Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!wuarchive!zaphod.mps.ohio-state.edu!uakari.primate.wisc.edu!aplcen!haven!mimsy!chris
From: chris@mimsy.umd.edu (Chris Torek)
Newsgroups: comp.unix.programmer
Subject: Re: when to use readv()/writev() ?
Message-ID: <27539@mimsy.umd.edu>
Date: 8 Nov 90 06:55:05 GMT
References: <1990Nov8.041357.29013@decuac.dec.com>
Organization: U of Maryland, Dept. of Computer Science, Coll. Pk., MD 20742
Lines: 21

In article <1990Nov8.041357.29013@decuac.dec.com> mjr@decuac.dec.com
(Marcus J. Ranum) writes:
>	If I have 2 iovecs with 500 and 524 bytes respectively is the
>operation performed analogous to write(fd,buf,1024) or is it simply
>write(fd,buf1,500), write(fd,buf2,524) with the kernel just doing
>the legwork?

The latter (except, potentially, to a character device, but there are
no character devices in any Unix I have seen that do anything special
with multiple IO vectors).

>	I see I still have to sum up the sizes of the contents of the
>scatter/gather arrays so I can check the return of the write - doesn't
>it get kind of icky when you have a partial writev()?

Yes, it does.  This is one of the reasons I elected not to use writev()
in my stdio implementation (which has a stdio-level writev-like function
whose main raison d'etre is printf()).
-- 
In-Real-Life: Chris Torek, Univ of MD Comp Sci Dept (+1 301 405 2750)
Domain:	chris@cs.umd.edu	Path:	uunet!mimsy!chris