[PATCH v8 3/6] vhost_user: Make source quit after reporting migration state

[Stefano Brivio <sbrivio@redhat.com>]

On migration, the source process asks passt-helper to set TCP sockets
in repair mode, dumps the information we need to migrate connections,
and closes them.

At this point, we can't pass them back to passt-helper using
SCM_RIGHTS, because they are closed, from that perspective, and
sendmsg() will give us EBADF. But if we don't clear repair mode, the
port they are bound to will not be available for binding in the
target.

Terminate once we're done with the migration and we reported the
state. This is equivalent to clearing repair mode on the sockets we
just closed.

Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
Message-ID: <20250205003904.2797491-6-sbrivio@redhat.com>
---
 vhost_user.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/vhost_user.c b/vhost_user.c
index 88efd17..4906e2a 100644
--- a/vhost_user.c
+++ b/vhost_user.c
@@ -998,6 +998,8 @@ static bool vu_send_rarp_exec(struct vu_dev *vdev,
 	return false;
 }
 
+static bool quit_on_device_state = false;
+
 /**
  * vu_set_device_state_fd_exec() - Set the device state migration channel
  * @vdev:	vhost-user device
@@ -1025,6 +1027,9 @@ static bool vu_set_device_state_fd_exec(struct vu_dev *vdev,
 	migrate_request(vdev->context, msg->fds[0],
 			direction == VHOST_USER_TRANSFER_STATE_DIRECTION_LOAD);
 
+	if (direction == VHOST_USER_TRANSFER_STATE_DIRECTION_SAVE)
+		quit_on_device_state = true;
+
 	/* We don't provide a new fd for the data transfer */
 	vmsg_set_reply_u64(msg, VHOST_USER_VRING_NOFD_MASK);
 
@@ -1202,4 +1207,10 @@ void vu_control_handler(struct vu_dev *vdev, int fd, uint32_t events)
 
 	if (reply_requested)
 		vu_send_reply(fd, &msg);
+
+	if (quit_on_device_state &&
+	    msg.hdr.request == VHOST_USER_CHECK_DEVICE_STATE) {
+		info("Migration complete, exiting");
+		exit(EXIT_SUCCESS);
+	}
 }
-- 
@@ -998,6 +998,8 @@ static bool vu_send_rarp_exec(struct vu_dev *vdev,
 	return false;
 }
 
+static bool quit_on_device_state = false;
+
 /**
  * vu_set_device_state_fd_exec() - Set the device state migration channel
  * @vdev:	vhost-user device
@@ -1025,6 +1027,9 @@ static bool vu_set_device_state_fd_exec(struct vu_dev *vdev,
 	migrate_request(vdev->context, msg->fds[0],
 			direction == VHOST_USER_TRANSFER_STATE_DIRECTION_LOAD);
 
+	if (direction == VHOST_USER_TRANSFER_STATE_DIRECTION_SAVE)
+		quit_on_device_state = true;
+
 	/* We don't provide a new fd for the data transfer */
 	vmsg_set_reply_u64(msg, VHOST_USER_VRING_NOFD_MASK);
 
@@ -1202,4 +1207,10 @@ void vu_control_handler(struct vu_dev *vdev, int fd, uint32_t events)
 
 	if (reply_requested)
 		vu_send_reply(fd, &msg);
+
+	if (quit_on_device_state &&
+	    msg.hdr.request == VHOST_USER_CHECK_DEVICE_STATE) {
+		info("Migration complete, exiting");
+		exit(EXIT_SUCCESS);
+	}
 }
-- 
2.43.0