This series does three things:
1) add a "-trace [enable=]foo" option to enable one or more trace
events, and a "-trace help" option to show the list of tracepoints
(patches 4-5)
2) change the stderr tracing backend so that it prints to the
-D log file, and enable it by default. "-trace file=..." is
now a synonym of -D if the log backend is enabled (patches 7-8)
3) add a "-d trace:foo" option that is a synonym for "-trace foo";
this makes the new functionality more discoverable to people used
to "-d", makes it available for user-mode emulation (which does
not have -trace), and is somewhat nice if you want to enable both
tracepoints and some other "-d" flag (patch 9). When globbing
it is also less susceptible to unwanted shell expansion.
For example, you can trace block device I/O and save the result
to a file just by adding "-trace bdrv_aio_*,file=trace.txt", or
correlate it to guest PCs with "-d exec,nochain,trace:bdrv_aio_*".
Opinions? I would like to have this in 2.5 if there is agreement.