From bb4be76cf358246ef04ea8a67f38ff2a25b6c580 Mon Sep 17 00:00:00 2001
From: Konstantin Belousov <kib@FreeBSD.org>
Date: Sat, 24 Sep 2022 23:23:31 +0300
Subject: [PATCH] snp(4): properly report detached/revoked ttys

PR:	257964
Reported by:	Bertrand Petit <bsdpr@phoe.frmug.org>
Reviewed by:	imp, markj
Sponsored by:	The FreeBSD Foundation
MFC after:	1 week
Differential revision:	https://reviews.freebsd.org/D36690
---
 share/man/man4/snp.4 | 8 ++------
 sys/dev/snp/snp.c    | 7 +++++--
 2 files changed, 7 insertions(+), 8 deletions(-)

diff --git a/share/man/man4/snp.4 b/share/man/man4/snp.4
index ce0ef66c5721..524e779ce081 100644
--- a/share/man/man4/snp.4
+++ b/share/man/man4/snp.4
@@ -1,7 +1,7 @@
 .\"
 .\" $FreeBSD$
 .\"
-.Dd November 5, 2008
+.Dd September 24, 2022
 .Dt SNP 4
 .Os
 .Sh NAME
@@ -58,8 +58,6 @@ ioctl returns a positive value equal to the number of characters
 in a read buffer.
 Special values defined are:
 .Bl -tag -width ".Dv SNP_TTYCLOSE"
-.It Dv SNP_OFLOW
-device overflow occurred, device detached.
 .It Dv SNP_TTYCLOSE
 tty not attached.
 .It Dv SNP_DETACH
@@ -92,8 +90,6 @@ were based on code written by
 .Sh BUGS
 This version of
 .Nm
-does not return proper error codes when calling
-.Dv FIONREAD .
-It also does not allow
+does not allow
 .Dv SNPSTTY
 to detach itself from the TTY.
diff --git a/sys/dev/snp/snp.c b/sys/dev/snp/snp.c
index 64e2d0f64537..3bcd2263809b 100644
--- a/sys/dev/snp/snp.c
+++ b/sys/dev/snp/snp.c
@@ -289,10 +289,13 @@ snp_ioctl(struct cdev *dev, u_long cmd, caddr_t data, int flags,
 		tp = ss->snp_tty;
 		if (tp != NULL) {
 			tty_lock(tp);
-			*(int *)data = ttyoutq_bytesused(&ss->snp_outq);
+			if (tty_gone(tp))
+				*(int *)data = SNP_TTYCLOSE;
+			else
+				*(int *)data = ttyoutq_bytesused(&ss->snp_outq);
 			tty_unlock(tp);
 		} else {
-			*(int *)data = 0;
+			*(int *)data = SNP_DETACH;
 		}
 		return (0);
 	default: