Re: [Qemu-devel] [Qemu-block] [PATCH 1/2] blockdev: Error out on negative throttling option values

[Fam Zheng <famz@redhat.com>]

On Tue, 01/12 16:00, Alberto Garcia wrote:
> On Mon 11 Jan 2016 06:42:38 AM CET, Fam Zheng <famz@redhat.com> wrote:
> 
> > The implicit casting from unsigned int to double changes negative
> > values into large positive numbers, whereas explicitly casting to
> > signed integer first will let us catch the invalid value and report
> > error correctly:
> >
> >     $ qemu-system-x86_64 -drive file=null-co://,iops=-1
> >     qemu-system-x86_64: -drive file=null-co://,iops=-1: bps/iops/maxs
> >     values must be 0 or greater
> >
> 
> >          throttle_cfg->buckets[THROTTLE_BPS_TOTAL].avg =
> > -            qemu_opt_get_number(opts, "throttling.bps-total", 0);
> > +            (int64_t)qemu_opt_get_number(opts, "throttling.bps-total", 0);
> 
> It seems to me that the problem is that qemu_opt_get_number() returns a
> value different from the one specified in the comand-line.
> 
> How do we even tell the difference between a negative number and its
> bit-to-bit positive equivalent?

We can't. :(

> 
> If we are going to reject very large numbers I would rather check that
> the throtting values are within a sane range and throw an error
> otherwise.

Yes, that is probably more accurate to the user.

Fam