memory: move preallocation code out of exec.c

So that backends can use it.

Since we need the page size for efficiency, move code to compute it
out of translate-all.c and into util/oslib-win32.c.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Hu Tao <hutao@cn.fujitsu.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

util/oslib-win32.c

@@ -350,3 +350,22 @@ gint g_poll_fixed(GPollFD *fds, guint nfds, gint timeout)
 
     return num_completed;
 }
+
+size_t getpagesize(void)
+{
+    SYSTEM_INFO system_info;
+
+    GetSystemInfo(&system_info);
+    return system_info.dwPageSize;
+}
+
+void os_mem_prealloc(int fd, char *area, size_t memory)
+{
+    int i;
+    size_t pagesize = getpagesize();
+
+    memory = (memory + pagesize - 1) & -pagesize;
+    for (i = 0; i < memory / pagesize; i++) {
+        memset(area + pagesize * i, 0, 1);
+    }
+}