[PATCH 16/19] libxl: suspend: Abolish usleeps in domain suspend wait

[Ian Jackson <ian.jackson@eu.citrix.com>]

Replace the use of a loop with usleep().

Instead, use a xenstore watch and an event system timeout.  xenstore
fires watches on @releaseDomain when a domain shuts down.

The logic which checks for the state of the domain is unchanged, and
not ideal, but we will leave that for the next patch.

There is not intended to be any semantic change, other than to make
the algorithm properly asynchronous and the consequential waiting on
xenstore, rather than polling.

Signed-off-by: Ian Jackson <Ian.Jackson@eu.citrix.com>
CC: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
CC: Ian Campbell <ian.campbell@citrix.com>
---
 tools/libxl/libxl_dom.c      |   80 ++++++++++++++++++++++++++++++------------
 tools/libxl/libxl_internal.h |    2 ++
 2 files changed, 60 insertions(+), 22 deletions(-)

diff --git a/tools/libxl/libxl_dom.c b/tools/libxl/libxl_dom.c
index dde7e33..6291115 100644
--- a/tools/libxl/libxl_dom.c
+++ b/tools/libxl/libxl_dom.c
@@ -1028,8 +1028,14 @@ static void domain_suspend_common_wait_guest(libxl__egc *egc,
                                              libxl__domain_suspend_state *dss);
 static void domain_suspend_common_guest_suspended(libxl__egc *egc,
                                          libxl__domain_suspend_state *dss);
+
 static void domain_suspend_common_pvcontrol_suspending(libxl__egc *egc,
       libxl__xswait_state *xswa, int rc, const char *state);
+static void suspend_common_wait_guest_watch(libxl__egc *egc,
+      libxl__ev_xswatch *xsw, const char *watch_path, const char *event_path);
+static void suspend_common_wait_guest_timeout(libxl__egc *egc,
+      libxl__ev_time *ev, const struct timeval *requested_abs);
+
 static void domain_suspend_common_failed(libxl__egc *egc,
                                          libxl__domain_suspend_state *dss);
 static void domain_suspend_common_done(libxl__egc *egc,
@@ -1175,36 +1181,59 @@ static void domain_suspend_common_wait_guest(libxl__egc *egc,
                                              libxl__domain_suspend_state *dss)
 {
     STATE_AO_GC(dss->ao);
+    int rc;
+
+    LOG(DEBUG, "wait for the guest to suspend");
+
+    rc = libxl__ev_xswatch_register(gc, &dss->guest_watch,
+                                    suspend_common_wait_guest_watch,
+                                    "@releaseDomain");
+    if (rc) goto err;
+
+    rc = libxl__ev_time_register_rel(gc, &dss->guest_timeout, 
+                                     suspend_common_wait_guest_timeout,
+                                     60*1000);
+    if (rc) goto err;
+    return;
+
+ err:
+    domain_suspend_common_failed(egc, dss);
+}
+
+static void suspend_common_wait_guest_watch(libxl__egc *egc,
+      libxl__ev_xswatch *xsw, const char *watch_path, const char *event_path)
+{
+    libxl__domain_suspend_state *dss =
+        CONTAINER_OF(xsw, *dss, guest_watch);
+    STATE_AO_GC(dss->ao);
+    xc_domaininfo_t info;
     int ret;
-    int watchdog;
 
     /* Convenience aliases */
     const uint32_t domid = dss->domid;
 
-    LOG(DEBUG, "wait for the guest to suspend");
-    watchdog = 60;
-    while (watchdog > 0) {
-        xc_domaininfo_t info;
-
-        usleep(100000);
-        ret = xc_domain_getinfolist(CTX->xch, domid, 1, &info);
-        if (ret == 1 && info.domain == domid &&
-            (info.flags & XEN_DOMINF_shutdown)) {
-            int shutdown_reason;
-
-            shutdown_reason = (info.flags >> XEN_DOMINF_shutdownshift)
-                & XEN_DOMINF_shutdownmask;
-            if (shutdown_reason == SHUTDOWN_suspend) {
-                LOG(DEBUG, "guest has suspended");
-                domain_suspend_common_guest_suspended(egc, dss);
-                return;
-            }
+    ret = xc_domain_getinfolist(CTX->xch, domid, 1, &info);
+    if (ret == 1 && info.domain == domid &&
+        (info.flags & XEN_DOMINF_shutdown)) {
+        int shutdown_reason;
+
+        shutdown_reason = (info.flags >> XEN_DOMINF_shutdownshift)
+            & XEN_DOMINF_shutdownmask;
+        if (shutdown_reason == SHUTDOWN_suspend) {
+            LOG(DEBUG, "guest has suspended");
+            domain_suspend_common_guest_suspended(egc, dss);
+            return;
         }
-
-        watchdog--;
     }
+    /* otherwise, keep waiting */
+}
 
-    LOG(ERROR, "guest did not suspend");
+static void suspend_common_wait_guest_timeout(libxl__egc *egc,
+      libxl__ev_time *ev, const struct timeval *requested_abs)
+{
+    libxl__domain_suspend_state *dss = CONTAINER_OF(ev, *dss, guest_timeout);
+    STATE_AO_GC(dss->ao);
+    LOG(ERROR, "guest did not suspend, timed out");
     domain_suspend_common_failed(egc, dss);
 }
 
@@ -1214,6 +1243,9 @@ static void domain_suspend_common_guest_suspended(libxl__egc *egc,
     STATE_AO_GC(dss->ao);
     int ret;
 
+    libxl__ev_xswatch_deregister(gc, &dss->guest_watch);
+    libxl__ev_time_deregister(gc, &dss->guest_timeout);
+
     if (dss->hvm) {
         ret = libxl__domain_suspend_device_model(gc, dss);
         if (ret) {
@@ -1237,6 +1269,8 @@ static void domain_suspend_common_done(libxl__egc *egc,
 {
     EGC_GC;
     assert(!libxl__xswait_inuse(&dss->pvcontrol));
+    libxl__ev_xswatch_deregister(gc, &dss->guest_watch);
+    libxl__ev_time_deregister(gc, &dss->guest_timeout);
     dss->callback_common_done(egc, dss, ok);
 }
 
@@ -1423,6 +1457,8 @@ void libxl__domain_suspend(libxl__egc *egc, libxl__domain_suspend_state *dss)
 
     logdirty_init(&dss->logdirty);
     libxl__xswait_init(&dss->pvcontrol);
+    libxl__ev_xswatch_init(&dss->guest_watch);
+    libxl__ev_time_init(&dss->guest_timeout);
 
     switch (type) {
     case LIBXL_DOMAIN_TYPE_HVM: {
diff --git a/tools/libxl/libxl_internal.h b/tools/libxl/libxl_internal.h
index 5ac02cb..7ad15b5 100644
--- a/tools/libxl/libxl_internal.h
+++ b/tools/libxl/libxl_internal.h
@@ -2423,6 +2423,8 @@ struct libxl__domain_suspend_state {
     int xcflags;
     int guest_responded;
     libxl__xswait_state pvcontrol;
+    libxl__ev_xswatch guest_watch;
+    libxl__ev_time guest_timeout;
     const char *dm_savefile;
     int interval; /* checkpoint interval (for Remus) */
     libxl__save_helper_state shs;
-- 
1.7.10.4