From 2cf9eb6c4ead758c0083a30460e3244fab92f268 Mon Sep 17 00:00:00 2001
From: Edward Tomasz Napierala <trasz@FreeBSD.org>
Date: Mon, 16 Dec 2019 20:15:44 +0000
Subject: [PATCH] Add a hack to make ^T work for Linux binaries, enabled with
 'compat.linux.preserve_vstatus=1' sysctl.

MFC after:	2 weeks
Sponsored by:	The FreeBSD Foundation
Differential Revision:	https://reviews.freebsd.org/D21967
---
 share/man/man4/linux.4         | 8 ++++++++
 sys/compat/linux/linux_ioctl.c | 4 ++++
 sys/compat/linux/linux_ioctl.h | 1 +
 sys/compat/linux/linux_mib.c   | 4 ++++
 sys/compat/linux/linux_mib.h   | 2 ++
 5 files changed, 19 insertions(+)

diff --git a/share/man/man4/linux.4 b/share/man/man4/linux.4
index 04e7a82585f7..997dc16d7692 100644
--- a/share/man/man4/linux.4
+++ b/share/man/man4/linux.4
@@ -109,6 +109,14 @@ Recent versions of GNU libc are known to use different syscalls depending
 on the value of this sysctl.
 .It Va compat.linux.oss_version
 Linux Open Sound System version.
+.It Va compat.linux.preserve_vstatus
+When set to 1, it prevents Linux applications from resetting the
+.Xr termios 4
+VSTATUS setting.
+From a user perspective, this makes
+.Va SIGINFO
+work for Linux executables.
+Defaults to 0.
 .Sh FILES
 .Bl -tag -width /compat/linux/dev/shm -compact
 .It Pa /compat/linux
diff --git a/sys/compat/linux/linux_ioctl.c b/sys/compat/linux/linux_ioctl.c
index d33ddd2bab88..75714cd3d3f2 100644
--- a/sys/compat/linux/linux_ioctl.c
+++ b/sys/compat/linux/linux_ioctl.c
@@ -500,6 +500,8 @@ bsd_to_linux_termios(struct termios *bios, struct linux_termios *lios)
 	lios->c_cc[LINUX_VDISCARD] = bios->c_cc[VDISCARD];
 	lios->c_cc[LINUX_VWERASE] = bios->c_cc[VWERASE];
 	lios->c_cc[LINUX_VLNEXT] = bios->c_cc[VLNEXT];
+	if (linux_preserve_vstatus)
+		lios->c_cc[LINUX_VSTATUS] = bios->c_cc[VSTATUS];
 
 	for (i=0; i<LINUX_NCCS; i++) {
 		if (i != LINUX_VMIN && i != LINUX_VTIME &&
@@ -614,6 +616,8 @@ linux_to_bsd_termios(struct linux_termios *lios, struct termios *bios)
 	bios->c_cc[VDISCARD] = lios->c_cc[LINUX_VDISCARD];
 	bios->c_cc[VWERASE] = lios->c_cc[LINUX_VWERASE];
 	bios->c_cc[VLNEXT] = lios->c_cc[LINUX_VLNEXT];
+	if (linux_preserve_vstatus)
+		bios->c_cc[VSTATUS] = lios->c_cc[LINUX_VSTATUS];
 
 	for (i=0; i<NCCS; i++) {
 		if (i != VMIN && i != VTIME &&
diff --git a/sys/compat/linux/linux_ioctl.h b/sys/compat/linux/linux_ioctl.h
index e529f6494969..d860a708f498 100644
--- a/sys/compat/linux/linux_ioctl.h
+++ b/sys/compat/linux/linux_ioctl.h
@@ -435,6 +435,7 @@
 #define	LINUX_VWERASE		14
 #define	LINUX_VLNEXT		15
 #define	LINUX_VEOL2		16
+#define	LINUX_VSTATUS		18
 #define	LINUX_NCCS		19
 
 #define	LINUX_POSIX_VDISABLE	'\0'
diff --git a/sys/compat/linux/linux_mib.c b/sys/compat/linux/linux_mib.c
index d74313056b32..a7e2273f12ff 100644
--- a/sys/compat/linux/linux_mib.c
+++ b/sys/compat/linux/linux_mib.c
@@ -62,6 +62,10 @@ static unsigned linux_osd_jail_slot;
 
 SYSCTL_NODE(_compat, OID_AUTO, linux, CTLFLAG_RW, 0, "Linux mode");
 
+int linux_preserve_vstatus = 0;
+SYSCTL_INT(_compat_linux, OID_AUTO, preserve_vstatus, CTLFLAG_RWTUN,
+    &linux_preserve_vstatus, 0, "Preserve VSTATUS termios(4) flag");
+
 static int	linux_set_osname(struct thread *td, char *osname);
 static int	linux_set_osrelease(struct thread *td, char *osrelease);
 static int	linux_set_oss_version(struct thread *td, int oss_version);
diff --git a/sys/compat/linux/linux_mib.h b/sys/compat/linux/linux_mib.h
index d5ced52e3398..aea4b1a71c50 100644
--- a/sys/compat/linux/linux_mib.h
+++ b/sys/compat/linux/linux_mib.h
@@ -62,4 +62,6 @@ int	linux_kernver(struct thread *td);
 
 #define	linux_use26(t)		(linux_kernver(t) >= LINUX_KERNVER_2006000)
 
+extern int linux_preserve_vstatus;
+
 #endif /* _LINUX_MIB_H_ */