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

[Eric Blake <eblake@redhat.com>]

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On 01/30/2018 10:22 AM, Alberto Garcia wrote:
> On Tue 30 Jan 2018 05:17:47 PM CET, Eric Blake wrote:
>> 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, BLOCK_OPT_SIZE, 0),
>>>>> +    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
> 
> ...which is what align_offset() was doing in the first place. I can
> still modify that function to use the macro internally.

Nah. I think the ROUND_UP naming is enough to remind us to be careful,
and since this was the only affected spot in your conversion, it's nicer
to drop align_offset() and just do:

virtual_size = qemu_opt_get_size_del(opts, BLOCK_OPT_SIZE, 0);
virtual_size = ROUND_UP(virtual_size, cluster_size);

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


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