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/uart/uart_tty.c b/sys/dev/uart/uart_tty.c
index 2170108..97ee08d 100644
--- a/sys/dev/uart/uart_tty.c
+++ b/sys/dev/uart/uart_tty.c
@@ -54,6 +54,8 @@ static cn_init_t uart_cninit;
 static cn_term_t uart_cnterm;
 static cn_getc_t uart_cngetc;
 static cn_putc_t uart_cnputc;
+static cn_grab_t uart_cngrab;
+static cn_ungrab_t uart_cnungrab;
 
 CONSOLE_DRIVER(uart);
 
@@ -108,6 +110,16 @@ uart_cnterm(struct consdev *cp)
 }
 
 static void
+uart_cngrab(struct consdev *cp)
+{
+}
+
+static void
+uart_cnungrab(struct consdev *cp)
+{
+}
+
+static void
 uart_cnputc(struct consdev *cp, int c)
 {