Hi Paolo and Stefano,

Sorry for the (super) late reply! I haven't had much time to work on
it, I hope to send a v3 by the end of this month! Thanks both of you
for your comments and reviews! :)

quoted

This will add 2 atomic operations per packet, possibly on contended
cachelines. Have you considered leveraging the existing transport-level
lock to protect the counter updates?

Good point!

Maybe we can handle it together with `tx_cnt` in
virtio_transport_get_credit()/virtio_transport_put_credit().

WDYT?

I'll take a look at it! That's a very good idea.

Should virtio_transport_bytes_unsent() returns size_t?

Yes! int was because of atomic_int, size_t is more appropriate.

Thanks,
Luigi