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From: Terry Lambert <terry@lambert.org>
Message-Id: <199708032058.NAA02222@phaeton.artisoft.com>
Subject: Re: tty-level buffer overflows
To: henrich@crh.cl.msu.edu (Charles Henrich)
Date: Sun, 3 Aug 1997 13:58:23 -0700 (MST)
Cc: msmith@atrad.adelaide.edu.au, tom@sdf.com, freebsd-hackers@FreeBSD.ORG
In-Reply-To: <19970803112147.21483@crh.cl.msu.edu> from "Charles Henrich" at Aug 3, 97 11:21:47 am
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> > Your application is busted; data is arriving faster than your app is reading
> > it, and the kernel has run out of patience and started throwing the data
> > away.
> 
> Im afraid not, the application is a software Upload, with a singly byte ack
> every 2k, if the serial port cant handle that, theres a problem.  I would
> presume that if the buffer is full, a write() should block.  

Input and output buffers are seperate.  If they weren't, the original
"cu" program, which forked using a reader and a writer as seperate
processes to create the illusion of a full duplex connection, would
have failed (nb: "cu" predates the select(2) and poll(2) calls).

For async I/O, it would mean that a queued read request would need
to complete before a queued write request could complete (nb: this
was a bad problem with VMS QIO() services for full duplex protocols
on serial ports, and is generally a problem for most "multidrop"
serial port board drivers for commercial UNIX implementations; for
example, the Altos 2000).


So anyway, your input buffer is filling up.  Please see my other
posting for what you can do about it.


					Terry Lambert
					terry@lambert.org
---
Any opinions in this posting are my own and not those of my present
or previous employers.