If this is supposed to be an actual copyright attribution, you should add the appropriate year to the existing set attributed to Swinburne University in the main copyright block, and then extend the second informative comment block with these additional author attribution details.

That being said, given the size of the change it probably doesn't warrant copyright changes, so merging this in to the informative comment block is probably all that's needed.

This #ifndef block is not needed

What about treating these as permanently defined variables which default to non-ABE behaviour i.e. 50 and 50, and toggling ABE simply explicitly sets them to draft-specified values? Perhaps renaming newreno_beta_loss to newreno_beta would also make sense, which specifies the default beta that gets overridden by other variables on a case by case basis.

Let's avoid gratuitous code duplication, and perhaps reinstate this line as something like:

factor = (type == CC_ECN ? V_newreno_beta_ecn : V_newreno_beta_loss);
cwin = max((cwin * factor) / (100 * mss), 2) * mss;

This can change to sysctl_handle_int()

Please note in the sysctl description that net.inet.tcp.abe must be 1 for this variable to be settable.

Perhaps include name of ABE draft in description, or at minimum in the file as a comment.

Please do the following:

• Bump the document date .Dd field.

• Add a "SEE ALSO" section with a reference to the ABE draft (as an example, you can copy from cc_cubic for draft-rhee-tcpm-cubic-02.txt). While you're at it, perhaps also add a normative reference to RFC 5681 as the first ref in SEE ALSO.

• Add a new ".Ss Socket options" sub-section above the "MIB Variables" sub-section to document "struct cc_newreno_opts" (see mod_cc(9) for an example of documenting a struct in a man page) and to document the 2 socket options added. You should also reference TCP_CCALGOOPT from tcp(4) and mod_cc(4).

FYI, "man mdoc" has details on all the mdoc macros you might need.

You should use the longest MIB variable name here for width sizing i.e. beta_ecn

I wonder where these were copied from... please be mindful of paying more attention to detail.

How about (note man page style is to start new sentences on a new line):

Multiplicative window decrease factor, specified as a percentage, applied to the congestion window in response to a congestion signal per: cwnd = (cwnd * beta) / 100.
Default is 50.

ABE should be explicitly referenced here. Perhaps something like:

Multiplicative window decrease factor, specified as a percentage, applied to the congestion window in response to an ECN congestion signal when
.Va net.inet.tcp.abe=1
per: cwnd = (cwnd * beta_ecn) / 100.
Default is 80.

Feel free to give yourself/the funding project some kudos in the "HISTORY" and/or "AUTHORS" sections for adding ABE support if you wish.

Perhaps be a bit more descriptive and point people in the right direction:

..., which alters the window decrease factor applied to the congestion window in response to an ECN congestion signal.
Refer to
.Xr 4 mod_cc
and individual congestion control man pages to determine if they implement support for ABE and for configuration details.

If this is sponsored work, you may need to check whether you retain copyright, or the funding project/institution does. Normally the body paying for your time owns and should be assigned the copyright, and you should assign yourself author attribution in a comment block below the main copyright block.

Nit: spacing looks off here. Make sure there is a hard tab between type and name so that names align on same column.

s/the following/these/