document that ibuf_write() and msgbuf_write() can now return EAGAIN

from and with deraadt@

src/lib/libutil/imsg_init.3

@@ -1,4 +1,4 @@
-.\" $OpenBSD: imsg_init.3,v 1.9 2013/06/05 03:40:26 tedu Exp $
+.\" $OpenBSD: imsg_init.3,v 1.10 2013/11/13 21:04:46 benno Exp $
 .\"
 .\" Copyright (c) 2010 Nicholas Marriott <nicm@openbsd.org>
 .\"
@@ -14,7 +14,7 @@
 .\" IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING
 .\" OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 .\"
-.Dd $Mdocdate: June 5 2013 $
+.Dd $Mdocdate: November 13 2013 $
 .Dt IMSG_INIT 3
 .Os
 .Sh NAME
@@ -395,6 +395,9 @@ using
 .Xr writev 2 .
 It returns 1 if it succeeds, \-1 on error and 0 when an EOF condition on the
 socket is detected.
+Temporary resource shortages are returned with errno
+.Er EAGAIN
+and require the application to retry again in the future.
 .Pp
 .Fn ibuf_free
 frees
@@ -423,6 +426,9 @@ to transmit buffers queued in
 .Fa msgbuf .
 It returns 1 if it succeeds, \-1 on error, and 0 when an EOF condition on the
 socket is detected.
+Temporary resource shortages are returned with errno
+.Er EAGAIN
+and require the application to retry again in the future.
 .Pp
 .Fn msgbuf_drain
 discards data from buffers queued in
@@ -492,7 +498,7 @@ library is used to monitor the socket file descriptor.
 When the socket is ready for writing, queued messages are transmitted with
 .Fn msgbuf_write :
 .Bd -literal -offset indent
-	if (msgbuf_write(&ibuf-\*(Gtw) \*(Lt 0) {
+	if (msgbuf_write(&ibuf-\*(Gtw) \*(Lt 0 && errno != EAGAIN) {
 		/* handle write failure */
 	}
 .Ed