Software Systems
Spring 2005

For today, you should have:

1) worked on your project

2) read Silberschatz and Galvin, I/O Systems, part 1

3) written a draft of your final report


Outline:

1) questions from I/O Systems

2) "evolution of I/O function"

3) journaling file systems


For next time you should:

1) work on your project

2) read Silberschatz and Galvin, I/O Systems, part 2


Reading questions
-----------------

Silberschatz and Galvin, I/O Systems, part 2

1) What are two reasons for the OS to reschedule I/O requests?




2) What are the three reasons for the OS to provide I/O buffering?




3) Given that the OS provides buffering, how can you get a little
   bit of caching free (mostly)?




4) What is the goal of spooling?




5) What is the difference between spooling and buffering?




6) What kind of errors can the OS compensate for?




7) What state does the OS need to maintain for an open file?




8) Page 420 lists some of the services most operating systems
   provide.  For each service, can you name a data structure
   the OS maintains in order to provide the service?




9) In UNIX, how can you tell by looking at a path which device
   the file is on?





10) What are the pros and cons of implementing an I/O feature
    at the application level?  In the kernel?  In hardware?




Regarding that last question, read the following article from
eWeek (eweek.com/article2/0,1759,1787112,00.asp)

Kernel Changes Draw Concern from Open-Source Community
By Peter Galli
April 17, 2005 	

Members of the open-source community are expressing concern over rapid
feature changes in the Linux 2.6 kernel, which they say are too
focused on the desktop and could make the kernel too large.

Sam Greenblatt, a senior vice president at Computer Associates
International Inc., in Islandia, N.Y., said that while the kernel is
evolving for the desktop, server and embedded markets, more and more
technology is being included, and the kernel is "getting fatter. We
are not interested in the game drivers and music drivers that are
being added to the kernel. We are interested in a more stable kernel."

Andrew Morton, the current maintainer of the Linux 2.6 kernel, who
works for Open Source Development Labs Inc., in Beaverton, Ore., said
there is no formal road map for an enterprise Linux feature set since
the development of those technologies rests largely with vendors such
as Red Hat Inc., IBM, Novell Inc. and CA.

"We are pumping feature changes into the kernel at an enormous rate,"
said Morton.

Still, Morton took issue with Greenblatt's contention, saying that
most new features are optional and that their use is at the discretion
of organizations compiling their builds of the kernel.

Morton said new features should continue to be added to the stable 2.6
tree rather than forming a new 2.7 development tree.

Critics of the development process point to growing competition among
vendors to get code for new features accepted. But Morton maintains
that the competition is healthy because it helps top-level kernel
developers understand what subfeatures are required and what other
users need.