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Modern Operating Systems by Herbert Bos and Andrew S. Tanenb...
Modern_Operating_Systems_by_Herbert_Bos_and_Andrew_S._Tanenbaum_4th_Ed.pdf
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Modern Operating Systems by Herbert Bos and Andrew...
Modern_Operating_Systems_by_Herbert_Bos_and_Andrew_S._Tanenbaum_4th_Ed.pdf-M ODERN O PERATING S YSTEMS
Modern Operating Systems by Herbert...
Modern_Operating_Systems_by_Herbert_Bos_and_Andrew_S._Tanenbaum_4th_Ed.pdf-M ODERN O PERATING S YSTEMS
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CASE STUDY 2: WINDOWS 8
CHAP. 11
pool of high-priority worker threads mentioned earlier which can be used to run
bounded tasks by queuing a request and signaling the synchronization event that
the worker threads are waiting on.
The
object manager
manages most of the interesting kernel-mode objects
used in the executive layer.
These include processes, threads, files, semaphores,
I/O devices and drivers, timers, and many others. As described previously, kernel-
mode objects are really just data structures allocated and used by the kernel. In
Windows, kernel data structures have enough in common that it is very useful to
manage many of them in a unified facility.
The facilities provided by the object manager include managing the allocation
and freeing of memory for objects, quota accounting, supporting access to objects
using handles, maintaining reference counts for kernel-mode pointer references as
well as handle references, giving objects names in the NT namespace, and provid-
ing an extensible mechanism for managing the lifecycle for each object.
Kernel
data structures which need some of these facilities are managed by the object man-
ager.
Object-manager objects each have a type which is used to specify exactly how
the lifecycle of objects of that type is to be managed.
These are not types in the
object-oriented sense, but are simply a collection of parameters specified when the
object type is created.
To create a new type, an executive component calls an ob-
ject-manager API to create a new type. Objects are so central to the functioning of
Windows that the object manager will be discussed in more detail in the next sec-
tion.
The
I/O manager
provides the framework for implementing I/O device drivers
and provides a number of executive services specific to configuring, accessing, and
performing operations on devices. In Windows, device drivers not only manage
physical devices but they also provide extensibility to the operating system.
Many
functions that are compiled into the kernel on other systems are dynamically load-
ed and linked by the kernel on Windows, including network protocol stacks and
file systems.
Recent versions of Windows have a lot more support for running device drivers
in user mode, and this is the preferred model for new device drivers. There are
hundreds of thousands of different device drivers for Windows working with more
than a million distinct devices. This represents a lot of code to get correct.
It is
much better if bugs cause a device to become inaccessible by crashing in a user-
mode process rather than causing the system to crash.
Bugs in kernel-mode device
drivers are the major source of the dreaded
BSOD
(
Blue Screen Of Death
) where
Windows detects a fatal error within kernel mode and shuts down or reboots the
system. BSOD’s are comparable to kernel panics on UNIX systems.
In essence, Microsoft has now officially recognized what researchers in the
area of microkernels such as MINIX 3 and L4 have known for years: the more
code there is in the kernel, the more bugs there are in the kernel. Since device driv-
ers make up something in the vicinity of 70% of the code in the kernel, the more
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