openssh unix dev - May 2021 - Channel documentation?

Hello all,

Is there any documentation (outside of the code) describing the channel 
functions? I'm looking at using a secondary channel to periodically 
report back receiver side TCP metrics (via the TCP_INFO struct) to the 
caller for flow diagnostics. Alternatively, is there a good place in the 
code base I can use as a starting point to understand the process?

Thanks!

Hi,

rapier wrote:
> Is there any documentation (outside of the code) describing the channel 
> functions?
The channel functions in the OpenSSH codebase? Probably no.

> I'm looking at using a secondary channel to periodically report back
> receiver side TCP metrics (via the TCP_INFO struct) to the caller for
> flow diagnostics. Alternatively, is there a good place in the code
> base I can use as a starting point to understand the process?
Are you familiar with channels in general? RFC 4254 5. Channel Mechanism.

If you want to control exactly when data from (your metric) channels
are sent on the wire I think you have to do quite a deep dive into the code.

If you care less about jitter then you can maybe look at SFTP but
probably much better any of the socket forwarding.

If you want to implement the metric completely in the application layer
you could investigate creating it in a subsystem, which (like SFTP) is
also just a channel.


//Peter