DTrace for FreeBSD - sources available via cvsup

Thanks to our p4 admins and cvsup hosts, the Perforce project containing
DTrace changes is now available for CVSup from cvsup10.freebsd.org using
the tag:

p4-cvs-dtrace

This is a full source tree which is updated to reflect CURRENT once or
twice a week.

**** This only applies to single processor i386 at the moment ****

The GENERIC kernel has an additional option called KDTRACE which compiles
in just the hooks that the DTrace modules require. Without that option
you'll just get a vanilla kernel that should be as reliable as current is.
WMMV.

The boot loader menu has an extra option that lets you boot with the DTrace
modules loaded. This is intended to allow anonymous traces which are still
a work in progress. I'm working on getting the anon trace DOF into the
kernel environment so that tracing can begin as soon as the modules are
initialised by the kernel (which is pretty early on).

With the development as it stands at the moment, take care using the FBT
provider because you can easily cause the system to go kaboom. I'm still
trying to track down the problems there. It's not in FBT itself -- just
the fact that the DTrace probe context isn't allowed to call anything that
FBT can instrument. If that happens you will either get a reboot or a
double fault will leave you in kdb. I recommend only enabling a few FBT
probes at a time just so you know which ones could cause a fault. There is
no point telling me that you enabled fbt::: and the system went kaboom!
If you get a double fault that drops you into kdb, type:

p *dtrace_invop_addr

and look up the address in an objdump of the kernel to find out what
function it was in when the fault occurred.

--
John Birrell