kunit stopped working

[Petr Mladek]

On Tue 2020-12-22 09:43:48, David Gow wrote:
> On Tue, Dec 22, 2020 at 4:02 AM Andy Shevchenko
> <andriy.shevchenko at linux.intel.com> wrote:
> >
> > On Mon, Dec 21, 2020 at 09:40:08PM +0200, Andy Shevchenko wrote:
> > > +Cc people from culprit commit
> >
> > Guys, revert helps. I am open to test any solution you may propose, thanks!
> >
> > ...
> >
> > > # first bad commit: [757055ae8dedf5333af17b3b5b4b70ba9bc9da4e] init/console: Use ttynull as a fallback when there is no console
> >
> > --
> 
> +CC linux-um
> 
> There appear to be two problems here:
> 1. UML now no longer has console output by default (which KUnit needs
> to get results)

> This can be worked around for KUnit by passing console=tty to the
> kernel. I don't think this is a "correct" fix

It is rather a workaround. ttynull was supposed to be an ultimate
fallback to provide a "valid" stdin, stdout, and stderr for
the init process. ttyX still should be used by default when
there is no console defined on the command line.

So the question is why ttyX was not registered with this patch.

I see the problem even when I revert the commit
757055ae8dedf5333af ("init/console: Use ttynull as a fallback when
there is no console") and enable the ttynull driver as built in:

     CONFIG_NULL_TTY=y

By other words, the problem existed even before. The commit only
made it visible by default.

I am still trying to understand arch/um and kunit code. I wonder
if it is somehow related to stdiocons implemented in
arch/um/drivers/stdio_console.c.

Best Regards,
Petr