pty bugs & features

[Piercarlo Grandi]

On 29 Aug 90 15:33:06 GMT, les at chinet.chi.il.us (Leslie Mikesell) said:

les> In article <13650 at smoke.BRL.MIL> gwyn at smoke.BRL.MIL (Doug Gwyn)
les> writes:

gwyn> In article <6038 at muffin.cme.nist.gov> libes at cme.nist.gov (Don
gwyn> Libes) writes:

libes> Why do pty's return EIO instead of 0 upon EOF?

gwyn> If they do this, it is clearly wrong and would most likely be due to
gwyn> UNIX development now being done, or at least directed, by people who
gwyn> don't understand UNIX.  read() should not return -1 upon encountering
gwyn> normal EOF on ANY object.

les> Is this meant to imply that the developers of STREAMS don't understand
les> unix?

As I understand it, several people have a grudge against USG/USO for
taking the research streams and hacking them (mostly disagreeably).

les> A read on a STREAMS file is documented to return -1 when O_NDELAY
les> is set and there is no data available (which has unfortunately been
les> propagated into the tty emulation of at least some network
les> implimentations).  Apparently there is some reason to want to know
les> about zero length messages.

Yes, *if you do messages*. Unfortunately all of UNIX is based, right or
wrong, on the idea that the fundamental abstraction is a byte stream,
not a message/record stream.

The UNIX philosophy is that if you want boundaries you use an higher
level protocol (prefix each messages/record by its length, out-of-band
record boundaries, whatever).

	I actually prefer discrete packets (that can be typed) to virtual
	circuits (which are untyped byte streams) as fundamental IPC
	abstraction, but after all you can always build one from the
	other.

Reread how Rochking ("Advanced Unix programming") discusses the various
IPC possibilities under various Unixes, concludes that named pipes are
the right thing, and then proceeds to implement records/messages on top
of named pipes. Originally streams were essentially named pipes with
dynamically selectable line disciplines.
--
Piercarlo "Peter" Grandi           | ARPA: pcg%uk.ac.aber.cs at nsfnet-relay.ac.uk
Dept of CS, UCW Aberystwyth        | UUCP: ...!mcsun!ukc!aber-cs!pcg
Penglais, Aberystwyth SY23 3BZ, UK | INET: pcg at cs.aber.ac.uk