linux-kernel - Re: [PATCH] sched/isolation: Allow "isolcpus=" to skip unknown sub-parameters

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Date:   Thu, 2 Apr 2020 09:14:14 -0400
From:   Peter Xu <peterx@...hat.com>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     linux-kernel@...r.kernel.org, Ming Lei <ming.lei@...hat.com>,
        Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Juri Lelli <juri.lelli@...hat.com>,
        Luiz Capitulino <lcapitulino@...hat.com>
Subject: Re: [PATCH] sched/isolation: Allow "isolcpus=" to skip unknown
 sub-parameters

On Thu, Apr 02, 2020 at 10:40:49AM +0200, Thomas Gleixner wrote:
> Peter Xu <peterx@...hat.com> writes:
> > On Thu, Apr 02, 2020 at 01:29:14AM +0200, Thomas Gleixner wrote:
> >> Peter Xu <peterx@...hat.com> writes:
> >> >> +		/*
> >> >> +		 * Skip unknown sub-parameter and validate that it is not
> >> >> +		 * containing an invalid character.
> >> >> +		 */
> >> >> +		for (par = str, len = 0; isalpha(*str); str++, len++);
> >> >> +		if (*str != ',') {
> >> >> +			pr_warn("isolcpus: Invalid flag %*s\n", len, par);
> >> >
> >> > ... this will dump "isolcpus: Invalid flag domain1,3,5", is this what
> >> > we wanted?  Maybe only dumps "domain1"?
> >> 
> >> No, it will dump: "domain1" at least if my understanding of is_alpha()
> >> and the '%*s' format option is halfways correct
> >
> > It will dump "isolcpus: Invalid flag domain1,3,5". Do you mean "%.*s"
> > instead?
> 
> Obviously.
> 
> > Another issue is even if to use "%.*s" it'll only dump "domain".  How
> > about something like (declare "illegal" as bool):
> >
> > 		/*
> > 		 * Skip unknown sub-parameter and validate that it is not
> > 		 * containing an invalid character.
> > 		 */
> > 		for (par = str, len = 0; *str && *str != ','; str++, len++)
> > 			if (!isalpha(*str))
> > 				illegal = true;
> >
> > 		if (illegal) {
> > 			pr_warn("isolcpus: Invalid flag %.*s\n", len, par);
> 
> You can achieve the same thing without the illegal indirection with
> 
> 	pr_warn("....", len + 1, par);

I think it will stop working with "isolcpus=nohz,domain11,12,13".

I'll repost soon.  Thanks,

-- 
Peter Xu