[PATCH 2/2] expert_mode: Add a new configuration option for expert users.

[Konrad Rzeszutek Wilk <konrad@kernel.org>]

This could also be called 'seatbelt' option.

libxl has a variety of checks where it will fail out an operation
unless the user has provided an --force (or --ignore) parameter.
Currently one such check is for the 'vcpu-set' command which
will error out if the count of virtual cpus is greater than the
physical cpus. This parameter will ignore such checks and allow
the user to do the operations without the need for override flags.

Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
---
 docs/man/xl.conf.pod.5   |   24 ++++++++++++++++++++++++
 tools/examples/xl.conf   |    6 ++++++
 tools/libxl/xl.c         |    4 ++++
 tools/libxl/xl.h         |    1 +
 tools/libxl/xl_cmdimpl.c |    6 ++++++
 5 files changed, 41 insertions(+), 0 deletions(-)

diff --git a/docs/man/xl.conf.pod.5 b/docs/man/xl.conf.pod.5
index 125f786..ed67472 100644
--- a/docs/man/xl.conf.pod.5
+++ b/docs/man/xl.conf.pod.5
@@ -158,6 +158,30 @@ massively huge guests).
 
 =back
 
+=item B<expert_mode=BOOLEAN>
+
+Do not act on host performed checks that might lead to performance
+degradations. Currently checks are made for following operations:
+ - C<vcpu-set> - if the number of VCPUs set for a guest is higher than the
+   physical count the operation will error out.
+
+
+Default: C<1>
+
+=over 4
+
+=item C<0>
+
+The checks are active and the operation will fail if the checks
+are triggered.
+
+=item C<1>
+
+The checks are active but will be ignored and the operations
+will commence.
+
+=back
+
 =back
 
 =head1 SEE ALSO
diff --git a/tools/examples/xl.conf b/tools/examples/xl.conf
index a80b8e7..6f27d67 100644
--- a/tools/examples/xl.conf
+++ b/tools/examples/xl.conf
@@ -33,3 +33,9 @@
 # (which can take a long time to find out if launching huge guests).
 # see xl.conf(5) for details.
 claim_mode=1
+
+# The user knows what to do. Currently enabling this option will mean that:
+#  vcpu-set won't check the physical CPU count - which means the guest can
+#           over-subscribe (more vCPUS than pCPUS).
+# see xl.conf(5) for details.
+expert_mode=1
diff --git a/tools/libxl/xl.c b/tools/libxl/xl.c
index 1ce820c..4063b7c 100644
--- a/tools/libxl/xl.c
+++ b/tools/libxl/xl.c
@@ -47,6 +47,7 @@ char *default_bridge = NULL;
 char *default_gatewaydev = NULL;
 enum output_format default_output_format = OUTPUT_FORMAT_JSON;
 int claim_mode = 0;
+int expert_mode = 0;
 
 static xentoollog_level minmsglevel = XTL_PROGRESS;
 
@@ -173,6 +174,9 @@ static void parse_global_config(const char *configfile,
     if (!xlu_cfg_get_long (config, "claim_mode", &l, 0))
         claim_mode = l;
 
+    if (!xlu_cfg_get_long (config, "expert_mode", &l, 0))
+        expert_mode = l;
+
     xlu_cfg_destroy(config);
 }
 
diff --git a/tools/libxl/xl.h b/tools/libxl/xl.h
index 5ad3e17..51b7008 100644
--- a/tools/libxl/xl.h
+++ b/tools/libxl/xl.h
@@ -147,6 +147,7 @@ extern int autoballoon;
 extern int run_hotplug_scripts;
 extern int dryrun_only;
 extern int claim_mode;
+extern int expert_mode;
 extern char *lockfile;
 extern char *default_vifscript;
 extern char *default_bridge;
diff --git a/tools/libxl/xl_cmdimpl.c b/tools/libxl/xl_cmdimpl.c
index 8a478ba..a55c66a 100644
--- a/tools/libxl/xl_cmdimpl.c
+++ b/tools/libxl/xl_cmdimpl.c
@@ -4560,6 +4560,12 @@ int main_vcpuset(int argc, char **argv)
         break;
     }
 
+    /*
+     * No seatbelts for the user.
+     */
+    if (expert_mode)
+        check_host = 0;
+
     vcpuset(find_domain(argv[optind]), argv[optind + 1], check_host);
     return 0;
 }
-- 
1.7.7.6