This reverts commit f4a3e0bceb. 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>
6c2754c28f