console: add /proc/consoles

It allows users to see what consoles are currently known to the system
and with what flags.

It is based on Werner's patch, the part about traversing fds was
removed, the code was moved to kernel/printk.c, where consoles are
handled and it makes more sense to me.

Signed-off-by: Jiri Slaby <jslaby@suse.cz> [cleanups]
Signed-off-by: "Dr. Werner Fink" <werner@suse.de>
Cc: Al Viro <viro@ZenIV.linux.org.uk>
Cc: Greg Kroah-Hartman <gregkh@suse.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

fs/proc/Makefile

@@ -15,6 +15,7 @@ proc-y	+= devices.o
 proc-y	+= interrupts.o
 proc-y	+= loadavg.o
 proc-y	+= meminfo.o
+proc-y	+= proc_console.o
 proc-y	+= stat.o
 proc-y	+= uptime.o
 proc-y	+= version.o

fs/proc/proc_console.c

@@ -0,0 +1,114 @@
+/*
+ * Copyright (c) 2010 Werner Fink, Jiri Slaby
+ *
+ * Licensed under GPLv2
+ */
+
+#include <linux/console.h>
+#include <linux/kernel.h>
+#include <linux/proc_fs.h>
+#include <linux/seq_file.h>
+#include <linux/tty_driver.h>
+
+/*
+ * This is handler for /proc/consoles
+ */
+static int show_console_dev(struct seq_file *m, void *v)
+{
+	static const struct {
+		short flag;
+		char name;
+	} con_flags[] = {
+		{ CON_ENABLED,		'E' },
+		{ CON_CONSDEV,		'C' },
+		{ CON_BOOT,		'B' },
+		{ CON_PRINTBUFFER,	'p' },
+		{ CON_BRL,		'b' },
+		{ CON_ANYTIME,		'a' },
+	};
+	char flags[ARRAY_SIZE(con_flags) + 1];
+	struct console *con = v;
+	unsigned int a;
+	int len;
+	dev_t dev = 0;
+
+	if (con->device) {
+		const struct tty_driver *driver;
+		int index;
+		driver = con->device(con, &index);
+		if (driver) {
+			dev = MKDEV(driver->major, driver->minor_start);
+			dev += index;
+		}
+	}
+
+	for (a = 0; a < ARRAY_SIZE(con_flags); a++)
+		flags[a] = (con->flags & con_flags[a].flag) ?
+			con_flags[a].name : ' ';
+	flags[a] = 0;
+
+	seq_printf(m, "%s%d%n", con->name, con->index, &len);
+	len = 21 - len;
+	if (len < 1)
+		len = 1;
+	seq_printf(m, "%*c%c%c%c (%s)", len, ' ', con->read ? 'R' : '-',
+			con->write ? 'W' : '-', con->unblank ? 'U' : '-',
+			flags);
+	if (dev)
+		seq_printf(m, " %4d:%d", MAJOR(dev), MINOR(dev));
+
+	seq_printf(m, "\n");
+
+	return 0;
+}
+
+static void *c_start(struct seq_file *m, loff_t *pos)
+{
+	struct console *con;
+	loff_t off = 0;
+
+	acquire_console_sem();
+	for_each_console(con)
+		if (off++ == *pos)
+			break;
+
+	return con;
+}
+
+static void *c_next(struct seq_file *m, void *v, loff_t *pos)
+{
+	struct console *con = v;
+	++*pos;
+	return con->next;
+}
+
+static void c_stop(struct seq_file *m, void *v)
+{
+	release_console_sem();
+}
+
+static const struct seq_operations consoles_op = {
+	.start	= c_start,
+	.next	= c_next,
+	.stop	= c_stop,
+	.show	= show_console_dev
+};
+
+static int consoles_open(struct inode *inode, struct file *file)
+{
+	return seq_open(file, &consoles_op);
+}
+
+static const struct file_operations proc_consoles_operations = {
+	.open		= consoles_open,
+	.read		= seq_read,
+	.llseek		= seq_lseek,
+	.release	= seq_release,
+};
+
+static int register_proc_consoles(void)
+{
+	proc_create("consoles", 0, NULL, &proc_consoles_operations);
+	return 0;
+}
+module_init(register_proc_consoles);