libxl: suspend: New libxl__domain_pvcontrol_xspath

Factor out the pv control node xenstore path calculation into
libxl__domain_pvcontrol_xspath.

This xs path calculation was open coded in
libxl__domain_pvcontrol_read and _write.  This is undesirable because
it duplicates the code and because it makes the path inaccessible to
other parts of libxl (which are soon going to want it).

No functional change.

Signed-off-by: Ian Jackson <Ian.Jackson@eu.citrix.com>
CC: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
Acked-by: Ian Campbell <ian.campbell@citrix.com>

tools/libxl/libxl.c

@@ -894,17 +894,23 @@ int libxl__domain_pvcontrol_available(libxl__gc *gc, uint32_t domid)
     return !!pvdriver;
 }
 
-char * libxl__domain_pvcontrol_read(libxl__gc *gc, xs_transaction_t t,
-                                    uint32_t domid)
+const char *libxl__domain_pvcontrol_xspath(libxl__gc *gc, uint32_t domid)
 {
-    const char *shutdown_path;
     const char *dom_path;
 
     dom_path = libxl__xs_get_dompath(gc, domid);
     if (!dom_path)
         return NULL;
 
-    shutdown_path = libxl__sprintf(gc, "%s/control/shutdown", dom_path);
+    return GCSPRINTF("%s/control/shutdown", dom_path);
+}
+
+char * libxl__domain_pvcontrol_read(libxl__gc *gc, xs_transaction_t t,
+                                    uint32_t domid)
+{
+    const char *shutdown_path;
+
+    shutdown_path = libxl__domain_pvcontrol_xspath(gc, domid);
     if (!shutdown_path)
         return NULL;
 
@@ -915,13 +921,8 @@ int libxl__domain_pvcontrol_write(libxl__gc *gc, xs_transaction_t t,
                                   uint32_t domid, const char *cmd)
 {
     const char *shutdown_path;
-    const char *dom_path;
 
-    dom_path = libxl__xs_get_dompath(gc, domid);
-    if (!dom_path)
-        return ERROR_FAIL;
-
-    shutdown_path = libxl__sprintf(gc, "%s/control/shutdown", dom_path);
+    shutdown_path = libxl__domain_pvcontrol_xspath(gc, domid);
     if (!shutdown_path)
         return ERROR_FAIL;
 

tools/libxl/libxl_internal.h

@@ -999,6 +999,7 @@ _hidden int libxl__domain_resume(libxl__gc *gc, uint32_t domid,
 /* returns 0 or 1, or a libxl error code */
 _hidden int libxl__domain_pvcontrol_available(libxl__gc *gc, uint32_t domid);
 
+_hidden const char *libxl__domain_pvcontrol_xspath(libxl__gc*, uint32_t domid);
 _hidden char * libxl__domain_pvcontrol_read(libxl__gc *gc,
                                             xs_transaction_t t, uint32_t domid);
 _hidden int libxl__domain_pvcontrol_write(libxl__gc *gc, xs_transaction_t t,