Re: [Qemu-devel] [PATCH] qemu/units: Move out QCow2 specific definitions

[Eric Blake <eblake@redhat.com>]

On 11/2/18 9:10 AM, Kevin Wolf wrote:
> Am 02.11.2018 um 13:37 hat Philippe Mathieu-Daudé geschrieben:
>> Hi Kevin,
>>
>> On 2/11/18 12:07, Kevin Wolf wrote:
>>> Am 02.11.2018 um 09:58 hat Philippe Mathieu-Daudé geschrieben:
>>>> This definitions are QCow2 specific, there is no need to expose them
>>>> in the global namespace.
>>>>
>>>> This partially reverts commit 540b8492618eb.
>>>>
>>>> Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
>>>
>>> If we don't want this globally, I think we also don't want it in qcow2.

Agreed. I didn't want it in the first place, arguing that if we want 
stringification of defaults, it would be better to have a runtime 
function do that, rather than adding a set of near-duplicate macro names.

>>
>> I only see this definitions used by block/qcow2.h (b6a95c6d1007).
>>
>> Per 540b8492618eb description "This is needed when a size has to be
>> stringified" but I can't find other code requiring these definitions in the
>> codebase.
> 
> I guess the real question is: Is qcow2 the only place that needs
> stringification of sizes?

Probably not. It seems like stringifying a default value is a common desire.

> 
> The only value where this actually seems to be used in qcow2 is for
> DEFAULT_CLUSTER_SIZE, as the default value for QemuOpts. Other drivers
> still use plain numbers, but this is less readable.
> 
> Then there is VDI which uses (1 * MiB), but that is compiled out and if
> you enable it, it breaks. So it needs the same fix.
> 
> Are block drivers the only places where we stringify a size? I imagine
> some device models might use something like it, too?

Indeed, I would prefer a patch that makes it possible for QemuOpts to 
pretty-print a default value using a generic runtime stringifier, rather 
than keeping these S_ macros around.

> 
> I don't mind too much which solution we end up using, but I'd prefer it
> to be universal.

Agree.

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