[PATCH, RFC, BAD IDEA] /proc/tty/console

[Bill Nottingham <notting@redhat.com>]

I'm not seriously proposing this. But, as far as I can tell, this
information isn't exposed to userspace anywhere, and it's a useful
thing to know. I'm certainly open for better ideas on how to expose
this (sysfs attributes? other?)

....

The attached patch adds /proc/tty/console. The contents of it are
simply a description of the current drivers attached to /dev/console.
For example, a boot with 'console=ttyS3,115200n1 console=tty0' would
yield:

# cat /proc/tty/console
unknown             /dev/tty0
serial              /dev/ttyS3

Bill

---
diff -ru linux-2.6.24.noarch/fs/proc/proc_tty.c linux/fs/proc/proc_tty.c
--- linux-2.6.24.noarch/fs/proc/proc_tty.c	2008-02-27 12:50:59.000000000 -0500
+++ linux/fs/proc/proc_tty.c	2008-02-27 12:25:54.000000000 -0500
@@ -6,6 +6,7 @@
 
 #include <asm/uaccess.h>
 
+#include <linux/console.h>
 #include <linux/init.h>
 #include <linux/errno.h>
 #include <linux/time.h>
@@ -129,6 +130,38 @@
 	return seq_open(file, &tty_drivers_op);
 }
 
+static int show_tty_console(struct seq_file *m, void *v)
+{
+	int index;
+	struct console *c;
+
+	for (c = console_drivers; c ; c = c->next) {
+		struct tty_driver *t = NULL;
+		if (!c->device)
+			continue;
+		t = c->device(c, &index);
+		seq_printf(m, "%-20s", t->driver_name ? t->driver_name : "unknown");
+		seq_printf(m, "/dev/%s%d", t->name, c->index);
+		seq_printf(m, "\n");
+	}
+	return 0;
+}
+
+static void *c_start(struct seq_file *m, loff_t *pos)
+{
+	return *pos == 0 ? &c_start : NULL;
+}
+
+static void *c_next(struct seq_file *m, void *v, loff_t *pos)
+{
+	++*pos;
+	return c_start(m, pos);
+}
+
+static void c_stop(struct seq_file *m, void *v)
+{
+}
+
 static const struct file_operations proc_tty_drivers_operations = {
 	.open		= tty_drivers_open,
 	.read		= seq_read,
@@ -136,6 +169,25 @@
 	.release	= seq_release,
 };
 
+static const struct seq_operations tty_console_op = {
+	.start		= c_start,
+	.next		= c_next,
+	.stop		= c_stop,
+	.show		= show_tty_console
+};
+
+static int tty_console_open(struct inode *inode, struct file *file)
+{
+	return seq_open(file, &tty_console_op);
+}
+
+static const struct file_operations proc_tty_console_operations = {
+	.open		= tty_console_open,
+	.read		= seq_read,
+	.llseek		= seq_lseek,
+	.release	= seq_release
+};
+
 /*
  * This is the handler for /proc/tty/ldiscs
  */
@@ -230,4 +282,7 @@
 	entry = create_proc_entry("tty/drivers", 0, NULL);
 	if (entry)
 		entry->proc_fops = &proc_tty_drivers_operations;
+	entry = create_proc_entry("tty/console", 0, NULL);
+	if (entry)
+		entry->proc_fops = &proc_tty_console_operations;
 }