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PDEVICE_OBJECTIoGetRelatedDeviceObject( IN PFILE_OBJECT FileObject )/*++Routine Description: This routine returns a pointer to the actual device object than an I/O Request Packet (IRP) should be given to based on the specified file object. N.B. - Callers of this function must ensure no device object is attaching or detaching from this stack for the duration of this call. This is because the database lock is *not* held!Arguments: FileObject - Pointer to the file object representing the open file.Return Value: The return value is a pointer to the device object for the driver to whom the request is to be given.--*/{ PDEVICE_OBJECT deviceObject; // // If the file object was taken out against the mounted file system, it // will have a Vpb. Traverse it to get to the DeviceObject. Note that in // this case we should never follow FileObject->DeviceObject, as that // mapping may be invalid after a forced dismount. // if
(FileObject->Vpb != NULL && FileObject->Vpb->DeviceObject != NULL) { ASSERT(!(FileObject->Flags & FO_DIRECT_DEVICE_OPEN)); deviceObject = FileObject->Vpb->DeviceObject; // // If a driver opened a disk device using direct device open and // later on it uses IoGetRelatedTargetDeviceObject to find the // device object it wants to send an IRP then it should not get the // filesystem device object. This is so that if the device object is in the // process of being mounted then vpb is not stable. // } else
if (!(FileObject->Flags & FO_DIRECT_DEVICE_OPEN) && FileObject->DeviceObject->Vpb != NULL && FileObject->DeviceObject->Vpb->DeviceObject != NULL) { deviceObject = FileObject->DeviceObject->Vpb->DeviceObject; // // This is a direct open against the device stack (and there is no mounted // file system to strain the IRPs through). // } else
{ deviceObject = FileObject->DeviceObject; } ASSERT( deviceObject != NULL ); // // Check to see whether or not the device has any associated devices. // If so, return the highest level device; otherwise, return a pointer // to the device object itself. // if
(deviceObject->AttachedDevice != NULL) { if
(FileObject->Flags & FO_FILE_OBJECT_HAS_EXTENSION) { PIOP_FILE_OBJECT_EXTENSION fileObjectExtension = (PIOP_FILE_OBJECT_EXTENSION)(FileObject + 1); ASSERT(!(FileObject->Flags & FO_DIRECT_DEVICE_OPEN)); if
(fileObjectExtension->TopDeviceObjectHint != NULL && IopVerifyDeviceObjectOnStack(deviceObject, fileObjectExtension->TopDeviceObjectHint)) { return
fileObjectExtension->TopDeviceObjectHint; } } deviceObject = IoGetAttachedDevice( deviceObject ); } return
deviceObject;} |
这个也是网上很普及的东西了。传入开启设备或者文件产生的文件对象 获得文件对象对应的设备所在的设备堆栈的最顶层设备。
根据 FileObject->Vpb != NULL && FileObject->Vpb->DeviceObject != NULL (!(FileObject->Flags & FO_DIRECT_DEVICE_OPEN 来判断设备对象的获取方式。 FILE_DEVICE_DISK等磁盘设备类型，如果卷设备挂载完成，则fileobject->vpb是存在的，那么获取到fileobject->vpb->deviceobject,。 如果卷设备挂载进行中，那么fileobject->vpb可能不存在，返回fileobject->devieobject->vpb->deviceobject。
对于非磁盘设备等设备类型 上述两种条件是无法满足的 函数获取文件对象结构中的设备对象。
然后通过不断轮询设备的AttachedDevice 直到为NULL 获取设备堆栈中最顶层设备（IoGetAttachedDevice）
获取文件对象的fileObjectExtension 验证这个设备 fileObjectExtension->TopDeviceObjectHint != NULL && IopVerifyDeviceObjectOnStack()
然后返回获得的设备对象
IoGetRelatedDeviceObject学习,布布扣,bubuko.com
原文地址：http://www.cnblogs.com/itdef/p/3759989.html
