On 14 Dec 2016, at 17:05, Vladimir Sementsov-Ogievskiy <vsementsov@...2319...> 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.