[RFC] Add support for changing the flow ID of TCP connections

[Hans Petter Selasky]

Hi,

I'm working on a new feature which will allow TCP connections to be 
timing controlled by the ethernet hardware driver, actually the mlxen 
driver. The main missing piece in the kernel is to allow the mbuf's 
flowid value to be overwritten in "struct inpcb" once the connection is 
established and to have a callback once the TCP connection is gone so 
that the assigned "flowid" can be freed by the ethernet hardware driver.

The "flowid" will be used to assign the outgoing data traffic of a 
specific TCP connections to a hardware controlled queue, which in 
advance contain certain parameters about the timing for the transmitted 
packets.

To be able to set the flowid I'm using existing functions in the kernel 
TCP code to lookup the "inpcb" structure based on the 4-tuple, via the 
"ifp->if_ioctl()" callback of the network adapter. I'm also registering 
a function method table so that I get a callback when the TCP connection 
is gone.

A this point of development I would like to get some feedback from 
FreeBSD network guys about my attached patch proposal.

The motivation for this work is to have a more reliable TCP 
transmissions typically for fixed-rate media content going some 
distance. To illustrate this I will give you an example from the world 
of VoIP, which is using UDP. When doing long-distance VoIP calls through 
various unknown networks and routers it makes a very big difference if 
you are sending data 20ms apart or 40ms apart, even at the exact same 
rate. In the one case you might experience a bunch of packet drops, and 
in the other case, everything is fine. Why? Because the number of 
packets you send per second, and the timing is important. The goal is to 
apply some timing rules for TCP, to increase the factor of successful 
transmission, and to reduce the amount of data loss. For high throughput 
applications we want to do this by means of hardware.


While at it I would like to "typedef" the flowid used by mbufs, "struct 
inpcb" and many more places.  Where would the right place be to put such 
a definition? In "sys/mbuf.h"?


Comments are appreciated!

--HPS
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