nbd/client: Pass mode through to nbd_send_request

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>
Message-ID: <20230829175826.377251-21-eblake@redhat.com>

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);
 
@@ -520,6 +520,7 @@ 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);
 
@@ -1465,7 +1466,7 @@ 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);

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 {

nbd/client.c

@@ -1218,7 +1218,7 @@ 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);
         }
@@ -1348,6 +1348,7 @@ 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));