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From: Thomas Gleixner <tglx@linutronix.de>
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To: Randy Dunlap <rdunlap@infradead.org>, LKML <linux-kernel@vger.kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>, Mathieu Desnoyers
 <mathieu.desnoyers@efficios.com>, "Paul E. McKenney" <paulmck@kernel.org>,
 Boqun Feng <boqun.feng@gmail.com>, Jonathan Corbet <corbet@lwn.net>,
 Prakash Sangappa <prakash.sangappa@oracle.com>, Madadi Vineeth Reddy
 <vineethr@linux.ibm.com>, K Prateek Nayak <kprateek.nayak@amd.com>, Steven
 Rostedt <rostedt@goodmis.org>, Sebastian Andrzej Siewior
 <bigeasy@linutronix.de>, Arnd Bergmann <arnd@arndb.de>,
 linux-arch@vger.kernel.org
Subject: Re: [patch V3 03/12] rseq: Provide static branch for time slice
 extensions
In-Reply-To: <6204274d-a6b7-4e37-8e5c-deb1caa98317@infradead.org>
References: <20251029125514.496134233@linutronix.de>
 <20251029130403.606732100@linutronix.de>
 <6204274d-a6b7-4e37-8e5c-deb1caa98317@infradead.org>
Date: Wed, 29 Oct 2025 22:12:33 +0100
Message-ID: <87pla5tnsu.ffs@tglx>
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On Wed, Oct 29 2025 at 10:23, Randy Dunlap wrote:
> On 10/29/25 6:22 AM, Thomas Gleixner wrote:
>> +static int __init rseq_slice_cmdline(char *str)
>> +{
>> +	bool on;
>> +
>> +	if (kstrtobool(str, &on))
>> +		return -EINVAL;
>
> The norm for __setup function returns is:
>
> 		return 0;	/* param not handled - will be added to ENV */
> or
> 		return 1;	/* param is handled (anything non-zero) */
>
>
> Anything non-zero means param is handled, so maybe -EINVAL is OK here,
> since return 0 means that the string is added to init's environment.
>
> If the parsing function recognizes the cmdline option string
> (rseq_slice_ext) but the value is invalid, it should pr_error()
> or something like that but still return 1; (IMHO).
> No need to have "rseq_slice_ext=foo" added to init's ENV.
>
> So return -EINVAL is like return 1 in this case.
> IOW it works as needed.  :)

Bah. I hate this logic so much and I never will memorize it.