Revert "tty: Add a new file /proc/tty/consoles"

This reverts commit f4a3e0bceb57466c31757f25e4e0ed108d1299ec.  Jiri
Sladby points out that the tty structure we're using may already be
gone, and Al Viro doesn't hold back in complaining about the random
loading of 'filp->private_data' which doesn't have to be a pointer at
all, nor does checking the magic field for TTY_MAGIC prove anything.

Belated review by Al:

 "a) global variable depending on stdin of the last opener? Affecting
     output of read(2)? Really?

  b) iterator is broken; list should be locked in ->start(), unlocked in
     ->stop() and *NOT* unlocked/relocked in ->next()

  c) ->show() ought to do nothing in case of ->device == NULL, instead
     of skipping those in ->next()/->start()

  d) regardless of the merits of the bright idea about asterisk at that
     line in output *and* regardless of (a), the implementation is not
     only atrociously ugly, it's actually very likely to be a roothole.
     Verifying that Cthulhu knows what number happens to be address of a
     tty_struct by blindly dereferencing memory at that address...
     Ouch.

  Please revert that crap."

And Christoph pipes in and NAK's the approach of walking fd tables etc
too.  So it's pretty unanimous.

Noticed-by: Jri Slaby <jslaby@suse.cz>
Requested-by: Al Viro <viro@zeniv.linux.org.uk>
Cc: Greg Kroah-Hartman <gregkh@suse.de>
Cc: Werner Fink <werner@suse.de>
Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>
Cc: Christoph Hellwig <hch@infradead.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

Documentation/filesystems/proc.txt

@@ -1075,7 +1075,6 @@ Table 1-11: Files in /proc/tty
  drivers       list of drivers and their usage                
  ldiscs        registered line disciplines                    
  driver/serial usage statistic and status of single tty lines 
- consoles      registered system console lines
 ..............................................................................
 
 To see  which  tty's  are  currently in use, you can simply look into the file
@@ -1094,37 +1093,6 @@ To see  which  tty's  are  currently in use, you can simply look into the file
   /dev/tty             /dev/tty        5       0 system:/dev/tty 
   unknown              /dev/tty        4    1-63 console 
 
-To see which character device lines are currently used for the system console
-/dev/console, you may simply look into the file /proc/tty/consoles:
-
-  > cat /proc/tty/consoles
-  tty0                 -WU (ECp)       4:7
-  ttyS0                -W- (Ep)        4:64
-
-The columns are:
-
-  device               name of the device
-  operations           R = can do read operations
-                       W = can do write operations
-                       U = can do unblank
-  flags                E = it is enabled
-                       C = it is prefered console
-                       B = it is primary boot console
-                       p = it is used for printk buffer
-                       b = it is not a TTY but a Braille device
-                       a = it is safe to use when cpu is offline
-                       * = it is standard input of the reading process
-  major:minor          major and minor number of the device separated by a colon
-
-If the reading process holds /dev/console open at the regular standard input
-stream the active device will be marked by an asterisk:
-
-  > cat /proc/tty/consoles < /dev/console
-  tty0                 -WU (ECp*)      4:7
-  ttyS0                -W- (Ep)        4:64
-  > tty
-  /dev/pts/3
-
 
 1.8 Miscellaneous kernel statistics in /proc/stat
 -------------------------------------------------

fs/proc/proc_tty.c

@@ -12,10 +12,7 @@
 #include <linux/proc_fs.h>
 #include <linux/stat.h>
 #include <linux/tty.h>
-#include <linux/tty_driver.h>
-#include <linux/console.h>
 #include <linux/seq_file.h>
-#include <linux/fdtable.h>
 #include <linux/bitops.h>
 
 /*
@@ -139,160 +136,6 @@ static const struct file_operations proc_tty_drivers_operations = {
 	.release	= seq_release,
 };
 
-/*
- * The device ID of file descriptor 0 of the current reading
- * task if a character device...
- */
-static dev_t current_dev;
-
-/*
- * This is the handler for /proc/tty/consoles
- */
-static int show_console_dev(struct seq_file *m, void *v)
-{
-	const struct tty_driver *driver;
-	struct console *con;
-	int index, len;
-	char flags[10];
-	dev_t dev;
-
-	if (v == SEQ_START_TOKEN)
-		return 0;
-	con = (struct console *)v;
-	if (!con)
-		return 0;
-	driver = con->device(con, &index);
-	if (!driver)
-		return 0;
-	dev = MKDEV(driver->major, driver->minor_start) + index;
-
-	index = 0;
-	if (con->flags & CON_ENABLED)
-		flags[index++] = 'E';
-	if (con->flags & CON_CONSDEV)
-		flags[index++] = 'C';
-	if (con->flags & CON_BOOT)
-		flags[index++] = 'B';
-	if (con->flags & CON_PRINTBUFFER)
-		flags[index++] = 'p';
-	if (con->flags & CON_BRL)
-		flags[index++] = 'b';
-	if (con->flags & CON_ANYTIME)
-		flags[index++] = 'a';
-	if (current_dev == dev)
-		flags[index++] = '*';
-	flags[index] = 0;
-
-	seq_printf(m, "%s%d%n", con->name, con->index, &len);
-	len = 21 - len;
-	if (len < 1)
-		len = 1;
-	seq_printf(m, "%*c", len, ' ');
-	seq_printf(m, "%c%c%c (%s)%n", con->read ? 'R' : '-',
-			con->write ? 'W' : '-', con->unblank ? 'U' : '-',
-			flags, &len);
-	len = 13 - len;
-	if (len < 1)
-		len = 1;
-	seq_printf(m, "%*c%4d:%d\n", len, ' ', MAJOR(dev), MINOR(dev));
-
-	return 0;
-}
-
-/* iterator for consoles */
-static void *c_start(struct seq_file *m, loff_t *pos)
-{
-	struct console *con;
-	loff_t off = 0;
-
-	if (*pos == 0)
-		return SEQ_START_TOKEN;
-
-	acquire_console_sem();
-	for (con = console_drivers; con; con = con->next) {
-		if (!con->device)
-			continue;
-		if (++off == *pos)
-			break;
-	}
-	release_console_sem();
-
-	return con;
-}
-
-static void *c_next(struct seq_file *m, void *v, loff_t *pos)
-{
-	struct console *con;
-
-	acquire_console_sem();
-	if (v == SEQ_START_TOKEN)
-		con = console_drivers;
-	else
-		con = ((struct console *)v)->next;
-	for (; con; con = con->next) {
-		if (!con->device)
-			continue;
-		++*pos;
-		break;
-	}
-	release_console_sem();
-
-	return con;
-}
-
-static void c_stop(struct seq_file *m, void *v)
-{
-}
-
-static const struct seq_operations tty_consoles_op = {
-	.start	= c_start,
-	.next	= c_next,
-	.stop	= c_stop,
-	.show	= show_console_dev
-};
-
-/*
- * Used for open /proc/tty/consoles. Before this detect
- * the device ID of file descriptor 0 of the current
- * reading task if a character device...
- */
-static int tty_consoles_open(struct inode *inode, struct file *file)
-{
-	struct files_struct *curfiles;
-
-	current_dev = 0;
-	curfiles = get_files_struct(current);
-	if (curfiles) {
-		const struct file *curfp;
-		spin_lock(&curfiles->file_lock);
-		curfp = fcheck_files(curfiles, 0);
-		if (curfp && curfp->private_data) {
-			const struct inode *inode;
-			dget(curfp->f_dentry);
-			inode = curfp->f_dentry->d_inode;
-			if (S_ISCHR(inode->i_mode)) {
-				struct tty_struct *tty;
-				tty = (struct tty_struct *)curfp->private_data;
-				if (tty && tty->magic == TTY_MAGIC) {
-					tty = tty_pair_get_tty(tty);
-					current_dev = tty_devnum(tty);
-				}
-			}
-			dput(curfp->f_dentry);
-		}
-		spin_unlock(&curfiles->file_lock);
-		put_files_struct(curfiles);
-	}
-	return seq_open(file, &tty_consoles_op);
-}
-
-static const struct file_operations proc_tty_consoles_operations = {
-	.open		= tty_consoles_open,
-	.read		= seq_read,
-	.llseek		= seq_lseek,
-	.release	= seq_release,
-};
-
 /*
  * This function is called by tty_register_driver() to handle
  * registering the driver's /proc handler into /proc/tty/driver/<foo>
@@ -343,5 +186,4 @@ void __init proc_tty_init(void)
 	proc_tty_driver = proc_mkdir_mode("tty/driver", S_IRUSR|S_IXUSR, NULL);
 	proc_create("tty/ldiscs", 0, NULL, &tty_ldiscs_proc_fops);
 	proc_create("tty/drivers", 0, NULL, &proc_tty_drivers_operations);
-	proc_create("tty/consoles", 0, NULL, &proc_tty_consoles_operations);
 }