Re: [RFC] Regression testing framework for the kernel

[Jack Stone <jwjstone@fastmail.fm>]

On Mon, May 11, 2009 at 05:44:12AM -0400, Christoph Hellwig wrote:
> On Thu, Apr 30, 2009 at 11:05:56PM +0200, Jack Stone wrote:
> > Hi All,
> > 
> > I would like to suggest a new framework to test the kernel. This
> > framework would have the following goals:
> >     * Only runs at build time and has no effect on running kernel
> 
> I don't think we should ever run tests at build time unconditionally.
> If we want to integrate it with make it should at least be a separate
> make check.

Sorry I should have said explicitly, that was my intention.

> > The best way of acheiving this that I have thought of it to compile the
> > kernel source in question and
> > to link it with special framework files. These files would serve two
> > purposes: to provide the main function
> > of the program and to provide the missing symbols for the kernel code.
> > This would allow the replacement of
> > certain functions in the code. For example replacing the spin_lock and
> > spin_unlock functions would allow the
> > locking behavior to be checked.
> 
> That's going to be a lot of stubs if we want to have a wide coverage.
> Then again people are alredy doing this in various places, either with
> the code in-tree but not easily buildable or out of tree, so having
> all this in a common place and a common test driver would be a defintive
> improvement.  The right approach would probably be to add stubs on a
> as-needed basis instead of trying to provide full coverage.

I agree. It would be too error prone to add it as 1 huge patch. Taking
bite sized chunks would be better, as long as they are all functional.
 
> > Usage examples:
> >     * Test the behavior of a device driver
> >          As various kernel functions can be overridden a test case could
> >          be written to simulate a given device and
> >          check that there are no regressions in the driver
> 
> Not sure that is a good use.  If we want to emulate hardware I think
> we're better of using qemu for it and run a normal kernel under it.

Agreed.

> >     * Regression testing
> >          Any time a regression is found and fixed in the kernel a test
> >          case could be written to check that the
> >          regression does not reoccur later on.
> 
> I think that is the primary use case. Regresion-tests for library-ish
> code that doesn't require much global state.

I think that would be a good starting point, but I would like to extend
the testing to as much of the kernel as possible over time. I know it's
difficult because of the global state but in theory it should be
possible.

Thanks,

Jack