[PATCH for-4.5 v20 08/12] xl/remus: cmdline switch to explicitly enable unsafe configurations

[Yang Hongyang <yanghy@cn.fujitsu.com>]

By default, network buffering and disk replication are enabled;
checkpoints are replicated to another standby VM.

This patch allows the user to disable any of these features by
explicitly specifying a 'run in unsafe mode' switch when invoking
the 'xl remus' command.  While running Remus in an unsafe mode
makes little sense under normal circumstances, it is useful to be
able to disable one or more features mentioned above for
testing/debugging/profiling purposes.

Unless this option is enabled, it will not be possible to
replicate memory checkpoints to /dev/null (blackhole replication),
disable network buffering or disk replication.

As a starter, the use of blackhole replication now requires that
the unsafe mode be enabled. Subsequent patches will add support
for disabling network buffering and disk replication in a similar
manner.

Signed-off-by: Yang Hongyang <yanghy@cn.fujitsu.com>
Signed-off-by: Shriram Rajagopalan <rshriram@cs.ubc.ca>
---
 docs/man/xl.pod.1           | 15 ++++++++++-----
 tools/libxl/libxl.c         |  7 +++++++
 tools/libxl/libxl_types.idl |  1 +
 tools/libxl/xl_cmdimpl.c    |  5 ++++-
 tools/libxl/xl_cmdtable.c   |  7 +++++--
 5 files changed, 27 insertions(+), 8 deletions(-)

diff --git a/docs/man/xl.pod.1 b/docs/man/xl.pod.1
index f9bc812..2ae3007 100644
--- a/docs/man/xl.pod.1
+++ b/docs/man/xl.pod.1
@@ -446,11 +446,6 @@ B<OPTIONS>
 
 Checkpoint domain memory every MS milliseconds (default 200ms).
 
-=item B<-b>
-
-Replicate memory checkpoints to /dev/null (blackhole).
-Generally useful for debugging.
-
 =item B<-u>
 
 Disable memory checkpoint compression.
@@ -465,6 +460,16 @@ If empty, run <host> instead of ssh <host> xl migrate-receive -r [-e].
 On the new host, do not wait in the background (on <host>) for the death
 of the domain. See the corresponding option of the I<create> subcommand.
 
+=item B<-F>
+
+Run Remus in unsafe mode. Use this option with caution as failover may
+not work as intended.
+
+=item B<-b>
+
+Replicate memory checkpoints to /dev/null (blackhole).
+Generally useful for debugging. Requires enabling unsafe mode.
+
 =back
 
 =item B<pause> I<domain-id>
diff --git a/tools/libxl/libxl.c b/tools/libxl/libxl.c
index 9e0a800..cc5c3ac 100644
--- a/tools/libxl/libxl.c
+++ b/tools/libxl/libxl.c
@@ -804,9 +804,16 @@ int libxl_domain_remus_start(libxl_ctx *ctx, libxl_domain_remus_info *info,
         goto out;
     }
 
+    libxl_defbool_setdefault(&info->unsafe, false);
     libxl_defbool_setdefault(&info->blackhole, false);
     libxl_defbool_setdefault(&info->compression, true);
 
+    if (!libxl_defbool_val(info->unsafe) &&
+        libxl_defbool_val(info->blackhole)) {
+        LOG(ERROR, "Unsafe mode must be enabled to replicate to /dev/null");
+        goto out;
+    }
+
     GCNEW(dss);
     dss->ao = ao;
     dss->callback = remus_failover_cb;
diff --git a/tools/libxl/libxl_types.idl b/tools/libxl/libxl_types.idl
index 16e374f..348f794 100644
--- a/tools/libxl/libxl_types.idl
+++ b/tools/libxl/libxl_types.idl
@@ -611,6 +611,7 @@ libxl_sched_credit_params = Struct("sched_credit_params", [
 
 libxl_domain_remus_info = Struct("domain_remus_info",[
     ("interval",     integer),
+    ("unsafe",       libxl_defbool),
     ("blackhole",    libxl_defbool),
     ("compression",  libxl_defbool),
     ])
diff --git a/tools/libxl/xl_cmdimpl.c b/tools/libxl/xl_cmdimpl.c
index e9e8900..3463d45 100644
--- a/tools/libxl/xl_cmdimpl.c
+++ b/tools/libxl/xl_cmdimpl.c
@@ -7497,10 +7497,13 @@ int main_remus(int argc, char **argv)
     r_info.interval = 200;
     libxl_defbool_setdefault(&r_info.blackhole, false);
 
-    SWITCH_FOREACH_OPT(opt, "bui:s:e", NULL, "remus", 2) {
+    SWITCH_FOREACH_OPT(opt, "Fbui:s:e", NULL, "remus", 2) {
     case 'i':
         r_info.interval = atoi(optarg);
         break;
+    case 'F':
+        libxl_defbool_set(&r_info.unsafe, true);
+        break;
     case 'b':
         libxl_defbool_set(&r_info.blackhole, true);
         break;
diff --git a/tools/libxl/xl_cmdtable.c b/tools/libxl/xl_cmdtable.c
index dd15947..08f3c90 100644
--- a/tools/libxl/xl_cmdtable.c
+++ b/tools/libxl/xl_cmdtable.c
@@ -495,13 +495,16 @@ struct cmd_spec cmd_table[] = {
       "Enable Remus HA for domain",
       "[options] <Domain> [<host>]",
       "-i MS                   Checkpoint domain memory every MS milliseconds (def. 200ms).\n"
-      "-b                      Replicate memory checkpoints to /dev/null (blackhole)\n"
       "-u                      Disable memory checkpoint compression.\n"
       "-s <sshcommand>         Use <sshcommand> instead of ssh.  String will be passed\n"
       "                        to sh. If empty, run <host> instead of \n"
       "                        ssh <host> xl migrate-receive -r [-e]\n"
       "-e                      Do not wait in the background (on <host>) for the death\n"
-      "                        of the domain."
+      "                        of the domain.\n"
+      "-F                      Enable unsafe configurations [-b flags]. Use this option\n"
+      "                        with caution as failover may not work as intended.\n"
+      "-b                      Replicate memory checkpoints to /dev/null (blackhole).\n"
+      "                        Works only in unsafe mode."
     },
 #endif
     { "devd",
-- 
1.9.1