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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
Page 979
948
CASE STUDY 2: WINDOWS 8
CHAP. 11
the attributes of a specific file—but these are just wrappers around the other I/O
manager operations we have listed and did not really need to be implemented as
separate system calls.
There are also system calls for dealing with
I/O completion
ports
, a queuing facility in Windows that helps multithreaded servers make ef-
ficient use of asynchronous I/O operations by readying threads by demand and
reducing the number of context switches required to service I/O on dedicated
threads.
11.7.3 Implementation of I/O
The Windows I/O system consists of the plug-and-play services, the device
power manager, the I/O manager, and the device-driver model. Plug-and-play
detects changes in hardware configuration and builds or tears down the device
stacks for each device, as well as causing the loading and unloading of device driv-
ers. The device power manager adjusts the power state of the I/O devices to reduce
system power consumption when devices are not in use.
The I/O manager pro-
vides support for manipulating I/O kernel objects, and IRP-based operations like
IoCallDrivers
and
IoCompleteRequest
.
But most of the work required to support
Windows I/O is implemented by the device drivers themselves.
Device Drivers
To makesure that device drivers work well with the rest of Windows, Micro-
soft has defined the
WDM
(
Windows Driver Model
) that device drivers are ex-
pected to conform with.
The
WDK
(
Windows Driver Kit
) contains docu-
mentation and examples to help developers produce drivers which conform to the
WDM. Most Windows drivers start out as copies of an appropriate sample driver
from the WDK, which is then modified by the driver writer.
Microsoft also provides a
driver verifier
which validates many of the actions
of drivers to be sure that they conform to the WDM requirements for the structure
and protocols for I/O requests, memory management, and so on.
The verifier ships
with the system, and administrators can control it by running
verifier.exe
, which al-
lows them to configure which drivers are to be checked and how extensive (i.e., ex-
pensive) the checks should be.
Even with all the support for driver development and verification, it is still very
difficult to write even simple drivers in Windows, so Microsoft has built a system
of wrappers called the
WDF
(
Windows Driver Foundation
) that runs on top of
WDM and simplifies many of the more common requirements, mostly related to
correct interaction with device power management and plug-and-play operations.
To further simplify driver writing, as well as increase the robustness of the sys-
tem, WDF includes the
UMDF
(
User-Mode Driver Framework
) for writing driv-
ers as services that execute in processes. And there is the
KMDF
(
Kernel-Mode
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