linux-kernel - Re: [PATCH v2 03/14] selftests/nolibc: print running log to screen

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Message-ID: <20230722122926.GF17311@1wt.eu>
Date:   Sat, 22 Jul 2023 14:29:26 +0200
From:   Willy Tarreau <w@....eu>
To:     Zhangjin Wu <falcon@...ylab.org>
Cc:     thomas@...ch.de, arnd@...db.de, linux-kernel@...r.kernel.org,
        linux-kselftest@...r.kernel.org
Subject: Re: [PATCH v2 03/14] selftests/nolibc: print running log to screen

On Wed, Jul 19, 2023 at 09:20:17PM +0800, Zhangjin Wu wrote:
> When poweroff fails, qemu-system will hang there without any output.
> 
> It is very hard to debug in such case, let's print the running log to
> the screen to allow users to learn what is happening at the first
> glance, without editing the Makefile manually every time.
> 
> To get a clean output, the 'grep status' command can be used.

The problem with doing this is that it rolls back to the initial
version that breaks with qemu. When its stdout is sent to a pipe, we've
found that the output got randomly mangled and/or missing contents.
It's only when sent to a file that it's OK. I suspect it has something
to do with non-blocking writes being used to avoid blocking the
emulation but I could be totally wrong. That's the reason why we had
to switch to a file.

And I'd rather avoid starting it in the background as well. Maybe
you'd want to run the qemu command under the "timeout" one ? That
could be better than nothing.

Willy