b ook reviews
The Definitive Guide to the Xen Hypervisor
(Prentice Hall Open Source Software
David Chisnall, Prentice Hall PTR, 2007,
$49.99, ISBN: 013234971X.
Any book claiming to be definitive
sets a high standard for itself. David
Chisnall’s Definitive Guide to the Xen
Hypervisor certainly meets that stan-
dard. This is not a how-to guide for end
users of Xen virtualization technology.
It is a comprehensive exploration of
the design and internal workings of
the Xen hypervisor.
The book opens with Chisnall’s overview of the nature
and history of virtualization. Hypervisor performance is
a major concern for those who use such technology, and
the book explains the design and implementation of Xen
as it relates to performance, particularly in the areas of
guest operating system privileged instruction handling,
memory allocation and management, and device-driver
construction. The five-chapter section on device I/O is
extremely valuable for those designing or improving
guest kernels and their device interfaces and for sharing
file resources among multiple virtual machines.
The book includes an appendix “cheat sheet” that
advises the reader on building new guests or porting
existing kernels to the Xen hypervisor.
The final chapter discusses some future directions of
the Xen project, including new platforms, desktop virtualization, power management, and large-scale virtualized
Chisnall includes a variety of highly detailed exercises
with source code at the end of several key chapters to
illustrate Xen internals. These exercises assist the reader
in understanding the hypervisor and make the book a
valuable resource for use in advanced operating system
courses in the computer science curriculum, especially
where students are designing and testing their own guest
operating system kernels.
Readers who are seeking installation and deployment
assistance with Xen-based virtualization should consider
other books. For those who need to understand the Xen
internals and design philosophy, either as guest kernel
implementers, instructors, or students, Chisnall’s book is,
indeed, the definitive resource. —Harry J. Foxwell
Practical Myth TV: Building a PVR and
Media Center PC
Stewart Smith and Michael Still, Apress, 2007,
$29.99, ISBN: 1590597796.
The VCR changed the world of the
television viewer. The PVR (personal
video recorder)—also known as the
DVR (digital video recorder) or HDR
(high-definition recorder)—seems an
incremental rather than a revolutionary change, but it is certainly a big step
forward. With few exceptions, though, PVRs tend to be
proprietary, commercially sold (and licensed) boxes that
may (now or in the future) restrict the ways in which we
can use recorded content.
Myth TV is an open-source (Linux-based) system that
serves as a PVR. Given the right hardware (reasonable
processor, enough memory, a TV tuner card, and enough
disk), you can build it yourself.
When I first started reading Practical Myth TV, I
thought that I would build a system, but then I discovered that the old, unused machine I had in my basement
would probably not support it without more hardware
upgrades than I really wanted to commit to. By the
time I’d finished the book, though, I was persuaded that
Myth TV would be powerful enough and easy enough to
install that I suspect I will now be trying it out.
The book discusses the details of building a Myth TV
system, including the hardware required, basic installation, how to get program guide data, and how to do basic
recording and playback. It also covers more advanced topics: converting recordings to other formats; making your
own themes; adding multiple tuners; interfacing with
Myth TV through a Web-based front end; and even using
VoIP with Myth TV. Since publishing delays almost always
ensure that a book of this type lags behind the latest version of the software, it also has a chapter on how to get
help, including information on updating the source code.
There are some rough edges, mostly processes (such
as expanding your disk space) that may be intimidating,
but overall this is a persuasive book. As more full distributions, such as Mythbuntu, KnoppMyth, and MythDora,
become available, installing Myth TV should become even
easier, and Myth TV itself more flexible and powerful.