[PATCH 12/29] libxl: events: Permit timeouts to signal cancellation

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

The callback functions provided by users must take an rc value.  This
rc value can be ERROR_TIMEDOUT or ERROR_CANCELLED.

Users of xswait are now expected to deal correctly with
ERROR_CANCELLED.  If they experience this, it hasn't been logged.
And the caller won't log it either since it's not TIMEDOUT.
Luckily this is correct, so we can just change the doc comment.

Currently nothing generates ERROR_CANCELLED; in particular the
timeouts cannot in fact signal cancellation.

There should be no publicly visible change except that some error
returns from libxl will change from ERROR_FAIL to ERROR_TIMEDOUT, and
some changes to debugging messages.

Signed-off-by: Ian Jackson <Ian.Jackson@eu.citrix.com>
---
 tools/libxl/libxl_aoutils.c        |   11 ++++++++---
 tools/libxl/libxl_device.c         |    8 +++++---
 tools/libxl/libxl_dom.c            |   29 ++++++++++++++++++++---------
 tools/libxl/libxl_event.c          |    8 ++++----
 tools/libxl/libxl_internal.h       |   12 +++++++-----
 tools/libxl/libxl_test_timedereg.c |    8 +++++---
 6 files changed, 49 insertions(+), 27 deletions(-)

diff --git a/tools/libxl/libxl_aoutils.c b/tools/libxl/libxl_aoutils.c
index 891cdb8..0b6d750 100644
--- a/tools/libxl/libxl_aoutils.c
+++ b/tools/libxl/libxl_aoutils.c
@@ -80,12 +80,13 @@ void xswait_xswatch_callback(libxl__egc *egc, libxl__ev_xswatch *xsw,
 }
 
 void xswait_timeout_callback(libxl__egc *egc, libxl__ev_time *ev,
-                             const struct timeval *requested_abs)
+                             const struct timeval *requested_abs,
+                             int rc)
 {
     EGC_GC;
     libxl__xswait_state *xswa = CONTAINER_OF(ev, *xswa, time_ev);
     LOG(DEBUG, "%s: xswait timeout (path=%s)", xswa->what, xswa->path);
-    xswait_report_error(egc, xswa, ERROR_TIMEDOUT);
+    xswait_report_error(egc, xswa, rc);
 }
 
 static void xswait_report_error(libxl__egc *egc, libxl__xswait_state *xswa,
@@ -455,11 +456,15 @@ int libxl__openptys(libxl__openpty_state *op,
 
 static void async_exec_timeout(libxl__egc *egc,
                                libxl__ev_time *ev,
-                               const struct timeval *requested_abs)
+                               const struct timeval *requested_abs,
+                               int rc)
 {
     libxl__async_exec_state *aes = CONTAINER_OF(ev, *aes, time);
     STATE_AO_GC(aes->ao);
 
+    if (!aes->rc)
+        aes->rc = rc;
+
     libxl__ev_time_deregister(gc, &aes->time);
 
     assert(libxl__ev_child_inuse(&aes->child));
diff --git a/tools/libxl/libxl_device.c b/tools/libxl/libxl_device.c
index 84114ff..3b1c3b2 100644
--- a/tools/libxl/libxl_device.c
+++ b/tools/libxl/libxl_device.c
@@ -717,7 +717,7 @@ out:
 
 /* This callback is part of the Qemu devices Badge */
 static void device_qemu_timeout(libxl__egc *egc, libxl__ev_time *ev,
-                                const struct timeval *requested_abs);
+                                const struct timeval *requested_abs, int rc);
 
 static void device_backend_callback(libxl__egc *egc, libxl__ev_devstate *ds,
                                    int rc);
@@ -880,7 +880,7 @@ out:
 }
 
 static void device_qemu_timeout(libxl__egc *egc, libxl__ev_time *ev,
-                                const struct timeval *requested_abs)
+                                const struct timeval *requested_abs, int rc)
 {
     libxl__ao_device *aodev = CONTAINER_OF(ev, *aodev, timeout);
     STATE_AO_GC(aodev->ao);
@@ -888,7 +888,9 @@ static void device_qemu_timeout(libxl__egc *egc, libxl__ev_time *ev,
     char *state_path = GCSPRINTF("%s/state", be_path);
     const char *xs_state;
     xs_transaction_t t = 0;
-    int rc = 0;
+
+    if (rc != ERROR_TIMEDOUT)
+        goto out;
 
     libxl__ev_time_deregister(gc, &aodev->timeout);
 
diff --git a/tools/libxl/libxl_dom.c b/tools/libxl/libxl_dom.c
index e292cb3..87b5fdd 100644
--- a/tools/libxl/libxl_dom.c
+++ b/tools/libxl/libxl_dom.c
@@ -943,7 +943,8 @@ static void domain_suspend_callback_common_done(libxl__egc *egc,
  */
 
 static void switch_logdirty_timeout(libxl__egc *egc, libxl__ev_time *ev,
-                                    const struct timeval *requested_abs);
+                                    const struct timeval *requested_abs,
+                                    int rc);
 static void switch_logdirty_xswatch(libxl__egc *egc, libxl__ev_xswatch*,
                             const char *watch_path, const char *event_path);
 static void switch_logdirty_done(libxl__egc *egc,
@@ -1069,7 +1070,8 @@ void libxl__domain_suspend_common_switch_qemu_logdirty
     }
 }
 static void switch_logdirty_timeout(libxl__egc *egc, libxl__ev_time *ev,
-                                    const struct timeval *requested_abs)
+                                    const struct timeval *requested_abs,
+                                    int rc)
 {
     libxl__domain_suspend_state *dss = CONTAINER_OF(ev, *dss, logdirty.timeout);
     STATE_AO_GC(dss->ao);
@@ -1218,7 +1220,7 @@ static void suspend_common_wait_guest_watch(libxl__egc *egc,
 static void suspend_common_wait_guest_check(libxl__egc *egc,
         libxl__domain_suspend_state *dss);
 static void suspend_common_wait_guest_timeout(libxl__egc *egc,
-      libxl__ev_time *ev, const struct timeval *requested_abs);
+      libxl__ev_time *ev, const struct timeval *requested_abs, int rc);
 
 static void domain_suspend_common_done(libxl__egc *egc,
                                        libxl__domain_suspend_state *dss,
@@ -1452,12 +1454,15 @@ static void suspend_common_wait_guest_check(libxl__egc *egc,
 }
 
 static void suspend_common_wait_guest_timeout(libxl__egc *egc,
-      libxl__ev_time *ev, const struct timeval *requested_abs)
+      libxl__ev_time *ev, const struct timeval *requested_abs, int rc)
 {
     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_done(egc, dss, ERROR_GUEST_TIMEDOUT);
+    if (rc == ERROR_TIMEDOUT) {
+        LOG(ERROR, "guest did not suspend, timed out");
+        rc = ERROR_GUEST_TIMEDOUT;
+    }
+    domain_suspend_common_done(egc, dss, rc);
 }
 
 static void domain_suspend_common_guest_suspended(libxl__egc *egc,
@@ -1690,7 +1695,8 @@ static void remus_devices_commit_cb(libxl__egc *egc,
                                     libxl__remus_devices_state *rds,
                                     int rc);
 static void remus_next_checkpoint(libxl__egc *egc, libxl__ev_time *ev,
-                                  const struct timeval *requested_abs);
+                                  const struct timeval *requested_abs,
+                                  int rc);
 
 static void libxl__remus_domain_checkpoint_callback(void *data)
 {
@@ -1765,7 +1771,8 @@ out:
 }
 
 static void remus_next_checkpoint(libxl__egc *egc, libxl__ev_time *ev,
-                                  const struct timeval *requested_abs)
+                                  const struct timeval *requested_abs,
+                                  int rc)
 {
     libxl__domain_suspend_state *dss =
                             CONTAINER_OF(ev, *dss, checkpoint_timeout);
@@ -1777,7 +1784,11 @@ static void remus_next_checkpoint(libxl__egc *egc, libxl__ev_time *ev,
      * (xc_domain_save.c). in order to continue executing the infinite loop
      * (suspend, checkpoint, resume) in xc_domain_save().
      */
-    libxl__xc_domain_saverestore_async_callback_done(egc, &dss->shs, 1);
+
+    if (rc)
+        dss->rc = rc;
+
+    libxl__xc_domain_saverestore_async_callback_done(egc, &dss->shs, !rc);
 }
 
 /*----- main code for suspending, in order of execution -----*/
diff --git a/tools/libxl/libxl_event.c b/tools/libxl/libxl_event.c
index 1a97cf8..7b4b141 100644
--- a/tools/libxl/libxl_event.c
+++ b/tools/libxl/libxl_event.c
@@ -383,7 +383,7 @@ void libxl__ev_time_deregister(libxl__gc *gc, libxl__ev_time *ev)
     return;
 }
 
-static void time_occurs(libxl__egc *egc, libxl__ev_time *etime)
+static void time_occurs(libxl__egc *egc, libxl__ev_time *etime, int rc)
 {
     DBG("ev_time=%p occurs abs=%lu.%06lu",
         etime, (unsigned long)etime->abs.tv_sec,
@@ -391,7 +391,7 @@ static void time_occurs(libxl__egc *egc, libxl__ev_time *etime)
 
     libxl__ev_time_callback *func = etime->func;
     etime->func = 0;
-    func(egc, etime, &etime->abs);
+    func(egc, etime, &etime->abs, rc);
 }
 
 
@@ -1187,7 +1187,7 @@ static void afterpoll_internal(libxl__egc *egc, libxl__poller *poller,
 
         time_deregister(gc, etime);
 
-        time_occurs(egc, etime);
+        time_occurs(egc, etime, ERROR_TIMEDOUT);
     }
 }
 
@@ -1271,7 +1271,7 @@ void libxl_osevent_occurred_timeout(libxl_ctx *ctx, void *for_libxl)
 
     LIBXL_TAILQ_REMOVE(&CTX->etimes, ev, entry);
 
-    time_occurs(egc, ev);
+    time_occurs(egc, ev, ERROR_TIMEDOUT);
 
  out:
     CTX_UNLOCK;
diff --git a/tools/libxl/libxl_internal.h b/tools/libxl/libxl_internal.h
index 02cac7b..accbab8 100644
--- a/tools/libxl/libxl_internal.h
+++ b/tools/libxl/libxl_internal.h
@@ -175,7 +175,8 @@ struct libxl__ev_fd {
 
 typedef struct libxl__ev_time libxl__ev_time;
 typedef void libxl__ev_time_callback(libxl__egc *egc, libxl__ev_time *ev,
-                                     const struct timeval *requested_abs);
+                                     const struct timeval *requested_abs,
+                                     int rc); /* TIMEDOUT or CANCELLED */
 struct libxl__ev_time {
     /* caller should include this in their own struct */
     /* read-only for caller, who may read only when registered: */
@@ -1108,13 +1109,13 @@ typedef struct libxl__xswait_state libxl__xswait_state;
  *     Otherwise, xswait will continue waiting and watching and
  *     will call you back later.
  *
- * rc==ERROR_TIMEDOUT
+ * rc==ERROR_TIMEDOUT, rc==ERROR_CANCELLED
  *
  *     The specified timeout was reached.
  *     This has NOT been logged (except to the debug log).
  *     xswait will not continue (but calling libxl__xswait_stop is OK).
  *
- * rc!=0, !=ERROR_TIMEDOUT
+ * rc!=0, !=ERROR_TIMEDOUT, !=ERROR_CANCELLED
  *
  *     Some other error occurred.
  *     This HAS been logged.
@@ -1154,8 +1155,9 @@ int libxl__xswait_start(libxl__gc*, libxl__xswait_state*);
 typedef struct libxl__ev_devstate libxl__ev_devstate;
 typedef void libxl__ev_devstate_callback(libxl__egc *egc, libxl__ev_devstate*,
                                          int rc);
-  /* rc will be 0, ERROR_TIMEDOUT, ERROR_INVAL (meaning path was removed),
-   * or ERROR_FAIL if other stuff went wrong (in which latter case, logged) */
+  /* rc will be 0, ERROR_TIMEDOUT, ERROR_CANCELLED, ERROR_INVAL
+   * (meaning path was removed), or ERROR_FAIL if other stuff went
+   * wrong (in which latter case, logged) */
 
 struct libxl__ev_devstate {
     /* read-only for caller, who may read only when waiting: */
diff --git a/tools/libxl/libxl_test_timedereg.c b/tools/libxl/libxl_test_timedereg.c
index e2cc27d..c464663 100644
--- a/tools/libxl/libxl_test_timedereg.c
+++ b/tools/libxl/libxl_test_timedereg.c
@@ -28,7 +28,7 @@ static libxl__ao *tao;
 static int seq;
 
 static void occurs(libxl__egc *egc, libxl__ev_time *ev,
-                   const struct timeval *requested_abs);
+                   const struct timeval *requested_abs, int rc);
 
 static void regs(libxl__ao *ao, int j)
 {
@@ -59,13 +59,15 @@ int libxl_test_timedereg(libxl_ctx *ctx, libxl_asyncop_how *ao_how)
 }
 
 static void occurs(libxl__egc *egc, libxl__ev_time *ev,
-                   const struct timeval *requested_abs)
+                   const struct timeval *requested_abs, int rc)
 {
     EGC_GC;
     int i;
 
     int off = ev - &et[0][0];
-    LOG(DEBUG,"occurs[%d][%d] seq=%d", off/NTIMES, off%NTIMES, seq);
+    LOG(DEBUG,"occurs[%d][%d] seq=%d rc=%d", off/NTIMES, off%NTIMES, seq, rc);
+
+    assert(!rc);
 
     switch (seq) {
     case 0:
-- 
1.7.10.4