original bug diagnosed by sthen: automatic retry in msgbuf_write on

EAGAIN causes spinning.
fix from claudio:
"Let msgbuf_write return -1 with errno EAGAIN. The users then must
check if this was the case and readd the event or poll again.  The
current handling in the imsg code is wrong for sure."
ok gilles

src/lib/libutil/imsg-buffer.c

@@ -1,4 +1,4 @@
-/*	$OpenBSD: imsg-buffer.c,v 1.2 2012/06/02 21:46:53 gilles Exp $	*/
+/*	$OpenBSD: imsg-buffer.c,v 1.3 2013/11/13 20:40:24 benno Exp $	*/
 
 /*
  * Copyright (c) 2003, 2004 Henning Brauer <henning@openbsd.org>
@@ -159,7 +159,7 @@ ibuf_write(struct msgbuf *msgbuf)
 
 again:
 	if ((n = writev(msgbuf->fd, iov, i)) == -1) {
-		if (errno == EAGAIN || errno == EINTR)
+		if (errno == EINTR)
 			goto again;
 		if (errno == ENOBUFS)
 			errno = EAGAIN;
@@ -259,7 +259,7 @@ msgbuf_write(struct msgbuf *msgbuf)
 
 again:
 	if ((n = sendmsg(msgbuf->fd, &msg, 0)) == -1) {
-		if (errno == EAGAIN || errno == EINTR)
+		if (errno == EINTR)
 			goto again;
 		if (errno == ENOBUFS)
 			errno = EAGAIN;