keeping track of connections

I would love a way to keep track of the connections/attempted
connections to the postmaster.  I'm thinking that when the postmaster
accept()s a connection, it can just insert a record into a table
(system catalog or not) with the information, which can be updated
after the authentication succeeds/fails or whatnot.

something like 'smbstatus' for the samba system.

So, my question is: how should I go about doing this?  should I look
into SPI, which I know nothing about?  or, what..  I don't think the
catalog cache stuff needs to be changed, it isn't as if this info
needs to be immediately accessible.