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From: wls@astrovax.UUCP (William L. Sebok)
Newsgroups: net.unix-wizards
Subject: Re: 4.2 readv() and writev()
Message-ID: <249@astrovax.UUCP>
Date: Fri, 23-Mar-84 11:34:35 EST
Article-I.D.: astrovax.249
Posted: Fri Mar 23 11:34:35 1984
Date-Received: Sun, 25-Mar-84 08:38:31 EST
References: <619@hammer.UUCP>
Organization: Princeton Univ. Astrophysics
Lines: 24

> I am in the process of implementing a couple of device
> drivers to run with a 4.2 BSD kernel.  The devices use DMA, 
> so I am planning not to implement the scatter/gather I/O
> functionality of the "readv" and "writev" system calls 
> for these drivers.
> Can anyone tell me if this will break Unix?  I cannot
> find any examples of utilities or systems that use 
> readv/writev now, so do not believe that it should
> make much difference.
> Dave Cobbley		Tektronix, Inc.

 I myself have been writing a driver for an image display card from Peritec Inc.
Implementing the scatter/gather code complicates things quite a bit.  I would
also like to know when this need for this to be implemented in one system call
(above and beyond using a series of read/write calls), is great enough to
justify the extra trouble in the kernel (where after all there is supposed to
be some attempt to keep things "simple").
 All of the dma drivers in the distribution implement the scatter/gather
stuff in the higher level routines that are used by/call the driver.  For
instance the scatter/gather for the raw unbuffered devices is implemented in
physio().
-- 
Bill Sebok			Princeton University, Astrophysics
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