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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 1059
1028
OPERATING SYSTEM DESIGN
CHAP. 12
4.
Corbato
´’s dictum is that the system should provide minimal mechanism. Here is a list
of POSIX calls that were also present in UNIX Version 7.
Which ones are redundant,
that is, could be removed with no loss of functionality because simple combinations of
other ones could do the same job with about the same performance?
Access
,
alarm
,
chdir
,
chmod
,
chown
,
chroot
,
close
,
creat
,
dup
,
exec
,
exit
,
fcntl
,
fork
,
fstat
,
ioctl
,
kill
,
link
,
lseek
,
mkdir
,
mknod
,
open
,
pause
,
pipe
,
read
,
stat
,
time
,
times
,
umask
,
unlink
,
utime
,
wait
, and
write
.
5.
Suppose that layers 3 and 4 in Fig. 12-2 were exchanged. What implications would
that have for the design of the system?
6.
In a microkernel-based client-server system, the microkernel just does message passing
and nothing else.
Is it possible for user processes to nevertheless create and use sema-
phores? If so, how? If not, why not?
7.
Careful optimization can improve system-call performance. Consider the case in which
one system call is made every 10 msec.
The average time of a call is 2 msec.
If the
system calls can be speeded up by a factor of two, how long does a process that took
10 sec to run now take?
8.
Operating systems often do naming at two different levels: external and internal. What
are the differences between these names with respect to
(a) Length?
(b) Uniqueness?
(c) Hierarchies?
9.
One way to handle tables whose size is not known in advance is to make them fixed,
but when one fills up, to replace it with a bigger one, copy the old entries over to the
new one, then release the old one. What are the advantages and disadvantages of mak-
ing the new one 2
×
the size of the original one, as compared to making it only 1.5
×
as
big?
10.
In Fig. 12-5, a flag,
found
, is used to tell whether the PID was located. Would it b pos-
sible to forget about
found
and just test
p
at the end of the loop to see whether it got to
the end or not?
11.
In Fig. 12-6, the differences between the x86 and the UltraSPARC are hidden by con-
ditional compilation. Could the same approach be used to hide the difference between
x86 machines with an IDE disk as the only disk and x86 machines with a SCSI disk as
the only disk?
Would it be a good idea?
12.
Indirection is a way of making an algorithm more flexible. Does it have any disadvan-
tages, and if so, what are they?
13.
Can reentrant procedures have private static global variables? Discuss your answer.
14.
The macro of Fig. 12-7(b) is clearly much more efficient than the procedure of
Fig. 12-7(a).
One disadvantage, however, is that it is hard to read. Are there any other
disadvantages? If so, what are they?
15.
Suppose that we need a way of computing whether the number of bits in a 32-bit word
is odd or even. Devise an algorithm for performing this computation as fast as possible.
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