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Date:   Mon, 4 Oct 2021 17:36:15 -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] kunit: tool: yield output from run_kernel in real time

On Mon, Oct 4, 2021 at 4:58 PM David Gow <davidgow@...gle.com> wrote:
>
> On Tue, Oct 5, 2021 at 7:46 AM Daniel Latypov <dlatypov@...gle.com> wrote:
> >
> > On Mon, Oct 4, 2021 at 4:34 PM 'David Gow' via KUnit Development
> > <kunit-dev@...glegroups.com> wrote:
> > >
> > > On Tue, Oct 5, 2021 at 1:01 AM Daniel Latypov <dlatypov@...gle.com> wrote:
> > > >
> > > > Currently, `run_kernel()` dumps all the kernel output to a file
> > > > (.kunit/test.log) and then opens the file and yields it to callers.
> > > > This made it easier to respect the requested timeout, if any.
> > > >
> > > > But it means that we can't yield the results in real time, either to the
> > > > parser or to stdout (if --raw_output is set).
> > > >
> > > > This change spins up a background thread to enforce the timeout, which
> > > > allows us to yield the kernel output in real time, while also copying it
> > > > to the .kunit/test.log file.
> > > > It's also careful to ensure that the .kunit/test.log file is complete,
> > > > even in the kunit_parser throws an exception/otherwise doesn't consume
> > > > every line, see the new `finally` block and unit test.
> > > >
> > > > For example:
> > > >
> > > > $ ./tools/testing/kunit/kunit.py run --arch=x86_64 --raw_output
> > > > <configure + build steps>
> > > > ...
> > > > <can now see output from QEMU in real time>
> > > >
> > > > This does not currently have a visible effect when --raw_output is not
> > > > passed, as kunit_parser.py currently only outputs everything at the end.
> > > > But that could change, and this patch is a necessary step towards
> > > > showing parsed test results in real time.
> > > >
> > > > Signed-off-by: Daniel Latypov <dlatypov@...gle.com>
> > > > ---
> > > >  tools/testing/kunit/kunit_kernel.py    | 73 +++++++++++++++-----------
> > > >  tools/testing/kunit/kunit_tool_test.py | 17 ++++++
> > > >  2 files changed, 60 insertions(+), 30 deletions(-)
> > > >
> > > > diff --git a/tools/testing/kunit/kunit_kernel.py b/tools/testing/kunit/kunit_kernel.py
> > > > index 2c6f916ccbaf..b8cba8123aa3 100644
> > > > --- a/tools/testing/kunit/kunit_kernel.py
> > > > +++ b/tools/testing/kunit/kunit_kernel.py
> > > > @@ -12,7 +12,8 @@ import subprocess
> > > >  import os
> > > >  import shutil
> > > >  import signal
> > > > -from typing import Iterator, Optional, Tuple
> > > > +import threading
> > > > +from typing import Iterator, List, Optional, Tuple
> > > >
> > > >  from contextlib import ExitStack
> > > >
> > > > @@ -103,8 +104,8 @@ class LinuxSourceTreeOperations(object):
> > > >                 if stderr:  # likely only due to build warnings
> > > >                         print(stderr.decode())
> > > >
> > > > -       def run(self, params, timeout, build_dir, outfile) -> None:
> > > > -               pass
> > > > +       def start(self, params: List[str], build_dir: str) -> subprocess.Popen:
> > > > +               raise RuntimeError('not implemented!')
> > > >
> > > >
> > > >  class LinuxSourceTreeOperationsQemu(LinuxSourceTreeOperations):
> > > > @@ -123,7 +124,7 @@ class LinuxSourceTreeOperationsQemu(LinuxSourceTreeOperations):
> > > >                 kconfig.parse_from_string(self._kconfig)
> > > >                 base_kunitconfig.merge_in_entries(kconfig)
> > > >
> > > > -       def run(self, params, timeout, build_dir, outfile):
> > > > +       def start(self, params: List[str], build_dir: str) -> subprocess.Popen:
> > > >                 kernel_path = os.path.join(build_dir, self._kernel_path)
> > > >                 qemu_command = ['qemu-system-' + self._qemu_arch,
> > > >                                 '-nodefaults',
> > > > @@ -134,18 +135,10 @@ class LinuxSourceTreeOperationsQemu(LinuxSourceTreeOperations):
> > > >                                 '-nographic',
> > > >                                 '-serial stdio'] + self._extra_qemu_params
> > > >                 print('Running tests with:\n$', ' '.join(qemu_command))
> > > > -               with open(outfile, 'w') as output:
> > > > -                       process = subprocess.Popen(' '.join(qemu_command),
> > > > -                                                  stdin=subprocess.PIPE,
> > > > -                                                  stdout=output,
> > > > -                                                  stderr=subprocess.STDOUT,
> > > > -                                                  text=True, shell=True)
> > > > -               try:
> > > > -                       process.wait(timeout=timeout)
> > > > -               except Exception as e:
> > > > -                       print(e)
> > > > -                       process.terminate()
> > > > -               return process
> > > > +               return subprocess.Popen(' '.join(qemu_command),
> > > > +                                          stdout=subprocess.PIPE,
> > > > +                                          stderr=subprocess.STDOUT,
> > > > +                                          text=True, shell=True)
> > > >
> > > >  class LinuxSourceTreeOperationsUml(LinuxSourceTreeOperations):
> > > >         """An abstraction over command line operations performed on a source tree."""
> > > > @@ -175,17 +168,13 @@ class LinuxSourceTreeOperationsUml(LinuxSourceTreeOperations):
> > > >                 kunit_parser.print_with_timestamp(
> > > >                         'Starting Kernel with all configs takes a few minutes...')
> > > >
> > > > -       def run(self, params, timeout, build_dir, outfile):
> > > > +       def start(self, params: List[str], build_dir: str) -> subprocess.Popen:
> > > >                 """Runs the Linux UML binary. Must be named 'linux'."""
> > > >                 linux_bin = get_file_path(build_dir, 'linux')
> > > > -               outfile = get_outfile_path(build_dir)
> > > > -               with open(outfile, 'w') as output:
> > > > -                       process = subprocess.Popen([linux_bin] + params,
> > > > -                                                  stdin=subprocess.PIPE,
> > >
> > > This breaks --raw_output under UML for me. Including the
> > > stdin=subprocess.PIPE again seems to fix it.
> >
> > Can you give an example of what it does?
> >
> > I don't see any issues with --raw_output under UML with the patch as-is.
> > I was mainly testing this with UML, and I must have ran it some 10s of
> > times, so I'm a bit surprised.
> >
> > On an earlier version, I saw some mangling of --raw_output (\n was
> > missing), but that went away after some revisions.
> >
>
> Yeah, that's the sort of thing I'm seeing: \n being treated as just a
> new line (without the carriage return).
> It happens pretty consistently, though sometimes the text wraps and
> sometimes (well, once) everything gets forced into the last column of
> the terminal. I've not been able to get it to work at all without
> having stdin be subprocess.PIPE.

I can't repro in the shell I was using while writing this.
Starting up a new session, I get:
* good
* bad x3
* good
* bad x3
* good
* bad x3
* bad, but not as bad (phew, I thought this was cursed)

.kunit/test.log contains the output with proper \n each time I checked.

Doesn't seem to repro when redirected into a file:

$ ./tools/testing/kunit/kunit.py exec --raw_output > /tmp/out && diff
/tmp/out .kunit/test.log | grep -m1 '^>'

Piping it through cat also seems 100% fine:
$ ./tools/testing/kunit/kunit.py exec --raw_output | cat

So having stdin be subprocess.PIPE sorta makes sense in some twisted way.
I can also now repro that setting stdin=subprocess.PIPE seems to fix it.

I don't want to put back subprocess.PIPE, but I'm not confident in
being able to find a better solution...

>
> It occurs both under tmux and not, and under Konsole and xterm, so it
> doesn't appear to be specific to any given terminal implementation.
> Still occurs even after running 'reset', and with a clean build.
> QEMU-based --raw_output works fine.
>
>

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