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/pc98/cbus/sio.c b/sys/pc98/cbus/sio.c
index 959726f..754d4ad 100644
--- a/sys/pc98/cbus/sio.c
+++ b/sys/pc98/cbus/sio.c
@@ -3460,6 +3460,8 @@ static cn_init_t sio_cninit;
 static cn_term_t sio_cnterm;
 static cn_getc_t sio_cngetc;
 static cn_putc_t sio_cnputc;
+static cn_grab_t sio_cngrab;
+static cn_ungrab_t sio_cnungrab;
 
 CONSOLE_DRIVER(sio);
 
@@ -3679,6 +3681,16 @@ sio_cnterm(cp)
 	comconsole = -1;
 }
 
+static void
+sio_cngrab(struct consdev *cp)
+{
+}
+
+static void
+sio_cnungrab(struct consdev *cp)
+{
+}
+
 static int
 sio_cngetc(struct consdev *cd)
 {