when using Virtio_user as Exception Path ,configure the port in the primary
process , virtio_user do rx and tx in the secondary process. it generates a
mistake in tx such as (virtio_user_notify_queue(): failed to kick backend: Bad
file descriptor).

in my opinion ,when initialize the second process , is it properly to copy the
callfd and kickfd  which are initialized by primay process  to the secondary
process ？ in this situation ，i don't think  the secondary process could find
the correct kickfd  ,and it make kthread work  abnormal.

please see the question ,thank you !!!