libxl: make LIBXL_INIT_GC a statement, not an initialiser

Previously LIBXL_INIT_GC was an initialiser, which you were expected
to use like this:
    libxl__gc gc = LIBXL_INIT_GC(ctx);

But we are going to want to put things in the gc which are to be
initialised using other macros.  That means that LIBXL_INIT_GC has to
become a statement too.  So instead, we make it so that it's used like this:
    libxl_gc gc;
    LIBXL_INIT_GC(gc,ctx);

In fact there are only a couple of callers now,
including GC_INIT which uses this trick:
    libxl_gc gc[1];
    LIBXL_INIT_GC(gc[0],ctx);

Signed-off-by: Ian Jackson <ian.jackson@eu.citrix.com>
Acked-by: Ian Campbell <ian.campbell@citrix.com>
Committed-by: Ian Jackson <Ian.Jackson@eu.citrix.com>

2 files changed, 8 insertions, 3 deletions

diff --git a/tools/libxl/libxl_internal.h b/tools/libxl/libxl_internal.h
index 288c03cbde..01d8ca8cbb 100644
--- a/tools/libxl/libxl_internal.h
+++ b/tools/libxl/libxl_internal.h
@@ -147,7 +147,12 @@ typedef struct {
     libxl_ctx *owner;
 } libxl__gc;
 
-#define LIBXL_INIT_GC(ctx) (libxl__gc){ .alloc_maxsize = 0, .alloc_ptrs = 0, .owner = ctx }
+#define LIBXL_INIT_GC(gc,ctx) do{               \
+        (gc).alloc_maxsize = 0;                 \
+        (gc).alloc_ptrs = 0;                    \
+        (gc).owner = (ctx);                     \
+    } while(0)
+
 static inline libxl_ctx *libxl__gc_owner(libxl__gc *gc)
 {
     return gc->owner;
@@ -725,7 +730,7 @@ libxl__device_model_version_running(libxl__gc *gc, uint32_t domid);
  * as a local variable.
  */
 
-#define GC_INIT(ctx)  libxl__gc gc[1] = { LIBXL_INIT_GC(ctx) }
+#define GC_INIT(ctx)  libxl__gc gc[1]; LIBXL_INIT_GC(gc[0],ctx)
 #define GC_FREE       libxl__free_all(gc)
 #define CTX           libxl__gc_owner(gc)
 
diff --git a/tools/libxl/libxl_qmp.c b/tools/libxl/libxl_qmp.c
index 1777e44ea4..3dfa43a366 100644
--- a/tools/libxl/libxl_qmp.c
+++ b/tools/libxl/libxl_qmp.c
@@ -513,7 +513,7 @@ static int qmp_send(libxl__qmp_handler *qmp,
 {
     char *buf = NULL;
     int rc = -1;
-    libxl__gc gc = LIBXL_INIT_GC(qmp->ctx);
+    libxl__gc gc; LIBXL_INIT_GC(gc,qmp->ctx);
 
     buf = qmp_send_prepare(&gc, qmp, cmd, args, callback, opaque, context);