xl.conf: introduce 'domid_policy'

This patch adds a new global 'domid_policy' configuration option to decide
how domain id values are allocated for new domains. It may be set to one of
two values:

"xen", the default value, will cause an invalid domid value to be passed
to do_domain_create() preserving the existing behaviour of having Xen
choose the domid value during domain_create().

"random" will cause the special RANDOM_DOMID value to be passed to
do_domain_create() such that libxl__domain_make() will select a random
domid value.

Signed-off-by: Paul Durrant <pdurrant@amazon.com>
Acked-by: Ian Jackson <ian.jackson@eu.citrix.com>

docs/man/xl.conf.5.pod

@@ -45,6 +45,16 @@ The semantics of each C<KEY> defines which form of C<VALUE> is required.
 
 =over 4
 
+=item B<domid_policy="xen"|"random">
+
+Determines how domain-id is set when creating a new domain.
+
+If set to "xen" then the hypervisor will allocate new domain-id values on a sequential basis.
+
+If set to "random" then a random domain-id value will be chosen.
+
+Default: "xen"
+
 =item B<autoballoon="off"|"on"|"auto">
 
 If set to "on" then C<xl> will automatically reduce the amount of

tools/examples/xl.conf

@@ -1,5 +1,9 @@
 ## Global XL config file ##
 
+# Set domain-id policy. "xen" means that the hypervisor will choose the
+# id of a new domain. "random" means that a random value will be chosen.
+#domid_policy="xen"
+
 # Control whether dom0 is ballooned down when xen doesn't have enough
 # free memory to create a domain.  "auto" means only balloon if dom0
 # starts with all the host's memory.

tools/xl/xl.c

@@ -54,6 +54,7 @@ int claim_mode = 1;
 bool progress_use_cr = 0;
 int max_grant_frames = -1;
 int max_maptrack_frames = -1;
+libxl_domid domid_policy = INVALID_DOMID;
 
 xentoollog_level minmsglevel = minmsglevel_default;
 
@@ -228,6 +229,15 @@ static void parse_global_config(const char *configfile,
     else
         libxl_bitmap_set_any(&global_pv_affinity_mask);
 
+    if (!xlu_cfg_get_string (config, "domid_policy", &buf, 0)) {
+        if (!strcmp(buf, "xen"))
+            domid_policy = INVALID_DOMID;
+        else if (!strcmp(buf, "random"))
+            domid_policy = RANDOM_DOMID;
+        else
+            fprintf(stderr, "invalid domid_policy option");
+    }
+
     xlu_cfg_destroy(config);
 }
 

tools/xl/xl.h

@@ -283,6 +283,7 @@ extern int max_maptrack_frames;
 extern libxl_bitmap global_vm_affinity_mask;
 extern libxl_bitmap global_hvm_affinity_mask;
 extern libxl_bitmap global_pv_affinity_mask;
+extern libxl_domid domid_policy;
 
 enum output_format {
     OUTPUT_FORMAT_JSON,

tools/xl/xl_vmcontrol.c

@@ -899,6 +899,8 @@ start:
         autoconnect_console_how = 0;
     }
 
+    d_config.c_info.domid = domid_policy;
+
     if ( restoring ) {
         libxl_domain_restore_params params;