VT notifier extension for accessibility

Some accessibility modules need to be able to catch the output on the
console before the VT interpretation, and possibly swallow it.

[akpm@linux-foundation.org: coding-style fixes]
Signed-off-by: Samuel Thibault <samuel.thibault@ens-lyon.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

2 files changed, 9 insertions, 0 deletions

diff --git a/drivers/char/vt.c b/drivers/char/vt.c
index 9b58b894f823..df4c3ead9e2b 100644
--- a/drivers/char/vt.c
+++ b/drivers/char/vt.c
@@ -2054,6 +2054,7 @@ static int do_con_write(struct tty_struct *tty, const unsigned char *buf, int co
         unsigned long draw_from = 0, draw_to = 0;
         struct vc_data *vc;
         unsigned char vc_attr;
+        struct vt_notifier_param param;
         uint8_t rescan;
         uint8_t inverse;
         uint8_t width;
@@ -2113,6 +2114,8 @@ static int do_con_write(struct tty_struct *tty, const unsigned char *buf, int co
         if (IS_FG(vc))
                 hide_cursor(vc);
 
+        param.vc = vc;
+
         while (!tty->stopped && count) {
                 int orig = *buf;
                 c = orig;
@@ -2201,6 +2204,11 @@ rescan_last_byte:
                     tc = vc->vc_translate[vc->vc_toggle_meta ? (c | 0x80) : c];
                 }
 
+                param.c = tc;
+                if (atomic_notifier_call_chain(&vt_notifier_list, VT_PREWRITE,
+                                        &param) == NOTIFY_STOP)
+                        continue;
+
                 /* If the original code was a control character we
                  * only allow a glyph to be displayed if the code is
                  * not normally used (such as for cursor movement) or
diff --git a/include/linux/notifier.h b/include/linux/notifier.h
index f4df40038f0c..20dfed590183 100644
--- a/include/linux/notifier.h
+++ b/include/linux/notifier.h
@@ -247,6 +247,7 @@ extern struct blocking_notifier_head reboot_notifier_list;
 #define VT_DEALLOCATE           0x0002 /* Console will be deallocated */
 #define VT_WRITE                0x0003 /* A char got output */
 #define VT_UPDATE               0x0004 /* A bigger update occurred */
+#define VT_PREWRITE             0x0005 /* A char is about to be written to the console */
 
 #endif /* __KERNEL__ */
 #endif /* _LINUX_NOTIFIER_H */