[pups] screen 3.9.9 vs. 2.11BSD write() to fifo and/or select() on socket

Steven M. Schultz sms at 2BSD.COM
Thu Feb 14 10:25:48 AEST 2002


> From: David W Talmage <talmage at cmf.nrl.navy.mil>
> Would someone please advise me about fifos and sockets in 2.11BSD?

	Ok ;)

	Don't use fifos - they don't exist (as you probably have found
	out by now :))

> I'm having 
> trouble porting screen 3.9.9, the multiplexing terminal emulator, to 2.11BSD 

	fifos and sockets are just the tip of the iceberg when it comes
	to 'screen'.   Eons ago (when screen was a fairly new program) I made
	an attempt at porting it and ran into the address space problems - seems
	that screen wants to use lots of large buffers, has lots of strings
	(all the help, etc) and so on. 

> because of them.  I'm running Mr. Schultz's 2.11BSD with all patches up to 
> #442 on Mr. Brandt's p11 emulator version 2.9.  FWIW, I have INET in my kernel
> but I've ifconfig-ed only lo0.

	Thanks for the "ownership" label but I think of it more as being
	a 'steward' and coordinator than anything else

	p11 2.9?   Wow, I've an old patched/hacked 2.5 because I can't seem
	to find p11's home now - begemot.org doesn't mention anything about

> The fifo test portion of the configure script fails when writing to the fifo.  
> The write() returns -1 and sets errno == 79, "Inappropriate file type or 

	Right, FIFOs don't exist.  One of those things I never could find
	the need or time for ;)

> format".  This happens when I run the test as root, as I must in order to use 
> mknod() to create the fifo.  See fifotest.c, below.

	If 2.11's mknod can create fifos that is _news_ to me.   I don't recall
	seeing (or adding) that capability.

> screen can use sockets instead of fifos.  That portion of the configure script
> fails as well.  It fails in that it does not return from the select() on the 
> socket until the alarm goes off.  See socketstest.c, below.

	Now that is very strange.   Unix domain sockets do work (syslogd
	uses them for example) so I'm at a loss to explain why the test
	program isn't working.

	One thing I did do is after running "./a.out&" was do an immediate
	'ps'.   That should see 2 a.out processes due to the 'fork()' call.
	I only say one.  This tells me that the alarm was started (obviously
	since alarm(5) is the first thing executed) but the child process
	raced thru and exited before the parent got to the select() call.

	With the child exited the select() will block until interrupted by
	the alarm() call.

	Steven Schultz
	sms at 2bsd.com

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