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Re: [Nbd] [PATCH v4 2/2] doc: Add details on block sizes



On 04/16/2016 11:12 AM, Wouter Verhelst wrote:
> On Fri, Apr 15, 2016 at 11:39:12AM +0100, Alex Bligh wrote:
>>
>> On 15 Apr 2016, at 08:09, Wouter Verhelst <w@...112...> wrote:
>>
>>>> If a server advertises a minimum
>>>> +block size, the advertised export size MUST be an integer multiple of
>>>> +that block size.
>>>
>>> I think this can be a SHOULD without problem?
>>
>> Actually I think this should be a MUST. If the server is imposing
>> restrictions, they should be consistent.
> 
> Which is why I said SHOULD, not MAY.
> 
>> The client actually can't access the export beyond the integer multiple
>> without violating the spec, so in my mind it's up to the server to round the
>> size down.
> 
> Sure. My point is that the client would have to have a <= test anyway,
> in which case it doesn't matter if the size isn't a nice integer
> multiple. It's not proper, and we should discourage people from doing it
> wrong (which is what SHOULD does), but it doesn't cause many problems if
> you did it wrong anyway.

Okay, I think I'll word it as SHOULD, with the caveat that a server
violating the SHOULD has made it impossible for the client to access the
tail of the file.

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

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