[PATCH v4 1/7] nbd: Utilize QAPI_CLONE for type conversion

[Eric Blake <eblake@redhat.com>]

Rather than open-coding the translation from the deprecated
NbdServerAddOptions type to the preferred BlockExportOptionsNbd, it's
better to utilize QAPI_CLONE_MEMBERS.  This solves a couple of issues:
first, if we do any more refactoring of the base type (which an
upcoming patch plans to do), we don't have to revisit the open-coding.
Second, our assignment to arg->name is fishy: the generated QAPI code
currently does not visit it if arg->has_name is false, but if it DID
visit it, we would have introduced a double-free situation when arg is
finally freed.

Signed-off-by: Eric Blake <eblake@redhat.com>
---
 blockdev-nbd.c | 15 ++++++---------
 1 file changed, 6 insertions(+), 9 deletions(-)

diff --git a/blockdev-nbd.c b/blockdev-nbd.c
index 8174023e5c47..43856c1058a5 100644
--- a/blockdev-nbd.c
+++ b/blockdev-nbd.c
@@ -14,6 +14,8 @@
 #include "sysemu/block-backend.h"
 #include "hw/block/block.h"
 #include "qapi/error.h"
+#include "qapi/clone-visitor.h"
+#include "qapi/qapi-visit-block-export.h"
 #include "qapi/qapi-commands-block-export.h"
 #include "block/nbd.h"
 #include "io/channel-socket.h"
@@ -195,7 +197,8 @@ void qmp_nbd_server_add(NbdServerAddOptions *arg, Error **errp)
      * the device name as a default here for compatibility.
      */
     if (!arg->has_name) {
-        arg->name = arg->device;
+        arg->has_name = true;
+        arg->name = g_steal_pointer(&arg->device);
     }

     export_opts = g_new(BlockExportOptions, 1);
@@ -205,15 +208,9 @@ void qmp_nbd_server_add(NbdServerAddOptions *arg, Error **errp)
         .node_name              = g_strdup(bdrv_get_node_name(bs)),
         .has_writable           = arg->has_writable,
         .writable               = arg->writable,
-        .u.nbd = {
-            .has_name           = true,
-            .name               = g_strdup(arg->name),
-            .has_description    = arg->has_description,
-            .description        = g_strdup(arg->description),
-            .has_bitmap         = arg->has_bitmap,
-            .bitmap             = g_strdup(arg->bitmap),
-        },
     };
+    QAPI_CLONE_MEMBERS(BlockExportOptionsNbd, &export_opts->u.nbd,
+                       qapi_NbdServerAddOptions_base(arg));

     /*
      * nbd-server-add doesn't complain when a read-only device should be
-- 
2.28.0