Preserve pipe select(2) semantics when the other end of the pipe is gone.

In preparation for implementing select(2) on top of kqueue.

ok mpi@

1 files changed, 17 insertions, 6 deletions

diff --git a/sys/kern/sys_pipe.c b/sys/kern/sys_pipe.c
index f9bae89aa46..fa855710712 100644
--- a/sys/kern/sys_pipe.c
+++ b/sys/kern/sys_pipe.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: sys_pipe.c,v 1.126 2020/12/30 17:02:32 visa Exp $	*/
+/*	$OpenBSD: sys_pipe.c,v 1.127 2021/10/22 05:00:26 anton Exp $	*/
 
 /*
  * Copyright (c) 1996 John S. Dyson
@@ -890,16 +890,27 @@ pipe_kqfilter(struct file *fp, struct knote *kn)
 		kn->kn_hook = rpipe;
 		klist_insert_locked(&rpipe->pipe_sel.si_note, kn);
 		break;
-	case EVFILT_WRITE:
+	case EVFILT_WRITE: {
+		struct pipe *kpipe = wpipe;
+
 		if (wpipe == NULL) {
 			/* other end of pipe has been closed */
-			error = EPIPE;
-			break;
+			if (kn->kn_flags & __EV_POLL) {
+				/*
+				 * select(2) semantics requires the pipe to
+				 * become ready only to deliver EPIPE.
+				 */
+				kpipe = rpipe;
+			} else {
+				error = EPIPE;
+				break;
+			}
 		}
 		kn->kn_fop = &pipe_wfiltops;
-		kn->kn_hook = wpipe;
-		klist_insert_locked(&wpipe->pipe_sel.si_note, kn);
+		kn->kn_hook = kpipe;
+		klist_insert_locked(&kpipe->pipe_sel.si_note, kn);
 		break;
+	}
 	default:
 		error = EINVAL;
 	}