kern cons: introduce infrastructure for console grabbing by kernel

At the moment grab and ungrab methods of all console drivers are no-ops.

Current intended meaning of the calls is that the kernel takes control of
console input.  In the future the semantics may be extended to mean that
the calling thread takes full ownership of the console (e.g. console
output from other threads could be suspended).

Inspired by:	bde
MFC after:	2 months

1 files changed, 10 insertions, 0 deletions

diff --git a/sys/sys/cons.h b/sys/sys/cons.h
index e84318f..bd599c0 100644
--- a/sys/sys/cons.h
+++ b/sys/sys/cons.h
@@ -44,6 +44,8 @@ struct tty;
 typedef	void	cn_probe_t(struct consdev *);
 typedef	void	cn_init_t(struct consdev *);
 typedef	void	cn_term_t(struct consdev *);
+typedef	void	cn_grab_t(struct consdev *);
+typedef	void	cn_ungrab_t(struct consdev *);
 typedef	int	cn_getc_t(struct consdev *);
 typedef	void	cn_putc_t(struct consdev *, int);
 
@@ -58,6 +60,10 @@ struct consdev_ops {
 				/* kernel getchar interface */
 	cn_putc_t	*cn_putc;
 				/* kernel putchar interface */
+	cn_grab_t	*cn_grab;
+				/* grab console for exclusive kernel use */
+	cn_ungrab_t	*cn_ungrab;
+				/* ungrab console */
 };
 
 struct consdev {
@@ -99,6 +105,8 @@ extern	struct tty *constty;	/* Temporary virtual console. */
 		.cn_term = name##_cnterm,				\
 		.cn_getc = name##_cngetc,				\
 		.cn_putc = name##_cnputc,				\
+		.cn_grab = name##_cngrab,				\
+		.cn_ungrab = name##_cnungrab,				\
 	};								\
 	CONSOLE_DEVICE(name##_consdev, name##_consdev_ops, NULL)
 
@@ -109,6 +117,8 @@ int	cnadd(struct consdev *);
 void	cnavailable(struct consdev *, int);
 void	cnremove(struct consdev *);
 void	cnselect(struct consdev *);
+void	cngrab(void);
+void	cnungrab(void);
 int	cncheckc(void);
 int	cngetc(void);
 void	cnputc(int);