Path: utzoo!attcan!uunet!lanai!ron
From: ron@Eyring.COM (Ron Holt)
Newsgroups: comp.realtime
Subject: Real-time Unix read()s?
Message-ID: <1990Nov19.161402.7646@Eyring.COM>
Date: 19 Nov 90 16:14:02 GMT
Organization: Eyring, Inc.
Lines: 30

It has been mentioned to me that Arix provides a alternative read() call
that can improve performance for real-time applications.  If I recall
correctly, the system call looks like this:

	n = rread(int fd, char **buf, int nbytes)

In other words, the OS returns a POINTER to the buffer that the OS
(not the user) selected into which the data is put.  The idea is that
by letting the OS tell the user where it already has the data, a data
copy can be avoided.  I believe there is also a rfree() call to free
this buffer.

I have several questions about this interface:

	Can anyone verify if my information is correct?
	
	Can you tell me more about this interface?  A summary from
	the man pages perhaps?

	Is there a counterpart to this scheme for write()?

	How much does this help application performance?  Does
	anybody have actual performance figures?

	What are the drawbacks to using this approach?

Thanks.
-- 
Ron Holt	ron@Eyring.COM  uunet!lanai!ron
Eyring Inc.	+1 801-375-2434 x434