Re: [Qemu-devel] [PATCH 1/2] memory: allow zero size for adjust_endianness()

[Peter Maydell <peter.maydell@linaro.org>]

On 27 August 2015 at 12:08, Michael S. Tsirkin <mst@redhat.com> wrote:
> On Thu, Aug 27, 2015 at 12:04:49PM +0100, Peter Maydell wrote:
>> On 27 August 2015 at 11:53, Michael S. Tsirkin <mst@redhat.com> wrote:
>> > On Thu, Aug 27, 2015 at 11:49:32AM +0100, Peter Maydell wrote:
>> >> But *why* does it require the size to be zero? I still think
>> >> the caller should just avoid trying to do zero-size memory
>> >> operations: they don't make sense. What is a zero size
>> >> operation supposed to mean?
>>
>> > This just mirrors an API we have in kvm: if you pass 0
>> > size when registering an ioeventfd, it will match on access
>> > of any size.
>>
>> Hrm. It feels to me like the memory APIs ought to filter
>> out bad access sizes at an earlier stage, rather than
>> trying to make them work all the way through.

> Why do you mention APIs? It's all internal to memory.c, isn't it?

adjust_endianness() is internal to memory.c. The APIs
memory.c exposes to the rest of the world are the ones
declared in memory.h. I'm suggesting that it would be
better to filter out rubbish like zero sizes at the
point where the rest of the world calls the memory
subsystem rather than ensuring that every part of the
memory subsystem code can handle what is basically
a completely meaningless request.

-- PMM