linux-kernel - RE: [PATCH v1 1/1] pktcdvd: Use clamp

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Message-ID: <cd039ed4855c4e78a0867c4b5173e879@AcuMS.aculab.com>
Date:   Tue, 20 Jun 2023 13:35:11 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Andy Shevchenko' <andriy.shevchenko@...ux.intel.com>
CC:     Jens Axboe <axboe@...nel.dk>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "linux-block@...r.kernel.org" <linux-block@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH v1 1/1] pktcdvd: Use clamp_val() instead of min()+max()

From: 'Andy Shevchenko'
> Sent: 20 June 2023 14:25
> 
> On Tue, Jun 20, 2023 at 12:06:49PM +0000, David Laight wrote:
> 
> ...
> 
> > > +		*hi = clamp_val(*hi, 500, 1000000);
> >
> > (standard rant about minmax.h)
> >
> > clamp_val() is pretty much broken by design.
> > It MIGHT be ok here but it casts both limits to the
> > type of the value being compared.
> > In general that is just plain wrong.
> >
> > Like min_t() it is generally ok because the kernel only uses
> > unsigned values between 0 and MAXINT.
> >
> > If min/max were ok, then using clamp() should also be ok.
> 
> Submit a patch to fix it, if you think you can make it better.
> Obviously your comment can be addressed separately if we even
> need that.

Did you try using clamp() ?

To see why clamp_val() is broken consider?
	unsigned char val = 200;
	...
	xxx = clamp_val(val, 10, 300);
 
This sets xxx to 44 - not exactly expected.

	David

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