[PATCH v2 07/16] block/export: stop using is_external in vhost-user-blk server

[Stefan Hajnoczi <stefanha@xxxxxxxxxx>]

vhost-user activity must be suspended during bdrv_drained_begin/end().
This prevents new requests from interfering with whatever is happening
in the drained section.

Previously this was done using aio_set_fd_handler()'s is_external
argument. In a multi-queue block layer world the aio_disable_external()
API cannot be used since multiple AioContext may be processing I/O, not
just one.

Switch to BlockDevOps->drained_begin/end() callbacks.

Signed-off-by: Stefan Hajnoczi <stefanha@xxxxxxxxxx>
---
 block/export/vhost-user-blk-server.c | 43 ++++++++++++++--------------
 util/vhost-user-server.c             | 10 +++----
 2 files changed, 26 insertions(+), 27 deletions(-)

diff --git a/block/export/vhost-user-blk-server.c 
b/block/export/vhost-user-blk-server.c
index dbf5207162..6e1bc196fb 100644
--- a/block/export/vhost-user-blk-server.c
+++ b/block/export/vhost-user-blk-server.c
@@ -207,22 +207,6 @@ static const VuDevIface vu_blk_iface = {
     .process_msg           = vu_blk_process_msg,
 };
 
-static void blk_aio_attached(AioContext *ctx, void *opaque)
-{
-    VuBlkExport *vexp = opaque;
-
-    vexp->export.ctx = ctx;
-    vhost_user_server_attach_aio_context(&vexp->vu_server, ctx);
-}
-
-static void blk_aio_detach(void *opaque)
-{
-    VuBlkExport *vexp = opaque;
-
-    vhost_user_server_detach_aio_context(&vexp->vu_server);
-    vexp->export.ctx = NULL;
-}
-
 static void
 vu_blk_initialize_config(BlockDriverState *bs,
                          struct virtio_blk_config *config,
@@ -254,6 +238,25 @@ static void vu_blk_exp_request_shutdown(BlockExport *exp)
     vhost_user_server_stop(&vexp->vu_server);
 }
 
+/* Called with vexp->export.ctx acquired */
+static void vu_blk_drained_begin(void *opaque)
+{
+    VuBlkExport *vexp = opaque;
+
+    vhost_user_server_detach_aio_context(&vexp->vu_server);
+}
+
+/* Called with vexp->export.blk AioContext acquired */
+static void vu_blk_drained_end(void *opaque)
+{
+    VuBlkExport *vexp = opaque;
+
+    /* Refresh AioContext in case it changed */
+    vexp->export.ctx = blk_get_aio_context(vexp->export.blk);
+
+    vhost_user_server_attach_aio_context(&vexp->vu_server, vexp->export.ctx);
+}
+
 /*
  * Ensures that bdrv_drained_begin() waits until in-flight requests complete.
  *
@@ -267,6 +270,8 @@ static bool vu_blk_drained_poll(void *opaque)
 }
 
 static const BlockDevOps vu_blk_dev_ops = {
+    .drained_begin = vu_blk_drained_begin,
+    .drained_end   = vu_blk_drained_end,
     .drained_poll  = vu_blk_drained_poll,
 };
 
@@ -309,13 +314,9 @@ static int vu_blk_exp_create(BlockExport *exp, 
BlockExportOptions *opts,
                              logical_block_size, num_queues);
 
     blk_set_dev_ops(exp->blk, &vu_blk_dev_ops, vexp);
-    blk_add_aio_context_notifier(exp->blk, blk_aio_attached, blk_aio_detach,
-                                 vexp);
 
     if (!vhost_user_server_start(&vexp->vu_server, vu_opts->addr, exp->ctx,
                                  num_queues, &vu_blk_iface, errp)) {
-        blk_remove_aio_context_notifier(exp->blk, blk_aio_attached,
-                                        blk_aio_detach, vexp);
         blk_set_dev_ops(exp->blk, NULL, NULL);
         g_free(vexp->handler.serial);
         return -EADDRNOTAVAIL;
@@ -328,8 +329,6 @@ static void vu_blk_exp_delete(BlockExport *exp)
 {
     VuBlkExport *vexp = container_of(exp, VuBlkExport, export);
 
-    blk_remove_aio_context_notifier(exp->blk, blk_aio_attached, blk_aio_detach,
-                                    vexp);
     blk_set_dev_ops(exp->blk, NULL, NULL);
     g_free(vexp->handler.serial);
 }
diff --git a/util/vhost-user-server.c b/util/vhost-user-server.c
index 2e6b640050..332aea9306 100644
--- a/util/vhost-user-server.c
+++ b/util/vhost-user-server.c
@@ -278,7 +278,7 @@ set_watch(VuDev *vu_dev, int fd, int vu_evt,
         vu_fd_watch->fd = fd;
         vu_fd_watch->cb = cb;
         qemu_socket_set_nonblock(fd);
-        aio_set_fd_handler(server->ioc->ctx, fd, true, kick_handler,
+        aio_set_fd_handler(server->ioc->ctx, fd, false, kick_handler,
                            NULL, NULL, NULL, vu_fd_watch);
         vu_fd_watch->vu_dev = vu_dev;
         vu_fd_watch->pvt = pvt;
@@ -299,7 +299,7 @@ static void remove_watch(VuDev *vu_dev, int fd)
     if (!vu_fd_watch) {
         return;
     }
-    aio_set_fd_handler(server->ioc->ctx, fd, true,
+    aio_set_fd_handler(server->ioc->ctx, fd, false,
                        NULL, NULL, NULL, NULL, NULL);
 
     QTAILQ_REMOVE(&server->vu_fd_watches, vu_fd_watch, next);
@@ -362,7 +362,7 @@ void vhost_user_server_stop(VuServer *server)
         VuFdWatch *vu_fd_watch;
 
         QTAILQ_FOREACH(vu_fd_watch, &server->vu_fd_watches, next) {
-            aio_set_fd_handler(server->ctx, vu_fd_watch->fd, true,
+            aio_set_fd_handler(server->ctx, vu_fd_watch->fd, false,
                                NULL, NULL, NULL, NULL, vu_fd_watch);
         }
 
@@ -403,7 +403,7 @@ void vhost_user_server_attach_aio_context(VuServer *server, 
AioContext *ctx)
     qio_channel_attach_aio_context(server->ioc, ctx);
 
     QTAILQ_FOREACH(vu_fd_watch, &server->vu_fd_watches, next) {
-        aio_set_fd_handler(ctx, vu_fd_watch->fd, true, kick_handler, NULL,
+        aio_set_fd_handler(ctx, vu_fd_watch->fd, false, kick_handler, NULL,
                            NULL, NULL, vu_fd_watch);
     }
 
@@ -417,7 +417,7 @@ void vhost_user_server_detach_aio_context(VuServer *server)
         VuFdWatch *vu_fd_watch;
 
         QTAILQ_FOREACH(vu_fd_watch, &server->vu_fd_watches, next) {
-            aio_set_fd_handler(server->ctx, vu_fd_watch->fd, true,
+            aio_set_fd_handler(server->ctx, vu_fd_watch->fd, false,
                                NULL, NULL, NULL, NULL, vu_fd_watch);
         }
 
-- 
2.39.2