14.12.2016 20:36, Alex Bligh wrote:
>> On 14 Dec 2016, at 17:05, Vladimir Sementsov-Ogievskiy
>> <[email protected]> wrote:
>>> However, this raises another question. Wouter deliberately made the
>>> query format freeform so that you could e.g. set a context like:
>>>
>>> backup:modtime>201612081034
>>>
>>> which might (in theory) return a list of blocks which are newer than
>>> the given timestamp. It would clearly be impossible to return all such
>>> contexts. I wonder if we should carve out an exception here.
>>>
>>>
>> Interesting. Even query 'backup:modtime>*' would be a problem, not only
>> empty query list.
>>
>> Actually, we do not need to 'list contexts', as it is about management, not
>> about data transfer. We only need a way to check, that particular query
>> selects all needed contexts and no others. Just to be sure that we are know,
>> what we will select by NBD_OPT_SET_META_CONTEXT with _same_ query.
>>
>> So, I suggest just to say, that _LIST_ can return error if too much contexts
>> are selected. And same should be done for _SET_. And it should be documented
>> that this result of query (list or error) should be equal for these two
>> commands.
> (two CCs that always bounce removed)
>
> Hmmm... Well in the '*' case, it's up to the namespace as to how it parses
> things, so '*' could be prohibited entirely or mean 'return the first 20
> matching' or similar. So that's less of a problem. And 'set all' doesn't
> exist (unlike 'list all').
>
> I think in the LIST case we should allow the server to omit contexts under
> certain circumstances, and allow SET to return ETOOBIG.
>
We can't prohibit '*' as query string as implementation defined. And we
shouldn't (I think) define its meaning. Opposite, we can define, that
query must not select more than 20 contexts, but I'm not sure that this
is good.
So, do you mean
list('backup:modtime>*') -> empty list
set('backup:modtime>*') -> ETOOBIG
? For me this looks strange.
--
Best regards,
Vladimir
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