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[Qemu-devel] [PATCH] exec: Rename and fix trace events for tracing I/O p

From: Richard W.M. Jones
Subject: [Qemu-devel] [PATCH] exec: Rename and fix trace events for tracing I/O port access.
Date: Tue, 29 Mar 2016 16:02:24 +0100

Back in the day you used to be able to set DEBUG_IOPORT in ioport.c
and get qemu to dump what (x86) I/O ports were being accessed by the
guest.  This was rather useful for finding out what closed source
device drivers were up to.

Now you're supposed to use cpu_in/cpu_out tracepoints instead.
However for the majority of guests these tracepoints will never be

So this patch tries to rationalize all of that.  It:

 - replaces cpu_in/cpu_out with ioport_in/ioport_out tracepoints

 - moves them down in the stack, so they actually get called

 - fixes various details like address size

It turns out this is still not particularly useful for debugging
because (a) it creates massive amounts of log messages and (b) there's
no way to select a range of addresses or a device of interest.  For
example, if you have a serial port, everything else gets swamped by
I/O access to the serial port.  Maybe using a different tracing
backend (eg. stap) would help?

Anyway, it still seems to me to be an improvement over the current


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