4.2bsd dump 2X speedup BUG +FIX

[Don Speck]

    Shortly after I posted my concurrent version of dumptape.c,
wallen at nprdc.arpa reported it bombing with a message
	"  DUMP: pipe error in command to slave...".
The concurrent dump was treating a short read on a pipe as an
error, when it really isn't.

    The belated fix follows.  It has been in use 2 weeks on our
(lightly-loaded) VAX/780 with TU77, and as rdump on a 750.  Since
we weren't getting short reads anyway, my testing proves nothing;
but I'm much too busy to try forcing the bug to manifest itself.
A better test will be when we get our CDC 92185 in a few weeks.

					Don Speck

P.S. We're looking for a competent, non-autocratic person to
     tend our 4.2bsd vaxen & Suns, a dozen now and more later...

diff dist/dumptape.c dumptape.c
347a348,357
> readpipe(fd,buf,count) int fd, count; char *buf; {
>	int i, n;
>	for (n=0; n<count; buf+=i, n+=i)
>		if ((i=read(fd,buf,count-n)) <= 0) {
>			if (i==0 && n==0) return(0);	/* Normal EOF */
>			senderr();
>		}
>	return(n);
> }
>
361c371
<	while (read(cmd, req, reqsiz) == reqsiz) {
---
>	while (readpipe(cmd, req, reqsiz) > 0) {
370c380
<				if (read(cmd,tblock[trecno],TP_BSIZE)!=TP_BSIZE)
---
>				if (readpipe(cmd,tblock[trecno],TP_BSIZE) <= 0)