rwhandler: simplified way to register for mem/io

Some users prefer a single callback with length passed as parameter to
using b/w/l callbacks. It would maybe be cleaner to just pass length to
existing callbacks but that's a lot of churn.  So for now add a wrapper.
For convenience use pcibus_t for address so a single callback can be
used for pci io and pci memory.

I did have to resort to preprocessor to reduce code duplication.  It is
however slightly more straightforward, and better contained than what we
had with pci_host_template.h. Again, it would go away if we just passed
len to existing callbacks.

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

rwhandler.h

@@ -0,0 +1,27 @@
+#ifndef READ_WRITE_HANDLER_H
+#define READ_WRITE_HANDLER_H
+
+#include "qemu-common.h"
+#include "ioport.h"
+
+typedef struct ReadWriteHandler ReadWriteHandler;
+
+/* len is guaranteed to be one of 1, 2 or 4, addr is guaranteed to fit in an
+ * appropriate type (io/memory/etc). They do not need to be range checked. */
+typedef void WriteHandlerFunc(ReadWriteHandler *, pcibus_t addr,
+                              uint32_t value, int len);
+typedef uint32_t ReadHandlerFunc(ReadWriteHandler *, pcibus_t addr, int len);
+
+struct ReadWriteHandler {
+    WriteHandlerFunc *write;
+    ReadHandlerFunc *read;
+};
+
+/* Helpers for when we want to use a single routine with length. */
+/* CPU memory handler: both read and write must be present. */
+int cpu_register_io_memory_simple(ReadWriteHandler *);
+/* io port handler: can supply only read or write handlers. */
+int register_ioport_simple(ReadWriteHandler *,
+                           pio_addr_t start, int length, int size);
+
+#endif