hw/rdma/vmw/pvrdma_cmd: Use correct struct in query_port()

In query_port() we pass the address of a local pvrdma_port_attr
struct to the rdma_query_backend_port() function.  Unfortunately,
rdma_backend_query_port() wants a pointer to a struct ibv_port_attr,
and the two are not the same length.

Coverity spotted this (CID 1507146): pvrdma_port_attr is 48 bytes
long, and ibv_port_attr is 52 bytes, because it has a few extra
fields at the end.

Fortunately, all we do with the attrs struct after the call is to
read a few specific fields out of it which are all at the same
offsets in both structs, so we can simply make the local variable the
correct type.  This also lets us drop the cast (which should have
been a bit of a warning flag that we were doing something wrong
here).

We do however need to add extra casts for the fields of the
struct that are enums: clang will complain about the implicit
cast to a different enum type otherwise.

Cc: qemu-stable@nongnu.org
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>
(cherry picked from commit 4ab9a74)

hw/rdma/vmw/pvrdma_cmd.c

@@ -129,23 +129,27 @@ static int query_port(PVRDMADev *dev, union pvrdma_cmd_req *req,
 {
     struct pvrdma_cmd_query_port *cmd = &req->query_port;
     struct pvrdma_cmd_query_port_resp *resp = &rsp->query_port_resp;
-    struct pvrdma_port_attr attrs = {};
+    struct ibv_port_attr attrs = {};
 
     if (cmd->port_num > MAX_PORTS) {
         return -EINVAL;
     }
 
-    if (rdma_backend_query_port(&dev->backend_dev,
-                                (struct ibv_port_attr *)&attrs)) {
+    if (rdma_backend_query_port(&dev->backend_dev, &attrs)) {
         return -ENOMEM;
     }
 
     memset(resp, 0, sizeof(*resp));
 
-    resp->attrs.state = dev->func0->device_active ? attrs.state :
-                                                    PVRDMA_PORT_DOWN;
-    resp->attrs.max_mtu = attrs.max_mtu;
-    resp->attrs.active_mtu = attrs.active_mtu;
+    /*
+     * The state, max_mtu and active_mtu fields are enums; the values
+     * for pvrdma_port_state and pvrdma_mtu match those for
+     * ibv_port_state and ibv_mtu, so we can cast them safely.
+     */
+    resp->attrs.state = dev->func0->device_active ?
+        (enum pvrdma_port_state)attrs.state : PVRDMA_PORT_DOWN;
+    resp->attrs.max_mtu = (enum pvrdma_mtu)attrs.max_mtu;
+    resp->attrs.active_mtu = (enum pvrdma_mtu)attrs.active_mtu;
     resp->attrs.phys_state = attrs.phys_state;
     resp->attrs.gid_tbl_len = MIN(MAX_PORT_GIDS, attrs.gid_tbl_len);
     resp->attrs.max_msg_sz = 1024;