/*++
Copyright (c) 1994  Microsoft Corporation

Module Name:
    callback.c

Abstract:
    This module implements user mode call back services.

Author:
    David N. Cutler (davec) 29-Oct-1994

Environment:
    Kernel mode only.
--*/

#include "ki.h"

NTSTATUS KeUserModeCallback (IN ULONG ApiNumber, IN PVOID InputBuffer, IN ULONG InputLength, OUT PVOID *OutputBuffer, IN PULONG OutputLength)
/*++
Routine Description:
    This function call out from kernel mode to a user mode function.
Arguments:
    ApiNumber - Supplies the API number.
    InputBuffer - Supplies a pointer to a structure that is copied to the user stack.
    InputLength - Supplies the length of the input structure.
    Outputbuffer - Supplies a pointer to a variable that receives the address of the output buffer.
    Outputlength - Supplies a pointer to a variable that receives the length of the output buffer.
Return Value:
    If the callout cannot be executed, then an error status is returned. Otherwise, the status returned by the callback function is returned.
--*/
{
    PUCALLOUT_FRAME CalloutFrame;
    ULONG Length;
    ULONG OldStack;
    NTSTATUS Status;
    PKTRAP_FRAME TrapFrame;
    PULONG UserStack;
    PVOID ValueBuffer;
    ULONG ValueLength;

    ASSERT(KeGetPreviousMode() == UserMode);

    // Get the user mode stack pointer and attempt to copy input buffer to the user stack.
    TrapFrame = KeGetCurrentThread()->TrapFrame;
    OldStack = (ULONG)TrapFrame->XIntSp;
    try {

        // Compute new user mode stack address, probe for writability, and copy the input buffer to the user stack.
        Length =  (InputLength + sizeof(QUAD) - 1 + sizeof(UCALLOUT_FRAME)) & ~(sizeof(QUAD) - 1);

        CalloutFrame = (PUCALLOUT_FRAME)(OldStack - Length);
        ProbeForWrite(CalloutFrame, Length, sizeof(QUAD));
        RtlMoveMemory(CalloutFrame + 1, InputBuffer, InputLength);

        // Allocate stack frame fill in callout arguments.
        CalloutFrame->Buffer = (PVOID)(CalloutFrame + 1);
        CalloutFrame->Length = InputLength;
        CalloutFrame->ApiNumber = ApiNumber;
        CalloutFrame->Pad = 0;
        CalloutFrame->Sp = TrapFrame->XIntSp;
        CalloutFrame->Ra = TrapFrame->XIntRa;
    } except (EXCEPTION_EXECUTE_HANDLER) {// If an exception occurs during the probe of the user stack,
        return GetExceptionCode();//then always handle the exception and return the exception code as the status value.
    }

    // Call user mode.
    TrapFrame->XIntSp = (LONG)CalloutFrame;
    Status = KiCallUserMode(OutputBuffer, OutputLength);
    TrapFrame->XIntSp = (LONG)OldStack;

    // If the GDI TEB batch contains any entries, it must be flushed.
    if (((PTEB)KeGetCurrentThread()->Teb)->GdiBatchCount > 0) {
        KeGdiFlushUserBatch();
    }

    return Status;
}

NTSTATUS NtW32Call (IN ULONG ApiNumber, IN PVOID InputBuffer, IN ULONG InputLength, OUT PVOID *OutputBuffer, OUT PULONG OutputLength)
/*++
Routine Description:
    This function calls a W32 function.
    N.B. ************** This is a temporary service *****************
Arguments:
    ApiNumber - Supplies the API number.
    InputBuffer - Supplies a pointer to a structure that is copied to the user stack.
    InputLength - Supplies the length of the input structure.
    Outputbuffer - Supplies a pointer to a variable that recevies the output buffer address.
    Outputlength - Supplies a pointer to a variable that recevies the output buffer length.
Return Value:
    TBS.
--*/
{
    PVOID ValueBuffer;
    ULONG ValueLength;
    NTSTATUS Status;

    ASSERT(KeGetPreviousMode() == UserMode);

    // If the current thread is not a GUI thread, then fail the service since the thread does not have a large stack.
    if (KeGetCurrentThread()->Win32Thread == (PVOID)&KeServiceDescriptorTable[0]) {
        return STATUS_NOT_IMPLEMENTED;
    }

    // Probe the output buffer address and length for writeability.
    try {
        ProbeForWriteUlong((PULONG)OutputBuffer);
        ProbeForWriteUlong(OutputLength);

    // If an exception occurs during the probe of the output buffer or length, then always handle the exception and return the exception code as the status value.
    } except(EXCEPTION_EXECUTE_HANDLER) {
        return GetExceptionCode();
    }

    // Call out to user mode specifying the input buffer and API number.
    Status = KeUserModeCallback(ApiNumber, InputBuffer, InputLength, &ValueBuffer, &ValueLength);
    if (NT_SUCCESS(Status)) {// If the callout is successful, then the output buffer address and length.
        try {
            *OutputBuffer = ValueBuffer;
            *OutputLength = ValueLength;
        } except(EXCEPTION_EXECUTE_HANDLER) {

        }
    }

    return Status;
}