linux-kernel - Re: [PATCH 3/3] kunit: tool: refactoring printing logic into kunit

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Date:   Wed, 18 May 2022 08:50:48 -0700
From:   Daniel Latypov <dlatypov@...gle.com>
To:     David Gow <davidgow@...gle.com>
Cc:     Brendan Higgins <brendanhiggins@...gle.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        KUnit Development <kunit-dev@...glegroups.com>,
        "open list:KERNEL SELFTEST FRAMEWORK" 
        <linux-kselftest@...r.kernel.org>,
        Shuah Khan <skhan@...uxfoundation.org>
Subject: Re: [PATCH 3/3] kunit: tool: refactoring printing logic into kunit_printer.py

On Wed, May 18, 2022 at 12:48 AM David Gow <davidgow@...gle.com> wrote:
>
> On Tue, May 17, 2022 at 3:48 AM Daniel Latypov <dlatypov@...gle.com> wrote:
> >
> > Context:
> > * kunit_kernel.py is importing kunit_parser.py just to use the
> >   print_with_timestamp() function
> > * the parser is directly printing to stdout, which will become an issue
> >   if we ever try to run multiple kernels in parallel
> >
> > This patch introduces a kunit_printer.py file and migrates callers of
> > kunit_parser.print_with_timestamp() to call
> > kunit_printer.stdout.print_with_timestamp() instead.
> >
> > Future changes:
> > If we want to support showing results for parallel runs, we could then
> > create new Printer's that don't directly write to stdout and refactor
> > the code to pass around these Printer objects.
> >
> > Signed-off-by: Daniel Latypov <dlatypov@...gle.com>
> > ---
>
> I agree that this will be useful down the line, as running multiple
> kernels in parallel is definitely something which could be useful. I
> know the original idea for that was to have multiple parsers, and just
> to combine the results they gave after the fact, but given that
> incremental output is so useful, I agree that this is the better path.
>
> My only super-minor gripe (which I can live with) is that importing
> 'stdout' and using it as 'stdout.print_with_timestamp()' is a little
> confusing: I'd've assumed an stdout variable imported into the global
> namespace was sys.stdout, not a wrapper. Explicitly using
> kunit_printer.stdout would be a little clearer, IMO. Up to you,
> though.

I was initially writing it that way, but then the following pattern
got super long

Old:
print_with_timestamp(red("[ERROR]") + " some error")

New options:
stdout.print_with_timestamp(stdout.red("[ERROR]") + " some error")
kunit_printer.stdout.print_with_timestamp(kunit_printer.stdout.red("[ERROR]")
+ " some error")

But yeah, I see what you mean about potential confusion with sys.stdout.
I couldn't think of a better (while still short name) for it.
E.g. "default_printer", "stdout_printer", etc.

FWIW, I have a local patch that drops 99% of the direct uses of
kunit_printer.stdout in the parser and passes around buffered
printers.
And in that case, the use of stdout becomes small enough that we could
do `kunit_printer.stdout` w/o as much pain/noise.

But I have no plans of sending that out until we need it, since it
muddies up the code quite a bit.
And I don't have a clear idea of what the interface to parallel
testing should look like, so that day is still far off.