Path: utzoo!utgpu!attcan!uunet!auspex!guy
From: guy@auspex.UUCP (Guy Harris)
Newsgroups: comp.unix.questions
Subject: Re: SunOS 3.5 dd (ibs == obs) != bs
Keywords: Bug or Feature
Message-ID: <429@auspex.UUCP>
Date: 10 Nov 88 22:34:30 GMT
References: <37@eplrx7.UUCP>
Reply-To: guy@auspex.UUCP (Guy Harris)
Organization: Auspex Systems, Santa Clara
Lines: 24

>I looked at the System V source for dd and saw something like:
>
>   if (bs) ibs = obs = bs;
>
>which leads me to believe that setting bs should do the same thing as 
>setting both ibs & obs.
>
>Does BSD do something different...

The BSD "dd" does:

	if (bs) {
		ibs = obs = bs;
		if (conv == null)
			fflag++;
	}

"fflag" appears, from a quick glance at the code, to make "dd" bypass
copying data from its input buffer to its output buffer, and just read
stuff into its input buffer and write it from that buffer.

The S5R3 "dd", although it has all the V7/BSD "dd" features, doesn't
have the "fflag" hack - it may copy stuff more efficiently and thus not
bother with that particular fast path.  Griff?