[PATCH 7/8] xl: generate a new random VM generation ID if requested

[David Vrabel <david.vrabel@citrix.com>]

If the "generation_id" option is set in the domain configuration,
generate and set a new random VM generation ID every time a domain is
created or restored.

xl lacks the infrastructure to fully track the lifecycle of VM images
as they are snapshotted and cloned (etc) so always using a new ID is
the safe option and ensures that a new one will be used where it matters.

Signed-off-by: David Vrabel <david.vrabel@citrix.com>
---
 docs/man/xl.cfg.pod.5    |   14 ++++++++++++++
 tools/libxl/xl_cmdimpl.c |    9 +++++++++
 2 files changed, 23 insertions(+)

diff --git a/docs/man/xl.cfg.pod.5 b/docs/man/xl.cfg.pod.5
index c087cbc..6176e2f 100644
--- a/docs/man/xl.cfg.pod.5
+++ b/docs/man/xl.cfg.pod.5
@@ -936,6 +936,20 @@ number of vendor defined SMBIOS structures (type 128 - 255). Since SMBIOS
 structures do not present their overall size, each entry in the file must be
 preceded by a 32b integer indicating the size of the next structure.
 
+=item B<generation_id=BOOLEAN>
+
+Provide a VM generation ID to the guest.
+
+The VM generation ID as a 128-bit random number that a guest may use
+to determine if the guest has been restored from an earlier snapshot,
+or cloned.
+
+This is required for Microsoft Windows Server 2012 (and later) domain
+controllers.
+
+See also "Virtual Machine Generation ID" by Microsoft
+(http://www.microsoft.com/en-us/download/details.aspx?id=30707).
+
 =back 
 
 =head3 Guest Virtual Time Controls
diff --git a/tools/libxl/xl_cmdimpl.c b/tools/libxl/xl_cmdimpl.c
index 64a1c77..ad50e21 100644
--- a/tools/libxl/xl_cmdimpl.c
+++ b/tools/libxl/xl_cmdimpl.c
@@ -1021,6 +1021,15 @@ static void parse_config_data(const char *config_source,
                                &b_info->u.hvm.smbios_firmware, 0);
         xlu_cfg_replace_string(config, "acpi_firmware",
                                &b_info->u.hvm.acpi_firmware, 0);
+
+        /* Generate and set a new random VM Generation ID? */
+        if (!xlu_cfg_get_long(config, "generation_id", &l, 0)) {
+            e = libxl_ms_vm_genid_generate(ctx, &b_info->u.hvm.ms_vm_genid);
+            if (e) {
+                fprintf(stderr, "ERROR: no random numbers available for \"generation_id\"\n");
+                exit(1);
+            }
+        }
         break;
     case LIBXL_DOMAIN_TYPE_PV:
     {
-- 
1.7.10.4