hostmem: Ignore ENOSYS while setting MPOL_DEFAULT

Currently hostmem backend fails if CONFIG_NUMA is enabled in QEMU
(the default) but NUMA is not supported by the kernel. This makes
it impossible to use ivshmem in such configurations.

This patch fixes the problem by ignoring ENOSYS error if policy is set to
MPOL_DEFAULT. This way the code behaves in the same way as if CONFIG_NUMA
was not defined. qemu will still fail if the user specifies some other
policy, so that the user knows it.
Signed-off-by: NPavel Fedin <p.fedin@samsung.com>
Reviewed-by: NEduardo Habkost <ehabkost@redhat.com>
Signed-off-by: NEduardo Habkost <ehabkost@redhat.com>

backends/hostmem.c

@@ -313,9 +313,11 @@ host_memory_backend_memory_complete(UserCreatable *uc, Error **errp)
         assert(maxnode <= MAX_NODES);
         if (mbind(ptr, sz, backend->policy,
                   maxnode ? backend->host_nodes : NULL, maxnode + 1, flags)) {
-            error_setg_errno(errp, errno,
-                             "cannot bind memory to host NUMA nodes");
-            return;
+            if (backend->policy != MPOL_DEFAULT || errno != ENOSYS) {
+                error_setg_errno(errp, errno,
+                                 "cannot bind memory to host NUMA nodes");
+                return;
+            }
         }
 #endif
         /* Preallocate memory after the NUMA policy has been instantiated.