> On 14 Dec 2016, at 18:18, Alex Bligh <a...@alex.org.uk> wrote:
>
> Let me have a go at a change.
OK I've pushed a change. I reordered a few bits (to put the
base:allocation next to the stuff that talks about metadata
queries at the start), but the main change is below.
--
Alex Bligh
@@ -970,15 +1029,38 @@ of the newstyle negotiation.
- String, query to list a subset of the available metadata
contexts.
- If zero queries are sent, then the server MUST return all
- the metadata contexts that are available to the client to select
- on the given export with `NBD_OPT_SET_META_CONTEXT`.
-
For details on the query string, see under `NBD_OPT_SET_META_CONTEXT`.
The server MUST either reply with an error (for instance `EINVAL`
if the option is not supported), or reply with a list of
`NBD_REP_META_CONTEXT` replies followed by `NBD_REP_ACK`.
+
+ If zero queries are sent, then the server MUST return all
+ the metadata contexts that are available to the client to select
+ on the given export with `NBD_OPT_SET_META_CONTEXT`, save that:
+
+ If one or more queries are sent, then the server MUST return
+ those metadata contexts that are available to the client to
+ select on the given export with `NBD_OPT_SET_META_CONTEXT`,
+ and which match one or more of the queries given. The
+ support of wildcarding within the leaf-name portion of
+ the query string is dependent upon the namespace.
+
+ In either case, however:
+
+ * the server MAY return an incomplete list if returning a
+ complete list would require undue resources.
+
+ * the server MAY return a context consisting of a namespace and
+ a colon only (i.e. omitting the leaf-name) to indicate that
+ the namespace contains a large number of possible contexts
+ within that namespace (for instance a namespace `X-backup` with
+ contexts that indicate whether blocks were written after
+ a given date might accept queries of the form
+ `'X-backup:modifiedtime>[unixdate]'` where `[unixdate]` is an
+ arbitrary integer, and in this case it might simply
+ return `X-backup:`)
+
The metadata context ID in these replies is reserved and SHOULD be
set to zero; clients MUST disregard it.
@@ -1009,7 +1091,9 @@ of the newstyle negotiation.
If zero queries are sent, the server MUST select no metadata contexts.
- The server MUST reply with a number of `NBD_REP_META_CONTEXT`
+ The server MAY return `NBD_REP_ERR_TOO_BIG` if a request
+ seeks to select too many contexts. Otherwise
+ the server MUST reply with a number of `NBD_REP_META_CONTEXT`
replies, one for each selected metadata context, each with a unique
metadata context ID, followed by `NBD_REP_ACK`. The metadata context
ID is transient and may vary across calls to `NBD_OPT_SET_META_CONTEXT`;
