[PATCH v6 02/17] nbd/client: Pass mode through to nbd_send_request

[Eric Blake <eblake@redhat.com>]

Once the 64-bit headers extension is enabled, the data layout we send
over the wire for a client request depends on the mode negotiated with
the server.  Rather than adding a parameter to nbd_send_request, we
can add a member to struct NBDRequest, since it already does not
reflect on-wire format.  Some callers initialize it directly; many
others rely on a common initialization point during
nbd_co_send_request().  At this point, there is no semantic change.

Signed-off-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@yandex-team.ru>
---

v5: R-b added
v4: new patch, based on ideas in v3 4/14, but by modifying NBDRequest
instead of adding a parameter
---
 include/block/nbd.h | 12 +++++++-----
 block/nbd.c         |  5 +++--
 nbd/client.c        |  3 ++-
 3 files changed, 12 insertions(+), 8 deletions(-)

diff --git a/include/block/nbd.h b/include/block/nbd.h
index abf6030b513..c4cbe130e07 100644
--- a/include/block/nbd.h
+++ b/include/block/nbd.h
@@ -63,17 +63,19 @@ typedef enum NBDMode {
     /* TODO add NBD_MODE_EXTENDED */
 } NBDMode;

-/* Transmission phase structs
- *
- * Note: these are _NOT_ the same as the network representation of an NBD
- * request and reply!
+/* Transmission phase structs */
+
+/*
+ * Note: NBDRequest is _NOT_ the same as the network representation of an NBD
+ * request!
  */
 typedef struct NBDRequest {
     uint64_t cookie;
     uint64_t from;
     uint32_t len;
     uint16_t flags; /* NBD_CMD_FLAG_* */
-    uint16_t type; /* NBD_CMD_* */
+    uint16_t type;  /* NBD_CMD_* */
+    NBDMode mode;   /* Determines which network representation to use */
 } NBDRequest;

 typedef struct NBDSimpleReply {
diff --git a/block/nbd.c b/block/nbd.c
index 5f88f7a819b..ca5991f868a 100644
--- a/block/nbd.c
+++ b/block/nbd.c
@@ -339,7 +339,7 @@ int coroutine_fn nbd_co_do_establish_connection(BlockDriverState *bs,
          * We have connected, but must fail for other reasons.
          * Send NBD_CMD_DISC as a courtesy to the server.
          */
-        NBDRequest request = { .type = NBD_CMD_DISC };
+        NBDRequest request = { .type = NBD_CMD_DISC, .mode = s->info.mode };

         nbd_send_request(s->ioc, &request);

@@ -521,6 +521,7 @@ nbd_co_send_request(BlockDriverState *bs, NBDRequest *request,

     qemu_co_mutex_lock(&s->send_mutex);
     request->cookie = INDEX_TO_COOKIE(i);
+    request->mode = s->info.mode;

     assert(s->ioc);

@@ -1466,7 +1467,7 @@ static void nbd_yank(void *opaque)
 static void nbd_client_close(BlockDriverState *bs)
 {
     BDRVNBDState *s = (BDRVNBDState *)bs->opaque;
-    NBDRequest request = { .type = NBD_CMD_DISC };
+    NBDRequest request = { .type = NBD_CMD_DISC, .mode = s->info.mode };

     if (s->ioc) {
         nbd_send_request(s->ioc, &request);
diff --git a/nbd/client.c b/nbd/client.c
index faa054c4527..40a1eb72346 100644
--- a/nbd/client.c
+++ b/nbd/client.c
@@ -1224,7 +1224,7 @@ int nbd_receive_export_list(QIOChannel *ioc, QCryptoTLSCreds *tlscreds,
         /* Send NBD_CMD_DISC as a courtesy to the server, but ignore all
          * errors now that we have the information we wanted. */
         if (nbd_drop(ioc, 124, NULL) == 0) {
-            NBDRequest request = { .type = NBD_CMD_DISC };
+            NBDRequest request = { .type = NBD_CMD_DISC, .mode = result };

             nbd_send_request(ioc, &request);
         }
@@ -1354,6 +1354,7 @@ int nbd_send_request(QIOChannel *ioc, NBDRequest *request)
 {
     uint8_t buf[NBD_REQUEST_SIZE];

+    assert(request->mode <= NBD_MODE_STRUCTURED); /* TODO handle extended */
     trace_nbd_send_request(request->from, request->len, request->cookie,
                            request->flags, request->type,
                            nbd_cmd_lookup(request->type));
-- 
2.41.0