block/export: Add blk_exp_close_all(_type)

This adds a function to shut down all block exports, and another one to
shut down the block exports of a single type. The latter is used for now
when stopping the NBD server. As soon as we implement support for
multiple NBD servers, we'll need a per-server list of exports and it
will be replaced by a function using that.

As a side effect, the BlockExport layer has a list tracking all existing
exports now. closed_exports loses its only user and can go away.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Reviewed-by: Max Reitz <mreitz@redhat.com>
Message-Id: <20200924152717.287415-18-kwolf@redhat.com>
Acked-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

1 files changed, 84 insertions, 2 deletions

diff --git a/block/export/export.c b/block/export/export.c
index 6b2b29078b..e94a68c183 100644
--- a/block/export/export.c
+++ b/block/export/export.c
@@ -24,6 +24,10 @@ static const BlockExportDriver *blk_exp_drivers[] = {
     &blk_exp_nbd,
 };
 
+/* Only accessed from the main thread */
+static QLIST_HEAD(, BlockExport) block_exports =
+    QLIST_HEAD_INITIALIZER(block_exports);
+
 static const BlockExportDriver *blk_exp_find_driver(BlockExportType type)
 {
     int i;
@@ -61,6 +65,7 @@ BlockExport *blk_exp_add(BlockExportOptions *export, Error **errp)
         return NULL;
     }
 
+    QLIST_INSERT_HEAD(&block_exports, exp, next);
     return exp;
 }
 
@@ -71,14 +76,91 @@ void blk_exp_ref(BlockExport *exp)
     exp->refcount++;
 }
 
+/* Runs in the main thread */
+static void blk_exp_delete_bh(void *opaque)
+{
+    BlockExport *exp = opaque;
+    AioContext *aio_context = exp->ctx;
+
+    aio_context_acquire(aio_context);
+
+    assert(exp->refcount == 0);
+    QLIST_REMOVE(exp, next);
+    exp->drv->delete(exp);
+    g_free(exp);
+
+    aio_context_release(aio_context);
+}
+
 /* Callers must hold exp->ctx lock */
 void blk_exp_unref(BlockExport *exp)
 {
     assert(exp->refcount > 0);
     if (--exp->refcount == 0) {
-        exp->drv->delete(exp);
-        g_free(exp);
+        /* Touch the block_exports list only in the main thread */
+        aio_bh_schedule_oneshot(qemu_get_aio_context(), blk_exp_delete_bh,
+                                exp);
+    }
+}
+
+/*
+ * Drops the user reference to the export and requests that all client
+ * connections and other internally held references start to shut down. When
+ * the function returns, there may still be active references while the export
+ * is in the process of shutting down.
+ *
+ * Acquires exp->ctx internally. Callers must *not* hold the lock.
+ */
+void blk_exp_request_shutdown(BlockExport *exp)
+{
+    AioContext *aio_context = exp->ctx;
+
+    aio_context_acquire(aio_context);
+    exp->drv->request_shutdown(exp);
+    aio_context_release(aio_context);
+}
+
+/*
+ * Returns whether a block export of the given type exists.
+ * type == BLOCK_EXPORT_TYPE__MAX checks for an export of any type.
+ */
+static bool blk_exp_has_type(BlockExportType type)
+{
+    BlockExport *exp;
+
+    if (type == BLOCK_EXPORT_TYPE__MAX) {
+        return !QLIST_EMPTY(&block_exports);
+    }
+
+    QLIST_FOREACH(exp, &block_exports, next) {
+        if (exp->drv->type == type) {
+            return true;
+        }
     }
+
+    return false;
+}
+
+/* type == BLOCK_EXPORT_TYPE__MAX for all types */
+void blk_exp_close_all_type(BlockExportType type)
+{
+    BlockExport *exp, *next;
+
+    assert(in_aio_context_home_thread(qemu_get_aio_context()));
+
+    QLIST_FOREACH_SAFE(exp, &block_exports, next, next) {
+        if (type != BLOCK_EXPORT_TYPE__MAX && exp->drv->type != type) {
+            continue;
+        }
+        blk_exp_request_shutdown(exp);
+    }
+
+    AIO_WAIT_WHILE(NULL, blk_exp_has_type(type));
+}
+
+void blk_exp_close_all(void)
+{
+    blk_exp_close_all_type(BLOCK_EXPORT_TYPE__MAX);
 }
 
 void qmp_block_export_add(BlockExportOptions *export, Error **errp)