systemtap enhancement update

Updated systemtap packages that add enhancements are now available.

SystemTap is an instrumentation system for systems running the Linux 2.6
kernel. Developers can write scripts to collect data on the operation of
the system.

These updated packages add the following enhancements:

* the crash utility can now dump relayfs buffers, which are used by
SystemTap. Certain data recorded by SystemTap may only reside in relayfs
buffers. As such, crash extensions for SystemTap have been added, allowing
users to extract pending SystemTap trace data from a kernel crash image.

* a pair of SystemTap command line options, "-DRELAYHOST" and
"-DRELAYGUEST", make it possible for a single, long-running script, to
share (host) its kernel trace buffers with a number of other concurrent
(guest) scripts. This can reduce overall memory consumption, and centralize
the trace message data.

* in the previous systemtap packages, "udelay()" was used to calculate
timestamps. This was not accurate. In these updated packages, algorithms
that are aware of dynamic CPU freqency changes are used to estimate
frequency, allowing precise timestamp calculations, which resolves this
issue.

* a new security model has been added. This allows a system administrator
to designate certain, otherwise unprivileged users, the ability to run
arbitrary SystemTap scripts, by adding them to the "stapdev" group. Other
unprivileged users are able to run pre-compiled scripts that someone else
created, by adding them to the "stapusr" group.

* the systemtap packages have been updated to the latest upstream version,
as of February 2008. For further information, refer to the
"/usr/share/doc/systemtap-[version]/NEWS" file.

Note: the Linux kernel may become unstable with excessive wildcard usage
that probes every part of the kernel. As well, certain test suite failures
can occur, which are of little consequence, due to debuginfo limitations,
or incomplete tapset porting.

SystemTap is no longer a technical preview, and now has production
support. It is recommended that scripts be run on development machines
before being deployed in production. Since SystemTap is an optional
diagnostic tool, if it causes problems, users can simply stop using the
tool in that way. Options such as "-g" for Guru mode, and "-D*", allow
users to disable several security checks. Scripts using these options may
not be supported.

Red Hat will endeavor to fix problems in SystemTap, or the Linux kernel,
as they arise in connection with new scripts. In some cases, a fix may
include extending the blacklist for known areas of the Linux kernel, which
are unsafe to probe. In such a case, scripts causing these problems would
have to be changed.

Users of systemtap are advised to upgrade to these updated packages, which
add these enhancements.

Before applying this update, make sure that all previously-released
errata relevant to your system have been applied.

This update is available via Red Hat Network. Details on how to use
the Red Hat Network to apply this update are available at
http://kbase.redhat.com/faq/FAQ_58_10188

You will also need to download some prerequisites:
yum --enablerepo=rhel-debuginfo kernel-debuginfo kernel-devel