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From: Steven Rostedt <rostedt <at> goodmis.org>
Subject: [ANNOUNCE v2] ktest.pl: Easy and flexible testing script for Linux Kernel Developers (now with config bisect)
Newsgroups: gmane.linux.kernel
Date: Monday 8th November 2010 23:45:10 UTC (over 5 years ago)
I previously posted the announcement about ktest (and shamelessly
promoted it at both Kernel Summit and Linux Plumbers), but I just
updated it with a new feature.

  TEST_TYPE = config_bisect

(See http://marc.info/?l=linux-kernel&m=128829496215347
for original

With the new config_bisect, the config is tested in halves. To handle
strange dependencies, the following is done.

First the "bad-config" needs to be prepared for the current working git
tree. As with all other tests, a "min-config" may be specified and that
will be override any config settings in the "bad-config". Since this may
produce new settings to be set (or removed) some preparation needs to be
done. This is done automatically with ktest:

1) overrides all configs with what is in the MIN_CONFIG or ADD_CONFIG

2) Runs the result through a make oldconfig to see if what may have been
added or removed (it reports these).

3) creates what is about to be tested and again runs the make oldconfig
to see if anything else might have been removed by dependencies.

All of the above changes are reported by the tool.

Finally, it gets into the bisect. It starts with a list of configs to
test. It cuts it in half, and then creates a .config file, and runs that
through oldconfig. If none of the configs in the list are enabled
(because they all depend on configs in the other half) then the second
half of the list is tried. If there's still no configs set, there must
be a circular dependency and the test fails here (but this should never

It compiles, and performs the type of test specified by the
CONFIG_BISECT_TYPE option (build, boot or test). If it passes, then all
the configs that were enabled in the .config are removed from the
configs to test and added to the good configs to always enable. This
allows for configs in the other half to be enabled if they depended on
these configs.

If the test fails, then we have a new subset of configs that is known to
cause the failure. Any config that was not set in the .config for this
run is removed from the test and will not be enabled again.

This iterates until we have one config left and that config will be

Because of dependencies and selects, the config reported may not be the
only config to cause the error. If you find that you can still produce
an error after disabling the config it reports, then simply disable it
and run the bisect again. Most likely it will turn up the problem. I may
automate this part in the future.

Anyway, you can download the latest ktest from:


I need to write up a man page and perhaps more documentation. The
sample.conf that comes in that repo has loads of information on how to
do the tests.

Have fun!

-- Steve
CD: 4ms