linux-kernel - Re: [PATCH 0/5] firmware: Add support for loading compressed files

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Date:   Mon, 20 May 2019 14:50:03 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Takashi Iwai <tiwai@...e.de>
Cc:     shuah <shuah@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Luis Chamberlain <mcgrof@...nel.org>,
        "Rafael J . Wysocki" <rafael@...nel.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/5] firmware: Add support for loading compressed files

On Mon, May 20, 2019 at 08:59:14PM +0200, Takashi Iwai wrote:
> So the problem is obvious: the commit above adjusts the stdout to be
> unbuffered via stdbuf, hence each invocation like
>   echo -n abc > /sys/....
> 
> would become writes of "a", "b" and "c", instead of "abc".
> 
> Although we can work around it in each test unit, I'm afraid that
> enforcing the unbuffered stdio is too fragile for scripts like the
> above case.

Oh this is nasty. Looks like stdbuf overrides all child processes too...
yeah, that's very broken. Let me try to see if I can find an
alternative.

Shuah, in the meantime, if you want a fix to restore test behavior,
but regress output flushing, this will work:

diff --git a/tools/testing/selftests/kselftest/runner.sh b/tools/testing/selftests/kselftest/runner.sh
index eff3ee303d0d..a529c19240fc 100644
--- a/tools/testing/selftests/kselftest/runner.sh
+++ b/tools/testing/selftests/kselftest/runner.sh
@@ -27,11 +27,11 @@ tap_prefix()
 # If stdbuf is unavailable, we must fall back to line-at-a-time piping.
 tap_unbuffer()
 {
-	if ! which stdbuf >/dev/null ; then
+	#if ! which asdfstdbuf >/dev/null ; then
 		"$@"
-	else
-		stdbuf -i0 -o0 -e0 "$@"
-	fi
+	#else
+	#	stdbuf -i0 -o0 -e0 "$@"
+	#fi
 }
 
 run_one()

Some tests will no longer show their output until they're entirely done,
but at least no test pass/fail results should regress.

I'll keep looking at solutions...

-- 
Kees Cook