[Xen-devel] [PATCH v2 04/10] libxl: synchronize device removal when using driver domains

[Roger Pau Monne <roger.pau@xxxxxxxxxx>]

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 Monnà <roger.pau@xxxxxxxxxx>
Cc: Ian Jackson <Ian.Jackson@xxxxxxxxxxxxx>
Cc: Ian Campbell <ian.campbell@xxxxxxxxxx>
---
Changes since v1:
 * Place cleanup of aodev events in device_hotplug_clean, get rid of
   some code duplication.

Changes since RFC:
 * This patch has been reworked to synchronize the toolstack and the
   driver domain, by making the driver domain only remove the first
   directory of the backend path, and the toolstack domain remove the
   rest.
---
 tools/libxl/libxl_device.c   |   81 ++++++++++++++++++++++++++++++++++++++++-
 tools/libxl/libxl_internal.h |    2 +
 2 files changed, 81 insertions(+), 2 deletions(-)

diff --git a/tools/libxl/libxl_device.c b/tools/libxl/libxl_device.c
index d726f0b..8987434 100644
--- a/tools/libxl/libxl_device.c
+++ b/tools/libxl/libxl_device.c
@@ -443,6 +443,11 @@ 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 */
@@ -722,6 +727,14 @@ 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);
@@ -781,12 +794,14 @@ 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)) {
         /*
          * TODO: 4.2 Bodge due to QEMU, see comment on top of
          * libxl__initiate_device_remove in libxl_internal.h
          */
+
         rc = libxl__ev_time_register_rel(gc, &aodev->timeout,
                                          device_qemu_timeout,
                                          LIBXL_QEMU_BODGE_TIMEOUT * 1000);
@@ -932,8 +947,28 @@ 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 */
@@ -1051,6 +1086,47 @@ 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);
@@ -1073,6 +1149,7 @@ 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 6ccd826..8ea654d 100644
--- a/tools/libxl/libxl_internal.h
+++ b/tools/libxl/libxl_internal.h
@@ -1906,6 +1906,8 @@ 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;
-- 
1.7.7.5 (Apple Git-26)


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