libxl: disable autoballooning

Xen 4.12 introduced a CONFIG_DOM0_MEM option, which our xen package uses
to configure dom0 with a sensible initial memory value and disables
autoballooning. This patch changes libvirt to also disable autoballooning
by default. It can only be enabled with the 'autoballoon' setting in
libxl.conf. See jsc#SLE-3059 for more details.

Index: libvirt-5.6.0/src/libxl/libxl.conf
===================================================================
--- libvirt-5.6.0.orig/src/libxl/libxl.conf
+++ libvirt-5.6.0/src/libxl/libxl.conf
@@ -4,12 +4,11 @@
 
 # Enable autoballooning of domain0
 #
-# By default, autoballooning of domain0 is enabled unless its memory
-# is already limited with Xen's "dom0_mem=" parameter, in which case
-# autoballooning is disabled.  Override the default behavior with the
-# autoballoon setting.
+# By default, autoballooning of domain0 is disabled. Traditionally it
+# could also be disabled by using Xen's "dom0_mem=" parameter. Set to
+# 1 to enable autoballooning.
 #
-#autoballoon = 1
+#autoballoon = 0
 
 
 # In order to prevent accidentally starting two domains that
Index: libvirt-5.6.0/src/libxl/libxl_conf.c
===================================================================
--- libvirt-5.6.0.orig/src/libxl/libxl_conf.c
+++ libvirt-5.6.0/src/libxl/libxl_conf.c
@@ -22,7 +22,6 @@
 
 #include <config.h>
 
-#include <regex.h>
 #include <libxl.h>
 #include <sys/types.h>
 #include <sys/socket.h>
@@ -1763,14 +1762,12 @@ libxlMakeBuildInfoVfb(virPortAllocatorRa
 /*
  * Get domain0 autoballoon configuration.  Honor user-specified
  * setting in libxl.conf first.  If not specified, autoballooning
- * is disabled when domain0's memory is set with 'dom0_mem'.
- * Otherwise autoballooning is enabled.
+ * is disabled.
  */
 static int
 libxlGetAutoballoonConf(libxlDriverConfigPtr cfg,
                         virConfPtr conf)
 {
-    regex_t regex;
     int res;
 
     res = virConfGetValueBool(conf, "autoballoon", &cfg->autoballoon);
@@ -1779,21 +1776,8 @@ libxlGetAutoballoonConf(libxlDriverConfi
     else if (res == 1)
         return 0;
 
-    if ((res = regcomp(&regex,
-                      "(^| )dom0_mem=((|min:|max:)[0-9]+[bBkKmMgG]?,?)+($| )",
-                       REG_NOSUB | REG_EXTENDED)) != 0) {
-        char error[100];
-        regerror(res, &regex, error, sizeof(error));
-        virReportError(VIR_ERR_INTERNAL_ERROR,
-                       _("Failed to compile regex %s"),
-                       error);
-
-        return -1;
-    }
-
-    res = regexec(&regex, cfg->verInfo->commandline, 0, NULL, 0);
-    regfree(&regex);
-    cfg->autoballoon = res == REG_NOMATCH;
+    /* make it explicit */
+    cfg->autoballoon = 0;
     return 0;
 }