tty: add 'active' sysfs attribute to tty0 and console device
Kay Sievers [Wed, 1 Dec 2010 17:51:05 +0000 (18:51 +0100)]
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

Documentation/ABI/testing/sysfs-tty [new file with mode: 0644]
drivers/tty/tty_io.c
drivers/tty/vt/vt.c
include/linux/console.h
kernel/printk.c

diff --git a/Documentation/ABI/testing/sysfs-tty b/Documentation/ABI/testing/sysfs-tty
new file mode 100644 (file)
index 0000000..b138b66
--- /dev/null
@@ -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.
index c05c5af..be5ab4a 100644 (file)
@@ -3232,9 +3232,45 @@ static int __init tty_class_init(void)
 postcore_initcall(tty_class_init);
 
 /* 3/2004 jmc: why do these devices exist? */
-
 static struct cdev tty_cdev, console_cdev;
 
+static ssize_t show_cons_active(struct device *dev,
+                               struct device_attribute *attr, char *buf)
+{
+       struct console *cs[16];
+       int i = 0;
+       struct console *c;
+       ssize_t count = 0;
+
+       acquire_console_sem();
+       for (c = console_drivers; c; c = c->next) {
+               if (!c->device)
+                       continue;
+               if (!c->write)
+                       continue;
+               if ((c->flags & CON_ENABLED) == 0)
+                       continue;
+               cs[i++] = c;
+               if (i >= ARRAY_SIZE(cs))
+                       break;
+       }
+       while (i--)
+               count += sprintf(buf + count, "%s%d%c",
+                                cs[i]->name, cs[i]->index, i ? ' ':'\n');
+       release_console_sem();
+
+       return count;
+}
+static DEVICE_ATTR(active, S_IRUGO, show_cons_active, NULL);
+
+static struct device *consdev;
+
+void console_sysfs_notify(void)
+{
+       if (consdev)
+               sysfs_notify(&consdev->kobj, NULL, "active");
+}
+
 /*
  * Ok, now we can initialize the rest of the tty devices and can count
  * on memory allocations, interrupts etc..
@@ -3245,15 +3281,18 @@ int __init tty_init(void)
        if (cdev_add(&tty_cdev, MKDEV(TTYAUX_MAJOR, 0), 1) ||
            register_chrdev_region(MKDEV(TTYAUX_MAJOR, 0), 1, "/dev/tty") < 0)
                panic("Couldn't register /dev/tty driver\n");
-       device_create(tty_class, NULL, MKDEV(TTYAUX_MAJOR, 0), NULL,
-                             "tty");
+       device_create(tty_class, NULL, MKDEV(TTYAUX_MAJOR, 0), NULL, "tty");
 
        cdev_init(&console_cdev, &console_fops);
        if (cdev_add(&console_cdev, MKDEV(TTYAUX_MAJOR, 1), 1) ||
            register_chrdev_region(MKDEV(TTYAUX_MAJOR, 1), 1, "/dev/console") < 0)
                panic("Couldn't register /dev/console driver\n");
-       device_create(tty_class, NULL, MKDEV(TTYAUX_MAJOR, 1), NULL,
+       consdev = device_create(tty_class, NULL, MKDEV(TTYAUX_MAJOR, 1), NULL,
                              "console");
+       if (IS_ERR(consdev))
+               consdev = NULL;
+       else
+               device_create_file(consdev, &dev_attr_active);
 
 #ifdef CONFIG_VT
        vty_init(&console_fops);
index a8ec48e..76407ec 100644 (file)
@@ -236,6 +236,14 @@ enum {
 };
 
 /*
+ * /sys/class/tty/tty0/
+ *
+ * the attribute 'active' contains the name of the current vc
+ * console and it supports poll() to detect vc switches
+ */
+static struct device *tty0dev;
+
+/*
  * Notifier list for console events.
  */
 static ATOMIC_NOTIFIER_HEAD(vt_notifier_list);
@@ -688,6 +696,8 @@ void redraw_screen(struct vc_data *vc, int is_switch)
                        save_screen(old_vc);
                        set_origin(old_vc);
                }
+               if (tty0dev)
+                       sysfs_notify(&tty0dev->kobj, NULL, "active");
        } else {
                hide_cursor(vc);
                redraw = 1;
@@ -2967,13 +2977,24 @@ static const struct tty_operations con_ops = {
 
 static struct cdev vc0_cdev;
 
+static ssize_t show_tty_active(struct device *dev,
+                               struct device_attribute *attr, char *buf)
+{
+       return sprintf(buf, "tty%d\n", fg_console + 1);
+}
+static DEVICE_ATTR(active, S_IRUGO, show_tty_active, NULL);
+
 int __init vty_init(const struct file_operations *console_fops)
 {
        cdev_init(&vc0_cdev, console_fops);
        if (cdev_add(&vc0_cdev, MKDEV(TTY_MAJOR, 0), 1) ||
            register_chrdev_region(MKDEV(TTY_MAJOR, 0), 1, "/dev/vc/0") < 0)
                panic("Couldn't register /dev/tty0 driver\n");
-       device_create(tty_class, NULL, MKDEV(TTY_MAJOR, 0), NULL, "tty0");
+       tty0dev = device_create(tty_class, NULL, MKDEV(TTY_MAJOR, 0), NULL, "tty0");
+       if (IS_ERR(tty0dev))
+               tty0dev = NULL;
+       else
+               device_create_file(tty0dev, &dev_attr_active);
 
        vcs_init();
 
index 875cfb1..9774fe6 100644 (file)
@@ -151,7 +151,7 @@ extern int is_console_locked(void);
 extern int braille_register_console(struct console *, int index,
                char *console_options, char *braille_options);
 extern int braille_unregister_console(struct console *);
-
+extern void console_sysfs_notify(void);
 extern int console_suspend_enabled;
 
 /* Suspend and resume console messages over PM events */
index bf0420a..5417784 100644 (file)
@@ -1332,6 +1332,7 @@ void register_console(struct console *newcon)
                spin_unlock_irqrestore(&logbuf_lock, flags);
        }
        release_console_sem();
+       console_sysfs_notify();
 
        /*
         * By unregistering the bootconsoles after we enable the real console
@@ -1390,6 +1391,7 @@ int unregister_console(struct console *console)
                console_drivers->flags |= CON_CONSDEV;
 
        release_console_sem();
+       console_sysfs_notify();
        return res;
 }
 EXPORT_SYMBOL(unregister_console);