tty: add 'active' sysfs attribute to tty0 and console device

tty: add 'active' sysfs attribute to tty0 and console device

Userspace can query the actual virtual console, and the configured
console devices behind /dev/tt0 and /dev/console.

The last entry in the list of devices is the active device, analog
to the console= kernel command line option.

The attribute supports poll(), which is raised when the virtual
console is changed or /dev/console is reconfigured.

Signed-off-by: Kay Sievers <kay.sievers@vrfy.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

index 0000000..b138b66

1 files changed, 19 insertions, 0 deletions

diff --git a/Documentation/ABI/testing/sysfs-tty b/Documentation/ABI/testing/sysfs-tty
new file mode 100644
index 00000000000..b138b663bf5
--- /dev/null
+++ b/Documentation/ABI/testing/sysfs-tty
@@ -0,0 +1,19 @@
+What:           /sys/class/tty/console/active
+Date:           Nov 2010
+Contact:        Kay Sievers <kay.sievers@vrfy.org>
+Description:
+                 Shows the list of currently configured
+                 console devices, like 'tty1 ttyS0'.
+                 The last entry in the file is the active
+                 device connected to /dev/console.
+                 The file supports poll() to detect virtual
+                 console switches.
+
+What:           /sys/class/tty/tty0/active
+Date:           Nov 2010
+Contact:        Kay Sievers <kay.sievers@vrfy.org>
+Description:
+                 Shows the currently active virtual console
+                 device, like 'tty1'.
+                 The file supports poll() to detect virtual
+                 console switches.