libxl: synchronize device removal when using driver domains

Synchronize the clean up of the backend from the toolstack domain when
the driver domain has actually finished closing the backend for the
device.

This is accomplished by waiting for the driver domain to  remove the
directory containing the backend keys, then the toolstack domain will
finish the cleanup by removing the empty folders on the backend path.

Signed-off-by: Roger Pau Monné <roger.pau@citrix.com>
Cc: Ian Campbell <ian.campbell@citrix.com>
Acked-by: Ian Jackson <ian.jackson@eu.citrix.com>

diff --git a/tools/libxl/libxl_device.c b/tools/libxl/libxl_device.c
index d5f23cfb408241502697b49ca4c5b18dcbc75d42..b7168d47fdab8c60fb8e9d6dd5abdd6e5b6ac592 100644 (file)
--- a/tools/libxl/libxl_device.c
+++ b/tools/libxl/libxl_device.c
@@ -432,6 +432,11 @@ void libxl__prepare_ao_device(libxl__ao *ao, libxl__ao_device *aodev)
     aodev->num_exec = 0;
     /* Initialize timer for QEMU Bodge and hotplug execution */
     libxl__ev_time_init(&aodev->timeout);
+    /*
+     * Initialize xs_watch, because it's not used on all possible
+     * execution paths, but it's unconditionally destroyed when finished.
+     */
+    libxl__ev_xswatch_init(&aodev->xs_watch);
     aodev->active = 1;
     /* We init this here because we might call device_hotplug_done
      * without actually calling any hotplug script */
@@ -709,6 +714,14 @@ static void device_hotplug_child_death_cb(libxl__egc *egc,
                                           libxl__ev_child *child,
                                           pid_t pid, int status);
 
+static void device_destroy_be_timeout_cb(libxl__egc *egc, libxl__ev_time *ev,
+                                         const struct timeval *requested_abs);
+
+static void device_destroy_be_watch_cb(libxl__egc *egc,
+                                       libxl__ev_xswatch *watch,
+                                       const char *watch_path,
+                                       const char *event_path);
+
 static void device_hotplug_done(libxl__egc *egc, libxl__ao_device *aodev);
 
 static void device_hotplug_clean(libxl__gc *gc, libxl__ao_device *aodev);
@@ -768,6 +781,7 @@ void libxl__initiate_device_remove(libxl__egc *egc,
         LOG(ERROR, "unable to get info for domain %d", domid);
         goto out;
     }
+
     if (QEMU_BACKEND(aodev->dev) &&
         (info.paused || info.dying || info.shutdown)) {
         /*
@@ -919,8 +933,28 @@ static void device_hotplug(libxl__egc *egc, libxl__ao_device *aodev)
      */
     rc = libxl__get_domid(gc, &domid);
     if (rc) goto out;
-    if (aodev->dev->backend_domid != domid)
-        goto out;
+    if (aodev->dev->backend_domid != domid) {
+        if (aodev->action != LIBXL__DEVICE_ACTION_REMOVE)
+            goto out;
+
+        rc = libxl__ev_time_register_rel(gc, &aodev->timeout,
+                                         device_destroy_be_timeout_cb,
+                                         LIBXL_DESTROY_TIMEOUT * 1000);
+        if (rc) {
+            LOG(ERROR, "setup of xs watch timeout failed");
+            goto out;
+        }
+
+        rc = libxl__ev_xswatch_register(gc, &aodev->xs_watch,
+                                        device_destroy_be_watch_cb,
+                                        be_path);
+        if (rc) {
+            LOG(ERROR, "setup of xs watch for %s failed", be_path);
+            libxl__ev_time_deregister(gc, &aodev->timeout);
+            goto out;
+        }
+        return;
+    }
 
     /* Check if we have to execute hotplug scripts for this device
      * and return the necessary args/env vars for execution */
@@ -1038,6 +1072,47 @@ error:
     device_hotplug_done(egc, aodev);
 }
 
+static void device_destroy_be_timeout_cb(libxl__egc *egc, libxl__ev_time *ev,
+                                         const struct timeval *requested_abs)
+{
+    libxl__ao_device *aodev = CONTAINER_OF(ev, *aodev, timeout);
+    STATE_AO_GC(aodev->ao);
+
+    LOG(ERROR, "timed out while waiting for %s to be removed",
+               libxl__device_backend_path(gc, aodev->dev));
+
+    aodev->rc = ERROR_TIMEDOUT;
+
+    device_hotplug_done(egc, aodev);
+    return;
+}
+
+static void device_destroy_be_watch_cb(libxl__egc *egc,
+                                       libxl__ev_xswatch *watch,
+                                       const char *watch_path,
+                                       const char *event_path)
+{
+    libxl__ao_device *aodev = CONTAINER_OF(watch, *aodev, xs_watch);
+    STATE_AO_GC(aodev->ao);
+    const char *dir;
+    int rc;
+
+    rc = libxl__xs_read_checked(gc, XBT_NULL, watch_path, &dir);
+    if (rc) {
+        LOG(ERROR, "unable to read backend path: %s", watch_path);
+        aodev->rc = rc;
+        goto out;
+    }
+    if (dir) {
+        /* backend path still exists, wait a little longer... */
+        return;
+    }
+
+out:
+    /* We are done, backend path no longer exists */
+    device_hotplug_done(egc, aodev);
+}
+
 static void device_hotplug_done(libxl__egc *egc, libxl__ao_device *aodev)
 {
     STATE_AO_GC(aodev->ao);
@@ -1060,6 +1135,7 @@ static void device_hotplug_clean(libxl__gc *gc, libxl__ao_device *aodev)
 {
     /* Clean events and check reentrancy */
     libxl__ev_time_deregister(gc, &aodev->timeout);
+    libxl__ev_xswatch_deregister(gc, &aodev->xs_watch);
     assert(!libxl__ev_child_inuse(&aodev->child));
 }
 

diff --git a/tools/libxl/libxl_internal.h b/tools/libxl/libxl_internal.h
index 23ff2651bbc9f8f113ca325f85fd62e9e957b676..e3b9fb4581bbe71464e6036203d97026a7a146eb 100644 (file)
--- a/tools/libxl/libxl_internal.h
+++ b/tools/libxl/libxl_internal.h
@@ -1928,6 +1928,8 @@ struct libxl__ao_device {
     libxl__ev_devstate backend_ds;
     /* Bodge for Qemu devices, also used for timeout of hotplug execution */
     libxl__ev_time timeout;
+    /* xenstore watch for backend path of driver domains */
+    libxl__ev_xswatch xs_watch;
     /* device hotplug execution */
     const char *what;
     int num_exec;