[PATCH 6/6] 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 |   14 ++++++++++++++
 2 files changed, 28 insertions(+)

diff --git a/docs/man/xl.cfg.pod.5 b/docs/man/xl.cfg.pod.5
index 0ca37bc..0ec0386 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 5195914..843ef14 100644
--- a/tools/libxl/xl_cmdimpl.c
+++ b/tools/libxl/xl_cmdimpl.c
@@ -155,6 +155,7 @@ struct domain_create {
     const char *restore_file;
     int migrate_fd; /* -1 means none */
     char **migration_domname_r; /* from malloc */
+    bool set_genid;
 };
 
 
@@ -1058,6 +1059,8 @@ 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);
+        if (dom_info && !xlu_cfg_get_long(config, "generation_id", &l, 0))
+            dom_info->set_genid = !!l;
         break;
     case LIBXL_DOMAIN_TYPE_PV:
     {
@@ -2254,6 +2257,17 @@ start:
     if ( ret )
         goto error_out;
 
+    /* Generate and set a new random VM Generation ID? */
+    if (dom_info->set_genid) {
+        libxl_uuid genid;
+
+        libxl_uuid_generate(&genid);
+
+        ret = libxl_vm_generation_id_set(ctx, domid, &genid);
+        if (ret)
+            goto error_out;
+    }
+
     /* If single vcpu to pcpu mapping was requested, honour it */
     if (vcpu_to_pcpu) {
         libxl_bitmap vcpu_cpumap;
-- 
1.7.10.4