xferpkt.c

Go to the documentation of this file.

/*++

Copyright (C) Microsoft Corporation, 1991 - 1999

Module Name:

    xferpkt.c

Abstract:

    Packet routines for CLASSPNP

Environment:

    kernel mode only

Notes:


Revision History:

--*/

#include "classp.h"

#ifdef ALLOC_PRAGMA
    #pragma alloc_text(PAGE, InitializeTransferPackets)
    #pragma alloc_text(PAGE, DestroyAllTransferPackets)
    #pragma alloc_text(PAGE, SetupEjectionTransferPacket)
    #pragma alloc_text(PAGE, SetupModeSenseTransferPacket)
#endif


ULONG MinWorkingSetTransferPackets = MIN_WORKINGSET_TRANSFER_PACKETS_Consumer;
ULONG MaxWorkingSetTransferPackets = MAX_WORKINGSET_TRANSFER_PACKETS_Consumer;


/*
 *  InitializeTransferPackets
 *
 *      Allocate/initialize TRANSFER_PACKETs and related resources.
 */
NTSTATUS NTAPI InitializeTransferPackets(PDEVICE_OBJECT Fdo)
{
    PCOMMON_DEVICE_EXTENSION commonExt = Fdo->DeviceExtension;
    PFUNCTIONAL_DEVICE_EXTENSION fdoExt = Fdo->DeviceExtension;
    PCLASS_PRIVATE_FDO_DATA fdoData = fdoExt->PrivateFdoData;
    PSTORAGE_ADAPTER_DESCRIPTOR adapterDesc = commonExt->PartitionZeroExtension->AdapterDescriptor;
    ULONG hwMaxPages;
    NTSTATUS status = STATUS_SUCCESS;

    PAGED_CODE();
    
    /*
     *  Precompute the maximum transfer length
     */
    ASSERT(adapterDesc->MaximumTransferLength);
    ASSERT(adapterDesc->MaximumPhysicalPages);
    hwMaxPages = adapterDesc->MaximumPhysicalPages ? adapterDesc->MaximumPhysicalPages-1 : 0;

#if defined(_AMD64_SIMULATOR_)

    //
    // The simulator appears to have a problem with large transfers.
    //

    if (hwMaxPages > 4) {
        hwMaxPages = 4;
    }

#endif

    fdoData->HwMaxXferLen = MIN(adapterDesc->MaximumTransferLength, hwMaxPages << PAGE_SHIFT);
    fdoData->HwMaxXferLen = MAX(fdoData->HwMaxXferLen, PAGE_SIZE);

    fdoData->NumTotalTransferPackets = 0;
    fdoData->NumFreeTransferPackets = 0;
    InitializeSListHead(&fdoData->FreeTransferPacketsList);
    InitializeListHead(&fdoData->AllTransferPacketsList);
    InitializeListHead(&fdoData->DeferredClientIrpList);
        
    /*
     *  Set the packet threshold numbers based on the Windows SKU.
     */
    if (ExVerifySuite(Personal)){
        // this is Windows Personal
        MinWorkingSetTransferPackets = MIN_WORKINGSET_TRANSFER_PACKETS_Consumer;
        MaxWorkingSetTransferPackets = MAX_WORKINGSET_TRANSFER_PACKETS_Consumer;
    }
    else if (ExVerifySuite(Enterprise) || ExVerifySuite(DataCenter)){
        // this is Advanced Server or Datacenter
        MinWorkingSetTransferPackets = MIN_WORKINGSET_TRANSFER_PACKETS_Enterprise;
        MaxWorkingSetTransferPackets = MAX_WORKINGSET_TRANSFER_PACKETS_Enterprise;
    }
    else if (ExVerifySuite(TerminalServer)){
        // this is standard Server or Pro with terminal server
        MinWorkingSetTransferPackets = MIN_WORKINGSET_TRANSFER_PACKETS_Server;
        MaxWorkingSetTransferPackets = MAX_WORKINGSET_TRANSFER_PACKETS_Server;
    }
    else {
        // this is Professional without terminal server
        MinWorkingSetTransferPackets = MIN_WORKINGSET_TRANSFER_PACKETS_Consumer;
        MaxWorkingSetTransferPackets = MAX_WORKINGSET_TRANSFER_PACKETS_Consumer;
    }

    while (fdoData->NumFreeTransferPackets < MIN_INITIAL_TRANSFER_PACKETS){
        PTRANSFER_PACKET pkt = NewTransferPacket(Fdo);
        if (pkt){
            InterlockedIncrement((PLONG)&fdoData->NumTotalTransferPackets);
            EnqueueFreeTransferPacket(Fdo, pkt);
        }
        else {
            status = STATUS_INSUFFICIENT_RESOURCES;
            break;
        }
    }
    fdoData->DbgPeakNumTransferPackets = fdoData->NumTotalTransferPackets;
    
    /*
     *  Pre-initialize our SCSI_REQUEST_BLOCK template with all
     *  the constant fields.  This will save a little time for each xfer.
     *  NOTE: a CdbLength field of 10 may not always be appropriate
     */
    RtlZeroMemory(&fdoData->SrbTemplate, sizeof(SCSI_REQUEST_BLOCK));
    fdoData->SrbTemplate.Length = sizeof(SCSI_REQUEST_BLOCK);
    fdoData->SrbTemplate.Function = SRB_FUNCTION_EXECUTE_SCSI;
    fdoData->SrbTemplate.QueueAction = SRB_SIMPLE_TAG_REQUEST;
    fdoData->SrbTemplate.SenseInfoBufferLength = sizeof(SENSE_DATA);
    fdoData->SrbTemplate.CdbLength = 10;

    return status;
}

VOID NTAPI DestroyAllTransferPackets(PDEVICE_OBJECT Fdo)
{
    PFUNCTIONAL_DEVICE_EXTENSION fdoExt = Fdo->DeviceExtension;
    PCLASS_PRIVATE_FDO_DATA fdoData = fdoExt->PrivateFdoData;
    TRANSFER_PACKET *pkt;

    PAGED_CODE();
    
    ASSERT(IsListEmpty(&fdoData->DeferredClientIrpList));

    while ((pkt = DequeueFreeTransferPacket(Fdo, FALSE))){
        DestroyTransferPacket(pkt);
        InterlockedDecrement((PLONG)&fdoData->NumTotalTransferPackets);    
    }

    ASSERT(fdoData->NumTotalTransferPackets == 0);
}

PTRANSFER_PACKET NTAPI NewTransferPacket(PDEVICE_OBJECT Fdo)
{
    PFUNCTIONAL_DEVICE_EXTENSION fdoExt = Fdo->DeviceExtension;
    PCLASS_PRIVATE_FDO_DATA fdoData = fdoExt->PrivateFdoData;
    PTRANSFER_PACKET newPkt;

    newPkt = ExAllocatePoolWithTag(NonPagedPool, sizeof(TRANSFER_PACKET), 'pnPC');
    if (newPkt){
        RtlZeroMemory(newPkt, sizeof(TRANSFER_PACKET)); // just to be sure

        /*
         *  Allocate resources for the packet.
         */
        newPkt->Irp = IoAllocateIrp(Fdo->StackSize, FALSE);
        if (newPkt->Irp){
            KIRQL oldIrql;
            
            newPkt->Fdo = Fdo;

            /*
             *  Enqueue the packet in our static AllTransferPacketsList
             *  (just so we can find it during debugging if its stuck somewhere).
             */
            KeAcquireSpinLock(&fdoData->SpinLock, &oldIrql);
            InsertTailList(&fdoData->AllTransferPacketsList, &newPkt->AllPktsListEntry);
            KeReleaseSpinLock(&fdoData->SpinLock, oldIrql);
        }
        else {
            ExFreePool(newPkt);
            newPkt = NULL;
        }
    }

    return newPkt;
}

/*
 *  DestroyTransferPacket
 *
 */
VOID NTAPI DestroyTransferPacket(PTRANSFER_PACKET Pkt)
{
    PFUNCTIONAL_DEVICE_EXTENSION fdoExt = Pkt->Fdo->DeviceExtension;
    PCLASS_PRIVATE_FDO_DATA fdoData = fdoExt->PrivateFdoData;
    KIRQL oldIrql;

    ASSERT(!Pkt->SlistEntry.Next);
    ASSERT(!Pkt->OriginalIrp);

    KeAcquireSpinLock(&fdoData->SpinLock, &oldIrql);

    /*
     *  Delete the packet from our all-packets queue.
     */
    ASSERT(!IsListEmpty(&Pkt->AllPktsListEntry));
    ASSERT(!IsListEmpty(&fdoData->AllTransferPacketsList));
    RemoveEntryList(&Pkt->AllPktsListEntry);
    InitializeListHead(&Pkt->AllPktsListEntry);

    KeReleaseSpinLock(&fdoData->SpinLock, oldIrql);

    IoFreeIrp(Pkt->Irp);
    ExFreePool(Pkt);
}

VOID NTAPI EnqueueFreeTransferPacket(PDEVICE_OBJECT Fdo, PTRANSFER_PACKET Pkt)
{
    PFUNCTIONAL_DEVICE_EXTENSION fdoExt = Fdo->DeviceExtension;
    PCLASS_PRIVATE_FDO_DATA fdoData = fdoExt->PrivateFdoData;
    KIRQL oldIrql;
    ULONG newNumPkts;
    
    ASSERT(!Pkt->SlistEntry.Next);

    InterlockedPushEntrySList(&fdoData->FreeTransferPacketsList, &Pkt->SlistEntry);
    newNumPkts = InterlockedIncrement((PLONG)&fdoData->NumFreeTransferPackets);
    ASSERT(newNumPkts <= fdoData->NumTotalTransferPackets);

    /*
     *  If the total number of packets is larger than MinWorkingSetTransferPackets,
     *  that means that we've been in stress.  If all those packets are now
     *  free, then we are now out of stress and can free the extra packets.
     *  Free down to MaxWorkingSetTransferPackets immediately, and
     *  down to MinWorkingSetTransferPackets lazily (one at a time).
     */
    if (fdoData->NumFreeTransferPackets >= fdoData->NumTotalTransferPackets){

        /*
         *  1.  Immediately snap down to our UPPER threshold.
         */
        if (fdoData->NumTotalTransferPackets > MaxWorkingSetTransferPackets){
            SLIST_ENTRY pktList;
            PSLIST_ENTRY slistEntry;
            PTRANSFER_PACKET pktToDelete;

            DBGTRACE(ClassDebugTrace, ("Exiting stress, block freeing (%d-%d) packets.", fdoData->NumTotalTransferPackets, MaxWorkingSetTransferPackets));

            /*
             *  Check the counter again with lock held.  This eliminates a race condition
             *  while still allowing us to not grab the spinlock in the common codepath.
             *
             *  Note that the spinlock does not synchronize with threads dequeuing free
             *  packets to send (DequeueFreeTransferPacket does that with a lightweight
             *  interlocked exchange); the spinlock prevents multiple threads in this function
             *  from deciding to free too many extra packets at once.
             */
            SimpleInitSlistHdr(&pktList);
            KeAcquireSpinLock(&fdoData->SpinLock, &oldIrql);
            while ((fdoData->NumFreeTransferPackets >= fdoData->NumTotalTransferPackets) && 
                   (fdoData->NumTotalTransferPackets > MaxWorkingSetTransferPackets)){
                   
                pktToDelete = DequeueFreeTransferPacket(Fdo, FALSE);   
                if (pktToDelete){
                    SimplePushSlist(&pktList, &pktToDelete->SlistEntry);
                    InterlockedDecrement((PLONG)&fdoData->NumTotalTransferPackets);    
                }
                else {
                    DBGTRACE(ClassDebugTrace, ("Extremely unlikely condition (non-fatal): %d packets dequeued at once for Fdo %p. NumTotalTransferPackets=%d (1).", MaxWorkingSetTransferPackets, Fdo, fdoData->NumTotalTransferPackets));
                    break;
                }
            }
            KeReleaseSpinLock(&fdoData->SpinLock, oldIrql);

            while ((slistEntry = SimplePopSlist(&pktList))){
                pktToDelete = CONTAINING_RECORD(slistEntry, TRANSFER_PACKET, SlistEntry);
                DestroyTransferPacket(pktToDelete);
            }

        }

        /*
         *  2.  Lazily work down to our LOWER threshold (by only freeing one packet at a time).
         */
        if (fdoData->NumTotalTransferPackets > MinWorkingSetTransferPackets){
            /*
             *  Check the counter again with lock held.  This eliminates a race condition
             *  while still allowing us to not grab the spinlock in the common codepath.
             *
             *  Note that the spinlock does not synchronize with threads dequeuing free
             *  packets to send (DequeueFreeTransferPacket does that with a lightweight
             *  interlocked exchange); the spinlock prevents multiple threads in this function
             *  from deciding to free too many extra packets at once.
             */
            PTRANSFER_PACKET pktToDelete = NULL; 

            DBGTRACE(ClassDebugTrace, ("Exiting stress, lazily freeing one of %d/%d packets.", fdoData->NumTotalTransferPackets, MinWorkingSetTransferPackets));
            
            KeAcquireSpinLock(&fdoData->SpinLock, &oldIrql);
            if ((fdoData->NumFreeTransferPackets >= fdoData->NumTotalTransferPackets) &&
                (fdoData->NumTotalTransferPackets > MinWorkingSetTransferPackets)){
                
                pktToDelete = DequeueFreeTransferPacket(Fdo, FALSE);
                if (pktToDelete){
                    InterlockedDecrement((PLONG)&fdoData->NumTotalTransferPackets);    
                }
                else {
                    DBGTRACE(ClassDebugTrace, ("Extremely unlikely condition (non-fatal): %d packets dequeued at once for Fdo %p. NumTotalTransferPackets=%d (2).", MinWorkingSetTransferPackets, Fdo, fdoData->NumTotalTransferPackets));
                }
            }
            KeReleaseSpinLock(&fdoData->SpinLock, oldIrql);

            if (pktToDelete){
                DestroyTransferPacket(pktToDelete);
            }
        }

    }
  
}

PTRANSFER_PACKET NTAPI DequeueFreeTransferPacket(PDEVICE_OBJECT Fdo, BOOLEAN AllocIfNeeded)
{
    PFUNCTIONAL_DEVICE_EXTENSION fdoExt = Fdo->DeviceExtension;
    PCLASS_PRIVATE_FDO_DATA fdoData = fdoExt->PrivateFdoData;
    PTRANSFER_PACKET pkt;
    PSLIST_ENTRY slistEntry;
    //KIRQL oldIrql;

    slistEntry = InterlockedPopEntrySList(&fdoData->FreeTransferPacketsList);
    if (slistEntry){
        slistEntry->Next = NULL;
        pkt = CONTAINING_RECORD(slistEntry, TRANSFER_PACKET, SlistEntry);
        ASSERT(fdoData->NumFreeTransferPackets > 0);
        InterlockedDecrement((PLONG)&fdoData->NumFreeTransferPackets);
    }
    else {
        if (AllocIfNeeded){
            /*
             *  We are in stress and have run out of lookaside packets.
             *  In order to service the current transfer, 
             *  allocate an extra packet.  
             *  We will free it lazily when we are out of stress.
             */
            pkt = NewTransferPacket(Fdo);
            if (pkt){
                InterlockedIncrement((PLONG)&fdoData->NumTotalTransferPackets);
                fdoData->DbgPeakNumTransferPackets = max(fdoData->DbgPeakNumTransferPackets, fdoData->NumTotalTransferPackets);
            }
            else {
                DBGWARN(("DequeueFreeTransferPacket: packet allocation failed"));
            }
        }
        else {
            pkt = NULL;
        }
    }
    
    return pkt;
}

/*
 *  SetupReadWriteTransferPacket
 *
 *        This function is called once to set up the first attempt to send a packet.
 *        It is not called before a retry, as SRB fields may be modified for the retry.
 *
 *      Set up the Srb of the TRANSFER_PACKET for the transfer.
 *        The Irp is set up in SubmitTransferPacket because it must be reset
 *        for each packet submission.
 */
VOID NTAPI SetupReadWriteTransferPacket(PTRANSFER_PACKET Pkt, 
                                        PVOID Buf, 
                                        ULONG Len, 
                                        LARGE_INTEGER DiskLocation,
                                        PIRP OriginalIrp)
{
    PFUNCTIONAL_DEVICE_EXTENSION fdoExt = Pkt->Fdo->DeviceExtension;
    PCLASS_PRIVATE_FDO_DATA fdoData = fdoExt->PrivateFdoData;
    PIO_STACK_LOCATION origCurSp = IoGetCurrentIrpStackLocation(OriginalIrp);
    UCHAR majorFunc = origCurSp->MajorFunction;
    ULONG logicalBlockAddr;
    ULONG numTransferBlocks;
    PCDB pCdb;
  
    logicalBlockAddr = (ULONG)Int64ShrlMod32(DiskLocation.QuadPart, fdoExt->SectorShift);
    numTransferBlocks = Len >> fdoExt->SectorShift;

    /*
     *  Slap the constant SRB fields in from our pre-initialized template.
     *  We'll then only have to fill in the unique fields for this transfer.
     *  Tell lower drivers to sort the SRBs by the logical block address 
     *  so that disk seeks are minimized.
     */
    Pkt->Srb = fdoData->SrbTemplate;    // copies _contents_ of SRB blocks
    Pkt->Srb.DataBuffer = Buf;
    Pkt->Srb.DataTransferLength = Len;
    Pkt->Srb.QueueSortKey = logicalBlockAddr;  
    Pkt->Srb.OriginalRequest = Pkt->Irp;
    Pkt->Srb.SenseInfoBuffer = &Pkt->SrbErrorSenseData;
    Pkt->Srb.TimeOutValue = (Len/0x10000) + ((Len%0x10000) ? 1 : 0);
    Pkt->Srb.TimeOutValue *= fdoExt->TimeOutValue;

    /*
     *  Arrange values in CDB in big-endian format.
     */
    pCdb = (PCDB)Pkt->Srb.Cdb;
    pCdb->CDB10.LogicalBlockByte0 = ((PFOUR_BYTE)&logicalBlockAddr)->Byte3;
    pCdb->CDB10.LogicalBlockByte1 = ((PFOUR_BYTE)&logicalBlockAddr)->Byte2;
    pCdb->CDB10.LogicalBlockByte2 = ((PFOUR_BYTE)&logicalBlockAddr)->Byte1;
    pCdb->CDB10.LogicalBlockByte3 = ((PFOUR_BYTE)&logicalBlockAddr)->Byte0;
    pCdb->CDB10.TransferBlocksMsb = ((PFOUR_BYTE)&numTransferBlocks)->Byte1;
    pCdb->CDB10.TransferBlocksLsb = ((PFOUR_BYTE)&numTransferBlocks)->Byte0;
    pCdb->CDB10.OperationCode = (majorFunc==IRP_MJ_READ) ? SCSIOP_READ : SCSIOP_WRITE;

    /*
     *  Set SRB and IRP flags    
     */
    Pkt->Srb.SrbFlags = fdoExt->SrbFlags;
    if (TEST_FLAG(OriginalIrp->Flags, IRP_PAGING_IO) ||
        TEST_FLAG(OriginalIrp->Flags, IRP_SYNCHRONOUS_PAGING_IO)){
        SET_FLAG(Pkt->Srb.SrbFlags, SRB_CLASS_FLAGS_PAGING);
    }
    SET_FLAG(Pkt->Srb.SrbFlags, (majorFunc==IRP_MJ_READ) ? SRB_FLAGS_DATA_IN : SRB_FLAGS_DATA_OUT);

    /*
     *  Allow caching only if this is not a write-through request.
     *  If write-through and caching is enabled on the device, force
     *  media access.
     */
    if (TEST_FLAG(origCurSp->Flags, SL_WRITE_THROUGH)){
        if (TEST_FLAG(fdoExt->DeviceFlags, DEV_WRITE_CACHE)){
            pCdb->CDB10.ForceUnitAccess = TRUE;
        }
    }
    else {
        SET_FLAG(Pkt->Srb.SrbFlags, SRB_FLAGS_ADAPTER_CACHE_ENABLE);
    } 

    /*
     *  Remember the buf and len in the SRB because miniports
     *  can overwrite SRB.DataTransferLength and we may need it again
     *  for the retry.
     */
    Pkt->BufPtrCopy = Buf;
    Pkt->BufLenCopy = Len;
    Pkt->TargetLocationCopy = DiskLocation;
    
    Pkt->OriginalIrp = OriginalIrp;
    Pkt->NumRetries = MAXIMUM_RETRIES;    
    Pkt->SyncEventPtr = NULL;
    Pkt->CompleteOriginalIrpWhenLastPacketCompletes = TRUE;
}

/*
 *  SubmitTransferPacket
 *
 *        Set up the IRP for the TRANSFER_PACKET submission and send it down.
 */
VOID NTAPI SubmitTransferPacket(PTRANSFER_PACKET Pkt)
{
    PCOMMON_DEVICE_EXTENSION commonExtension = Pkt->Fdo->DeviceExtension;
    PDEVICE_OBJECT nextDevObj = commonExtension->LowerDeviceObject;
    PIO_STACK_LOCATION nextSp = IoGetNextIrpStackLocation(Pkt->Irp);
    
    ASSERT(Pkt->Irp->CurrentLocation == Pkt->Irp->StackCount+1);

    /*
     *  Attach the SRB to the IRP.
     *  The reused IRP's stack location has to be rewritten for each retry
     *  call because IoCompleteRequest clears the stack locations.
     */
    IoReuseIrp(Pkt->Irp, STATUS_NOT_SUPPORTED);
    nextSp->MajorFunction = IRP_MJ_SCSI;
    nextSp->Parameters.Scsi.Srb = &Pkt->Srb;
    Pkt->Srb.ScsiStatus = Pkt->Srb.SrbStatus = 0;
    if (Pkt->CompleteOriginalIrpWhenLastPacketCompletes){
        /*
         *  Only dereference the "original IRP"'s stack location
         *  if its a real client irp (as opposed to a static irp 
         *  we're using just for result status for one of the non-IO scsi commands).
         *
         *  For read/write, propagate the storage-specific IRP stack location flags
         *  (e.g. SL_OVERRIDE_VERIFY_VOLUME, SL_WRITE_THROUGH).
         */
        PIO_STACK_LOCATION origCurSp = IoGetCurrentIrpStackLocation(Pkt->OriginalIrp);
        nextSp->Flags = origCurSp->Flags;
    }

    /*
     *  Write MDL address to new IRP. In the port driver the SRB DataBuffer
     *  field is used as the actual buffer pointer within the MDL, 
     *  so the same MDL can be used for each partial transfer. 
     *  This saves having to build a new MDL for each partial transfer.
     */
    Pkt->Irp->MdlAddress = Pkt->OriginalIrp->MdlAddress;
    
    IoSetCompletionRoutine(Pkt->Irp, TransferPktComplete, Pkt, TRUE, TRUE, TRUE);
    IoCallDriver(nextDevObj, Pkt->Irp);
}

NTSTATUS NTAPI TransferPktComplete(IN PDEVICE_OBJECT NullFdo, IN PIRP Irp, IN PVOID Context)
{
    PTRANSFER_PACKET pkt = (PTRANSFER_PACKET)Context;
    PFUNCTIONAL_DEVICE_EXTENSION fdoExt = pkt->Fdo->DeviceExtension;
    PCLASS_PRIVATE_FDO_DATA fdoData = fdoExt->PrivateFdoData;
    PIO_STACK_LOCATION origCurrentSp = IoGetCurrentIrpStackLocation(pkt->OriginalIrp);
    BOOLEAN packetDone = FALSE;

    /*
     *  Put all the assertions and spew in here so we don't have to look at them.
     */
    DBGCHECKRETURNEDPKT(pkt);    
    
    if (SRB_STATUS(pkt->Srb.SrbStatus) == SRB_STATUS_SUCCESS){
        
        fdoData->LoggedTURFailureSinceLastIO = FALSE;
        
        /*
         *  The port driver should not have allocated a sense buffer
         *  if the SRB succeeded.
         */
        ASSERT(!PORT_ALLOCATED_SENSE(fdoExt, &pkt->Srb));

        /*
         *  Add this packet's transferred length to the original IRP's.
         */
        InterlockedExchangeAdd((PLONG)&pkt->OriginalIrp->IoStatus.Information, 
                              (LONG)pkt->Srb.DataTransferLength);

        if (pkt->InLowMemRetry){
            packetDone = StepLowMemRetry(pkt);
        }
        else {
            packetDone = TRUE;
        }
        
    }
    else {
        /*
         *  The packet failed.  We may retry it if possible.
         */
        BOOLEAN shouldRetry;
        
        /*
         *  Make sure IRP status matches SRB error status (since we propagate it).
         */
        if (NT_SUCCESS(Irp->IoStatus.Status)){
            Irp->IoStatus.Status = STATUS_UNSUCCESSFUL;
        }

        /*
         *  Interpret the SRB error (to a meaningful IRP status)
         *  and determine if we should retry this packet.
         *  This call looks at the returned SENSE info to figure out what to do.
         */
        shouldRetry = InterpretTransferPacketError(pkt);

        /*
         *  Sometimes the port driver can allocates a new 'sense' buffer
         *  to report transfer errors, e.g. when the default sense buffer
         *  is too small.  If so, it is up to us to free it.
         *  Now that we're done interpreting the sense info, free it if appropriate.
         */
        if (PORT_ALLOCATED_SENSE(fdoExt, &pkt->Srb)) {
            DBGTRACE(ClassDebugSenseInfo, ("Freeing port-allocated sense buffer for pkt %ph.", pkt));
            FREE_PORT_ALLOCATED_SENSE_BUFFER(fdoExt, &pkt->Srb);
            pkt->Srb.SenseInfoBuffer = &pkt->SrbErrorSenseData;
            pkt->Srb.SenseInfoBufferLength = sizeof(SENSE_DATA);
        }

        /*
         *  If the SRB queue is locked-up, release it.
         *  Do this after calling the error handler.
         */
        if (pkt->Srb.SrbStatus & SRB_STATUS_QUEUE_FROZEN){
            ClassReleaseQueue(pkt->Fdo);
        }
        
        if (shouldRetry && (pkt->NumRetries > 0)){           
            packetDone = RetryTransferPacket(pkt);
        }
        else {
            packetDone = TRUE;
        }
        
    }

    /*
     *  If the packet is completed, put it back in the free list.
     *  If it is the last packet servicing the original request, complete the original irp.
     */
    if (packetDone){
        LONG numPacketsRemaining;
        PIRP deferredIrp;
        PDEVICE_OBJECT Fdo = pkt->Fdo;
        UCHAR uniqueAddr;
        
        /*
         *  In case a remove is pending, bump the lock count so we don't get freed
         *  right after we complete the original irp.
         */
        ClassAcquireRemoveLock(Fdo, (PIRP)&uniqueAddr);        

        /*
         *  The original IRP should get an error code
         *  if any one of the packets failed.
         */
        if (!NT_SUCCESS(Irp->IoStatus.Status)){
            pkt->OriginalIrp->IoStatus.Status = Irp->IoStatus.Status;

            /*
             *  If the original I/O originated in user space (i.e. it is thread-queued), 
             *  and the error is user-correctable (e.g. media is missing, for removable media),
             *  alert the user.
             *  Since this is only one of possibly several packets completing for the original IRP,
             *  we may do this more than once for a single request.  That's ok; this allows
             *  us to test each returned status with IoIsErrorUserInduced().
             */
            if (IoIsErrorUserInduced(Irp->IoStatus.Status) &&
                pkt->CompleteOriginalIrpWhenLastPacketCompletes &&
                pkt->OriginalIrp->Tail.Overlay.Thread){

                IoSetHardErrorOrVerifyDevice(pkt->OriginalIrp, pkt->Fdo);
            }
        }

        /*
         *  We use a field in the original IRP to count
         *  down the transfer pieces as they complete.
         */
        numPacketsRemaining = InterlockedDecrement(
            (PLONG)&pkt->OriginalIrp->Tail.Overlay.DriverContext[0]);
            
        if (numPacketsRemaining > 0){
            /*
             *  More transfer pieces remain for the original request.
             *  Wait for them to complete before completing the original irp.
             */
        }
        else {

            /*
             *  All the transfer pieces are done.
             *  Complete the original irp if appropriate.
             */
            ASSERT(numPacketsRemaining == 0);
            if (pkt->CompleteOriginalIrpWhenLastPacketCompletes){  
                if (NT_SUCCESS(pkt->OriginalIrp->IoStatus.Status)){
                    ASSERT((ULONG)pkt->OriginalIrp->IoStatus.Information == origCurrentSp->Parameters.Read.Length);
                    ClasspPerfIncrementSuccessfulIo(fdoExt);
                }
                ClassReleaseRemoveLock(pkt->Fdo, pkt->OriginalIrp);

                ClassCompleteRequest(pkt->Fdo, pkt->OriginalIrp, IO_DISK_INCREMENT);

                /*
                 *  We may have been called by one of the class drivers (e.g. cdrom)
                 *  via the legacy API ClassSplitRequest.  
                 *  This is the only case for which the packet engine is called for an FDO
                 *  with a StartIo routine; in that case, we have to call IoStartNextPacket
                 *  now that the original irp has been completed.
                 */
                if (fdoExt->CommonExtension.DriverExtension->InitData.ClassStartIo) {
                    if (TEST_FLAG(pkt->Srb.SrbFlags, SRB_FLAGS_DONT_START_NEXT_PACKET)){
                        DBGTRAP(("SRB_FLAGS_DONT_START_NEXT_PACKET should never be set here (?)"));
                    }
                    else {
                        KIRQL oldIrql;
                        KeRaiseIrql(DISPATCH_LEVEL, &oldIrql);
                        IoStartNextPacket(pkt->Fdo, FALSE);
                        KeLowerIrql(oldIrql);
                    }
                }              
            }            
        }

        /*
         *  If the packet was synchronous, write the final
         *  result back to the issuer's status buffer and
         *  signal his event.
         */
        if (pkt->SyncEventPtr){
            KeSetEvent(pkt->SyncEventPtr, 0, FALSE);
            pkt->SyncEventPtr = NULL;
        }

        /*
         *  Free the completed packet.
         */
        pkt->OriginalIrp = NULL;
        pkt->InLowMemRetry = FALSE;
        EnqueueFreeTransferPacket(pkt->Fdo, pkt);

        /*
         *  Now that we have freed some resources,
         *  try again to send one of the previously deferred irps.
         */
        deferredIrp = DequeueDeferredClientIrp(fdoData);
        if (deferredIrp){
            DBGWARN(("... retrying deferred irp %xh.", deferredIrp)); 
            ServiceTransferRequest(pkt->Fdo, deferredIrp);
        }

        ClassReleaseRemoveLock(Fdo, (PIRP)&uniqueAddr);        
    }

    return STATUS_MORE_PROCESSING_REQUIRED;
}

/*
 *  SetupEjectionTransferPacket
 *
 *      Set up a transferPacket for a synchronous Ejection Control transfer.
 */
VOID NTAPI SetupEjectionTransferPacket(   TRANSFER_PACKET *Pkt,
                                        BOOLEAN PreventMediaRemoval,
                                        PKEVENT SyncEventPtr,
                                        PIRP OriginalIrp)
{
    PFUNCTIONAL_DEVICE_EXTENSION fdoExt = Pkt->Fdo->DeviceExtension;
    PCDB pCdb;

    PAGED_CODE();

    RtlZeroMemory(&Pkt->Srb, sizeof(SCSI_REQUEST_BLOCK));
    
    Pkt->Srb.Length = sizeof(SCSI_REQUEST_BLOCK);
    Pkt->Srb.Function = SRB_FUNCTION_EXECUTE_SCSI;
    Pkt->Srb.QueueAction = SRB_SIMPLE_TAG_REQUEST;   
    Pkt->Srb.CdbLength = 6;
    Pkt->Srb.OriginalRequest = Pkt->Irp;
    Pkt->Srb.SenseInfoBuffer = &Pkt->SrbErrorSenseData;
    Pkt->Srb.SenseInfoBufferLength = sizeof(SENSE_DATA);
    Pkt->Srb.TimeOutValue = fdoExt->TimeOutValue;

    Pkt->Srb.SrbFlags = fdoExt->SrbFlags;
    SET_FLAG(Pkt->Srb.SrbFlags, SRB_FLAGS_DISABLE_SYNCH_TRANSFER);
    SET_FLAG(Pkt->Srb.SrbFlags, SRB_FLAGS_NO_QUEUE_FREEZE);

    pCdb = (PCDB)Pkt->Srb.Cdb;
    pCdb->MEDIA_REMOVAL.OperationCode = SCSIOP_MEDIUM_REMOVAL;
    pCdb->MEDIA_REMOVAL.Prevent = PreventMediaRemoval;

    Pkt->BufPtrCopy = NULL;
    Pkt->BufLenCopy = 0;

    Pkt->OriginalIrp = OriginalIrp;
    Pkt->NumRetries = NUM_LOCKMEDIAREMOVAL_RETRIES;          
    Pkt->SyncEventPtr = SyncEventPtr;
    Pkt->CompleteOriginalIrpWhenLastPacketCompletes = FALSE;
}

/*
 *  SetupModeSenseTransferPacket
 *
 *      Set up a transferPacket for a synchronous Mode Sense transfer.
 */
VOID NTAPI SetupModeSenseTransferPacket(TRANSFER_PACKET *Pkt,
                                        PKEVENT SyncEventPtr,
                                        PVOID ModeSenseBuffer,
                                        UCHAR ModeSenseBufferLen,
                                        UCHAR PageMode,
                                        PIRP OriginalIrp)
{
    PFUNCTIONAL_DEVICE_EXTENSION fdoExt = Pkt->Fdo->DeviceExtension;
    PCDB pCdb;

    PAGED_CODE();

    RtlZeroMemory(&Pkt->Srb, sizeof(SCSI_REQUEST_BLOCK));
    
    Pkt->Srb.Length = sizeof(SCSI_REQUEST_BLOCK);
    Pkt->Srb.Function = SRB_FUNCTION_EXECUTE_SCSI;
    Pkt->Srb.QueueAction = SRB_SIMPLE_TAG_REQUEST;   
    Pkt->Srb.CdbLength = 6;
    Pkt->Srb.OriginalRequest = Pkt->Irp;
    Pkt->Srb.SenseInfoBuffer = &Pkt->SrbErrorSenseData;
    Pkt->Srb.SenseInfoBufferLength = sizeof(SENSE_DATA);
    Pkt->Srb.TimeOutValue = fdoExt->TimeOutValue;
    Pkt->Srb.DataBuffer = ModeSenseBuffer;
    Pkt->Srb.DataTransferLength = ModeSenseBufferLen;

    Pkt->Srb.SrbFlags = fdoExt->SrbFlags;
    SET_FLAG(Pkt->Srb.SrbFlags, SRB_FLAGS_DATA_IN);    
    SET_FLAG(Pkt->Srb.SrbFlags, SRB_FLAGS_DISABLE_SYNCH_TRANSFER);
    SET_FLAG(Pkt->Srb.SrbFlags, SRB_FLAGS_NO_QUEUE_FREEZE);

    pCdb = (PCDB)Pkt->Srb.Cdb;
    pCdb->MODE_SENSE.OperationCode = SCSIOP_MODE_SENSE;
    pCdb->MODE_SENSE.PageCode = PageMode;
    pCdb->MODE_SENSE.AllocationLength = (UCHAR)ModeSenseBufferLen;

    Pkt->BufPtrCopy = ModeSenseBuffer;
    Pkt->BufLenCopy = ModeSenseBufferLen;
        
    Pkt->OriginalIrp = OriginalIrp;
    Pkt->NumRetries = NUM_MODESENSE_RETRIES;          
    Pkt->SyncEventPtr = SyncEventPtr;
    Pkt->CompleteOriginalIrpWhenLastPacketCompletes = FALSE;
}

/*
 *  SetupDriveCapacityTransferPacket
 *
 *      Set up a transferPacket for a synchronous Drive Capacity transfer.
 */
VOID NTAPI SetupDriveCapacityTransferPacket(TRANSFER_PACKET *Pkt,
                                            PVOID ReadCapacityBuffer,
                                            ULONG ReadCapacityBufferLen,
                                            PKEVENT SyncEventPtr,
                                            PIRP OriginalIrp)
{
    PFUNCTIONAL_DEVICE_EXTENSION fdoExt = Pkt->Fdo->DeviceExtension;
    PCDB pCdb;

    RtlZeroMemory(&Pkt->Srb, sizeof(SCSI_REQUEST_BLOCK));
    
    Pkt->Srb.Length = sizeof(SCSI_REQUEST_BLOCK);
    Pkt->Srb.Function = SRB_FUNCTION_EXECUTE_SCSI;
    Pkt->Srb.QueueAction = SRB_SIMPLE_TAG_REQUEST;   
    Pkt->Srb.CdbLength = 10;
    Pkt->Srb.OriginalRequest = Pkt->Irp;
    Pkt->Srb.SenseInfoBuffer = &Pkt->SrbErrorSenseData;
    Pkt->Srb.SenseInfoBufferLength = sizeof(SENSE_DATA);
    Pkt->Srb.TimeOutValue = fdoExt->TimeOutValue;
    Pkt->Srb.DataBuffer = ReadCapacityBuffer;
    Pkt->Srb.DataTransferLength = ReadCapacityBufferLen;

    Pkt->Srb.SrbFlags = fdoExt->SrbFlags;
    SET_FLAG(Pkt->Srb.SrbFlags, SRB_FLAGS_DATA_IN);    
    SET_FLAG(Pkt->Srb.SrbFlags, SRB_FLAGS_DISABLE_SYNCH_TRANSFER);
    SET_FLAG(Pkt->Srb.SrbFlags, SRB_FLAGS_NO_QUEUE_FREEZE);

    pCdb = (PCDB)Pkt->Srb.Cdb;
    pCdb->CDB10.OperationCode = SCSIOP_READ_CAPACITY;

    Pkt->BufPtrCopy = ReadCapacityBuffer;
    Pkt->BufLenCopy = ReadCapacityBufferLen;

    Pkt->OriginalIrp = OriginalIrp;
    Pkt->NumRetries = NUM_DRIVECAPACITY_RETRIES;          
    Pkt->SyncEventPtr = SyncEventPtr;
    Pkt->CompleteOriginalIrpWhenLastPacketCompletes = FALSE;
}

#if 0
    /*
     *  SetupSendStartUnitTransferPacket
     *
     *      Set up a transferPacket for a synchronous Send Start Unit transfer.
     */
    VOID SetupSendStartUnitTransferPacket(   TRANSFER_PACKET *Pkt,
                                                    PIRP OriginalIrp)
    {
        PFUNCTIONAL_DEVICE_EXTENSION fdoExt = Pkt->Fdo->DeviceExtension;
        PCLASS_PRIVATE_FDO_DATA fdoData = fdoExt->PrivateFdoData;
        PCDB pCdb;

        PAGED_CODE();

        RtlZeroMemory(&Pkt->Srb, sizeof(SCSI_REQUEST_BLOCK));

        /*
         *  Initialize the SRB.
         *  Use a very long timeout value to give the drive time to spin up.
         */
        Pkt->Srb.Length = sizeof(SCSI_REQUEST_BLOCK);
        Pkt->Srb.Function = SRB_FUNCTION_EXECUTE_SCSI;
        Pkt->Srb.TimeOutValue = START_UNIT_TIMEOUT;
        Pkt->Srb.CdbLength = 6;
        Pkt->Srb.OriginalRequest = Pkt->Irp;
        Pkt->Srb.SenseInfoBuffer = &Pkt->SrbErrorSenseData;
        Pkt->Srb.SenseInfoBufferLength = sizeof(SENSE_DATA);
        Pkt->Srb.Lun = 0;
        
        SET_FLAG(Pkt->Srb.SrbFlags, SRB_FLAGS_NO_DATA_TRANSFER);    
        SET_FLAG(Pkt->Srb.SrbFlags, SRB_FLAGS_DISABLE_AUTOSENSE);
        SET_FLAG(Pkt->Srb.SrbFlags, SRB_FLAGS_DISABLE_SYNCH_TRANSFER);

        pCdb = (PCDB)Pkt->Srb.Cdb;
        pCdb->START_STOP.OperationCode = SCSIOP_START_STOP_UNIT;
        pCdb->START_STOP.Start = 1;
        pCdb->START_STOP.Immediate = 0;
        pCdb->START_STOP.LogicalUnitNumber = 0;

        Pkt->OriginalIrp = OriginalIrp;
        Pkt->NumRetries = 0;          
        Pkt->SyncEventPtr = NULL;
        Pkt->CompleteOriginalIrpWhenLastPacketCompletes = FALSE;
    }
#endif