iothread: fix breakage on windows

OOB can enable iothread for parsing even on Windows.  We need some tunes
to enable that on Windows otherwise it'll break Windows users.  This
patch fixes the breakage on Windows with qemu-system-ppc.exe.
Reported-by: NHoward Spoelstra <hsp.cat7@gmail.com>
Tested-by: NHoward Spoelstra <hsp.cat7@gmail.com>
Suggested-by: NPaolo Bonzini <pbonzini@redhat.com>
Signed-off-by: NPeter Xu <peterx@redhat.com>
Message-Id: <20180322085630.23654-1-peterx@redhat.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

iothread.c

@@ -31,11 +31,15 @@ typedef ObjectClass IOThreadClass;
 #define IOTHREAD_CLASS(klass) \
    OBJECT_CLASS_CHECK(IOThreadClass, klass, TYPE_IOTHREAD)
 
+#ifdef CONFIG_POSIX
 /* Benchmark results from 2016 on NVMe SSD drives show max polling times around
  * 16-32 microseconds yield IOPS improvements for both iodepth=1 and iodepth=32
  * workloads.
  */
 #define IOTHREAD_POLL_MAX_NS_DEFAULT 32768ULL
+#else
+#define IOTHREAD_POLL_MAX_NS_DEFAULT 0ULL
+#endif
 
 static __thread IOThread *my_iothread;
 

util/aio-win32.c

@@ -410,5 +410,7 @@ void aio_context_setup(AioContext *ctx)
 void aio_context_set_poll_params(AioContext *ctx, int64_t max_ns,
                                  int64_t grow, int64_t shrink, Error **errp)
 {
-    error_setg(errp, "AioContext polling is not implemented on Windows");
+    if (max_ns) {
+        error_setg(errp, "AioContext polling is not implemented on Windows");
+    }
 }