vt,console,kdb: implement atomic console enter/leave functions

These functions allow the kernel debugger to save and restore the
state of the system console.

Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>
Signed-off-by: Jason Wessel <jason.wessel@windriver.com>
CC: David Airlie <airlied@linux.ie>
CC: Andrew Morton <akpm@linux-foundation.org>

1 files changed, 61 insertions, 0 deletions

diff --git a/drivers/char/vt.c b/drivers/char/vt.c
index 7cdb6ee569cd..117ce99115dc 100644
--- a/drivers/char/vt.c
+++ b/drivers/char/vt.c
@@ -187,10 +187,15 @@ static DECLARE_WORK(console_work, console_callback);
  * fg_console is the current virtual console,
  * last_console is the last used one,
  * want_console is the console we want to switch to,
+ * saved_* variants are for save/restore around kernel debugger enter/leave
  */
 int fg_console;
 int last_console;
 int want_console = -1;
+int saved_fg_console;
+int saved_last_console;
+int saved_want_console;
+int saved_vc_mode;
 
 /*
  * For each existing display, we have a pointer to console currently visible
@@ -3414,6 +3419,62 @@ int con_is_bound(const struct consw *csw)
 EXPORT_SYMBOL(con_is_bound);
 
 /**
+ * con_debug_enter - prepare the console for the kernel debugger
+ * @sw: console driver
+ *
+ * Called when the console is taken over by the kernel debugger, this
+ * function needs to save the current console state, then put the console
+ * into a state suitable for the kernel debugger.
+ *
+ * RETURNS:
+ * Zero on success, nonzero if a failure occurred when trying to prepare
+ * the console for the debugger.
+ */
+int con_debug_enter(struct vc_data *vc)
+{
+        int ret = 0;
+
+        saved_fg_console = fg_console;
+        saved_last_console = last_console;
+        saved_want_console = want_console;
+        saved_vc_mode = vc->vc_mode;
+        vc->vc_mode = KD_TEXT;
+        console_blanked = 0;
+        if (vc->vc_sw->con_debug_enter)
+                ret = vc->vc_sw->con_debug_enter(vc);
+        return ret;
+}
+EXPORT_SYMBOL_GPL(con_debug_enter);
+
+/**
+ * con_debug_leave - restore console state
+ * @sw: console driver
+ *
+ * Restore the console state to what it was before the kernel debugger
+ * was invoked.
+ *
+ * RETURNS:
+ * Zero on success, nonzero if a failure occurred when trying to restore
+ * the console.
+ */
+int con_debug_leave(void)
+{
+        struct vc_data *vc;
+        int ret = 0;
+
+        fg_console = saved_fg_console;
+        last_console = saved_last_console;
+        want_console = saved_want_console;
+        vc_cons[fg_console].d->vc_mode = saved_vc_mode;
+
+        vc = vc_cons[fg_console].d;
+        if (vc->vc_sw->con_debug_leave)
+                ret = vc->vc_sw->con_debug_leave(vc);
+        return ret;
+}
+EXPORT_SYMBOL_GPL(con_debug_leave);
+
+/**
  * register_con_driver - register console driver to console layer
  * @csw: console driver
  * @first: the first console to take over, minimum value is 0