Questions about the FreeBSD network subsystem

[Roger Pau Monné]

Hello,

I'm not very familiar with FreeBSD network subsystem and I'm trying to
import a new version of xen-netfront from Linux to FreeBSD. So far so
good, most stuff is pretty similar and I think I've _mostly_ figured it
out by myself. I have however a couple of questions regarding the
network subsystem.

I'm planning to use if_transmit/if_qflush instead of if_start. AFAICT I
have to create my own queue inside of the driver in order to queue
packets if the shared ring is full. What's the prefer way to do this? I
see there are functions to create a mbuf queue (mbufq) or a ifnet based
queue (drbr_* family of functions). I expect using drbr is TRTTD, but I
would like to get some confirmation before proceeding.

Also, the Xen PV network protocol allows signalling packets that contain
valid data or blank checksums. It allows specifying the following flags:

 - NET{RX/TR}F_data_validated: packet data has been validated against
protocol checksum.
 - NET{RX/TX}F_csum_blank: protocol checksum field is blank in the
packet (hardware offload)?.
 - No flag: checksum present and valid.

How do this options translate to the csum_flags present in mbufs on FreeBSD?

Thanks, Roger.