Add DEVPTS_MULTIPLE_INSTANCES config token

Signed-off-by: Sukadev Bhattiprolu <sukadev@linux.vnet.ibm.com>
Signed-off-by: Alan Cox <alan@redhat.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

drivers/char/Kconfig

@@ -443,6 +443,17 @@ config UNIX98_PTYS
 	  All modern Linux systems use the Unix98 ptys.  Say Y unless
 	  you're on an embedded system and want to conserve memory.
 
+config DEVPTS_MULTIPLE_INSTANCES
+	bool "Support multiple instances of devpts"
+	depends on UNIX98_PTYS
+	default n
+	---help---
+	  Enable support for multiple instances of devpts filesystem.
+	  If you want to have isolated PTY namespaces (eg: in containers),
+	  say Y here.  Otherwise, say N. If enabled, each mount of devpts
+	  filesystem with the '-o newinstance' option will create an
+	  independent PTY namespace.
+
 config LEGACY_PTYS
 	bool "Legacy (BSD) PTY support"
 	default y