KeCancelTimer returns false, the dpc is already running,
 *       so you have to wait until the dpc is completly done running, or else you'll race
 *       with the turner-offer
 *     - PAGED_CODE because we wait
 */
{
    PAGED_CODE();
    ASSERT(DriveInfo);

    TRACE_(FLOPPY, "StartMotor called\n");

    if(DriveInfo->ControllerInfo->StopDpcQueued && !KeCancelTimer(&DriveInfo->ControllerInfo->MotorTimer))
    {
        /* Motor turner-offer is already running; wait for it to finish */
        INFO_(FLOPPY, "StartMotor: motor turner-offer is already running; waiting for it\n");
        KeWaitForSingleObject(&DriveInfo->ControllerInfo->MotorStoppedEvent, Executive, KernelMode, FALSE, NULL);
        INFO_(FLOPPY, "StartMotor: wait satisfied\n");
    }

    DriveInfo->ControllerInfo->StopDpcQueued = FALSE;

    if(HwTurnOnMotor(DriveInfo) != STATUS_SUCCESS)
    {
        WARN_(FLOPPY, "StartMotor(): warning: HwTurnOnMotor failed\n");
    }
}


VOID NTAPI
StopMotor(PCONTROLLER_INFO ControllerInfo)
/*
 * FUNCTION: Stop all motors on the controller
 * ARGUMENTS:
 *     DriveInfo: Drive to stop
 * NOTES:
 *     - Never call HwTurnOffMotor() directly
 *     - This manages the timer cancelation race (see StartMotor for details).
 *       All we have to do is set up a timer.
 */
{
    LARGE_INTEGER StopTime;

    ASSERT(ControllerInfo);

    TRACE_(FLOPPY, "StopMotor called\n");

    /* one relative second, in 100-ns units */
    StopTime.QuadPart = 10000000;
    StopTime.QuadPart *= -1;

    KeClearEvent(&ControllerInfo->MotorStoppedEvent);
    KeSetTimer(&ControllerInfo->MotorTimer, StopTime, &ControllerInfo->MotorStopDpc);
    ControllerInfo->StopDpcQueued = TRUE;
}


VOID NTAPI
WaitForControllerInterrupt(PCONTROLLER_INFO ControllerInfo)
/*
 * FUNCTION: Wait for the controller to interrupt, and then clear the event
 * ARGUMENTS:
 *     ControllerInfo: Controller to wait for
 * NOTES:
 *     - There is a small chance that an unexpected or spurious interrupt could
 *       be lost with this clear/wait/clear scheme used in this driver.  This is
 *       deemed to be an acceptable risk due to the unlikeliness of the scenario,
 *       and the fact that it'll probably work fine next time.
 *     - PAGED_CODE because it waits
 */
{
    PAGED_CODE();
    ASSERT(ControllerInfo);

    KeWaitForSingleObject(&ControllerInfo->SynchEvent, Executive, KernelMode, FALSE, NULL);
    KeClearEvent(&ControllerInfo->SynchEvent);
}

static DRIVER_DISPATCH CreateClose;
static NTSTATUS NTAPI CreateClose(PDEVICE_OBJECT DeviceObject,
                                  PIRP Irp)
/*
 * FUNCTION: Dispatch function called for Create and Close IRPs
 * ARGUMENTS:
 *     DeviceObject: DeviceObject that is the target of the IRP
 *     Irp: IRP to process
 * RETURNS:
 *     STATUS_SUCCESS in all cases
 * NOTES:
 *     - The Microsoft sample drivers tend to return FILE_OPENED in Information, so I do too.
 *     - No reason to fail the device open
 *     - No state to track, so this routine is easy
 *     - Can be called <= DISPATCH_LEVEL
 *
 * TODO: Figure out why this isn't getting called
 */
{
    UNREFERENCED_PARAMETER(DeviceObject);

    TRACE_(FLOPPY, "CreateClose called\n");

    Irp->IoStatus.Status = STATUS_SUCCESS;
    Irp->IoStatus.Information = FILE_OPENED;

    IoCompleteRequest(Irp, IO_DISK_INCREMENT);

    return STATUS_SUCCESS;
}


static NTSTATUS NTAPI
Recalibrate(PDRIVE_INFO DriveInfo)
/*
 * FUNCTION: Start the recalibration process
 * ARGUMENTS:
 *     DriveInfo: Pointer to the driveinfo struct associated with the targeted drive
 * RETURNS:
 *     STATUS_SUCCESS on successful starting of the process
 *     STATUS_IO_DEVICE_ERROR if it fails
 * NOTES:
 *     - Sometimes you have to do two recalibrations, particularly if the disk has <80 tracks.
 *     - PAGED_CODE because we wait
 */
{
    NTSTATUS Status;
    ULONG i;

    PAGED_CODE();
    ASSERT(DriveInfo);

    /* first turn on the motor */
    /* Must stop after every start, prior to return */
    StartMotor(DriveInfo);

    /* set the data rate */
    WARN_(FLOPPY, "FIXME: UN-HARDCODE DATA RATE\n");
    if(HwSetDataRate(DriveInfo->ControllerInfo, 0) != STATUS_SUCCESS)
    {
        WARN_(FLOPPY, "Recalibrate: HwSetDataRate failed\n");
        StopMotor(DriveInfo->ControllerInfo);
        return STATUS_IO_DEVICE_ERROR;
    }

    /* clear the event just in case the last call forgot */
    KeClearEvent(&DriveInfo->ControllerInfo->SynchEvent);

    /* sometimes you have to do this twice; we'll just do it twice all the time since
     * we don't know if the people calling this Recalibrate routine expect a disk to
     * even be in the drive, and if so, if that disk is formatted.
     */
    for(i = 0; i < 2; i++)
    {
        /* Send the command */
        Status = HwRecalibrate(DriveInfo);
        if(Status != STATUS_SUCCESS)
        {
            WARN_(FLOPPY, "Recalibrate: HwRecalibrate returned error\n");
            continue;
        }

        WaitForControllerInterrupt(DriveInfo->ControllerInfo);

        /* Get the results */
        Status = HwRecalibrateResult(DriveInfo->ControllerInfo);
        if(Status != STATUS_SUCCESS)
        {
            WARN_(FLOPPY, "Recalibrate: HwRecalibrateResult returned error\n");
            break;
        }
    }

    KeClearEvent(&DriveInfo->ControllerInfo->SynchEvent);

    /* Must stop after every start, prior to return */
    StopMotor(DriveInfo->ControllerInfo);

    return Status;
}


NTSTATUS NTAPI
ResetChangeFlag(PDRIVE_INFO DriveInfo)
/*
 * FUNCTION: Reset the drive's change flag (as reflected in the DIR)
 * ARGUMENTS:
 *     DriveInfo: the drive to reset
 * RETURNS:
 *     STATUS_SUCCESS if the changeline is cleared
 *     STATUS_NO_MEDIA_IN_DEVICE if the changeline cannot be cleared
 *     STATUS_IO_DEVICE_ERROR if the controller cannot be communicated with
 * NOTES:
 *     - Change reset procedure: recalibrate, seek 1, seek 0
 *     - If the line is still set after that, there's clearly no disk in the
 *       drive, so we return STATUS_NO_MEDIA_IN_DEVICE
 *     - PAGED_CODE because we wait
 */
{
    BOOLEAN DiskChanged;

    PAGED_CODE();
    ASSERT(DriveInfo);

    TRACE_(FLOPPY, "ResetChangeFlag called\n");

    /* Try to recalibrate.  We don't care if it works. */
    Recalibrate(DriveInfo);

    /* clear spurious interrupts in prep for seeks */
    KeClearEvent(&DriveInfo->ControllerInfo->SynchEvent);

    /* must re-start the drive because Recalibrate() stops it */
    StartMotor(DriveInfo);

    /* Seek to 1 */
    if(HwSeek(DriveInfo, 1) != STATUS_SUCCESS)
    {
        WARN_(FLOPPY, "ResetChangeFlag(): HwSeek failed; returning STATUS_IO_DEVICE_ERROR\n");
        StopMotor(DriveInfo->ControllerInfo);
        return STATUS_IO_DEVICE_ERROR;
    }

    WaitForControllerInterrupt(DriveInfo->ControllerInfo);

    if(HwSenseInterruptStatus(DriveInfo->ControllerInfo) != STATUS_SUCCESS)
    {
        WARN_(FLOPPY, "ResetChangeFlag(): HwSenseInterruptStatus failed; bailing out\n");
        StopMotor(DriveInfo->ControllerInfo);
        return STATUS_IO_DEVICE_ERROR;
    }

    /* Seek back to 0 */
    if(HwSeek(DriveInfo, 0) != STATUS_SUCCESS)
    {
        WARN_(FLOPPY, "ResetChangeFlag(): HwSeek failed; returning STATUS_IO_DEVICE_ERROR\n");
        StopMotor(DriveInfo->ControllerInfo);
        return STATUS_IO_DEVICE_ERROR;
    }

    WaitForControllerInterrupt(DriveInfo->ControllerInfo);

    if(HwSenseInterruptStatus(DriveInfo->ControllerInfo) != STATUS_SUCCESS)
    {
        WARN_(FLOPPY, "ResetChangeFlag(): HwSenseInterruptStatus #2 failed; bailing\n");
        StopMotor(DriveInfo->ControllerInfo);
        return STATUS_IO_DEVICE_ERROR;
    }

    /* Check the change bit */
    if(HwDiskChanged(DriveInfo, &DiskChanged) != STATUS_SUCCESS)
    {
        WARN_(FLOPPY, "ResetChangeFlag(): HwDiskChanged failed; returning STATUS_IO_DEVICE_ERROR\n");
        StopMotor(DriveInfo->ControllerInfo);
        return STATUS_IO_DEVICE_ERROR;
    }

    StopMotor(DriveInfo->ControllerInfo);

    /* if the change flag is still set, there's probably no media in the drive. */
    if(DiskChanged)
        return STATUS_NO_MEDIA_IN_DEVICE;

    /* else we're done! */
    return STATUS_SUCCESS;
}


static VOID NTAPI
Unload(PDRIVER_OBJECT DriverObject)
/*
 * FUNCTION: Unload the driver from memory
 * ARGUMENTS:
 *     DriverObject - The driver that is being unloaded
 */
{
    ULONG i,j;

    PAGED_CODE();
    UNREFERENCED_PARAMETER(DriverObject);

    TRACE_(FLOPPY, "unloading\n");

    KeSetEvent(&QueueThreadTerminate, 0, FALSE);
    KeWaitForSingleObject(QueueThreadObject, Executive, KernelMode, FALSE, 0);
    ObDereferenceObject(QueueThreadObject);

    for(i = 0; i < gNumberOfControllers; i++)
    {
        if(!gControllerInfo[i].Initialized)
            continue;

        for(j = 0; j < gControllerInfo[i].NumberOfDrives; j++)
        {
            if(!gControllerInfo[i].DriveInfo[j].Initialized)
                continue;

            if(gControllerInfo[i].DriveInfo[j].DeviceObject)
            {
                UNICODE_STRING Link;

                RtlInitUnicodeString(&Link, gControllerInfo[i].DriveInfo[j].SymLinkBuffer);
                IoDeleteSymbolicLink(&Link);

                RtlInitUnicodeString(&Link, gControllerInfo[i].DriveInfo[j].ArcPathBuffer);
                IoDeassignArcName(&Link);

                IoDeleteDevice(gControllerInfo[i].DriveInfo[j].DeviceObject);
            }
        }

        IoDisconnectInterrupt(gControllerInfo[i].InterruptObject);

        /* Power down the controller */
        if(HwPowerOff(&gControllerInfo[i]) != STATUS_SUCCESS)
        {
            WARN_(FLOPPY, "unload: warning: HwPowerOff failed\n");
        }
    }
}


static NTSTATUS NTAPI
ConfigCallback(PVOID Context,
               PUNICODE_STRING PathName,
               INTERFACE_TYPE BusType,
               ULONG BusNumber,
               PKEY_VALUE_FULL_INFORMATION *BusInformation,
               CONFIGURATION_TYPE ControllerType,
               ULONG ControllerNumber,
               PKEY_VALUE_FULL_INFORMATION *ControllerInformation,
               CONFIGURATION_TYPE PeripheralType,
               ULONG PeripheralNumber,
               PKEY_VALUE_FULL_INFORMATION *PeripheralInformation)
/*
 * FUNCTION: Callback to IoQueryDeviceDescription, which tells us about our controllers
 * ARGUMENTS:
 *     Context: Unused
 *     PathName: Unused
 *     BusType: Type of the bus that our controller is on
 *     BusNumber: Number of the bus that our controller is on
 *     BusInformation: Unused
 *     ControllerType: Unused
 *     ControllerNumber: Number of the controller that we're adding
 *     ControllerInformation: Full configuration information for our controller
 *     PeripheralType: Unused
 *     PeripheralNumber: Unused
 *     PeripheralInformation: Full configuration information for each drive on our controller
 * RETURNS:
 *     STATUS_SUCCESS in all cases
 * NOTES:
 *     - The only documentation I've found about the contents of these structures is
 *       from the various Microsoft floppy samples and from the DDK headers.  They're
 *       very vague, though, so I'm only mostly sure that this stuff is correct, as
 *       the MS samples do things completely differently than I have done them.  Seems
 *       to work in my VMWare, though.
 *     - Basically, the function gets all of the information (port, dma, irq) about the
 *       controller, and then loops through all of the drives presented in PeripheralInformation.
 *     - Each controller has a CONTROLLER_INFO created for it, and each drive has a DRIVE_INFO.
 *     - Device objects are created for each drive (not controller), as that's the targeted
 *       device in the eyes of the rest of the OS.  Each DRIVE_INFO points to a single CONTROLLER_INFO.
 *     - We only support up to four controllers in the whole system, each of which supports up to four
 *       drives.
 */
{
    PKEY_VALUE_FULL_INFORMATION ControllerFullDescriptor = ControllerInformation[IoQueryDeviceConfigurationData];
    PCM_FULL_RESOURCE_DESCRIPTOR ControllerResourceDescriptor = (PCM_FULL_RESOURCE_DESCRIPTOR)((PCHAR)ControllerFullDescriptor +
            ControllerFullDescriptor->DataOffset);

    PKEY_VALUE_FULL_INFORMATION PeripheralFullDescriptor = PeripheralInformation[IoQueryDeviceConfigurationData];
    PCM_FULL_RESOURCE_DESCRIPTOR PeripheralResourceDescriptor = (PCM_FULL_RESOURCE_DESCRIPTOR)((PCHAR)PeripheralFullDescriptor +
            PeripheralFullDescriptor->DataOffset);

    PCM_PARTIAL_RESOURCE_DESCRIPTOR PartialDescriptor;
    PCM_FLOPPY_DEVICE_DATA FloppyDeviceData;
    UCHAR i;

    PAGED_CODE();
    UNREFERENCED_PARAMETER(PeripheralType);
    UNREFERENCED_PARAMETER(PeripheralNumber);
    UNREFERENCED_PARAMETER(BusInformation);
    UNREFERENCED_PARAMETER(Context);
    UNREFERENCED_PARAMETER(ControllerType);
    UNREFERENCED_PARAMETER(PathName);


    TRACE_(FLOPPY, "ConfigCallback called with ControllerNumber %d\n", ControllerNumber);

    gControllerInfo[gNumberOfControllers].ControllerNumber = ControllerNumber;
    gControllerInfo[gNumberOfControllers].InterfaceType = BusType;
    gControllerInfo[gNumberOfControllers].BusNumber = BusNumber;

    /* Get controller interrupt level/vector, dma channel, and port base */
    for(i = 0; i < ControllerResourceDescriptor->PartialResourceList.Count; i++)
    {
        KeInitializeEvent(&gControllerInfo[gNumberOfControllers].SynchEvent, NotificationEvent, FALSE);

        PartialDescriptor = &ControllerResourceDescriptor->PartialResourceList.PartialDescriptors[i];

        if(PartialDescriptor->Type == CmResourceTypeInterrupt)
        {
            gControllerInfo[gNumberOfControllers].Level = PartialDescriptor->u.Interrupt.Level;
            gControllerInfo[gNumberOfControllers].Vector = PartialDescriptor->u.Interrupt.Vector;

            if(PartialDescriptor->Flags & CM_RESOURCE_INTERRUPT_LATCHED)
                gControllerInfo[gNumberOfControllers].InterruptMode = Latched;
            else
                gControllerInfo[gNumberOfControllers].InterruptMode = LevelSensitive;
        }

        else if(PartialDescriptor->Type == CmResourceTypePort)
        {
            PHYSICAL_ADDRESS TranslatedAddress;
            ULONG AddressSpace = 0x1; /* I/O Port Range */

            if(!HalTranslateBusAddress(BusType, BusNumber, PartialDescriptor->u.Port.Start, &AddressSpace, &TranslatedAddress))
            {
                WARN_(FLOPPY, "HalTranslateBusAddress failed; returning\n");
                return STATUS_IO_DEVICE_ERROR;
            }

            if(AddressSpace == 0)
                gControllerInfo[gNumberOfControllers].BaseAddress = MmMapIoSpace(TranslatedAddress, FDC_PORT_BYTES, MmNonCached);
            else
                gControllerInfo[gNumberOfControllers].BaseAddress = (PUCHAR)(ULONG_PTR)TranslatedAddress.QuadPart;
        }

        else if(PartialDescriptor->Type == CmResourceTypeDma)
            gControllerInfo[gNumberOfControllers].Dma = PartialDescriptor->u.Dma.Channel;
    }

    /* Start with 0 drives, then go looking */
    gControllerInfo[gNumberOfControllers].NumberOfDrives = 0;

    /* learn about drives attached to controller */
    for(i = 0; i < PeripheralResourceDescriptor->PartialResourceList.Count; i++)
    {
        PDRIVE_INFO DriveInfo = &gControllerInfo[gNumberOfControllers].DriveInfo[i];

        PartialDescriptor = &PeripheralResourceDescriptor->PartialResourceList.PartialDescriptors[i];

        if(PartialDescriptor->Type != CmResourceTypeDeviceSpecific)
            continue;

        FloppyDeviceData = (PCM_FLOPPY_DEVICE_DATA)(PartialDescriptor + 1);

        DriveInfo->ControllerInfo = &gControllerInfo[gNumberOfControllers];
        DriveInfo->UnitNumber = i;

        DriveInfo->FloppyDeviceData.MaxDensity = FloppyDeviceData->MaxDensity;
        DriveInfo->FloppyDeviceData.MountDensity = FloppyDeviceData->MountDensity;
        DriveInfo->FloppyDeviceData.StepRateHeadUnloadTime = FloppyDeviceData->StepRateHeadUnloadTime;
        DriveInfo->FloppyDeviceData.HeadLoadTime = FloppyDeviceData->HeadLoadTime;
        DriveInfo->FloppyDeviceData.MotorOffTime = FloppyDeviceData->MotorOffTime;
        DriveInfo->FloppyDeviceData.SectorLengthCode = FloppyDeviceData->SectorLengthCode;
        DriveInfo->FloppyDeviceData.SectorPerTrack = FloppyDeviceData->SectorPerTrack;
        DriveInfo->FloppyDeviceData.ReadWriteGapLength = FloppyDeviceData->ReadWriteGapLength;
        DriveInfo->FloppyDeviceData.FormatGapLength = FloppyDeviceData->FormatGapLength;
        DriveInfo->FloppyDeviceData.FormatFillCharacter = FloppyDeviceData->FormatFillCharacter;
        DriveInfo->FloppyDeviceData.HeadSettleTime = FloppyDeviceData->HeadSettleTime;
        DriveInfo->FloppyDeviceData.MotorSettleTime = FloppyDeviceData->MotorSettleTime;
        DriveInfo->FloppyDeviceData.MaximumTrackValue = FloppyDeviceData->MaximumTrackValue;
        DriveInfo->FloppyDeviceData.DataTransferLength = FloppyDeviceData->DataTransferLength;

        /* Once it's all set up, acknowledge its existance in the controller info object */
        gControllerInfo[gNumberOfControllers].NumberOfDrives++;
    }

    gControllerInfo[gNumberOfControllers].Populated = TRUE;
    gNumberOfControllers++;

    return STATUS_SUCCESS;
}


static BOOLEAN NTAPI
Isr(PKINTERRUPT Interrupt, PVOID ServiceContext)
/*
 * FUNCTION: Interrupt service routine for the controllers
 * ARGUMENTS:
 *     Interrupt: Interrupt object representing the interrupt that occured
 *     ServiceContext: Pointer to the ControllerInfo object that caused the interrupt
 * RETURNS:
 *     TRUE in all cases (see notes)
 * NOTES:
 *     - We should always be the target of the interrupt, being an edge-triggered ISA interrupt, but
 *       this won't be the case with a level-sensitive system like PCI
 *     - Note that it probably doesn't matter if the interrupt isn't dismissed, as it's edge-triggered.
 *       It probably won't keep re-interrupting.
 *     - There are two different ways to dismiss a floppy interrupt.  If the command has a result phase
 *       (see intel datasheet), you dismiss the interrupt by reading the first data byte.  If it does
 *       not, you dismiss the interrupt by doing a Sense Interrupt command.  Again, because it's edge-
 *       triggered, this is safe to not do here, as we can just wait for the DPC.
 *     - Either way, we don't want to do this here.  The controller shouldn't interrupt again, so we'll
 *       schedule a DPC to take care of it.
 *     - This driver really cannot shrare interrupts, as I don't know how to conclusively say
 *       whether it was our controller that interrupted or not.  I just have to assume that any time
 *       my ISR gets called, it was my board that called it.  Dumb design, yes, but it goes back to
 *       the semantics of ISA buses.  That, and I don't know much about ISA drivers. :-)
 *       UPDATE: The high bit of Status Register A seems to work on non-AT controllers.
 *     - Called at DIRQL
 */
{
    PCONTROLLER_INFO ControllerInfo = (PCONTROLLER_INFO)ServiceContext;

    UNREFERENCED_PARAMETER(Interrupt);

    ASSERT(ControllerInfo);

    TRACE_(FLOPPY, "ISR called\n");

    /*
     * Due to the stupidity of the drive/controller relationship on the floppy drive, only one device object
     * can have an active interrupt pending.  Due to the nature of these IRPs, though, there will only ever
     * be one thread expecting an interrupt at a time, and furthermore, Interrupts (outside of spurious ones)
     * won't ever happen unless a thread is expecting them.  Therefore, all we have to do is signal an event
     * and we're done.  Queue a DPC and leave.
     */
    KeInsertQueueDpc(&ControllerInfo->Dpc, NULL, NULL);

    return TRUE;
}


VOID NTAPI
DpcForIsr(PKDPC UnusedDpc, PVOID Context, PVOID SystemArgument1, PVOID SystemArgument2)
/*
 * FUNCTION: This DPC gets queued by every ISR.  Does the real per-interrupt work.
 * ARGUMENTS:
 *     UnusedDpc: Pointer to the DPC object that represents our function
 *     DeviceObject: Device that this DPC is running for
 *     Irp: Unused
 *     Context: Pointer to our ControllerInfo struct
 * NOTES:
 *     - This function just kicks off whatever the SynchEvent is and returns.  We depend on
 *       the thing that caused the drive to interrupt to handle the work of clearing the interrupt.
 *       This enables us to get back to PASSIVE_LEVEL and not hog system time on a really stupid,
 *       slow, screwed-up piece of hardare.
 *     - If nothing is waiting for us to set the event, the interrupt is effectively lost and will
 *       never be dismissed.  I wonder if this will become a problem.
 *     - Called at DISPATCH_LEVEL
 */
{
    PCONTROLLER_INFO ControllerInfo = (PCONTROLLER_INFO)Context;

    UNREFERENCED_PARAMETER(UnusedDpc);
    UNREFERENCED_PARAMETER(SystemArgument1);
    UNREFERENCED_PARAMETER(SystemArgument2);

    ASSERT(ControllerInfo);

    TRACE_(FLOPPY, "DpcForIsr called\n");

    KeSetEvent(&ControllerInfo->SynchEvent, EVENT_INCREMENT, FALSE);
}


static NTSTATUS NTAPI
InitController(PCONTROLLER_INFO ControllerInfo)
/*
 * FUNCTION:  Initialize a newly-found controller
 * ARGUMENTS:
 *     ControllerInfo: pointer to the controller to be initialized
 * RETURNS:
 *     STATUS_SUCCESS if the controller is successfully initialized
 *     STATUS_IO_DEVICE_ERROR otherwise
 */
{
    int i;
    UCHAR HeadLoadTime;
    UCHAR HeadUnloadTime;
    UCHAR StepRateTime;
    UCHAR ControllerVersion;

    PAGED_CODE();
    ASSERT(ControllerInfo);

    TRACE_(FLOPPY, "InitController called with Controller 0x%p\n", ControllerInfo);

    /* Get controller in a known state */
    HwConfigure(ControllerInfo, FALSE, TRUE, TRUE, 0, 0);

    /* Get the controller version */
    ControllerVersion = HwGetVersion(ControllerInfo);

    KeClearEvent(&ControllerInfo->SynchEvent);

    /* Reset the controller */
    if(HwReset(ControllerInfo) != STATUS_SUCCESS)
    {
        WARN_(FLOPPY, "InitController: unable to reset controller\n");
        return STATUS_IO_DEVICE_ERROR;
    }

    INFO_(FLOPPY, "InitController: waiting for initial interrupt\n");

    /* Wait for an interrupt */
    WaitForControllerInterrupt(ControllerInfo);

    /* Reset means you have to clear each of the four interrupts (one per drive) */
    for(i = 0; i < MAX_DRIVES_PER_CONTROLLER; i++)
    {
        INFO_(FLOPPY, "InitController: Sensing interrupt %d\n", i);

        if(HwSenseInterruptStatus(ControllerInfo) != STATUS_SUCCESS)
        {
            WARN_(FLOPPY, "InitController: Unable to clear interrupt 0x%x\n", i);
            return STATUS_IO_DEVICE_ERROR;
        }
    }

    INFO_(FLOPPY, "InitController: done sensing interrupts\n");

    /* Next, see if we have the right version to do implied seek */
    if(ControllerVersion == VERSION_ENHANCED)
    {
        /* If so, set that up -- all defaults below except first TRUE for EIS */
        if(HwConfigure(ControllerInfo, TRUE, TRUE, TRUE, 0, 0) != STATUS_SUCCESS)
        {
            WARN_(FLOPPY, "InitController: unable to set up implied seek\n");
            ControllerInfo->ImpliedSeeks = FALSE;
        }
        else
        {
            INFO_(FLOPPY, "InitController: implied seeks set!\n");
            ControllerInfo->ImpliedSeeks = TRUE;
        }

        /*
         * FIXME: Figure out the answer to the below
         *
         * I must admit that I'm really confused about the Model 30 issue.  At least one
         * important bit (the disk change bit in the DIR) is flipped if this is a Model 30
         * controller.  However, at least one other floppy driver believes that there are only
         * two computers that are guaranteed to have a Model 30 controller:
         *  - IBM Thinkpad 750
         *  - IBM PS2e
         *
         * ...and another driver only lists a config option for "thinkpad", that flips
         * the change line.  A third driver doesn't mention the Model 30 issue at all.
         *
         * What I can't tell is whether or not the average, run-of-the-mill computer now has
         * a Model 30 controller.  For the time being, I'm going to wire this to FALSE,
         * and just not support the computers mentioned above, while I try to figure out
         * how ubiquitous these newfangled 30 thingies are.
         */
        //ControllerInfo->Model30 = TRUE;
        ControllerInfo->Model30 = FALSE;
    }
    else
    {
        INFO_(FLOPPY, "InitController: enhanced version not supported; disabling implied seeks\n");
        ControllerInfo->ImpliedSeeks = FALSE;
        ControllerInfo->Model30 = FALSE;
    }

    /* Specify */
    WARN_(FLOPPY, "FIXME: Figure out speed\n");
    HeadLoadTime = SPECIFY_HLT_500K;
    HeadUnloadTime = SPECIFY_HUT_500K;
    StepRateTime = SPECIFY_SRT_500K;
    
    INFO_(FLOPPY, "InitController: setting data rate\n");
    
    /* Set data rate */
    if(HwSetDataRate(ControllerInfo, DRSR_DSEL_500KBPS) != STATUS_SUCCESS)
    {
        WARN_(FLOPPY, "InitController: unable to set data rate\n");
        return STATUS_IO_DEVICE_ERROR;
    }

    INFO_(FLOPPY, "InitController: issuing specify command to controller\n");

    /* Don't disable DMA --> enable dma (dumb & confusing) */
    if(HwSpecify(ControllerInfo, HeadLoadTime, HeadUnloadTime, StepRateTime, FALSE) != STATUS_SUCCESS)
    {
        WARN_(FLOPPY, "InitController: unable to specify options\n");
        return STATUS_IO_DEVICE_ERROR;
    }

    /* Init the stop stuff */
    KeInitializeDpc(&ControllerInfo->MotorStopDpc, MotorStopDpcFunc, ControllerInfo);
    KeInitializeTimer(&ControllerInfo->MotorTimer);
    KeInitializeEvent(&ControllerInfo->MotorStoppedEvent, NotificationEvent, FALSE);
    ControllerInfo->StopDpcQueued = FALSE;

    /*
     * Recalibrate each drive on the controller (depends on StartMotor, which depends on the timer stuff above)
     * We don't even know if there is a disk in the drive, so this may not work, but that's OK.
     */
    for(i = 0; i < ControllerInfo->NumberOfDrives; i++)
    {
        INFO_(FLOPPY, "InitController: recalibrating drive 0x%x on controller 0x%p\n", i, ControllerInfo);
        Recalibrate(&ControllerInfo->DriveInfo[i]);
    }

    INFO_(FLOPPY, "InitController: done initializing; returning STATUS_SUCCESS\n");

    return STATUS_SUCCESS;
}


static BOOLEAN NTAPI
AddControllers(PDRIVER_OBJECT DriverObject)
/*
 * FUNCTION: Called on initialization to find our controllers and build device and controller objects for them
 * ARGUMENTS:
 *     DriverObject: Our driver's DriverObject (so we can create devices against it)
 * RETURNS:
 *     FALSE if we can't allocate a device, adapter, or interrupt object, or if we fail to find any controllers
 *     TRUE otherwise (i.e. we have at least one fully-configured controller)
 * NOTES:
 *     - Currently we only support ISA buses.
 *     - BUG: Windows 2000 seems to clobber the response from the IoQueryDeviceDescription callback, so now we
 *       just test a boolean value in the first object to see if it was completely populated.  The same value
 *       is tested for each controller before we build device objects for it.
 * TODO:
 *     - Report resource usage to the HAL
 */
{
    INTERFACE_TYPE InterfaceType = Isa;
    CONFIGURATION_TYPE ControllerType = DiskController;
    CONFIGURATION_TYPE PeripheralType = FloppyDiskPeripheral;
    KAFFINITY Affinity;
    DEVICE_DESCRIPTION DeviceDescription;
    UCHAR i;
    UCHAR j;

    PAGED_CODE();

    /* Find our controllers on all ISA buses */
    IoQueryDeviceDescription(&InterfaceType, 0, &ControllerType, 0, &PeripheralType, 0, ConfigCallback, 0);

    /*
     * w2k breaks the return val from ConfigCallback, so we have to hack around it, rather than just
     * looking for a return value from ConfigCallback.  We expect at least one controller.
     */
    if(!gControllerInfo[0].Populated)
    {
        WARN_(FLOPPY, "AddControllers: failed to get controller info from registry\n");
        return FALSE;
    }

    /* Now that we have a controller, set it up with the system */
    for(i = 0; i < gNumberOfControllers && gControllerInfo[i].NumberOfDrives > 0; i++)
    {
        /* 0: Report resource usage to the kernel, to make sure they aren't assigned to anyone else */
        /* FIXME: Implement me. */

        /* 1: Set up interrupt */
        gControllerInfo[i].MappedVector = HalGetInterruptVector(gControllerInfo[i].InterfaceType, gControllerInfo[i].BusNumber,
                                          gControllerInfo[i].Level, gControllerInfo[i].Vector,
                                          &gControllerInfo[i].MappedLevel, &Affinity);

        /* Must set up the DPC before we connect the interrupt */
        KeInitializeDpc(&gControllerInfo[i].Dpc, DpcForIsr, &gControllerInfo[i]);

        INFO_(FLOPPY, "Connecting interrupt %d to controller%d (object 0x%p)\n", gControllerInfo[i].MappedVector,
              i, &gControllerInfo[i]);

        /* NOTE: We cannot share our interrupt, even on level-triggered buses.  See Isr() for details. */
        if(IoConnectInterrupt(&gControllerInfo[i].InterruptObject, Isr, &gControllerInfo[i], 0, gControllerInfo[i].MappedVector,
                              gControllerInfo[i].MappedLevel, gControllerInfo[i].MappedLevel, gControllerInfo[i].InterruptMode,
                              FALSE, Affinity, 0) != STATUS_SUCCESS)
        {
            WARN_(FLOPPY, "AddControllers: unable to connect interrupt\n");
            continue;
        }

        /* 2: Set up DMA */
        memset(&DeviceDescription, 0, sizeof(DeviceDescription));
        DeviceDescription.Version = DEVICE_DESCRIPTION_VERSION;
        DeviceDescription.DmaChannel = gControllerInfo[i].Dma;
        DeviceDescription.InterfaceType = gControllerInfo[i].InterfaceType;
        DeviceDescription.BusNumber = gControllerInfo[i].BusNumber;
        DeviceDescription.MaximumLength = 2*18*512; /* based on a 1.44MB floppy */

        /* DMA 0,1,2,3 are 8-bit; 4,5,6,7 are 16-bit (4 is chain i think) */
        DeviceDescription.DmaWidth = gControllerInfo[i].Dma > 3 ? Width16Bits: Width8Bits;

        gControllerInfo[i].AdapterObject = HalGetAdapter(&DeviceDescription, &gControllerInfo[i].MapRegisters);

        if(!gControllerInfo[i].AdapterObject)
        {
            WARN_(FLOPPY, "AddControllers: unable to allocate an adapter object\n");
            IoDisconnectInterrupt(gControllerInfo[i].InterruptObject);
            continue;
        }

        /* 2b: Initialize the new controller */
        if(InitController(&gControllerInfo[i]) != STATUS_SUCCESS)
        {
            WARN_(FLOPPY, "AddControllers(): Unable to set up controller %d - initialization failed\n", i);
            IoDisconnectInterrupt(gControllerInfo[i].InterruptObject);
            continue;
        }

        /* 2c: Set the controller's initlized flag so we know to release stuff in Unload */
        gControllerInfo[i].Initialized = TRUE;

        /* 3: per-drive setup */
        for(j = 0; j < gControllerInfo[i].NumberOfDrives; j++)
        {
            WCHAR DeviceNameBuf[MAX_DEVICE_NAME];
            UNICODE_STRING DeviceName;
            UNICODE_STRING LinkName;
            UNICODE_STRING ArcPath;
            UCHAR DriveNumber;

            INFO_(FLOPPY, "AddControllers(): Configuring drive %d on controller %d\n", i, j);

            /*
             * 3a: create a device object for the drive
             * Controllers and drives are 0-based, so the combos are:
             * 0: 0,0
             * 1: 0,1
             * 2: 0,2
             * 3: 0,3
             * 4: 1,0
             * 5: 1,1
             * ...
             * 14: 3,2
             * 15: 3,3
             */

            DriveNumber = (UCHAR)(i*4 + j); /* loss of precision is OK; there are only 16 of 'em */

            RtlZeroMemory(&DeviceNameBuf, MAX_DEVICE_NAME * sizeof(WCHAR));
            swprintf(DeviceNameBuf, L"\\Device\\Floppy%d", DriveNumber);
            RtlInitUnicodeString(&DeviceName, DeviceNameBuf);

            if(IoCreateDevice(DriverObject, sizeof(PVOID), &DeviceName,
                              FILE_DEVICE_DISK, FILE_REMOVABLE_MEDIA | FILE_FLOPPY_DISKETTE, FALSE,
                              &gControllerInfo[i].DriveInfo[j].DeviceObject) != STATUS_SUCCESS)
            {
                WARN_(FLOPPY, "AddControllers: unable to register a Device object\n");
                IoDisconnectInterrupt(gControllerInfo[i].InterruptObject);
                continue; /* continue on to next drive */
            }

            INFO_(FLOPPY, "AddControllers: New device: %S (0x%p)\n", DeviceNameBuf, gControllerInfo[i].DriveInfo[j].DeviceObject);

            /* 3b.5: Create an ARC path in case we're booting from this drive */
            swprintf(gControllerInfo[i].DriveInfo[j].ArcPathBuffer,
                     L"\\ArcName\\multi(%d)disk(%d)fdisk(%d)", gControllerInfo[i].BusNumber, i, DriveNumber);

            RtlInitUnicodeString(&ArcPath, gControllerInfo[i].DriveInfo[j].ArcPathBuffer);
            IoAssignArcName(&ArcPath, &DeviceName);

            /* 3c: Set flags up */
            gControllerInfo[i].DriveInfo[j].DeviceObject->Flags |= DO_DIRECT_IO;

            /* 3d: Create a symlink */
            swprintf(gControllerInfo[i].DriveInfo[j].SymLinkBuffer, L"\\DosDevices\\%c:", DriveNumber + 'A');
            RtlInitUnicodeString(&LinkName, gControllerInfo[i].DriveInfo[j].SymLinkBuffer);
            if(IoCreateSymbolicLink(&LinkName, &DeviceName) != STATUS_SUCCESS)
            {
                WARN_(FLOPPY, "AddControllers: Unable to create a symlink for drive %d\n", DriveNumber);
                IoDisconnectInterrupt(gControllerInfo[i].InterruptObject);
                IoDeassignArcName(&ArcPath);
                continue; /* continue to next drive */
            }

            /* 3e: Increase global floppy drives count */
            IoGetConfigurationInformation()->FloppyCount++;

            /* 3f: Set up the DPC */
            IoInitializeDpcRequest(gControllerInfo[i].DriveInfo[j].DeviceObject, (PIO_DPC_ROUTINE)DpcForIsr);

            /* 3g: Point the device extension at our DriveInfo struct */
            gControllerInfo[i].DriveInfo[j].DeviceObject->DeviceExtension = &gControllerInfo[i].DriveInfo[j];

            /* 3h: neat comic strip */

            /* 3i: set the initial media type to unknown */
            memset(&gControllerInfo[i].DriveInfo[j].DiskGeometry, 0, sizeof(DISK_GEOMETRY));
            gControllerInfo[i].DriveInfo[j].DiskGeometry.MediaType = Unknown;

            /* 3j: Now that we're done, set the Initialized flag so we know to free this in Unload */
            gControllerInfo[i].DriveInfo[j].Initialized = TRUE;

            /* 3k: Clear the DO_DEVICE_INITIALIZING flag */
            gControllerInfo[i].DriveInfo[j].DeviceObject->Flags &= ~DO_DEVICE_INITIALIZING;
        }
    }

    INFO_(FLOPPY, "AddControllers: --------------------------------------------> finished adding controllers\n");

    return (IoGetConfigurationInformation()->FloppyCount != 0);
}


VOID NTAPI
SignalMediaChanged(PDEVICE_OBJECT DeviceObject, PIRP Irp)
/*
 * FUNCTION: Process an IRP when the media has changed, and possibly notify the user
 * ARGUMENTS:
 *     DeviceObject: DeviceObject associated with the IRP
 *     Irp: IRP that we're failing due to change
 * NOTES:
 *     - This procedure is documented in the DDK by "Notifying the File System of Possible Media Changes",
 *       "IoSetHardErrorOrVerifyDevice", and by "Responding to Check-Verify Requests from the File System".
 *     - Callable at <= DISPATCH_LEVEL
 */
{
    PDRIVE_INFO DriveInfo = DeviceObject->DeviceExtension;

    TRACE_(FLOPPY, "SignalMediaChanged called\n");

    DriveInfo->DiskChangeCount++;

    /* If volume is not mounted, do NOT set verify and return STATUS_IO_DEVICE_ERROR */
    if(!(DeviceObject->Vpb->Flags & VPB_MOUNTED))
    {
        Irp->IoStatus.Status = STATUS_IO_DEVICE_ERROR;
        Irp->IoStatus.Information = 0;
        return;
    }

    /* Notify the filesystem that it will need to verify the volume */
    DeviceObject->Flags |= DO_VERIFY_VOLUME;
    Irp->IoStatus.Status = STATUS_VERIFY_REQUIRED;
    Irp->IoStatus.Information = 0;

    /*
     * If this is a user-based, threaded request, let the IO manager know to pop up a box asking
     * the user to supply the correct media, but only if the error (which we just picked out above)
     * is deemed by the IO manager to be "user induced".  The reason we don't just unconditionally
     * call IoSetHardError... is because MS might change the definition of "user induced" some day,
     * and we don't want to have to remember to re-code this.
     */
    if(Irp->Tail.Overlay.Thread && IoIsErrorUserInduced(Irp->IoStatus.Status))
        IoSetHardErrorOrVerifyDevice(Irp, DeviceObject);
}


static VOID NTAPI
QueueThread(PVOID Context)
/*
 * FUNCTION: Thread that manages the queue and dispatches any queued requests
 * ARGUMENTS:
 *     Context: unused
 */
{
    PIRP Irp;
    PIO_STACK_LOCATION Stack;
    PDEVICE_OBJECT DeviceObject;
    PVOID Objects[2];

    PAGED_CODE();
    UNREFERENCED_PARAMETER(Context);

    Objects[0] = &QueueSemaphore;
    Objects[1] = &QueueThreadTerminate;

    for(;;)
    {
        KeWaitForMultipleObjects(2, Objects, WaitAny, Executive, KernelMode, FALSE, NULL, NULL);

        if(KeReadStateEvent(&QueueThreadTerminate))
        {
            INFO_(FLOPPY, "QueueThread terminating\n");
            return;
        }

        INFO_(FLOPPY, "QueueThread: servicing an IRP\n");

        Irp = IoCsqRemoveNextIrp(&Csq, 0);

        /* we won't get an irp if it was canceled */
        if(!Irp)
        {
            INFO_(FLOPPY, "QueueThread: IRP queue empty\n");
            continue;
        }

        DeviceObject = (PDEVICE_OBJECT)Irp->Tail.Overlay.DriverContext[0];

        ASSERT(DeviceObject);

        Stack = IoGetCurrentIrpStackLocation(Irp);

        /* Decide what to do with the IRP */
        switch(Stack->MajorFunction)
        {
        case IRP_MJ_READ:
        case IRP_MJ_WRITE:
            ReadWritePassive(DeviceObject->DeviceExtension, Irp);
            break;

        case IRP_MJ_DEVICE_CONTROL:
            DeviceIoctlPassive(DeviceObject->DeviceExtension, Irp);
            break;

        default:
            WARN_(FLOPPY, "QueueThread(): Unrecognized irp: mj: 0x%x\n", Stack->MajorFunction);
            Irp->IoStatus.Status = STATUS_NOT_SUPPORTED;
            Irp->IoStatus.Information = 0;
            IoCompleteRequest(Irp, IO_NO_INCREMENT);
        }
    }
}


NTSTATUS NTAPI
DriverEntry(PDRIVER_OBJECT DriverObject, PUNICODE_STRING RegistryPath)
/*
 * FUNCTION: Entry-point for the driver
 * ARGUMENTS:
 *     DriverObject: Our driver object
 *     RegistryPath: Unused
 * RETURNS:
 *     STATUS_SUCCESS on successful initialization of at least one drive
 *     STATUS_NO_SUCH_DEVICE if we didn't find even one drive
 *     STATUS_UNSUCCESSFUL otherwise
 */
{
    HANDLE ThreadHandle;

    UNREFERENCED_PARAMETER(RegistryPath);

    /*
     * Set up dispatch routines
     */
    DriverObject->MajorFunction[IRP_MJ_CREATE]         = (PDRIVER_DISPATCH)CreateClose;
    DriverObject->MajorFunction[IRP_MJ_CLOSE]          = (PDRIVER_DISPATCH)CreateClose;
    DriverObject->MajorFunction[IRP_MJ_READ]           = (PDRIVER_DISPATCH)ReadWrite;
    DriverObject->MajorFunction[IRP_MJ_WRITE]          = (PDRIVER_DISPATCH)ReadWrite;
    DriverObject->MajorFunction[IRP_MJ_DEVICE_CONTROL] = (PDRIVER_DISPATCH)DeviceIoctl;

    DriverObject->DriverUnload = Unload;

    /*
     * We depend on some zeroes in these structures.  I know this is supposed to be
     * initialized to 0 by the complier but this makes me feel beter.
     */
    memset(&gControllerInfo, 0, sizeof(gControllerInfo));

    /*
     * Set up queue.  This routine cannot fail (trust me, I wrote it).
     */
    IoCsqInitialize(&Csq, CsqInsertIrp, CsqRemoveIrp, CsqPeekNextIrp,
                    CsqAcquireLock, CsqReleaseLock, CsqCompleteCanceledIrp);

    /*
     * ...and its lock
     */
    KeInitializeSpinLock(&IrpQueueLock);

    /*
     * ...and the queue list itself
     */
    InitializeListHead(&IrpQueue);

    /*
     * The queue is counted by a semaphore.  The queue management thread
     * blocks on this semaphore, so if requests come in faster than the queue
     * thread can handle them, the semaphore count goes up.
     */
    KeInitializeSemaphore(&QueueSemaphore, 0, 0x7fffffff);

    /*
     * Event to terminate that thread
     */
    KeInitializeEvent(&QueueThreadTerminate, NotificationEvent, FALSE);

    /*
     * Create the queue processing thread.  Save its handle in the global variable
     * ThreadHandle so we can wait on its termination during Unload.
     */
    if(PsCreateSystemThread(&ThreadHandle, THREAD_ALL_ACCESS, 0, 0, 0, QueueThread, 0) != STATUS_SUCCESS)
    {
        WARN_(FLOPPY, "Unable to create system thread; failing init\n");
        return STATUS_INSUFFICIENT_RESOURCES;
    }

    if(ObReferenceObjectByHandle(ThreadHandle, STANDARD_RIGHTS_ALL, PsThreadType, KernelMode, &QueueThreadObject, NULL) != STATUS_SUCCESS)
    {
        WARN_(FLOPPY, "Unable to reference returned thread handle; failing init\n");
        return STATUS_UNSUCCESSFUL;
    }

    /*
     * Close the handle, now that we have the object pointer and a reference of our own.
     * The handle will certainly not be valid in the context of the caller next time we
     * need it, as handles are process-specific.
     */
    ZwClose(ThreadHandle);

    /*
     * Start the device discovery proces.  Returns STATUS_SUCCESS if
     * it finds even one drive attached to one controller.
     */
    if(!AddControllers(DriverObject))
        return STATUS_NO_SUCH_DEVICE;

    return STATUS_SUCCESS;
}