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Re: [Qemu-block] [Qemu-devel] [PATCH v4 0/2] block: Reject negative valu

From: Fam Zheng
Subject: Re: [Qemu-block] [Qemu-devel] [PATCH v4 0/2] block: Reject negative values for throttling options
Date: Wed, 20 Jan 2016 10:55:18 +0800
User-agent: Mutt/1.5.21 (2010-09-15)

On Tue, 01/19 10:50, Markus Armbruster wrote:
> Fam Zheng <address@hidden> writes:
> > v4: Add Max's rev-by in both patches, while fixing the "maxs" typo.
> >
> > v3: Address comments:
> >     - Add test for large value; [Berto]
> >     - Fix typos "negative" & "caught"; [Eric, Berto]
> >     - Use "LL" suffix to the upper limit constant. [Berto]
> >
> > v2: Check the value range and report an appropriate error. [Berto]
> >
> > Now the negative values are silently converted to a huge positive number
> > because we are doing implicit casting from uint64_t to double. Fix it and 
> > add a
> > test case (this was once fixed in 7d81c1413c9 but regressed when the block
> > device option parsing code was changed).
> I think PATCH 1's commit message could explain the problem in a bit more
> detail, and it should mention the changed valid range.

OK, I'll update the commit message.

> Other than that, I had two questions: why cast THROTTLE_VALUE_MAX for
> printing (in scope for the series),

Not quite intentionally. I started with "L" suffix and thought definitely 64
bit is safer than "%ld" for 32 bit machines, without realizing "L" suffix is
not safe for old compilers. Then it became "LL" and int64_t casting.

I can use "%lld" in v5 while fixing the commit message and covering the valid
range in iotests.

> and why parse the settings as
> integers even though they're really floating-point (probably not in
> scope).

I don't know if it's worth to extend the option interface with floating-point.
If it's for this case I'd say no, because using floating-point in the code is
more for the computation, rather than the precision we support on the
parameters (I might be wrong).


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