Early boot tapping

[alan dot brunelle at hp dot com]

Rather than continue down into the "rodent burrough" last night, I thought
I'd just send out an idea I had while this topic was being discussed.

While not sufficient for all situations, would it be possible to
investigate integrating with Xen to handle some of this? Basically,
providing some capability that would allow a modified SystemTap daemon to
be running in Xen, while booting up a guest Linux environment that has had
taps added to it. The modifications could be in the realm of having a
"quasi-shared memory" interface being used, where the Linux kernel would
be storing things in "its" memory, and the daemon in Xen would be
extracting data from the outside.

Providing a coordination mechanism between the two would then be left as
an exercise for the developer! :-)

As noted above, it certainly would _not_ be useful for all situations - in
particular, where timing considerations or specific hardware-interactions
are being debugged. But it would seem to be able to handle functional
issues in the early boot stages that require large amounts of events to be
emitted.

Alan