linux-kernel - Re: [PATCH] block: fix blk_stack_limits() regression due to lcm() change

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Date:	Mon, 30 Mar 2015 16:53:06 -0400
From:	"Martin K. Petersen" <martin.petersen@...cle.com>
To:	Mike Snitzer <snitzer@...hat.com>
Cc:	Jens Axboe <axboe@...nel.dk>,
	Andrew Morton <akpm@...ux-foundation.org>, dm-devel@...hat.com,
	linux-kernel@...r.kernel.org,
	"Martin K. Petersen" <martin.petersen@...cle.com>,
	Rasmus Villemoes <linux@...musvillemoes.dk>
Subject: Re: [PATCH] block: fix blk_stack_limits() regression due to lcm() change

>>>>> "Mike" == Mike Snitzer <snitzer@...hat.com> writes:

Mike> Linux 3.19 commit 69c953c ("lib/lcm.c: lcm(n,0)=lcm(0,n) is 0, not
Mike> n") caused blk_stack_limits() to not properly stack queue_limits
Mike> for stacked devices (e.g. DM).

Mike> Fix this regression by establishing lcm_not_zero() and switching
Mike> blk_stack_limits() over to using it.

I'm OK with that approach. The original lcm() behavior made sense when
we were the only user.

+unsigned long lcm_not_zero(unsigned long a, unsigned long b)
+{
+	unsigned long l = lcm(a, b);
+
+	if (l)
+		return l;
+
+	return (b ? : a);
+}

I always blink when I read b ?: a instead of b ? b : a. But no
biggie. That's just my personal preference.

Acked-by: Martin K. Petersen <martin.petersen@...cle.com>

-- 
Martin K. Petersen	Oracle Linux Engineering
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