tools: libxl: do not set the PoD target on ARM

ARM does not implemented PoD and so returns ENOSYS from XENMEM_set_pod_target.

The correct solution here would be to check for ENOSYS in libxl, unfortunately
xc_domain_set_pod_target suffers from the same broken error reporting as the
rest of libxc and throws away the errno.

So for now conditionally define xc_domain_set_pod_target to return success
(which is what PoD does if nothing needs doing). xc_domain_get_pod_target sets
errno==-1 and returns -1, which matches the broken error reporting of the
existing function. It appears to have no in tree callers in any case.

The conditional should be removed once libxc has been fixed.

This makes ballooning (xl mem-set) work for ARM domains.

Signed-off-by: Ian Campbell <ian.campbell@citrix.com>
Acked-by: Ian Jackson <ian.jackson@eu.citrix.com>
Acked-by: Julien Grall <julien.grall@linaro.org>
Cc: george.dunlap@citrix.com

tools/libxc/xc_domain.c

@@ -986,6 +986,12 @@ out:
     return rc;
 }
 
+/* Currently only implemented on x86. This cannot be handled in the
+ * caller, e.g. by looking for errno==ENOSYS because of the broken
+ * error reporting style. Once this is fixed then this condition can
+ * be removed.
+ */
+#if defined(__i386__)||defined(__x86_64__)
 static int xc_domain_pod_target(xc_interface *xch,
                                 int op,
                                 uint32_t domid,
@@ -1055,6 +1061,28 @@ int xc_domain_get_pod_target(xc_interface *xch,
                                 pod_cache_pages,
                                 pod_entries);
 }
+#else
+int xc_domain_set_pod_target(xc_interface *xch,
+                             uint32_t domid,
+                             uint64_t target_pages,
+                             uint64_t *tot_pages,
+                             uint64_t *pod_cache_pages,
+                             uint64_t *pod_entries)
+{
+    return 0;
+}
+int xc_domain_get_pod_target(xc_interface *xch,
+                             uint32_t domid,
+                             uint64_t *tot_pages,
+                             uint64_t *pod_cache_pages,
+                             uint64_t *pod_entries)
+{
+    /* On x86 (above) xc_domain_pod_target will incorrectly return -1
+     * with errno==-1 on error. Do the same for least surprise. */
+    errno = -1;
+    return -1;
+}
+#endif
 
 int xc_domain_max_vcpus(xc_interface *xch, uint32_t domid, unsigned int max)
 {