I did  add a few new features to LSX to deal with contiguous files and to handle asynchronous read/write's for real time applications. They are described in the LSX paper in the 1978 BSTJ on the UNIX Time-Sharing System. Heinz On 5/31/2020 9:46 AM, Warner Losh wrote: > Sorry to top post, but LSX or Miniunix had non blocking I/O as well. > It was in one of the documents that Clem scanned in the last year. It > specifically was an experiment into how to do it. > > Warner > > On Sun, May 31, 2020, 10:07 AM Clem Cole > wrote: > > > > On Sun, May 31, 2020 at 7:10 AM Paul Ruizendaal > wrote: > >  This behaviour seems to have continued into SysVR1, I’m not > sure when EAGAIN came into use as a return value for this use > case in the SysV lineage. Maybe with SysVR3 networking? > > Actually, I'm pretty sure that was a product of the POSIX > discussions.  BSD already had networking an EWOULDBLOCK.   We had > argued about EWOULDBLOCK a great deal, we also were arguing about > signal semantics. I've forgotten many of the details, Heinz may > remember more than I do.  EAGAIN was created as a compromise -- > IIRC neither system had it yet.   SVR3 networking was where it > went into System V, although some of the AT&T representatives were > none too happy about it. > > > In the Research lineage, the above SysIII approach does not > seem to exist, although the V8 manual page for open() says > under BUGS "It should be possible [...] to optionally call > open without the possibility of hanging waiting for carrier on > communication lines.” In the same location for V10 it reads > "It should be possible to call open without waiting for > carrier on communication lines.” > > The July 1981 design proposals for 4.2BSD note that SysIII > non-blocking files are a useful feature and should be included > in the new system. In Jan/Feb 1982 this appears to be coded > up, although not all affected files are under SCCS tracking at > that point in time. Non-blocking behaviour is changed from the > SysIII semantics, in that EWOULDBLOCK is returned instead of 0 > when progress is not possible. The non-blocking behaviour is > extended beyond TTY’s and pipes to sockets, with additional > errors (such as EINPROGRESS). At this time EWOULDBLOCK is not > the same error number as EGAIN. > > My memory is that Keith was the BSD (CSRG) person at the POSIX > meeting (he, Jim McGinness of DEC, and I created PAX at one point > as a compromise).   I wish I could remember all of the details, > but this was all argued at the POSIX meetings. > > As I said before the folks from AT&T just wanted to take the SVID > and rubber stamp it at the specification.  Part of it the problem > was they wanted to be free to do what things/make choices that the > rest of us might or might not like (for instance, they did not > want the sockets interface). > > > It would seem that the differences between the BSD and SysV > lineages in this area persisted until around 2000 or so. > > Yep - cause around then POSIX started to settle out and both > systems began to follow it. >