nbd: Switch from close to eject notifier

The NBD code uses the BDS close notifier to determine when a medium is
ejected. However, now it should use the BB's BDS removal notifier for
that instead of the BDS's close notifier.

Signed-off-by: Max Reitz <mreitz@redhat.com>
Reviewed-by: Fam Zheng <famz@redhat.com>
Reviewed-by: Kevin Wolf <kwolf@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

blockdev-nbd.c

@@ -45,37 +45,11 @@ void qmp_nbd_server_start(SocketAddress *addr, Error **errp)
     }
 }
 
-/*
- * Hook into the BlockBackend notifiers to close the export when the
- * backend is closed.
- */
-typedef struct NBDCloseNotifier {
-    Notifier n;
-    NBDExport *exp;
-    QTAILQ_ENTRY(NBDCloseNotifier) next;
-} NBDCloseNotifier;
-
-static QTAILQ_HEAD(, NBDCloseNotifier) close_notifiers =
-    QTAILQ_HEAD_INITIALIZER(close_notifiers);
-
-static void nbd_close_notifier(Notifier *n, void *data)
-{
-    NBDCloseNotifier *cn = DO_UPCAST(NBDCloseNotifier, n, n);
-
-    notifier_remove(&cn->n);
-    QTAILQ_REMOVE(&close_notifiers, cn, next);
-
-    nbd_export_close(cn->exp);
-    nbd_export_put(cn->exp);
-    g_free(cn);
-}
-
 void qmp_nbd_server_add(const char *device, bool has_writable, bool writable,
                         Error **errp)
 {
     BlockBackend *blk;
     NBDExport *exp;
-    NBDCloseNotifier *n;
 
     if (server_fd == -1) {
         error_setg(errp, "NBD server not running");
@@ -113,19 +87,15 @@ void qmp_nbd_server_add(const char *device, bool has_writable, bool writable,
 
     nbd_export_set_name(exp, device);
 
-    n = g_new0(NBDCloseNotifier, 1);
-    n->n.notify = nbd_close_notifier;
-    n->exp = exp;
-    blk_add_close_notifier(blk, &n->n);
-    QTAILQ_INSERT_TAIL(&close_notifiers, n, next);
+    /* The list of named exports has a strong reference to this export now and
+     * our only way of accessing it is through nbd_export_find(), so we can drop
+     * the strong reference that is @exp. */
+    nbd_export_put(exp);
 }
 
 void qmp_nbd_server_stop(Error **errp)
 {
-    while (!QTAILQ_EMPTY(&close_notifiers)) {
-        NBDCloseNotifier *cn = QTAILQ_FIRST(&close_notifiers);
-        nbd_close_notifier(&cn->n, nbd_export_get_blockdev(cn->exp));
-    }
+    nbd_export_close_all();
 
     if (server_fd != -1) {
         qemu_set_fd_handler(server_fd, NULL, NULL, NULL);

nbd/server.c

@@ -64,6 +64,8 @@ struct NBDExport {
     QTAILQ_ENTRY(NBDExport) next;
 
     AioContext *ctx;
+
+    Notifier eject_notifier;
 };
 
 static QTAILQ_HEAD(, NBDExport) exports = QTAILQ_HEAD_INITIALIZER(exports);
@@ -644,6 +646,12 @@ static void blk_aio_detach(void *opaque)
     exp->ctx = NULL;
 }
 
+static void nbd_eject_notifier(Notifier *n, void *data)
+{
+    NBDExport *exp = container_of(n, NBDExport, eject_notifier);
+    nbd_export_close(exp);
+}
+
 NBDExport *nbd_export_new(BlockBackend *blk, off_t dev_offset, off_t size,
                           uint32_t nbdflags, void (*close)(NBDExport *),
                           Error **errp)
@@ -666,6 +674,10 @@ NBDExport *nbd_export_new(BlockBackend *blk, off_t dev_offset, off_t size,
     exp->ctx = blk_get_aio_context(blk);
     blk_ref(blk);
     blk_add_aio_context_notifier(blk, blk_aio_attached, blk_aio_detach, exp);
+
+    exp->eject_notifier.notify = nbd_eject_notifier;
+    blk_add_remove_bs_notifier(blk, &exp->eject_notifier);
+
     /*
      * NBD exports are used for non-shared storage migration.  Make sure
      * that BDRV_O_INACTIVE is cleared and the image is ready for write
@@ -747,6 +759,7 @@ void nbd_export_put(NBDExport *exp)
         }
 
         if (exp->blk) {
+            notifier_remove(&exp->eject_notifier);
             blk_remove_aio_context_notifier(exp->blk, blk_aio_attached,
                                             blk_aio_detach, exp);
             blk_unref(exp->blk);