News Group Posts

two way bidirectional bi-directional pipe device

driver

From: johnd@sco.COM (John DuBois)
Newsgroups: comp.unix.sco.misc,comp.unix.sco.programmer
Subject: Re: 'Emulate' a device
Date: 17 Nov 2000 01:00:45 GMT
Message-ID: <8v1vvt$nud$1@hobbes.sco.com> 
References: <8v1ps6$e84$1@slb2.atl.mindspring.net> 


In article <8v1ps6$e84$1@slb2.atl.mindspring.net>,
Lars Oberg <lars_oberg@hotmail.com> wrote:
+What I am looking for is a device driver that simply acts as a two-way pipe
+between two devices.  Example:
+
+1) App 1 writes the string "Hello" to /dev/ttyA
+2) The device driver receives the string "Hello" on
+   /dev/ttyA and sends out the string on /dev/ttyB
+3) App 2 reads "Hello" from /dev/ttyB

Here are three possibilities:
If you don't need to do any serial ioctls or any such on the device and the
exact semantics you specified aren't neccessary, the simplest solution is to
use a pair of named pipes.  "man C mknod".  This doesn't work exactly the way
you specified: both processes would need to open both devices, and a string
written to a device appears on that same device.
A UNIX domain socket is similar but bidirectional, so you need only a single
device; anything pushed in one end comes out the other end.  More complex,
though.  
A pty behaves as you described, but has its own complexities.

        John
-- 
John DuBois     johnd@sco.com       KC6QKZ/AE
I wish to God these calculations had been executed by steam. - Charles Babbage

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