libxc: Provide set_xen_guest_handle_offset macro

Add set_xen_guest_handle_offset() macro that can be used for setting
xen_guest_handle to an offset into hypercall buffer.

Signed-off-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Acked-by: Ian Campbell <ian.campbell@citrix.com>

diff --git a/tools/libxc/include/xenctrl.h b/tools/libxc/include/xenctrl.h
index a40485528518645eec13512939c32ce635081f7c..4b3c26ec226abdc4837aa74c6c1e03deb798506f 100644 (file)
--- a/tools/libxc/include/xenctrl.h
+++ b/tools/libxc/include/xenctrl.h
@@ -322,16 +322,24 @@ typedef struct xc_hypercall_buffer xc_hypercall_buffer_t;
  * Set a xen_guest_handle in a type safe manner, ensuring that the
  * data pointer has been correctly allocated.
  */
-#undef set_xen_guest_handle
-#define set_xen_guest_handle(_hnd, _val)                        \
+#define set_xen_guest_handle_impl(_hnd, _val, _byte_off)        \
     do {                                                        \
         xc_hypercall_buffer_t _hcbuf_hnd1;                      \
         typeof(XC__HYPERCALL_BUFFER_NAME(_val)) *_hcbuf_hnd2 =  \
                 HYPERCALL_BUFFER(_val);                         \
         (void) (&_hcbuf_hnd1 == _hcbuf_hnd2);                   \
-        set_xen_guest_handle_raw(_hnd, (_hcbuf_hnd2)->hbuf);    \
+        set_xen_guest_handle_raw(_hnd,                          \
+                (_hcbuf_hnd2)->hbuf + (_byte_off));             \
     } while (0)
 
+#undef set_xen_guest_handle
+#define set_xen_guest_handle(_hnd, _val)                        \
+    set_xen_guest_handle_impl(_hnd, _val, 0)
+
+#define set_xen_guest_handle_offset(_hnd, _val, _off)           \
+    set_xen_guest_handle_impl(_hnd, _val,                       \
+            ((sizeof(*_val)*(_off))))
+
 /* Use with set_xen_guest_handle in place of NULL */
 extern xc_hypercall_buffer_t XC__HYPERCALL_BUFFER_NAME(HYPERCALL_BUFFER_NULL);