Re: [Qemu-devel] [PATCH v6 02/20] block: Drop private ioctl-only members of BlockRequest

[Eric Blake <eblake@redhat.com>]

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On 05/06/2016 04:37 AM, Kevin Wolf wrote:
> Am 05.05.2016 um 01:55 hat Eric Blake geschrieben:
>> I was thrown by the fact that the public type BlockRequest had
>> an anonymous union, but no obvious discriminator.  Turns out
>> that the only client of the second branch of the union was code
>> internal to io.c, and that with a slight abuse of QEMUIOVector*
>> to pass a void* pointer, we can make the public interface less
>> confusing.
>>
>> (Yes, I know that strict C doesn't guarantee that you can cast
>> void* to the wrong type and then back to void* - it only
>> guarantees the reverse direction of the original pointer to
>> void* and back to the original type - but we already have other
>> assumptions throughout the qemu code base that assume that all
>> pointers are interchangeable in representation).
>>
>> Signed-off-by: Eric Blake <eblake@redhat.com>
> 
> Do you really think abusing fields makes things clearer than using a
> union? We could just add comments instead that tell which branch is used
> for what. And after my patch "block: Remove bdrv_aio_multiwrite()", I
> think the struct isn't part of a public interface any more anyway.

Oh, you're right!  Consider this patch severed from the series (I may
still send a documentation patch, and/or move the struct out of the
public header into block_int.h, but it is sufficiently unrelated to the
rest of the series).

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org


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