Re: [Qemu-devel] [PATCH] qcow2: Fix Coverity warning when calculating the refcount cache size

[Eric Blake <eblake@redhat.com>]

On 05/28/2018 10:01 AM, Alberto Garcia wrote:
> MIN_REFCOUNT_CACHE_SIZE is 4 and the cluster size is guaranteed to be
> at most 2MB, so the minimum refcount cache size (in bytes) is always
> going to fit in a 32-bit integer.
> 
> Coverity doesn't know that, and since we're storing the result in a
> uint64_t (*refcount_cache_size) it thinks that we need the 64 bits and
> that we probably want to do a 64-bit multiplication to prevent the
> result from being truncated.
> 
> This is a false positive in this case, but it's a fair warning.
> We could do a 64-bit multiplication to get rid of it, but since we
> know that a 32-bit variable is enough to store this value let's simply
> reuse min_refcount_cache, make it a normal int and stop doing casts.
> 
> Signed-off-by: Alberto Garcia <berto@igalia.com>
> Reported-by: Peter Maydell <peter.maydell@linaro.org>
> ---
>   block/qcow2.c | 5 ++---
>   1 file changed, 2 insertions(+), 3 deletions(-)
> 

Reviewed-by: Eric Blake <eblake@redhat.com>

-- 
Eric Blake, Principal Software Engineer
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