context.c

文件系统过滤驱动程序的框架

    StreamContext->FileName.MaximumLength = FileName->Length;
    status = CtxAllocateUnicodeString(&StreamContext->FileName);
    if (NT_SUCCESS(status)) {

        RtlCopyUnicodeString(&StreamContext->FileName, FileName);
    }

    return status;
}




NTSTATUS
CtxCreateOrReplaceStreamHandleContext (
    IN PFLT_CALLBACK_DATA Cbd,
    IN BOOLEAN ReplaceIfExists,
    OUT PCTX_STREAMHANDLE_CONTEXT *StreamHandleContext,
    OUT PBOOLEAN ContextReplaced OPTIONAL
    )
/*++

Routine Description:

    This routine creates a stream handle context for the target stream
    handle. Optionally, if the context already exists, this routine
    replaces it with the new context and releases the old context

Arguments:

    Cbd                   - Supplies a pointer to the callbackData which
                            declares the requested operation.
    ReplaceIfExists       - Supplies if the stream handle context must be
                            replaced if already present
    StreamContext         - Returns the stream context
    ContextReplaced       - Returns if an existing context was replaced

Return Value:

    Status

--*/
{
    NTSTATUS status;
    PCTX_STREAMHANDLE_CONTEXT streamHandleContext;
    PCTX_STREAMHANDLE_CONTEXT oldStreamHandleContext;

    PAGED_CODE();

    *StreamHandleContext = NULL;
    if (ContextReplaced != NULL) *ContextReplaced = FALSE;

    //
    //  Create a stream context
    //

    DebugTrace( DEBUG_TRACE_STREAMHANDLE_CONTEXT_OPERATIONS,
                ("[Ctx]: Creating stream handle context (FileObject = %p, Instance = %p)\n",
                 Cbd->Iopb->TargetFileObject,
                 Cbd->Iopb->TargetInstance) );

    status = CtxCreateStreamHandleContext( &streamHandleContext );

    if (!NT_SUCCESS( status )) {

        DebugTrace( DEBUG_TRACE_ERROR | DEBUG_TRACE_STREAMHANDLE_CONTEXT_OPERATIONS,
                    ("[Ctx]: Failed to create stream context with status 0x%x. (FileObject = %p, Instance = %p)\n",
                    status,
                    Cbd->Iopb->TargetFileObject,
                    Cbd->Iopb->TargetInstance) );

        return status;
    }

    //
    //  Set the new context we just allocated on the file object
    //

    DebugTrace( DEBUG_TRACE_STREAMHANDLE_CONTEXT_OPERATIONS,
                ("[Ctx]: Setting stream context %p (FileObject = %p, Instance = %p, ReplaceIfExists = %x)\n",
                 streamHandleContext,
                 Cbd->Iopb->TargetFileObject,
                 Cbd->Iopb->TargetInstance,
                 ReplaceIfExists) );

    status = FltSetStreamHandleContext( Cbd->Iopb->TargetInstance,
                                        Cbd->Iopb->TargetFileObject,
                                        ReplaceIfExists ? FLT_SET_CONTEXT_REPLACE_IF_EXISTS : FLT_SET_CONTEXT_KEEP_IF_EXISTS,
                                        streamHandleContext,
                                        &oldStreamHandleContext );

    if (!NT_SUCCESS( status )) {

        DebugTrace( DEBUG_TRACE_STREAMHANDLE_CONTEXT_OPERATIONS,
                    ("[Ctx]: Failed to set stream handle context with status 0x%x. (FileObject = %p, Instance = %p)\n",
                    status,
                    Cbd->Iopb->TargetFileObject,
                    Cbd->Iopb->TargetInstance) );

        //
        //  We release the context here because FltSetStreamContext failed
        //
        //  If FltSetStreamContext succeeded then the context will be returned
        //  to the caller. The caller will use the context and then release it
        //  when he is done with the context.
        //

        DebugTrace( DEBUG_TRACE_STREAM_CONTEXT_OPERATIONS,
                    ("[Ctx]: Releasing stream handle context %p (FileObject = %p, Instance = %p)\n",
                     streamHandleContext,
                     Cbd->Iopb->TargetFileObject,
                     Cbd->Iopb->TargetInstance) );

        FltReleaseContext( streamHandleContext );

        if (status != STATUS_FLT_CONTEXT_ALREADY_DEFINED) {

            //
            //  FltSetStreamContext failed for a reason other than the context already
            //  existing on the stream. So the object now does not have any context set
            //  on it. So we return failure to the caller.
            //

            DebugTrace( DEBUG_TRACE_ERROR | DEBUG_TRACE_STREAMHANDLE_CONTEXT_OPERATIONS,
                        ("[Ctx]: Failed to set stream context with status 0x%x != STATUS_FLT_CONTEXT_ALREADY_DEFINED. (FileObject = %p, Instance = %p)\n",
                        status,
                        Cbd->Iopb->TargetFileObject,
                        Cbd->Iopb->TargetInstance) );

            return status;
        }

        //
        //  We will reach here only if we have failed with STATUS_FLT_CONTEXT_ALREADY_DEFINED
        //  and we can fail with that code only if the context already exists and we have used
        //  the FLT_SET_CONTEXT_KEEP_IF_EXISTS flag

        ASSERT( ReplaceIfExists  == FALSE );

        //
        //  Race condition. Someone has set a context after we queried it.
        //  Use the already set context instead
        //

        DebugTrace( DEBUG_TRACE_STREAMHANDLE_CONTEXT_OPERATIONS,
                    ("[Ctx]: Stream context already defined. Retaining old stream context %p (FileObject = %p, Instance = %p)\n",
                     oldStreamHandleContext,
                     Cbd->Iopb->TargetFileObject,
                     Cbd->Iopb->TargetInstance) );

        //
        //  Return the existing context. Note that the new context that we allocated has already been
        //  realeased above.
        //

        streamHandleContext = oldStreamHandleContext;
    } else {

        //
        //  FltSetStreamContext has suceeded. The new context will be returned
        //  to the caller. The caller will use the context and then release it
        //  when he is done with the context.
        //
        //  However, if we have replaced an existing context then we need to
        //  release the old context so as to decrement the ref count on it.
        //
        //  Note that the memory allocated to the objects within the context
        //  will be freed in the context cleanup and must not be done here.
        //

        if ( ReplaceIfExists &&
             oldStreamHandleContext != NULL) {

            DebugTrace( DEBUG_TRACE_STREAM_CONTEXT_OPERATIONS,
                        ("[Ctx]: Releasing old stream handle context %p (FileObject = %p, Instance = %p)\n",
                         oldStreamHandleContext,
                         Cbd->Iopb->TargetFileObject,
                         Cbd->Iopb->TargetInstance) );

            FltReleaseContext( oldStreamHandleContext );
            if (ContextReplaced != NULL) *ContextReplaced = TRUE;
        }
    }

    *StreamHandleContext = streamHandleContext;

    return status;
}





NTSTATUS
CtxCreateStreamHandleContext (
    OUT PCTX_STREAMHANDLE_CONTEXT *StreamHandleContext
    )
/*++

Routine Description:

    This routine creates a new stream context

Arguments:

    StreamContext         - Returns the stream context

Return Value:

    Status

--*/
{
    NTSTATUS status;
    PCTX_STREAMHANDLE_CONTEXT streamHandleContext;

    PAGED_CODE();

    //
    //  Allocate a stream context
    //

    DebugTrace( DEBUG_TRACE_STREAMHANDLE_CONTEXT_OPERATIONS,
                ("[Ctx]: Allocating stream handle context \n") );

    status = FltAllocateContext( Globals.Filter,
                                 FLT_STREAMHANDLE_CONTEXT,
                                 CTX_STREAMHANDLE_CONTEXT_SIZE,
                                 PagedPool,
                                 &streamHandleContext );

    if (!NT_SUCCESS( status )) {

        DebugTrace( DEBUG_TRACE_STREAM_CONTEXT_OPERATIONS | DEBUG_TRACE_ERROR,
                    ("[Ctx]: Failed to allocate stream handle context with status 0x%x \n",
                     status) );

        return status;
    }

    //
    //  Initialize the newly created context
    //

    RtlZeroMemory( streamHandleContext, CTX_STREAMHANDLE_CONTEXT_SIZE );

    streamHandleContext->Resource = CtxAllocateResource();
    if(streamHandleContext->Resource == NULL) {

        FltReleaseContext( streamHandleContext );
        return STATUS_INSUFFICIENT_RESOURCES;
    }
    ExInitializeResourceLite( streamHandleContext->Resource );

    *StreamHandleContext = streamHandleContext;

    return STATUS_SUCCESS;
}



NTSTATUS
CtxUpdateNameInStreamHandleContext (
    IN PUNICODE_STRING FileName,
    OUT PCTX_STREAMHANDLE_CONTEXT StreamHandleContext
    )
/*++

Routine Description:

    This routine updates the name of the target in the supplied stream handle context

Arguments:

    FileName              - Supplies the directory name
    StreamHandleContext   - Returns the updated name in the stream context

Return Value:

    Status

Note:

    The caller must synchronize access to the context. This routine does no
    synchronization

--*/
{
    NTSTATUS status;

    //
    //  Free any existing name
    //

    if (StreamHandleContext->FileName.Buffer != NULL) {

        CtxFreeUnicodeString(&StreamHandleContext->FileName);
    }


    //
    //  Allocate and copy off the directory name
    //

    StreamHandleContext->FileName.MaximumLength = FileName->Length;
    status = CtxAllocateUnicodeString(&StreamHandleContext->FileName);
    if (NT_SUCCESS(status)) {

        RtlCopyUnicodeString(&StreamHandleContext->FileName, FileName);
    }

    return status;
}