[Xen-devel] [PATCH v19 08/12] xl/remus: cmdline switch to explicitly enable unsafe configurations

[Yang Hongyang <yanghy@xxxxxxxxxxxxxx>]

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@xxxxxxxxxxxxxx>
Signed-off-by: Shriram Rajagopalan <rshriram@xxxxxxxxx>
---
 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 9d1c2a5..a1a254f 100644
--- a/docs/man/xl.pod.1
+++ b/docs/man/xl.pod.1
@@ -441,11 +441,6 @@ 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.
@@ -460,6 +455,16 @@ 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 5c9d41b..543c48d 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 f3274d3..0211e51 100644
--- a/tools/libxl/libxl_types.idl
+++ b/tools/libxl/libxl_types.idl
@@ -593,6 +593,7 @@ 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 001596a..7b6e835 100644
--- a/tools/libxl/xl_cmdimpl.c
+++ b/tools/libxl/xl_cmdimpl.c
@@ -7286,10 +7286,13 @@ 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 7b7fa92..637ba43 100644
--- a/tools/libxl/xl_cmdtable.c
+++ b/tools/libxl/xl_cmdtable.c
@@ -485,13 +485,16 @@ 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


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