/*
 * ReactOS Cancel-Safe Queue library
 * Copyright (c) 2004, Vizzini (vizzini@plasmic.com)
 * Licensed under the GNU GPL for the ReactOS project
 *
 * This file implements the ReactOS CSQ library.  For background and overview
 * information on these routines, read csq.h.   For the authoritative reference
 * to using these routines, see the current DDK (IoCsqXXX and CsqXxx callbacks).
 *
 * There are a couple of subtle races that this library is designed to avoid.
 * Please read the code (particularly IoCsqInsertIrpEx and IoCsqRemoveIrp) for
 * some details.
 *
 * In general, we try here to avoid the race between these queue/dequeue
 * interfaces and our own cancel routine.  This library supplies a cancel
 * routine that is used in all IRPs that are queued to it.  The major race
 * conditions surround the proper handling of in-between cases, such as in-progress
 * queue and de-queue operations.
 *
 * When you're thinking about these operations, keep in mind that three or four
 * processors can have queue and dequeue operations in progress simultaneously,
 * and a user thread may cancel any IRP at any time.  Also, these operations don't
 * all happen at DISPATCH_LEVEL all of the time, so thread switching on a single
 * processor can create races too.
 */

#include <ntdef.h>
#undef DECLSPEC_IMPORT
#define DECLSPEC_IMPORT
#include <ntifs.h>


/*!
 * @brief Cancel routine that is installed on any IRP that this library manages
 *
 * @param DeviceObject
 * @param Irp
 *
 * @note
 *     - We assume that Irp->Tail.Overlay.DriverContext[3] has either a IO_CSQ
 *       or an IO_CSQ_IRP_CONTEXT in it, but we have to figure out which it is
 *     - By the time this routine executes, the I/O Manager has already cleared
 *       the cancel routine pointer in the IRP, so it will only be canceled once
 *     - Because of this, we're guaranteed that Irp is valid the whole time
 *     - Don't forget to release the cancel spinlock ASAP --> #1 hot lock in the
 *       system
 *     - May be called at high IRQL
 */
_Function_class_(DRIVER_CANCEL)
static
VOID
NTAPI
IopCsqCancelRoutine(
    _Inout_ PDEVICE_OBJECT DeviceObject,
    _Inout_ _IRQL_uses_cancel_ PIRP Irp)
{
    PIO_CSQ Csq;
    KIRQL Irql;

    /* First things first: */
    IoReleaseCancelSpinLock(Irp->CancelIrql);

    /* We could either get a context or just a csq */
    Csq = (PIO_CSQ)Irp->Tail.Overlay.DriverContext[3];

    if(Csq->Type == IO_TYPE_CSQ_IRP_CONTEXT)
    {
        PIO_CSQ_IRP_CONTEXT Context = (PIO_CSQ_IRP_CONTEXT)Csq;
        Csq = Context->Csq;

        /* clean up context while we're here */
        Context->Irp = NULL;
    }

    /* Now that we have our CSQ, complete the IRP */
    Csq->CsqAcquireLock(Csq, &Irql);
    Csq->CsqRemoveIrp(Csq, Irp);
    Csq->CsqReleaseLock(Csq, Irql);

    Csq->CsqCompleteCanceledIrp(Csq, Irp);
}


/*!
 * @brief Set up a CSQ struct to initialize the queue
 *
 * @param Csq - Caller-allocated non-paged space for our IO_CSQ to be initialized
 * @param CsqInsertIrp - Insert routine
 * @param CsqRemoveIrp - Remove routine
 * @param CsqPeekNextIrp - Routine to paeek at the next IRP in queue
 * @param CsqAcquireLock - Acquire the queue's lock
 * @param CsqReleaseLock - Release the queue's lock
 * @param CsqCompleteCanceledIrp - Routine to complete IRPs when they are canceled
 *
 * @return
 *     - STATUS_SUCCESS in all cases
 *
 * @note
 *     - Csq must be non-paged, as the queue is manipulated with a held spinlock
 */
NTSTATUS
NTAPI
IoCsqInitialize(
    _Out_ PIO_CSQ Csq,
    _In_ PIO_CSQ_INSERT_IRP CsqInsertIrp,
    _In_ PIO_CSQ_REMOVE_IRP CsqRemoveIrp,
    _In_ PIO_CSQ_PEEK_NEXT_IRP CsqPeekNextIrp,
    _In_ PIO_CSQ_ACQUIRE_LOCK CsqAcquireLock,
    _In_ PIO_CSQ_RELEASE_LOCK CsqReleaseLock,
    _In_ PIO_CSQ_COMPLETE_CANCELED_IRP CsqCompleteCanceledIrp)
{
    Csq->Type = IO_TYPE_CSQ;
    Csq->CsqInsertIrp = CsqInsertIrp;
    Csq->CsqRemoveIrp = CsqRemoveIrp;
    Csq->CsqPeekNextIrp = CsqPeekNextIrp;
    Csq->CsqAcquireLock = CsqAcquireLock;
    Csq->CsqReleaseLock = CsqReleaseLock;
    Csq->CsqCompleteCanceledIrp = CsqCompleteCanceledIrp;
    Csq->ReservePointer = NULL;

    return STATUS_SUCCESS;
}


/*!
 * @brief Set up a CSQ struct to initialize the queue (extended version)
 *
 * @param Csq - Caller-allocated non-paged space for our IO_CSQ to be initialized
 * @param CsqInsertIrpEx - Extended insert routine
 * @param CsqRemoveIrp - Remove routine
 * @param CsqPeekNextIrp - Routine to paeek at the next IRP in queue
 * @param CsqAcquireLock - Acquire the queue's lock
 * @param CsqReleaseLock - Release the queue's lock
 * @param CsqCompleteCanceledIrp - Routine to complete IRPs when they are canceled
 *
 * @return
 *     - STATUS_SUCCESS in all cases
 * @note
 *     - Csq must be non-paged, as the queue is manipulated with a held spinlock
 */
NTSTATUS
NTAPI
IoCsqInitializeEx(
    _Out_ PIO_CSQ Csq,
    _In_ PIO_CSQ_INSERT_IRP_EX CsqInsertIrpEx,
    _In_ PIO_CSQ_REMOVE_IRP CsqRemoveIrp,
    _In_ PIO_CSQ_PEEK_NEXT_IRP CsqPeekNextIrp,
    _In_ PIO_CSQ_ACQUIRE_LOCK CsqAcquireLock,
    _In_ PIO_CSQ_RELEASE_LOCK CsqReleaseLock,
    _In_ PIO_CSQ_COMPLETE_CANCELED_IRP CsqCompleteCanceledIrp)
{
    Csq->Type = IO_TYPE_CSQ_EX;
    Csq->CsqInsertIrp = (PIO_CSQ_INSERT_IRP)CsqInsertIrpEx;
    Csq->CsqRemoveIrp = CsqRemoveIrp;
    Csq->CsqPeekNextIrp = CsqPeekNextIrp;
    Csq->CsqAcquireLock = CsqAcquireLock;
    Csq->CsqReleaseLock = CsqReleaseLock;
    Csq->CsqCompleteCanceledIrp = CsqCompleteCanceledIrp;
    Csq->ReservePointer = NULL;

    return STATUS_SUCCESS;
}


/*!
 * @brief Insert an IRP into the CSQ
 *
 * @param Csq - Pointer to the initialized CSQ
 * @param Irp - Pointer to the IRP to queue
 * @param Context - Context record to track the IRP while queued
 *
 * @return
 *     - Just passes through to IoCsqInsertIrpEx, with no InsertContext
 */
VOID
NTAPI
IoCsqInsertIrp(
    _Inout_ PIO_CSQ Csq,
    _Inout_ PIRP Irp,
    _Out_opt_ PIO_CSQ_IRP_CONTEXT Context)
{
    IoCsqInsertIrpEx(Csq, Irp, Context, 0);
}


/*!
 * @brief Insert an IRP into the CSQ, with additional tracking context
 *
 * @param Csq - Pointer to the initialized CSQ
 * @param Irp - Pointer to the IRP to queue
 * @param Context - Context record to track the IRP while queued
 * @param InsertContext - additional data that is passed through to CsqInsertIrpEx
 *
 * @note
 *     - Passes the additional context through to the driver-supplied callback,
 *       which can be used with more sophistocated queues
 *     - Marks the IRP pending in all cases
 *     - Guaranteed to not queue a canceled IRP
 *     - This is complicated logic, and is patterend after the Microsoft library.
 *       I'm sure I have gotten the details wrong on a fine point or two, but
 *       basically this works with the MS-supplied samples.
 */
NTSTATUS
NTAPI
IoCsqInsertIrpEx(
    _Inout_ PIO_CSQ Csq,
    _Inout_ PIRP Irp,
    _Out_opt_ PIO_CSQ_IRP_CONTEXT Context,
    _In_opt_ PVOID InsertContext)
{
    NTSTATUS Retval = STATUS_SUCCESS;
    KIRQL Irql;

    Csq->CsqAcquireLock(Csq, &Irql);

    do
    {
        /* mark all irps pending -- says so in the cancel sample */
        IoMarkIrpPending(Irp);

        /* set up the context if we have one */
        if(Context)
        {
            Context->Type = IO_TYPE_CSQ_IRP_CONTEXT;
            Context->Irp = Irp;
            Context->Csq = Csq;
            Irp->Tail.Overlay.DriverContext[3] = Context;
        }
        else
            Irp->Tail.Overlay.DriverContext[3] = Csq;

        /*
         * NOTE!  This is very sensitive to order.  If you set the cancel routine
         * *before* you queue the IRP, our cancel routine will get called back for
         * an IRP that isn't in its queue.
         *
         * There are three possibilities:
         * 1) We get an IRP, we queue it, and it is valid the whole way
         * 2) We get an IRP, and the IO manager cancels it before we're done here
         * 3) We get an IRP, queue it, and the IO manager cancels it.
         *
         * #2 is is a booger.
         *
         * When the IO manger receives a request to cancel an IRP, it sets the cancel
         * bit in the IRP's control byte to TRUE.  Then, it looks to see if a cancel
         * routine is set.  If it isn't, the IO manager just returns to the caller.
         * If there *is* a routine, it gets called.
         *
         * If we test for cancel first and then set the cancel routine, there is a spot
         * between test and set that the IO manager can cancel us without our knowledge,
         * so we miss a cancel request.  That is bad.
         *
         * If we set a routine first and then test for cancel, we race with our completion
         * routine:  We set the routine, the IO Manager sets cancel, we test cancel and find
         * it is TRUE.  Meanwhile the IO manager has called our cancel routine already, so
         * we can't complete the IRP because it'll rip it out from under the cancel routine.
         *
         * The IO manager does us a favor though: it nulls out the cancel routine in the IRP
         * before calling it.  Therefore, if we test to see if the cancel routine is NULL
         * (after we have just set it), that means our own cancel routine is already working
         * on the IRP, and we can just return quietly.  Otherwise, we have to de-queue the
         * IRP and cancel it ourselves.
         *
         * We have to go through all of this mess because this API guarantees that we will
         * never return having left a canceled IRP in the queue.
         */

        /* Step 1: Queue the IRP */
        if(Csq->Type == IO_TYPE_CSQ)
            Csq->CsqInsertIrp(Csq, Irp);
        else
        {
            PIO_CSQ_INSERT_IRP_EX pCsqInsertIrpEx = (PIO_CSQ_INSERT_IRP_EX)Csq->CsqInsertIrp;
            Retval = pCsqInsertIrpEx(Csq, Irp, InsertContext);
            if(Retval != STATUS_SUCCESS)
                break;
        }

        /* Step 2: Set our cancel routine */
        (void)IoSetCancelRoutine(Irp, IopCsqCancelRoutine);

        /* Step 3: Deal with an IRP that is already canceled */
        if(!Irp->Cancel)
            break;

        /*
         * Since we're canceled, see if our cancel routine is already running
         * If this is NULL, the IO Manager has already called our cancel routine
         */
        if(!IoSetCancelRoutine(Irp, NULL))
            break;


        Irp->Tail.Overlay.DriverContext[3] = 0;

        /* OK, looks like we have to de-queue and complete this ourselves */
        Csq->CsqRemoveIrp(Csq, Irp);
        Csq->CsqCompleteCanceledIrp(Csq, Irp);

        if(Context)
            Context->Irp = NULL;
    }
    while(0);

    Csq->CsqReleaseLock(Csq, Irql);

    return Retval;
}


/*!
 * @brief Remove anb IRP from the queue
 *
 * @param Csq - Queue to remove the IRP from
 * @param Context - Context record containing the IRP to be dequeued
 *
 * @return
 *     - Pointer to an IRP if we found it
 *
 * @note
 *     - Don't forget that we can be canceled any time up to the point
 *       where we unset our cancel routine
 */
PIRP
NTAPI
IoCsqRemoveIrp(
    _Inout_ PIO_CSQ Csq,
    _Inout_ PIO_CSQ_IRP_CONTEXT Context)
{
    KIRQL Irql;
    PIRP Irp = NULL;

    Csq->CsqAcquireLock(Csq, &Irql);

    do
    {
        /* It's possible that this IRP could have been canceled */
        Irp = Context->Irp;

        if(!Irp)
            break;

        ASSERT(Context->Csq == Csq);

        /* Unset the cancel routine and see if it has already been canceled */
        if(!IoSetCancelRoutine(Irp, NULL))
        {
            /*
             * already gone, return NULL  --> NOTE  that we cannot touch this IRP *or* the context,
             * since the context is being simultaneously twiddled by the cancel routine
             */
            Irp = NULL;
            break;
        }

        ASSERT(Context == Irp->Tail.Overlay.DriverContext[3]);

        /* This IRP is valid and is ours.  Dequeue it, fix it up, and return */
        Csq->CsqRemoveIrp(Csq, Irp);

        Context = (PIO_CSQ_IRP_CONTEXT)InterlockedExchangePointer(&Irp->Tail.Overlay.DriverContext[3], NULL);

        if (Context && Context->Type == IO_TYPE_CSQ_IRP_CONTEXT)
        {
            Context->Irp = NULL;

            ASSERT(Context->Csq == Csq);
        }

        Irp->Tail.Overlay.DriverContext[3] = 0;
    }
    while(0);

    Csq->CsqReleaseLock(Csq, Irql);

    return Irp;
}

/*!
 * @brief IoCsqRemoveNextIrp - Removes the next IRP from the queue
 *
 * @param Csq - Queue to remove the IRP from
 * @param PeekContext - Identifier of the IRP to be removed
 *
 * @return
 *     Pointer to the IRP that was removed, or NULL if one
 *     could not be found
 *
 * @note
 *     - This function is sensitive to yet another race condition.
 *       The basic idea is that we have to return the first IRP that
 *       we get that matches the PeekContext >that is not already canceled<.
 *       Therefore, we have to do a trick similar to the one done in Insert
 *       above.
 */
PIRP
NTAPI
IoCsqRemoveNextIrp(
    _Inout_ PIO_CSQ Csq,
    _In_opt_ PVOID PeekContext)
{
    KIRQL Irql;
    PIRP Irp = NULL;
    PIO_CSQ_IRP_CONTEXT Context;

    Csq->CsqAcquireLock(Csq, &Irql);

    while((Irp = Csq->CsqPeekNextIrp(Csq, Irp, PeekContext)))
    {
        /*
         * If the cancel routine is gone, we're already canceled,
         * and are spinning on the queue lock in our own cancel
         * routine.  Move on to the next candidate.  It'll get
         * removed by the cance routine.
         */
        if(!IoSetCancelRoutine(Irp, NULL))
            continue;

        Csq->CsqRemoveIrp(Csq, Irp);

        /* Unset the context stuff and return */
        Context = (PIO_CSQ_IRP_CONTEXT)InterlockedExchangePointer(&Irp->Tail.Overlay.DriverContext[3], NULL);

        if (Context && Context->Type == IO_TYPE_CSQ_IRP_CONTEXT)
        {
            Context->Irp = NULL;

            ASSERT(Context->Csq == Csq);
        }

        Irp->Tail.Overlay.DriverContext[3] = 0;

        break;
    }

    Csq->CsqReleaseLock(Csq, Irql);

    return Irp;
}