Make count=0 set cpy_cnt to -1, which is slight overloading, but makes

what I was trying to do work much better (ie at all.  I could have sworn
it was working...) Fix a SEEK_SET to be SEEK_CUR, and make Bruce's
lseek() test work correctly.

bin/dd/args.c

@@ -209,6 +209,8 @@ f_count(arg)
 	cpy_cnt = get_num(arg);
 	if (cpy_cnt < 0)
 		errx(1, "count cannot be negative");
+	if (cpy_cnt == 0)
+		cpy_cnt = -1;
 }
 
 static void

bin/dd/dd.c

@@ -225,10 +225,13 @@ getfdtype(io)
 			if (S_ISCHR(sb.st_mode) && (type & D_TAPE) == 0)
 				io->flags |= ISCHR;
 		}
-	} else if (lseek(io->fd, (off_t)0, SEEK_CUR) == 0)
-		io->flags |= ISSEEK;
-	else if (errno == ESPIPE)
+		return;
+	}
+	errno = 0;
+	if (lseek(io->fd, (off_t)0, SEEK_CUR) == -1 && errno == ESPIPE)
 		io->flags |= ISPIPE;
+	else
+		io->flags |= ISSEEK;
 }
 
 static void
@@ -237,8 +240,16 @@ dd_in()
 	ssize_t n;
 
 	for (;;) {
-		if (cpy_cnt && (st.in_full + st.in_part) >= cpy_cnt)
+		switch (cpy_cnt) {
+		case -1:			/* count=0 was specified */
 			return;
+		case 0:
+			break;
+		default:
+			if (st.in_full + st.in_part >= cpy_cnt)
+				return;
+			break;
+		}
 
 		/*
 		 * Zero the buffer first if sync; if doing block operations,

bin/dd/position.c

@@ -132,7 +132,7 @@ pos_out()
 	 */
 	if (!(out.flags & ISTAPE)) {
 		errno = 0;
-		if (lseek(out.fd, out.offset * out.dbsz, SEEK_SET) == -1 &&
+		if (lseek(out.fd, out.offset * out.dbsz, SEEK_CUR) == -1 &&
 		    errno != 0)
 			err(1, "%s", out.name);
 		return;