libchannel was accepted as a project for Google Summer of Code (or just GSoC) in 2007. It was written by Carl Fredrik Hammar who was mentored by Richard Braun.
libchannel was intended to be used to cleanly and efficiently implement channel translators that would correspond to character device files. In other words, translators for input devices, sound, network and the like.
There are many cases where one wishes to stack translators over one another. Take networking as an example, you may wish to have a pseudo network device that balance traffic over two real devices.
The problem with stacking translators this way is that it's inefficient, for every RPC to the balancer a RPC is made to each of the real devices. Now a RPC isn't really that expensive, but in a more complex example with more layers the overhead of these RPC's makes such a stacking infeasible.
However, by using libchannel a translator can provide a description of what it does (i.e. the code and data it uses), which a translator layered untop can fetch and use directly. Now only strictly required RPC's needs to be sent.
By the end of GSoC 2007, libchannel had mostly reached the initial goals. There some code missing, most notably the code for transferring channels via RPC, but similar code was already present in libstore and can be trivially adapted for libchannel. It also needed more debugging.
Despite these minor deficiencies, the project was considered a success, never the less.
However, while libchannel matched the original specifications. It's believed that it's too inflexible to make use of in many specific cases and that a more general solution is desired. While the discussion isn't over yet, it seems libchannel will become a support library to implement specialized channel libraries, e.g. libaudio and libnetwork or similar.
So work on libchannel will continue, in one form or another.
- Van Jacobson's network channels (2006-01-31) by Jonathan Corbet.