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Re: [Qemu-block] [Qemu-devel] [PULL 20/37] qcow2: Give the refcount cach


From: Alberto Garcia
Subject: Re: [Qemu-block] [Qemu-devel] [PULL 20/37] qcow2: Give the refcount cache the minimum possible size by default
Date: Mon, 28 May 2018 10:58:17 +0200
User-agent: Notmuch/0.18.2 (http://notmuchmail.org) Emacs/24.4.1 (i586-pc-linux-gnu)

On Mon 28 May 2018 10:38:55 AM CEST, Kevin Wolf wrote:
>> > +        if (!refcount_cache_size_set) {
>> > +            *refcount_cache_size = MIN_REFCOUNT_CACHE_SIZE * 
>> > s->cluster_size;
>> 
>> ...but in the else clause down here, we don't have the cast, and
>> Coverity complains that we evaluate a 32-bit result and then put it
>> in a 64-bit variable. Should this have the (uint64_t) cast as well ?

I suppose that's not because we put a 32-bit result in a 64-bit
variable, but because it could theoretically overflow (if
s->cluster_size > INT32_MAX / 4).

> It's a false positive, MIN_REFCOUNT_CACHE_SIZE is 4 and
> s->cluster_size is at most 2 MB, so this will never overflow.
>
> I guess we can change the code anyway to silence it?

Same opinion here, no problem with adding a cast to silence the warning.

Berto



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