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Re: [Qemu-block] [PATCH] qcow2: Replace align_offset() with ROUND_UP()

From: Eric Blake
Subject: Re: [Qemu-block] [PATCH] qcow2: Replace align_offset() with ROUND_UP()
Date: Tue, 30 Jan 2018 10:17:47 -0600
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.5.2

On 01/30/2018 10:08 AM, Alberto Garcia wrote:
> On Tue 30 Jan 2018 05:03:16 PM CET, Eric Blake wrote:
>>> -    virtual_size = align_offset(qemu_opt_get_size_del(opts, 
>>> +    virtual_size = ROUND_UP(qemu_opt_get_size_del(opts, BLOCK_OPT_SIZE, 0),
>>>                                  cluster_size);
> I just realized that the first parameter here is a function call with
> side effects, it it safe to use ROUND_UP() in this case?
> #define ROUND_UP(n, d) (((n) + (d) - 1) & -(0 ? (n) : (d)))

Oh, good catch.  No, we need a temporary variable to hold the result of
the function call (or we could rewrite ROUND_UP to have evaluate-once
semantics using gcc/clang extensions).

Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3266
Virtualization:  qemu.org | libvirt.org

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