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, 12 insertions, 0 deletions

diff --git a/sys/dev/syscons/syscons.c b/sys/dev/syscons/syscons.c
index db678a5..f25026e 100644
--- a/sys/dev/syscons/syscons.c
+++ b/sys/dev/syscons/syscons.c
@@ -229,6 +229,8 @@ static cn_init_t	sc_cninit;
 static cn_term_t	sc_cnterm;
 static cn_getc_t	sc_cngetc;
 static cn_putc_t	sc_cnputc;
+static cn_grab_t	sc_cngrab;
+static cn_ungrab_t	sc_cnungrab;
 
 CONSOLE_DRIVER(sc);
 
@@ -1609,6 +1611,16 @@ sc_cnterm(struct consdev *cp)
 }
 
 static void
+sc_cngrab(struct consdev *cp)
+{
+}
+
+static void
+sc_cnungrab(struct consdev *cp)
+{
+}
+
+static void
 sc_cnputc(struct consdev *cd, int c)
 {
     u_char buf[1];