Re: [Libguestfs] [libnbd PATCH v2 11/12] api: Add nbd_[aio_]opt_set_meta_context
On Wed, Aug 31, 2022 at 09:39:27AM -0500, Eric Blake wrote:
Make it possible for the client to choose when to manually request
meta contexts when using nbd_set_opt_mode(). By itself, this patch
allows us to test how a server reacts to NBD_OPT_SET_META_CONTEXT
without a previous negotiation of structured headers; then an upcoming
patch will also add APIs for choosing when to negotiate OPT_STARTTLS
and OPT_STRUCTURED_REPLY for even more fine-grained testing control.
Most users won't need this API (the automatic defaults are good
enough), but when writing a server, this level of integration testing
can be useful.
Overhaul the comment on OPT_META_CONTEXT.START to explain 5 different
scenarios that this state group can be reached in, to better document
which conditionals are in use later in the state machine:
- h->current_opt == opt is a witness of whether we are doing a
mandatory manual LIST/SET request with an expected callback and
transition to NEGOTIATIONG, or a conditional SET request dependent on
nbd_set_request_meta_context() and prior negotiation and transition to
OPT_GO
- h->current_opt == NBD_OPT_LIST_META_CONTEXT is a witness of whether
we are stateless or modifying h->meta_contexts
As this is a new API, the unit test in C is included in this patch;
there is no point in splitting it as reordering the patches would not
compile. However, porting the tests to other languages will be done
in the next commit.
---
Also intended to be squashed into this patch:
diff --git a/generator/states-newstyle-opt-meta-context.c
b/generator/states-newstyle-opt-meta-context.c
index 03b63c6..49e08bc 100644
--- a/generator/states-newstyle-opt-meta-context.c
+++ b/generator/states-newstyle-opt-meta-context.c
@@ -23,9 +23,24 @@ STATE_MACHINE {
size_t i;
uint32_t len, opt;
- /* If the server doesn't support SRs then we must skip this group.
- * Also we skip the group if the client didn't request any metadata
- * contexts, when doing SET (but an empty LIST is okay).
+ /* This state group is reached from:
+ * h->opt_mode == false (h->current_opt == 0):
+ * nbd_connect_*()
+ * -> conditionally use SET, next state OPT_GO
+ * h->opt_mode == true (h->current_opt matches calling API):
+ * nbd_opt_info(), nbd_opt_go()
+ * -> conditionally use SET, next state OPT_GO
+ * nbd_opt_list_meta_context()
+ * -> unconditionally use LIST, next state NEGOTIATING
+ * nbd_opt_set_meta_context()
+ * -> unconditionally use SET, next state NEGOTIATING
+ *
+ * If the next state is OPT_GO, we want to clear h->exportsize and friends.
+ * If SET is conditional, we skip it if h->request_meta is false, if
+ * structured replies were not negotiated, or if no contexts to request.
+ * There is a callback if and only if the command is unconditional.
+ * If we use SET, we clear h->meta_contexts and rebuild it.
+ * If we use LIST, we are stateless.
*/
assert (h->gflags & LIBNBD_HANDSHAKE_FLAG_FIXED_NEWSTYLE);
if (h->opt_current == NBD_OPT_LIST_META_CONTEXT) {
--
Eric Blake, Principal Software Engineer
Red Hat, Inc. +1-919-301-3266
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