From 006eb44926d6949e0b60b21920f1ea93f03efd2f Mon Sep 17 00:00:00 2001
From: Vladimir Kondratyev <wulf@FreeBSD.org>
Date: Sun, 29 Mar 2020 23:01:36 +0000
Subject: [PATCH] evdev: return error rather than zero-length data on blocked
 read()

if blocked process has been woken up by evdev device destruction.

MFC after:	2 weeks
---
 sys/dev/evdev/cdev.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/sys/dev/evdev/cdev.c b/sys/dev/evdev/cdev.c
index f945101932c7..cd40d1f218a7 100644
--- a/sys/dev/evdev/cdev.c
+++ b/sys/dev/evdev/cdev.c
@@ -217,6 +217,8 @@ evdev_read(struct cdev *dev, struct uio *uio, int ioflag)
 				client->ec_blocked = true;
 				ret = mtx_sleep(client, &client->ec_buffer_mtx,
 				    PCATCH, "evread", 0);
+				if (ret == 0 && client->ec_revoked)
+					ret = ENODEV;
 			}
 		}
 	}