[PATCH 3/4] vhost-user: Monitor slave channel in vhost_user_read()

[Greg Kurz <groug@kaod.org>]

Now that everything is in place, have the nested event loop to monitor
the slave channel. The source in the main event loop is destroyed and
recreated to ensure any pending even for the slave channel that was
previously detected is purged. This guarantees that the main loop
wont invoke slave_read() based on an event that was already handled
by the nested loop.

Signed-off-by: Greg Kurz <groug@kaod.org>
---
 hw/virtio/vhost-user.c | 27 +++++++++++++++++++++++++++
 1 file changed, 27 insertions(+)

diff --git a/hw/virtio/vhost-user.c b/hw/virtio/vhost-user.c
index e395d0d1fd81..7669b3f2a99f 100644
--- a/hw/virtio/vhost-user.c
+++ b/hw/virtio/vhost-user.c
@@ -345,6 +345,9 @@ end:
     return G_SOURCE_REMOVE;
 }
 
+static gboolean slave_read(QIOChannel *ioc, GIOCondition condition,
+                           gpointer opaque);
+
 static int vhost_user_read(struct vhost_dev *dev, VhostUserMsg *msg)
 {
     struct vhost_user *u = dev->opaque;
@@ -352,6 +355,7 @@ static int vhost_user_read(struct vhost_dev *dev, VhostUserMsg *msg)
     GMainContext *prev_ctxt = chr->chr->gcontext;
     GMainContext *ctxt = g_main_context_new();
     GMainLoop *loop = g_main_loop_new(ctxt, FALSE);
+    GSource *slave_src = NULL;
     struct vhost_user_read_cb_data data = {
         .dev = dev,
         .loop = loop,
@@ -363,8 +367,30 @@ static int vhost_user_read(struct vhost_dev *dev, VhostUserMsg *msg)
     qemu_chr_be_update_read_handlers(chr->chr, ctxt);
     qemu_chr_fe_add_watch(chr, G_IO_IN | G_IO_HUP, vhost_user_read_cb, &data);
 
+    if (u->slave_ioc) {
+        /*
+         * This guarantees that all pending events in the main context
+         * for the slave channel are purged. They will be re-detected
+         * and processed now by the nested loop.
+         */
+        g_source_destroy(u->slave_src);
+        g_source_unref(u->slave_src);
+        u->slave_src = NULL;
+        slave_src = qio_channel_add_watch_source(u->slave_ioc, G_IO_IN,
+                                                 slave_read, dev, NULL,
+                                                 ctxt);
+    }
+
     g_main_loop_run(loop);
 
+    if (u->slave_ioc) {
+        g_source_destroy(slave_src);
+        g_source_unref(slave_src);
+        u->slave_src = qio_channel_add_watch_source(u->slave_ioc, G_IO_IN,
+                                                    slave_read, dev, NULL,
+                                                    NULL);
+    }
+
     /*
      * Restore the previous context. This also destroys/recreates event
      * sources : this guarantees that all pending events in the original
@@ -372,6 +398,7 @@ static int vhost_user_read(struct vhost_dev *dev, VhostUserMsg *msg)
      */
     qemu_chr_be_update_read_handlers(chr->chr, prev_ctxt);
 
+
     g_main_loop_unref(loop);
     g_main_context_unref(ctxt);
 
-- 
2.26.2