linux-kernel - Re: [PATCH v2 2/2] drivers: staging: lustre: Track sign separately

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Date:	Wed, 17 Dec 2014 06:54:06 +0000
From:	"Dilger, Andreas" <andreas.dilger@...el.com>
To:	Chris Rorvick <chris@...vick.com>,
	"Drokin, Oleg" <oleg.drokin@...el.com>
CC:	Rickard Strandqvist <rickard_strandqvist@...ctrumdigital.se>,
	"Greg Kroah-Hartman" <gregkh@...uxfoundation.org>,
	Julia Lawall <Julia.Lawall@...6.fr>,
	Greg Donald <gdonald@...il.com>,
	"Hammond, John" <john.hammond@...el.com>,
	Andriy Skulysh <Andriy_Skulysh@...atex.com>,
	Fabian Frederick <fabf@...net.be>,
	James Simmons <uja.ornl@...il.com>,
	"Dan Carpenter" <dan.carpenter@...cle.com>,
	"HPDD-discuss@...ts.01.org" <HPDD-discuss@...ts.01.org>,
	"devel@...verdev.osuosl.org" <devel@...verdev.osuosl.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 2/2] drivers: staging: lustre: Track sign separately

On 2014/12/16, 9:24 PM, "Chris Rorvick" <chris@...vick.com> wrote:

>The `mult' parameter is negated if the user data begins with a '-' so
>that the final value has the appropriate sign.  But `mult' is only used
>if the user data does not include a "units" suffix.  In this case,
>`mult' is overridden with the numeric scale conveyed by the units suffix,
>but retains the sign of the original value.
>
>Having `mult' serving double-duty works but is confusing.  Use a new
>local variable to store the sign of the user data instead.  This also
>fixes a pitfall of passing 0 to `mult', expecting it to be ignored when
>a units suffix is specified, but having the effect of taking the
>absolute value of the user-provided data.
>
>Signed-off-by: Chris Rorvick <chris@...vick.com>

Both patches look good to me.
Reviewed-by: Andreas Dilger <andreas.dilger@...el.com>

>---
> drivers/staging/lustre/lustre/obdclass/lprocfs_status.c | 7 ++++---
> 1 file changed, 4 insertions(+), 3 deletions(-)
>
>diff --git a/drivers/staging/lustre/lustre/obdclass/lprocfs_status.c
>b/drivers/staging/lustre/lustre/obdclass/lprocfs_status.c
>index 92ed0a0..b6c3352 100644
>--- a/drivers/staging/lustre/lustre/obdclass/lprocfs_status.c
>+++ b/drivers/staging/lustre/lustre/obdclass/lprocfs_status.c
>@@ -1864,6 +1864,7 @@ int lprocfs_write_frac_u64_helper(const char
>*buffer, unsigned long count,
> 	char kernbuf[22], *end, *pbuf;
> 	__u64 whole, frac = 0, units;
> 	unsigned frac_d = 1;
>+	int sign = 1;
> 
> 	if (count > (sizeof(kernbuf) - 1))
> 		return -EINVAL;
>@@ -1874,7 +1875,7 @@ int lprocfs_write_frac_u64_helper(const char
>*buffer, unsigned long count,
> 	kernbuf[count] = '\0';
> 	pbuf = kernbuf;
> 	if (*pbuf == '-') {
>-		mult = -mult;
>+		sign = -1;
> 		pbuf++;
> 	}
> 
>@@ -1911,11 +1912,11 @@ int lprocfs_write_frac_u64_helper(const char
>*buffer, unsigned long count,
> 	}
> 	/* Specified units override the multiplier */
> 	if (units > 1)
>-		mult = mult < 0 ? -units : units;
>+		mult = units;
> 
> 	frac *= mult;
> 	do_div(frac, frac_d);
>-	*val = whole * mult + frac;
>+	*val = sign * (whole * mult + frac);
> 	return 0;
> }
> EXPORT_SYMBOL(lprocfs_write_frac_u64_helper);
>-- 
>2.1.0
>
>


Cheers, Andreas
-- 
Andreas Dilger

Lustre Software Architect
Intel High Performance Data Division


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