windows-nt/Source/XPSP1/NT/base/fs/mailslot/readsup.c

/*++

Copyright (c) 1989  Microsoft Corporation

Module Name:

    readsup.c

Abstract:

    This module implements the read support routine.  This is a common
    read function that is called to do read and peek.

Author:

    Manny Weiser (mannyw)    15-Jan-1991

Revision History:

--*/

#include "mailslot.h"

//
// The debug trace level
//

#define Dbg                              (DEBUG_TRACE_READSUP)

#ifdef ALLOC_PRAGMA
#pragma alloc_text( PAGE, MsReadDataQueue )
#pragma alloc_text( PAGE, MsTimeoutRead )
#endif

IO_STATUS_BLOCK
MsReadDataQueue (
    IN PDATA_QUEUE ReadQueue,
    IN ENTRY_TYPE Operation,
    IN PUCHAR ReadBuffer,
    IN ULONG ReadLength,
    OUT PULONG MessageLength
    )

/*++

Routine Description:

    This function reads data from the read queue and fills up the
    read buffer.  It will also dequeue the data entry if this is not
    a peek operation.

    It will only be called if there is at least one message to read.


Arguments:

    ReadQueue - Provides the read queue to examine.  Its state must
        already be set to WriteEntries.

    Operation - Indicates the type of operation to perform.  If the
        operation is Peek, the write data entry is not dequeued.

    ReadBuffer - Supplies a buffer to receive the data

    ReadLength - Supplies the length, in bytes, of ReadBuffer.

    MessageLength - Returns the full size of the message, even if the
        read buffer is not large enough to contain the entire message.

Return Value:

    IO_STATUS_BLOCK - Indicates the result of the operation.

--*/

{
    IO_STATUS_BLOCK iosb;

    PLIST_ENTRY listEntry;
    PDATA_ENTRY dataEntry;
    PFCB fcb;

    PUCHAR writeBuffer;
    ULONG writeLength;

    ULONG amountRead;

    PAGED_CODE();
    DebugTrace(+1, Dbg, "MsReadDataQueue\n", 0);
    DebugTrace( 0, Dbg, "ReadQueue     = %08lx\n", (ULONG)ReadQueue);
    DebugTrace( 0, Dbg, "Operation     = %08lx\n", Operation);
    DebugTrace( 0, Dbg, "ReadBuffer    = %08lx\n", (ULONG)ReadBuffer);
    DebugTrace( 0, Dbg, "ReadLength    = %08lx\n", ReadLength);

    //
    // Read the first message out of the data queue.
    //

    iosb.Status = STATUS_SUCCESS;
    iosb.Information = 0;

    listEntry = MsGetNextDataQueueEntry( ReadQueue );
    ASSERT( listEntry != &ReadQueue->DataEntryList );

    dataEntry = CONTAINING_RECORD( listEntry, DATA_ENTRY, ListEntry );

    //
    // Calculate how much data is in this entry.
    //

    writeBuffer = dataEntry->DataPointer;
    writeLength = dataEntry->DataSize;

    DebugTrace(0, Dbg, "WriteBuffer    = %08lx\n", (ULONG)writeBuffer);
    DebugTrace(0, Dbg, "WriteLength    = %08lx\n", writeLength);

    //
    // Fail this operation, if it is a read and the buffer is not large
    // enough.
    //

    if (ReadLength < writeLength) {

        if (Operation != Peek) {
            iosb.Information = 0;
            iosb.Status = STATUS_BUFFER_TOO_SMALL;

            return iosb;
        }
        iosb.Status = STATUS_BUFFER_OVERFLOW;

        DebugTrace(0, Dbg, "Overflowed peek buffer\n", 0);

        amountRead = ReadLength;
    } else {
        amountRead = writeLength;
    }


    //
    // Copy data from the write buffer at write offset to the
    // read buffer by the mininum of write remaining or read length
    //
    // This copy may take an exception and thats why this call needs to be enclosed
    // in try/except.
    //

    try {

        RtlCopyMemory (ReadBuffer,
                       writeBuffer,
                       amountRead);

    } except (EXCEPTION_EXECUTE_HANDLER) {

        iosb.Status = GetExceptionCode ();
        return iosb;

    }

    *MessageLength = dataEntry->DataSize;


    //
    // If write length is larger than read length, this must be an
    // overflowed peek.
    //

    if (writeLength <= ReadLength) {
        //
        // The write entry is done so remove it from the read
        // queue, if this is not a peek operation.  This might
        // also have an IRP that needs to be completed.
        //

        if (Operation != Peek) {

            PIRP writeIrp;

            if ((writeIrp = MsRemoveDataQueueEntry( ReadQueue,
                                                    dataEntry )) != NULL) {
                //
                // Writes don't get queued. This is an error
                //
                KeBugCheckEx( MAILSLOT_FILE_SYSTEM,
                              1,
                              (ULONG_PTR) writeIrp,
                              (ULONG_PTR) ReadQueue,
                              (ULONG_PTR) dataEntry );

            }
        }

        DebugTrace(0, Dbg, "Successful mailslot read\n", 0);

        //
        // Indicate success.
        //

        iosb.Status = STATUS_SUCCESS;
    }


    DebugTrace(0, Dbg, "Amount read = %08lx\n", amountRead);

    iosb.Information = amountRead;
    DebugTrace(-1, Dbg, "MsReadDataQueue -> iosb.Status = %08lx\n", iosb.Status);
    return iosb;
}


VOID
MsTimeoutRead (
    IN PDEVICE_OBJECT DeviceObject,
    IN PVOID Context
    )

/*++

Routine Description:

    This routine times out a read operation.  It gains exclusive
    access to the FCB, and searches the data queue of read operations.

    If the timed out read operation is not found, it is assumed that
    a write IRP completed the read after the time out DPC ran, but
    before this function could complete the read IRP.

Arguments:

    Context - a pointer to our WorkContext

Return Value:

    None.

--*/

{
    PDATA_QUEUE dataQueue;
    PLIST_ENTRY listEntry;
    PIRP queuedIrp;
    PDATA_ENTRY dataEntry;
    PWORK_CONTEXT workContext;
    PIRP irp;
    PFCB fcb;

    PAGED_CODE();

    //
    // Reference our local variables.
    //

    workContext = (PWORK_CONTEXT)Context;

    fcb = workContext->Fcb;

    dataQueue = &fcb->DataQueue;
    //
    // Acquire exclusive access to the FCB.  This must succeed.
    //

    MsAcquireExclusiveFcb( fcb );

    //
    // There are two cases to consider here. Either this timer is the first completion
    // event for this IRP or we werent but we started running before they could cancel the timer.
    // When the second case is detected the other thread NULL's out the IRP pointer.
    //
    irp = workContext->Irp;
    if (irp) {


        dataEntry = (PDATA_ENTRY)IoGetNextIrpStackLocation( irp );
        //
        // Nobody else should touch this once we release the lock.
        //
        dataEntry->TimeoutWorkContext = NULL;

        //
        // If cancel isn't active for the IRP.
        //

        irp = MsRemoveDataQueueEntry( dataQueue, dataEntry );
    }


    //
    // Release the FCB, and derefernce it.
    //

    MsReleaseFcb( fcb );
    MsDereferenceFcb( fcb );

    //
    // Free the work context and the work item. We have to do this unconditionaly
    // if we started running
    //
    IoFreeWorkItem (workContext->WorkItem);
    ExFreePool( workContext );

    if (irp != NULL) {
        DebugTrace(0, Dbg, "Completing IRP %p\n", irp );

        MsCompleteRequest( irp, STATUS_IO_TIMEOUT );
    }
}