Many existing kernels, particularly those derived from Unix or BSD, implement a range of ``interrupt priority levels,'' typically assigning different levels to different classes of devices such as block, character, or network devices. In addition, some processor architectures, such as the 680x0, directly support and require the use of some kind of IPL-based scheme. Although the OSKit device drivers and other OSKit components do not directly support a notion of interrupt priority levels, it can be simulated fairly easily in IPL-based kernels by assigning a particular IPL to each component used by the kernel. In this case, the osenv_intr_disable routine provided by the kernel does not disable all interrupts, but instead only disables interrupts at the interrupt priority level that the client OS has assigned to the calling component, and at all lower priority levels. This way, although the code in each component is only aware of interrupts being ``enabled'' or ``disabled,'' the host OS can in effect enforce a general IPL-based scheme.
An obvious limitation, of course, is that all of the device drivers in a particular driver set must generally have the same IPL. However, this is usually not a problem, since the drivers in a set are usually closely related anyway.