Implementing POSIX Sockets for Linux Fast-STREAMS
Brian Bidulock · 2007
Background UNIX networking has a rich history. The TCP/IP protocol suite was first implemented by BBN using Sockets under a DARPA research project on 4.1aBSD and then incorporated by the CSRG into 4.2BSD (MBKQ97). Lachmann and As- sociates (Legent) subsequently implemented one of the first TCP/IP protocol suite based on the Transport Layer Inter- face (TLI) (TLI92) and STREAMS (GC94). Two other pre- dominant TCP/IP implementations on STREAMS surfaced at about the same time: Wollongong and Mentat. 1.1 STREAMS STREAMS is a facility first presented in a paper by Den- nis M. Ritchie in 1984 (Rit84), originally implemented on 4.1BSD and later part of the Bell Laboratories Eighth Edi- tion UNIX, incorporated into UNIX System V Release 3 and enhanced in UNIX System V Release 4 and further in UNIX System V Release 4.2. STREAMS was used in SVR4 for terminal input-output, pseudo-terminals, pipes, named pipes (FIFOs), interprocess communication and net- working. STREAMS was used in SVR3 for networking (in the NSU package). Since its release in System V Release 3, STREAMS has been implemented across a wide range of UNIX, UNIX-like and UNIX-based systems, making its implementation and use an ipso facto standard. STREAMS is a facility that allows for a reconfigurable full duplex communications path, Stream, between a user process and a driver in the kernel. Kernel protocol modules can be pushed onto and popped from the Stream between the user process and driver. The Stream can be reconfigured in this way by a user process. The user process, neighbour- ing protocol modules and the driver communicate with each other using a message passing scheme. This permits a loose coupling between protocol modules, drivers and user pro- cesses, allowing a third-party and loadable kernel module approach to be taken toward the provisioning of protocol modules on platforms supporting STREAMS. On UNIX System V Release 4.2, STREAMS was used for terminal input-output, pipes, FIFOs (named pipes), and network communications. Modern UNIX, UNIX-like and UNIX-based systems providing STREAMS normally support some degree of network communications using STREAMS; however, many do not support STREAMS- based pipe and FIFOs 1 or terminal input-output 2 without