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Re: [Qemu-block] [PATCH v2 1/2] blockdev: Error out on negative throttli

From: Fam Zheng
Subject: Re: [Qemu-block] [PATCH v2 1/2] blockdev: Error out on negative throttling option values
Date: Wed, 13 Jan 2016 19:02:00 +0800
User-agent: Mutt/1.5.21 (2010-09-15)

On Wed, 01/13 11:17, Alberto Garcia wrote:
> On Wed 13 Jan 2016 01:52:29 AM CET, Fam Zheng wrote:
> > The implicit casting from unsigned int to double changes negative values
> > into large positive numbers and accepts them.  We should instead print
> > an error.
> >
> > Check the number range so this case is catched and reported.
> I still don't know why qemu_opt_get_number() convert silently negative
> numbers into positive ones, shouldn't it just fail with an "invalid
> parameter" error?

Because the parsing is done with strtoull(3) and unfortunately its man page
says "negative values are considered valid input and are silently converted to
the equivalent unsigned long int value."

> > +#define THROTTLE_VALUE_MAX 1000000000000000L
> This is larger than LONG_MAX in 32-bit systems, I don't know if you need
> to use LL instead.

I assume a compiler will handle that okay but yes it's safer to use LL.


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