Re: [RFC] Regression testing framework for the kernel

[Christoph Hellwig <hch@infradead.org>]

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.

> 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.

> 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.

>     * 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.