xl/remus: cmdline switches and config vars to control network buffering

Add two members in libxl_domain_remus_info:
    netbuf: whether netbuf is enabled
    netbufscript: the path of the script which will be run to setup
                  and tear down the guest's interface.

Add cmdline switches to 'xl remus' command to enable or disable
network buffering and a domain-specific hotplug script to setup
network buffering.

Add a new config var 'remus.default.netbufscript' to xl.conf, that
allows the user to override the default global script used to
setup network buffering.

Note: Network buffering is enabled by default. Disabling network
buffering requires enabling unsafe mode.

Signed-off-by: Shriram Rajagopalan <rshriram@cs.ubc.ca>
Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
Reviewed-by: Wen Congyang <wency@cn.fujitsu.com>
Acked-by: Ian Jackson <ian.jackson@eu.citrix.com>
Acked-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>

docs/man/xl.conf.pod.5

@@ -105,6 +105,12 @@ Configures the default gateway device to set for virtual network devices.
 
 Default: C<None>
 
+=item B<remus.default.netbufscript="PATH">
+
+Configures the default script used by Remus to setup network buffering.
+
+Default: C</etc/xen/scripts/remus-netbuf-setup>
+
 =item B<output_format="json|sxp">
 
 Configures the default output format used by xl when printing "machine

docs/man/xl.pod.1

@@ -436,7 +436,7 @@ Enable Remus HA for domain. By default B<xl> relies on ssh as a transport
 mechanism between the two hosts.
 
 N.B: Remus support in xl is still in experimental (proof-of-concept) phase.
-     There is no support for network or disk buffering at the moment.
+     There is no support for disk buffering at the moment.
 
 B<OPTIONS>
 
@@ -460,6 +460,11 @@ 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<-N> I<netbufscript>
+
+Use <netbufscript> to setup network buffering instead of the
+default script (/etc/xen/scripts/remus-netbuf-setup).
+
 =item B<-F>
 
 Run Remus in unsafe mode. Use this option with caution as failover may
@@ -470,6 +475,10 @@ not work as intended.
 Replicate memory checkpoints to /dev/null (blackhole).
 Generally useful for debugging. Requires enabling unsafe mode.
 
+=item B<-n>
+
+Disable network output buffering. Requires enabling unsafe mode.
+
 =back
 
 =item B<pause> I<domain-id>

tools/libxl/libxl.c

@@ -807,13 +807,17 @@ int libxl_domain_remus_start(libxl_ctx *ctx, libxl_domain_remus_info *info,
     libxl_defbool_setdefault(&info->allow_unsafe, false);
     libxl_defbool_setdefault(&info->blackhole, false);
     libxl_defbool_setdefault(&info->compression, true);
+    libxl_defbool_setdefault(&info->netbuf, true);
 
     if (!libxl_defbool_val(info->allow_unsafe) &&
-        libxl_defbool_val(info->blackhole)) {
-        LOG(ERROR, "Unsafe mode must be enabled to replicate to /dev/null");
+        (libxl_defbool_val(info->blackhole) ||
+         !libxl_defbool_val(info->netbuf))) {
+        LOG(ERROR, "Unsafe mode must be enabled to replicate to /dev/null and "
+                   "disable network buffering");
         goto out;
     }
 
+
     GCNEW(dss);
     dss->ao = ao;
     dss->callback = remus_failover_cb;
@@ -830,11 +834,13 @@ int libxl_domain_remus_start(libxl_ctx *ctx, libxl_domain_remus_info *info,
     /* Convenience aliases */
     libxl__remus_devices_state *const rds = &dss->rds;
 
-    if (!libxl__netbuffer_enabled(gc)) {
-        LOG(ERROR, "Remus: No support for network buffering");
-        goto out;
+    if (libxl_defbool_val(info->netbuf)) {
+        if (!libxl__netbuffer_enabled(gc)) {
+            LOG(ERROR, "Remus: No support for network buffering");
+            goto out;
+        }
+        rds->device_kind_flags |= (1 << LIBXL__DEVICE_KIND_VIF);
     }
-    rds->device_kind_flags |= (1 << LIBXL__DEVICE_KIND_VIF);
     rds->device_kind_flags |= (1 << LIBXL__DEVICE_KIND_VBD);
 
     rds->ao = ao;

tools/libxl/libxl_netbuffer.c

@@ -41,6 +41,7 @@ int libxl__netbuffer_enabled(libxl__gc *gc)
 int init_subkind_nic(libxl__remus_devices_state *rds)
 {
     int rc, ret;
+    libxl__domain_suspend_state *dss = CONTAINER_OF(rds, *dss, rds);
 
     STATE_AO_GC(rds->ao);
 
@@ -68,8 +69,12 @@ int init_subkind_nic(libxl__remus_devices_state *rds)
         goto out;
     }
 
-    rds->netbufscript = GCSPRINTF("%s/remus-netbuf-setup",
-                                  libxl__xen_script_dir_path());
+    if (dss->remus->netbufscript) {
+        rds->netbufscript = libxl__strdup(gc, dss->remus->netbufscript);
+    } else {
+        rds->netbufscript = GCSPRINTF("%s/remus-netbuf-setup",
+                                      libxl__xen_script_dir_path());
+    }
 
     rc = 0;
 

tools/libxl/libxl_types.idl

@@ -614,6 +614,8 @@ libxl_domain_remus_info = Struct("domain_remus_info",[
     ("allow_unsafe", libxl_defbool),
     ("blackhole",    libxl_defbool),
     ("compression",  libxl_defbool),
+    ("netbuf",       libxl_defbool),
+    ("netbufscript", string),
     ])
 
 libxl_event_type = Enumeration("event_type", [

tools/libxl/xl.c

@@ -44,6 +44,7 @@ char *default_vifscript = NULL;
 char *default_bridge = NULL;
 char *default_gatewaydev = NULL;
 char *default_vifbackend = NULL;
+char *default_remus_netbufscript = NULL;
 enum output_format default_output_format = OUTPUT_FORMAT_JSON;
 int claim_mode = 1;
 bool progress_use_cr = 0;
@@ -176,6 +177,9 @@ static void parse_global_config(const char *configfile,
     if (!xlu_cfg_get_long (config, "claim_mode", &l, 0))
         claim_mode = l;
 
+    xlu_cfg_replace_string (config, "remus.default.netbufscript",
+        &default_remus_netbufscript, 0);
+
     xlu_cfg_destroy(config);
 }
 

tools/libxl/xl.h

@@ -171,6 +171,7 @@ extern char *default_vifscript;
 extern char *default_bridge;
 extern char *default_gatewaydev;
 extern char *default_vifbackend;
+extern char *default_remus_netbufscript;
 extern char *blkdev_start;
 
 enum output_format {

tools/libxl/xl_cmdimpl.c

@@ -7497,7 +7497,7 @@ int main_remus(int argc, char **argv)
     r_info.interval = 200;
     libxl_defbool_setdefault(&r_info.blackhole, false);
 
-    SWITCH_FOREACH_OPT(opt, "Fbui:s:e", NULL, "remus", 2) {
+    SWITCH_FOREACH_OPT(opt, "Fbuni:s:N:e", NULL, "remus", 2) {
     case 'i':
         r_info.interval = atoi(optarg);
         break;
@@ -7510,6 +7510,12 @@ int main_remus(int argc, char **argv)
     case 'u':
         libxl_defbool_set(&r_info.compression, false);
         break;
+    case 'n':
+        libxl_defbool_set(&r_info.netbuf, false);
+        break;
+    case 'N':
+        r_info.netbufscript = optarg;
+        break;
     case 's':
         ssh_command = optarg;
         break;
@@ -7521,6 +7527,9 @@ int main_remus(int argc, char **argv)
     domid = find_domain(argv[optind]);
     host = argv[optind + 1];
 
+    if (!r_info.netbufscript)
+        r_info.netbufscript = default_remus_netbufscript;
+
     if (libxl_defbool_val(r_info.blackhole)) {
         send_fd = open("/dev/null", O_RDWR, 0644);
         if (send_fd < 0) {
@@ -7558,13 +7567,19 @@ int main_remus(int argc, char **argv)
     /* Point of no return */
     rc = libxl_domain_remus_start(ctx, &r_info, domid, send_fd, recv_fd, 0);
 
-    /* If we are here, it means backup has failed/domain suspend failed.
-     * Try to resume the domain and exit gracefully.
+    /* check if the domain exists. User may have xl destroyed the
+     * domain to force failover
+     */
+    if (libxl_domain_info(ctx, 0, domid)) {
+        fprintf(stderr, "Remus: Primary domain has been destroyed.\n");
+        close(send_fd);
+        return 0;
+    }
+
+    /* If we are here, it means remus setup/domain suspend/backup has
+     * failed. Try to resume the domain and exit gracefully.
      * TODO: Split-Brain check.
      */
-    fprintf(stderr, "remus sender: libxl_domain_suspend failed"
-            " (rc=%d)\n", rc);
-
     if (rc == ERROR_GUEST_TIMEDOUT)
         fprintf(stderr, "Failed to suspend domain at primary.\n");
     else {

tools/libxl/xl_cmdtable.c

@@ -501,10 +501,13 @@ struct cmd_spec cmd_table[] = {
       "                        ssh <host> xl migrate-receive -r [-e]\n"
       "-e                      Do not wait in the background (on <host>) for the death\n"
       "                        of the domain.\n"
-      "-F                      Enable unsafe configurations [-b flags]. Use this option\n"
+      "-N <netbufscript>       Use netbufscript to setup network buffering instead of the\n"
+      "                        default script (/etc/xen/scripts/remus-netbuf-setup).\n"
+      "-F                      Enable unsafe configurations [-b|-n 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."
+      "                        Works only in unsafe mode.\n"
+      "-n                      Disable network output buffering. Works only in unsafe mode."
     },
 #endif
     { "devd",