[Xen-devel] [PATCH v18 07/11] 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         |  5 +++++
 tools/libxl/libxl_types.idl |  1 +
 tools/libxl/xl_cmdimpl.c    | 11 ++++++++++-
 tools/libxl/xl_cmdtable.c   |  7 +++++--
 5 files changed, 31 insertions(+), 8 deletions(-)

diff --git a/docs/man/xl.pod.1 b/docs/man/xl.pod.1
index 30bd4bf..3aedead 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 021d77c..6e488ca 100644
--- a/tools/libxl/libxl.c
+++ b/tools/libxl/libxl.c
@@ -797,6 +797,11 @@ int libxl_domain_remus_start(libxl_ctx *ctx, 
libxl_domain_remus_info *info,
     libxl__domain_suspend_state *dss;
     int rc;
 
+    if (!info->unsafe && info->blackhole) {
+        LOG(ERROR, "Unsafe mode must be enabled to replicate to /dev/null");
+        goto out;
+    }
+
     libxl_domain_type type = libxl__domain_type(gc, domid);
     if (type == LIBXL_DOMAIN_TYPE_INVALID) {
         rc = ERROR_FAIL;
diff --git a/tools/libxl/libxl_types.idl b/tools/libxl/libxl_types.idl
index 25bd8f3..f4cff51 100644
--- a/tools/libxl/libxl_types.idl
+++ b/tools/libxl/libxl_types.idl
@@ -588,6 +588,7 @@ libxl_sched_credit_params = Struct("sched_credit_params", [
 
 libxl_domain_remus_info = Struct("domain_remus_info",[
     ("interval",     integer),
+    ("unsafe",       bool),
     ("blackhole",    bool),
     ("compression",  bool),
     ])
diff --git a/tools/libxl/xl_cmdimpl.c b/tools/libxl/xl_cmdimpl.c
index 01bce2f..3234d45 100644
--- a/tools/libxl/xl_cmdimpl.c
+++ b/tools/libxl/xl_cmdimpl.c
@@ -7175,13 +7175,17 @@ int main_remus(int argc, char **argv)
     memset(&r_info, 0, sizeof(libxl_domain_remus_info));
     /* Defaults */
     r_info.interval = 200;
+    r_info.unsafe = 0;
     r_info.blackhole = 0;
     r_info.compression = 1;
 
-    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':
+        r_info.unsafe = 1;
+        break;
     case 'b':
         r_info.blackhole = 1;
         break;
@@ -7196,6 +7200,11 @@ int main_remus(int argc, char **argv)
         break;
     }
 
+    if (!r_info.unsafe && r_info.blackhole) {
+        perror("Unsafe mode must be enabled to replicate to /dev/null");
+        exit(-1);
+    }
+
     domid = find_domain(argv[optind]);
     host = argv[optind + 1];
 
diff --git a/tools/libxl/xl_cmdtable.c b/tools/libxl/xl_cmdtable.c
index 4279b9f..1e24f1d 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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