Re: [Qemu-devel] [PATCH] Further tidy-up on block status

[Alex Bligh <alex@alex.org.uk>]

> On 14 Dec 2016, at 17:05, Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com> 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.

-- 
Alex Bligh