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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 92
SEC. 1.6
SYSTEM CALLS
61
The number of Win32 API calls is extremely large, numbering in the thou-
sands. Furthermore, while many of them do invoke system calls, a substantial num-
ber are carried out entirely in user space.
As a consequence, with Windows it is
impossible to see what is a system call (i.e., performed by the kernel) and what is
simply a user-space library call.
In fact, what is a system call in one version of
Windows may be done in user space in a different version, and vice versa. When
we discuss the Windows system calls in this book, we will use the Win32 proce-
dures (where appropriate) since Microsoft guarantees that these will be stable over
time. But it is worth remembering that not all of them are true system calls (i.e.,
traps to the kernel).
The Win32 API has a huge number of calls for managing windows, geometric
figures, text, fonts, scrollbars, dialog boxes, menus, and other features of the GUI.
To the extent that the graphics subsystem runs in the kernel (true on some versions
of Windows but not on all), these are system calls; otherwise they are just library
calls. Should we discuss these calls in this book or not?
Since they are not really
related to the function of an operating system, we have decided not to, even though
they may be carried out by the kernel. Readers interested in the Win32 API should
consult one of the many books on the subject (e.g., Hart, 1997; Rector and New-
comer, 1997; and Simon, 1997).
Even introducing all the Win32 API calls here is out of the question, so we will
restrict ourselves to those calls that roughly correspond to the functionality of the
UNIX calls listed in Fig. 1-18.
These are listed in Fig. 1-23.
Let us now briefly go through the list of Fig. 1-23.
CreateProcess
creates a
new process. It does the combined work of
fork
and
execve
in UNIX.
It has many
parameters specifying the properties of the newly created process.
Windows does
not have a process hierarchy as UNIX does so there is no concept of a parent proc-
ess and a child process. After a process is created, the creator and createe are
equals.
WaitForSingleObject
is used to wait for an event. Many possible events can
be waited for.
If the parameter specifies a process, then the caller waits for the
specified process to exit, which is done using
ExitProcess
.
The next six calls operate on files and are functionally similar to their UNIX
counterparts although they differ in the parameters and details. Still, files can be
opened, closed, read, and written pretty much as in UNIX.
The
SetFilePointer
and
GetFileAttributesEx
calls set the file position and get some of the file attributes.
Windows has directories and they are created with
CreateDirectory
and
RemoveDirectory
API calls, respectively. There is also a notion of a current direc-
tory, set by
SetCurrentDirectory
.
The current time of day is acquired using
GetLo-
calTime
.
The Win32 interface does not have links to files, mounted file systems, securi-
ty, or signals, so the calls corresponding to the UNIX ones do not exist. Of course,
Win32 has a huge number of other calls that UNIX does not have, especially for
managing the GUI.
Windows Vista has an elaborate security system and also sup-
ports file links.
Windows 7 and 8 add yet more features and system calls.
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