From mboxrd@z Thu Jan  1 00:00:00 1970
Message-Id: <200007310115.VAA03125@cse.psu.edu>
To: 9fans@cse.psu.edu
Subject: Re: [9fans] pipefile
From: "rob pike" <rob@plan9.bell-labs.com>
Date: Sun, 30 Jul 2000 21:14:55 -0400
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> If you don't mind, could you also say a word as to what made the
> /dev/cons case special?  Who was writing to /dev/cons all of the 
> keyboard input so that it worked? (rio?)

/dev/cons is connected to standard in and standard out, that's all.
I stupidly had file descriptors 0 and 1 wired into the code.
Nobody was writing any keyboard input of any kind to /dev/cons.

What pipefile does is place filters between the file and
any subsequent program that opens it for i/o, by binding a pipe
onto the file and then connecting the filters to the pipe.  The other
end of the pipe is connected to the underlying file.

Normally you have, in effect,

	</dev/cons  rc   >/dev/cons

but after

	pipefile -r 'readcmd' -w 'writecmd' /dev/cons
	rc < /dev/cons >/dev/cons

you have, almost literally,

	</dev/cons readcmd | rc | writecmd >/dev/cons

(The only difference is that it uses one full duplex pipe instead
of two half duplex ones.)

What was special about /dev/cons was that I had this
example in mind when I wrote the program, so what
it actually did was closer to

	</fd/0 readcmd | rc | writecmd >/fd/1

The fix was to open the file explicitly.

Hope that helps.

-rob