系统如何分配IRP栈单元

一个IRP的所有IRP栈单元所占用的内存是不是有IO管理器来分配的?系统是如何知道要分配几个IRP栈单元的?

1.对.
2.从DEVICE OBJECT中获得.

Windows maintains several IRP pools (lookaside list) with different number of stack count (for example, 2, 4, 6, 8 stacks), when the I/O manager was asked to allocate an IRP, it will get an IRP from the approiate IRP pool according to value of StackCount in the DeviceObject.

请教个问题了:)

OpenIrp = IoAllocateIrp(
(CCHAR)(ATTACHED_DEVICE_OBJECT->StackSize),
FALSE);

对于这样的irp，
according to value of StackCount in the DeviceObject.

此时的DeviceObject是谁呢, 从何处获取来的？？