Hello!

quoted

 Here you ignore errors. And this particular request for some reason ends up
in EBADF. The most magic part is that sometimes it just
works...
 Not sure if i can finish it today, and here in Russia we have New Year holidays
until 11th.

Oops, I made a mistake here. I got vhost_user_read() and vhost_user_write() backwards.

 But nevertheless they do the right thing. vhost_user_read() actually writes the message into socket, and vhost_user_write() reads
it. So they should work correctly.
 I've just checked, fd number is not corrupted.

Kind regards,
Pavel Fedin
Expert Engineer
Samsung Electronics Research center Russia